Category Archives: Machinist Tips and Tricks

This category contains a variety of machining and machinist tips and tricks derive from our 25+ years of real world chipmaking.

Shop Efficiency Series Part 1 : Cycletime VS Workholding

It’s the age old manufacturing quest … how to reduce the cycletime and machine parts faster. And although cycletime is a major factor in the making profits equation … concentrating too much on cycletime can sometimes make you miss the bigger problems … the bigger deficiencies in the shop … the bigger money wasting issues. While you are trying to shave seconds off the machining … the time your machine spends not running is hands down a much bigger problem. Any machine not cutting is burning money and profits. It’s easy to focus attention on cutting speeds and feeds … it’s a fairly obvious item especially for non-professional metalworkers. The fact is, however, every second or even minute you shave off the cycletime is probably no match for the large quantity of time you’re machine spends not machining.

What is the BIGGEST cause of your machine not cutting chips ??

The biggest contributing factor for shop machines not cutting chips and therefore making money (  other than not having work for the machines ) are primarily load / unload operations and changeover of the machine from one job to another.

money_burning

We are starting a new series here in our CNC MACHINIST BLOG to deal with these biggest money wasting areas in almost every shop … fixturing and workholding. Whether it’s the time needed to changeover the machine from one job to another … or the time required to load and unload the part … non-machining time is the biggest profit killer in any shop.

To start things out … I would invite you to take a walk out to your shop floor … and count the number of machines that are running? … how many IN-CYCLE lights are lit? I am betting you will be amazed at what you find. And if you look deeper into why the machine is not running … the reasons can usually be classified into two categories. The machine is being set-up to run production … or the workpiece is being loaded for machining.

Everywhere people are jumping on the “lean” manufacturing bandwagon … as they should … and striving to achieve the 80%-85% percent “in the cut” time target. The fact of the matter is that lean manufacturing goes well beyond just direct chip making. The time spent … or lost … in changeover or part loading / unloading … is probably a bigger profit losing factor than the time the tool spends in the cut.

This series will pull from our shop floor experiences to talk about the various areas of workholding for both milling and turning and machine / fixture changeover … two topics that are certainly inter-connected. We will publish new articles interspersed with our other topics of interest … so we invite you to check back frequently and keep up with the discussion.

Series Topic #1 :

Bringing The VMC Machine Table
Into the 21st Century

If you take a look at the table on your new VMC … and compare it to the table on a 1940’s milling machine … you’ll quickly notice that not much has changed. T-SLOTS, T-SLOTS and more T-SLOTS. Not much has changed in the design of the milling machine table since around 1940 … and that’s our first issue to tackle.

vmc_table_1

While no one will deny that the T-SLOT is an essential element in the table design … in today’s day and age we really need to think outside the box … or in this case outside the T-SLOT. A couple flaws enhanced by relying on the T-SLOT design include not utilizing all of the space available in the Y axis … and not having the flexibility of positioning fixturing anywhere on the table to maximize the whole table surface. The first step in accomplishing this is to change the table surface.

One way of altering the surface of the machine table is to use a sub-table … made from aluminum tooling plate or other suitable material. The main criteria is that the material is durable … while being fairly easy to machine because we will want to machine a variety of locating options into the sub-table. The two biggest advantages with a sub-table as mentioned above is that we now have the freedom to machine locating components to accommodate a wide variety of fixturing … we can more easily utilize all the area of the table surface … and we can always remove the sub-table and go back to the original table configuration if required.

vmc_table_2 Some of the major points for consideration when considering a sub-table and it’s design :

  1. Material : durable yet fairly easy to machine … aluminum tooling plate is one recommendation.
  2. Size : it should cover the majority of the table … thickness should be kept to a minimum as to not reduce the Z axis travels by an unreasonable amount … but thick enough to accommodate our locating components and maintain rigidity.
  3. Weight : aluminum will keep the weight down … but lifting components should be included in the event the sub-table needs to be removed or re-installed.
  4. Locating the sub-table can either be done with keys machined into the bottom surface or with the use of locating pins and dowels that can be used in conjunction with the original table T-SLOTS.locating_pin
  5. Once the table is installed … it may be necessary to skim the top surface to insure it’s parallelism with the machine axis. Keep this in mind when determining the size of the plate and the travels of the machine to allow for this type of machining. Periodically … this may have to be repeated if excessive wear of the table surface occurs. Also make sure to account for this when selecting and installing your locating components … which will most likely be hardened materials and not easily machined … and will need to be installed below the top surface of the sub-table.

Best Ways to Utilize Your New Table Surface

Now that you have transformed your table surface into a 21st century table … how can you get the most out of it? That really is only limited now by your imagination and design capabilities … but here  we will tackle what we would consider the top option.

fixt_2

Our recommendation … we have used this system extensively … is to utilize fixture plates located and clamped by a “ball lock” system. Fixture plates should be used for everything mounted to the sub-table … from a simple vise to multiple vises to dedicated fixturing. This allows for greater flexibility for positioning of workholding components and allows for quick changeover to other workholding components.

ball_lock1

The ball-lock system allows for quick and accurate positioning of the fixture plates to the sub-table. When designing the sub-table surface … create as many ball-lock receiver positions as possible to allow for multiple positioning options for your various fixture plate assemblies. You can machine and install these receivers prior to mounting the sub-table … but they can also be machined in place as their need arises.

fixt_1

Fixture plates can also be made from the same aluminum tooling plate material used for the sub-table. They should, of course, be quite thinner for weight considerations and should always include some kind of lifting component. Handles, as the ones included in the illustration, may need to be removable with a quick attachment mechanisms to reduce their interference in the machining motions.

If you have an HMC … you can take the same lessons learnt here and apply them to your tombstone or angle plate. Rather than using the standard “vise tombstone” … a tombstone which utilizes fixture plates can open up new possibilities for your HMC as well.

hmc_complete

Changeover Advantages

As mentioned above, the cycle start light goes out and the profit stops flowing when the machine is being changed over from one job to the next. The system described above can have a massive impact in reducing that downtime. Take for example the simplest task of working with a vise. To remove the  the vise … just un-clamp the plate with the vise and remove it. When re-installing it … just lock the plate with the ball-lock system … no tramming … no indicating … no center locating. The ball lock system locates the vise in a known position in seconds every time.

The same applies for all your fixtures … they mount in seconds in known positions. Fixture design will also be improved because the know facets of the fixture plate location and much of the needed configuration is pre-determined. With pre-set variables in place … your engineering mind will run rampant and you’ll be exploring many more time and money saving options as you go down the road.

Seems Like a Lot of Work and Expense

The above statement is true …  but it’s not easy to get from 1940 to the 21st century. The fact is that once you have completed the transformation … the possibilities for added efficiency are endless and the reduction of lost machining time will be fantastic … the payback and ROI will be fast. You will have new flexibility to :

  1.  Utilize more of the machine table and Y axis available stroke … more chip making means more profit.
  2. Quickly and easily mount your fixture plates making for faster changeovers … which means more time cutting chips … and making money.
  3. Have new capabilities to mount multiple jobs with multiple fixture types … easily run more than one job at a time.
  4. If utilizing a 4th axis … the new table design will give you more positioning options and result in faster mounting and removal of the 4th axis table.

Final Thoughts and What’s Next

As you can see from some of the ideas outlined here, changing the surface design of your machining center’s table can have quite an impact. While everyone is concerned with shaving seconds of the chip making … shaving hours off your set-up’s and changeovers will have an even greater impact on your bottom line. We hope that some of the ideas outlined here spur on your engineering juices allowing you to realize even more efficient fixture designs and ideas.

Make sure to return and check out other articles in this Series that will deal with fixturing and workholding … for both turning and milling. We’ll touch on things like vises … face drivers for turning … chucks and chuck workholding … and much more.

After all … we’re MACHINISTS … WE BUILD THINGS !!

At Kentech Inc. we are MACHINISTS who create Real World Machine Shop Software. Who creates the machine shop software guiding your shop’s future ?? 

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Check out all our REAL WORLD CNC & MACHINE SHOP titles at  www.KentechInc.com

Kenney Skonieczny – President
Kentech Inc.

Product Spotlight : ID Clamps from Carr Lane Manufacturing

Every once in a while we like to bring attention for our readers to new and innovative machining and workholding products and process that we feel are beneficial to our readers. Such is the case in the Making Chips post as we focus and bring attention to a new workholding clamp from Carr Lane Manufacturing – a leading supplier of workholding and fixture components.

Additional information and specs on the Carr Lane ID Clamps are available on their website through this link : CARR LANE MANUFACTURING

Carr Lane ID Clamps – A Brief Outline

id_clamps

Many of you will undoubtedly be familiar with expanding mandrels … most commonly used to grip on the ID when turning on the OD. The new Carr Lane ID CLAMPS bring that concept to locating and workholding for milling fixtures. As the image illustrates … the ID CLAMP is similar to the expanding mandrel technique where the id CLAMP expands and clamps on the ID of a workpiece, leaving the outside free for machining.  Tightening the tapered center screw with a hex wrench pushes the clamping segments outward, and slightly downward, to exert force on the workpiece’s internal bore. These clamps are designed to have their outside diameter finish machined by the customer to suit the bore size, because maximum diameter expansion is limited.

The flange diameter on the ID CLAMP is a machined to a close tolerance … which allows for maximum locational accuracy. A recess can be machined in the fixture base to fit exactly with the clamp’s close-tolerance flange diameter and the ID CLAMP can be mounted using flat-head mounting screws.
id_clamps2

In the image above … you can see how the larger ID is used for locating as well as clamping … and a smaller ID CLAMP is used in the slot to provide additional locating and holding force. With this type of set-up, the entire outside contour is available for machining.

This set-up also illustrates the fact that these ID clamps need not be confined to round holes … they can be utilized in almost an unlimited number of ID clamping roles … use that machinist mind and explore !!

Estimating

We are always on the look-out for new and innovative machining processes … techniques …. and workholding tips. If you see one which you think would be of interest to our followers of professional machinists and engineers … please drop us a line at Sales at KentechInc.com.

Until next time … Happy Chip Making !!

www.KentechInc.com

At Kentech Inc. we are MACHINISTS who create Real World Machine Shop Software.

Who creates the machine shop software guiding your shop’s future ??

CNC Lathe Headstock – Alignment Checks and Adjustments

We’ve all been there … Crashville. It’s not a place you want to visit frequently … but inevitably, we all make a visit. When I first started in CNC, one of my mentors told me “If you don’t bump it once in a while … you’re not experimenting … not trying new approaches … and not using it to it’s full potential.” Well … I’m not sure about that but there is a little truth in the concept.

Once you visit Crashville, you may notice some cutting errors and quirks developing in your workpieces. In this post we will be dealing with some of those unintended consequences of your visit to Crashville.

The first … tapers developing on your CNC lathe when turning or boring … the result of your headstock being bumped and not being square to the X axis ways. The result is that as the turret rides on the machine axis ways … and the headstock and ways are not “square” … you will be machining a taper. The amount of taper is the result of the amount of the mis-match between the headstock and the ways. It’s important to remember that the ways ( base ) of the machine and the headstock are not one-piece ( normally ) … the headstock is bolted onto the base. The illustrations below will give you a better idea.

Lathe-Design

So in our first post in our series … we would like to point you in the right direction and give some tips on re-aligning your headstock.

As the above pic and notes convey, the headstock is normally bolted onto the machine base … making the X / Z ways and the headstock independent of each other. Normally … there are alignment screws on the headstock assembly that allow you to move the headstock and thus align it “square” to the machine ways. When you visit Crashville … oftentimes one of those un-intended consequences is that that alignment is off because the headstock may have moved. So how do you get the correct alignment back?

There are a couple of methods … let’s start with my favorite … the one I consider the simplest and the one I used most in the field.

Conversational

First … you’ll need a piece of stock. Qualifications? You need a good material, easy to machine yet with the ability to produce a good finish. I didn’t like using aluminum … I preferred some grade of steel like cold rolled or similar. We want to insure that everything we do is reflected in the material … not the workholding. So it’s best to use hard jaws on the chuck … and you want to make certain that the chucked material is not flexing … so the material diameter to overhang factor should be appropriate to insure that the material isn’t flexing when you’re cutting. You also want to have a good length sticking out of the chuck … after all the longer the area to measure the better your readings and the better your adjustments. Yes … there are a lot of factors to consider here … but you’re a machinist !!! You know what to do and what is appropriate.

It’s important to note here also what may be obvious … don’t use the tailstock. We don’t want any mis-alignment in the tailstock to reflect in our measurements.

Next … chuck up the material and clean up the stock by cutting the material the entire length. Take whatever cuts you need to clean up the stock … just make sure the last cut is a nice finish cut and leaves a nice finish. Usually using MDI or the job / feed manual options are the best method. Creating a program is a little overkill and using the handwheel may result in an uneven cut and finish.

Now measure the diameter at the furthest and closest points to the chuck along the turned diameter. Not the same? That’s the reflection of your headstock mis-alignment.

tip_image

To adjust … you’ll need to find those adjusting screws on the headstock … the above illustration might shed some light on where they might be and how they work. You will need to slightly crack the bolts holding down the headstock body to it’s base … then use the adjusting screws to move it in the direction you feel you need to move it to re-align it. Tighten everything back up … and take another skim cut on the material. Repeat and re-adjust as necessary until the results are to your satisfaction. What should that be? As close as you can get it. If the material length in the chuck is short … it really needs to be spot on because obviously the error will get magnified on a longer piece of material. As with everything you do as a professional machinist … do it to the best of your ability.

One valuable hint : Place an indicator somewhere on the headstock to measure the amount you move the headstock with the adjusting screws. This will help you understand the relationship between the amount of movement with the amount of taper correction.

Another method which some people prefer … instead of using a piece of stock and turning the diameter … they will use a test bar. A test bar is a piece of stock that has already been machined and usually ground … it’s perfectly straight and true. They mount it in the chuck … indicate it in … and then use an indicator mounted to the turret which they then run back and forth along the test bar in Z as they adjust the screws on the headstock. This method works fine also … but you need a qualified test bar to start … and there are more variables that come into play. Is the bar indicated in and running true? Is your indicator on the turret reflecting the actual center of the test bar … etc.. For my liking … too many other variables … and a piece of stock is simpler, more readily available and cheaper.

So as you can see … this repair is not that hard … a little time consuming … but the result will leave you with a more accurate machine tool and a lot more money in your pocket … the amount you’ll save in a repair bill.

Hope this helps you recover from your inevitable visit to Crashville … and insures you are good chips … for years to come !!

Thanks in advance to everyone … and Happy Chip Making !!

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CNC Turret Alignment – Tips and Tricks

In this post we are continuing our series dealing with the aftermath of that inevitable visit to Crashville that we all make in our production lives. Our last post dealt with the spindle alignment … this post we’re going to take a look at turret alignment. Oftentimes these repairs cannot be accomplished without professional assistance ( and their tools ) … but there are some repair options available to the layman.

First … lets take a look at the types of misalignment that can exist.

Turret Body Misalignment :

How to Diagnose :
(1) Mount an indicator to the chuck face or spindle nose face … with the indicator point against the face of the turret as shown in the illustration below.
(2) Move the X axis up and down and check the amount of deviation along the face of the turret where the indicator is touching.

turret_illustration_1

Repair :
This type of misalignment is very similar to the headstock misalignment we discussed in the last post. As the headstock is usually bolted onto the base … so the turret assembly may be bolted onto the X axis slide. As the illustration below shows … turret misalignment that is detected during the diagnosis … can be fixed by loosening the hold down bolts as shown and shifting the turret around till the alignment is repaired … very similar to the headstock alignment procedure.

Some turret bodies may also be pinned to the base using taper dowel pins. These pins would need to be removed … hold down bolts loosened and the turret aligned … and then the taper pin holes in both the base and turret body should be reamed in line until “clean” … and then the taper pins replaced. Not replacing and realigning the taper pins will result with the turret body being simply bolted to the base … and will shift with even the slightest nudge … not a stable situation and not recommended. No matter how tight you tighten the hold down bolts … if the turret is equipped with taper alignment pins … those should be repaired and restored.

Rotary Turret Misalignment :

How to Diagnose :
(1) Mount an ID tool holder on the turret
(2) Mount an indicator to the chuck face or spindle nose face … move the X axis so that indicator is sweeping the ID of the ID tool holder.
(3) Adjust the X axis so that the two points parallel with X axis slide movement read 0 … in other words, bring the ID tool holder to the centerline of the spindle.
(4) The remaining two points and their indicator reading will illustrate the amount of rotary misalignment in the turret.

turret_illustration_3

In the illustration above … looking through the spindle and onto the ID tool holder. Points #1 and #2 can be aligned to zero by adjusting the X axis … as they are parallel to the X axis “slant” or movement. Points #3 and #4 will reflect the amount of rotary misalignment … they cannot be adjusted but require a physical repair.

 There are a variety of ways the turret mechanism may work … and therefore the type of physical repair required to realign Points #3 and #4 can vary significantly. The most common method involves a curvic coupling mechanism. One half  of the coupling is mounted on the turret mounting body … and a meshing coupling is mounted on the back of the turret face. When the turret indexes … the turret face unclamps from the matching coupling by moving forward … the turret indexes to the desired location … and the turret clamps as the coupling faces mesh together … and confirm the rotary turret alignment. When you visit Crashville … usually when the turret is in the clamped position … the turret rotates pulling the both halves of the curvic coupling mechanism with it. So now that even though the turret is clamped … the curvic coupling has been rotated and the rotary alignment is now off. So even though the turret mechanism appears to work correctly … unclamps – indexes – clamps … both halves of the curvic coupling have been rotated as a pair … and the alignment is off.
curvic_coupling
This image illustrates the curvic coupling mounted on the turret mounting body.
curvic_coupling2

Oftentimes the coupling on the turret face can be accessed on the front face of the turret … but most often the turret face will need to be removed to access the matching side of the curvic coupling.

Repair of the curvic coupling is best left to a professional … as most times the turret must be removed from the body to access both side of the curvic coupling. The repair usually entails :

  1. Removing the turret face from the turret body
  2. Removing the taper pins on both sides of the curvic coupling … face and body
  3. Slightly loosening the hold down bolts for the coupling halves
  4. Remounting the turret face and physically moving the turret … until the correct ID tool holder alignment can be achieved.
  5. Removing the turret face again
  6. Reaming all taper pin holes in line to clean
  7. Replacing the taper pins
  8. Tightening up all coupling hold on down bolts
  9. Reassembly and recheck.

As you can see … best left to a professional with the correct tool-set.

Estimating

Tricks of the Trade …
Rotary Turret Mis-Alignment Work Arounds

But fear not … there are some work arounds … not very professional, but work arounds … to get around the turret rotary misalignment issue.

 What effect does rotary axis misalignment have on my machining?

Rotary turret misalignment will show up in many different machining scenarios :

  1. Facing … you will leave that nub at the spindle centerline as the turning tool tip is either above or below centerline.
  2. Grooving – Cut-Off … since the edge of the grooving tool is either above or below centerline … grooving and cut-off operations do not machine easily with lots of tool rubbing and poor cutting. Cut-Offs will also leave the infamous nub at centerline.
  3. Drilling … since the drill tip is not on centerline, holes are oversize and in the case of a carbide insert type drill … machining is just not good at all with lots of rubbing and poor cutting.

Work Arounds For a Temporary Fix?

There a couple of options we have discovered through experience over the years that can get you by in a pinch … until the repairman shows up. Not guaranteed … but past experience shows that they can work … but the problem should be corrected properly as soon as possible.

  1. Turning – Grooving – Cut-Off Tools : Take an OD tool holder and machine the slot where the tool mounts to open up the tolerance. This will give you room to shim the tool in the holder to bring the tip of the tool onto center. We oftentimes made a holder that was oversize in both directions and kept it hanging around. When it was needed … we could pull it out and it gave us the ability to shim the tool in both directions … depending on which way was needed at that particular time.
  2. Drilling – Boring : This fix requires a little bit of work but is a good accurate fix. We would machine new bushings for the ID tool holders … first roughing them out on another machine either manually or with a CNC machine. To finish the hole in the bushing … we would mount an adjustable boring bar in the chuck of the misaligned machine … mount the rough bushing in the ID tool holder in the turret … and finish machine the bushing ID by feeding the bushing / tool holder over the boring bar mounted in the chuck. This will insure that the hole in the bushing in line with the centerline of the spindle. A little bit of work … but quite easy for a professional machinist.

So there you have it … your “crash” course in CNC turret alignment and repair. Of course … we always recommend that you employ a professional to repair the effects of your visit to Crashville professionally and correctly. But living in the real world we know that sometimes you just can’t wait. We hope that the points and tips mentioned here can assist you in keeping your CNC lathe Making Chips … and profits !!

Thanks in advance to everyone … and Happy Chip Making !!

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Multi-Part CNC Machining Series – Part #3

Machining Multiple – Different Parts

So far in our series we have looked at machining multiple parts of all the same part mounted in our fixtures during our machining cycle. What if we want to machine different parts during the cycle … we want to mount different fixtures on the table and machine one of each during the machining cycle.

First let’s look at some reasons WHY we might want to do this.

  1. Perhaps we will be delivering an assembly made of multiple parts we need to machine. If we machine all the components at the same time … during the machining cycle … we can better accomplish scheduling and production of the entire assembly.
  2. Perhaps similar parts utilize similar cutting tools … if we can machine them at the same time we can reduce and better control our tooling requirements both from a “tool in the machine” as well as from an inventory viewpoint.
  3. We need to break into a production run for some “special circumstance” … rather than halt the production all-together, we can sneak another fixture on the table and machine both parts during the same cycle.
  4. Having lived in the real world … we could go on and on and on … you know !!

Looking back at Part #1 and Part #2 in our series … any of these scenarios certainly becomes a fairly simple task.

Conversational

Fixture Offsets from Part #1
As we mount the different fixtures on the table … we can establish a Work Offset for each fixture. Now each fixture is independent of the others … and can be called with a simple G54-G59 call.

Sub-Programming from Part #2
We could use a variety of sub-programming options to accomplish the various scenarios. The easiest is to simply have a complete machining program for each fixture … and call it using the sub-program call in our main program. So we would utilize a main program to actually link all our different machining programs together. Something line this :

Main Program :
O0001
G54
M98 P1234 ( program to machine fixture #1 completely )
G55
M98 P5678 ( program to machine fixture #2 completely )
G56
M98 P8888 ( program to machine fixture #3 completely )
M30
%

When we press the cycle start at program O0001 …. it will call each of our compete machining programs and will machine the workpieces at each fixture completely. Simple. You could get very creative and efficient if you did some specific tooling / sub-programming calls … think about it.

And …. we still have our independent programs available should we need to just machine one of the parts for some reason.

As I’m writing this … different scenarios and reasons to utilize this approach keep popping into my head. But rather than write a long dissertation here … look around your shop … look at your work flow … and see if you can view some of your own scenarios where better work flow can be achieved using some of our talking points from this series.

If you are so inclined … please drop us an email at Sales@KentechInc.com … tell us some of your unique situations … or even ask us our recommendations … and we’ll publish / add them into this post for the benefit of others to review.

Thanks in advance to everyone … and Happy Chip Making !!

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Multi-Part Machining Series — Part #2

Programming for Multiple Fixtures

So the decision has been made … “We need production … which means we need to mount as many vises or fixtures on the table as we can fit … to make as many parts as possible.”

First scenario …

  1. We are going to make all the same part.
  2. For our example here … let’s say that we can fit 4 fixtures on the table … we are going to machine 4 parts in one cycle.

Some thoughts :

  1. When the tool is in the spindle … we want to do as much work with it as possible. That means hitting each part on each fixture while it’s in the spindle.
  2. As mentioned in Part #1 … each fixture is independent with it’s own work coordinate system.
  3. As a set-up … we want to make one part first … confirm that it is correct dimensionally and that the cutting conditions are optimal … and then expand those toolpaths to machine the other vises.
  4. For this article … we are not going to be concerned with the actual G code program … more with the flow of the program. How we can structure the program to machine all the parts.

So we mount the fixtures on the table … set up and record our Work Coordinate Offsets … G54 – G57.

How can we write the program to machine one part … then expand it to 3 more parts … with the least amount of effort. Our suggestion : Sub Programming ( for a more in-depth MAKING CHIPS blog post on sub-programming … go here http://kentechinc.biz/the-hows-and-whys-of-cnc-sub-programming/

Here is the structure of our initial set-up program :

O0001 ( Main Program )
N0001
G00G91G28Z0
T01M06
G90S3500M03
G43Z1.500H01M08 ——– Put the tool in the spindle, start the spindle, position Z to clearance
G00G54X0Y0 ————— Move to the first fixture, call the sub to do the work with this tool
M98 P1000
G00G91G28Z0 ————— End this tools sequence
M01
N0002
G00G91G28Z0
T02M06
G90S1200M03
G43Z1.500H02M08 ——– Put the next tool in the spindle, start the spindle, position Z to clearance
G00G54X0Y0 ————— Move to the first fixture, call the sub to do the work with this tool
M98 P1001
G00G91G28Z0 ————— End this tools sequence
M01
ETC
ETC ————————– Create similar cycles for all the remaining tools.
ETC
M30

Once all of the above is confirmed … w’re ready to rock and roll on all the fixtures.
Just make these simple edits :

O0001 ( Main Program )
N0001
G00G91G28Z0
T01M06
G90S3500M03
G43Z1.500H01M08
G00G54X0Y0
M98 P1000
G00G55X0Y0
M98 P1000
G00G56X0Y0
M98 P1000
G00G57X0Y0
M98 P1000
G00G91G28Z0
M01
N0002
G00G91G28Z0
T02M06
G90S1200M03
G43Z1.500H02M08
G00G54X0Y0
M98 P1001
G00G55X0Y0
M98 P1001
G00G56X0Y0
M98 P1001
G00G57X0Y0
M98 P1001
G00G91G28Z0
M01
ETC
ETC ————————– Create similar cycles for all the remaining tools.
ETC
M30

The above will work fine … one blaring item is that we are positioning back to the first fixture … from the last fixture each time … some wasted movement. Easy to fix because of our structure and the use of sub-programs … just start each tool at the last vise where the last tool was working … like this :

First Tool :
G00G54X0Y0
M98 P1000
G00G55X0Y0
M98 P1000
G00G56X0Y0
M98 P1000
G00G57X0Y0
M98 P1000
Next Tool ( work the offsets backwards ):
G00G57X0Y0
M98 P1001
G00G56X0Y0
M98 P1001
G00G55X0Y0
M98 P1001
G00G54X0Y0
M98 P1001
Next Tool :
G00G54X0Y0
M98 P1002
G00G55X0Y0
M98 P1002
G00G56X0Y0
M98 P1002
G00G57X0Y0
M98 P1002
ETC … ETC … ETC.

So there you have it … combining our knowledge of SUB-PROGRAMMING with WORK COORDINATE OFFSETS … we machined (4) parts on (4) fixtures … efficiently.

If you followed the other posts on SUB-PROGRAMMING and WORK COORDINATE OFFSETS… you will have an even better understanding of why these features will prove so useful when :

  1. Johnny “bumps” the middle fixture with his hammer
  2. Paul adds a revision …. an additional hole to the part
  3. “The Boss” decides he wants to take off one of the fixtures … who knows why !!!

Anyway … if you aren’t sure why the above are simple fixes … just go back and review the other posts !!
In the next post in the series … we’ll take a closer look at some other scenarios and options … Stay Tuned !!

Until Next Time … Happy Chip Making !!

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Multi-Part Machining Series — Part #1

Work Coordinate Systems

Most production shops will rarely utilize a one-vise or one-fixture setup on a VMC or HMC when running a multiple piece production run. The most efficient production will have the cutting tool performing it’s function on as many parts as possible while it is in the spindle. That normally means adding as many multiple vises or fixtures as the room on the table will permit.

We will be devoting the next couple of posts to set-up and programming tips and tricks dealing with multi-part machining.

What does that multi-part machining mean for programming? As with anything in life … first we want to reduce the amount of work … in this case, the amount of programming. The use of sub-programming to cut down on the amount of typing or data entry or whatever work … is one. ( We dealt with sub programming in a previous post here : http://kipware.blogspot.com/2013/02/the-hows-and-whys-of-sub-programming.html ). The other is a little feature on most machines called WORK OFFSETS. In our post here we will be explaining the Fanuc style and codes of Work Offsets … since about 95% of machines out there are what we refer to as “fanuc compatible.” And that includes the popular Haas machines as well.

Why Work Offsets?

Let’s take a simpler example of placing two vises on the VMC table … both will hold identical pieces of stock … and we want to machine two identical workpieces using the same identical tools.

Hole dimensions are identical for both workpieces.

We could always do something like use the top left corner on the part on the left as X0/Y0 and then add the 12.300 + 3.100 to program the two holes on the part on the right … sure, simple in this case. But even this scenario is fraught with potential problems.

  1. What if we “bump” the vise … and the 12.300 is no longer the case. We now have to go back into the program and adjust the X and Y coordinates to reflect the new distance.
  2. What if one vice is a different height / thickness than the other … the parts Z0 is different.
  3. Next time we run the job … we have to get the vises exactly 12.300 apart … or alter the program again.
  4. …. it goes on and on … none of the scenarios are nice to imagine.

This type of situation … and this is a simple one … begs for the use of Work Offsets.

What are Work Offsets?

The Work Offsets allow the user to designate distances from the fixed Zero Return position on the machine to a certain location on the machine through an offset table. The Work Offsets are recorded distances from a fixed position on the machine … usually the Zero Return or Reference Return position on the machine. This position is the only position that can be repeated on the machine without fail … because it is defined from a physical limit switch. Once the electronics on the machine are powered off … most internally recorded positions are lost … no power to keep the computer running, it loses it’s memory. When the machine is powered back on … we can find our Zero Return by utilizing that function on the machines panel because it searches for that physical limit switch … it doesn’t rely on any memorized position … it is dependent on the physical limit switch. For that reason … all Work Offset positions are recorded from that Zero Return position for all axis.

 The number of Work Offsets available on a machine tool can vary … some have as little as one or two and others have 300-500 … on Fanuc controlled machines the standard number is six … although options to add  more are available. They are designated by G code calls … G54, G55, G56, G57. G58 and G59.

If you were to look in the Work Offset table … you would see something similar to :

So the user measures the distance from the fixed Zero Return position to … let’s use our example … to the top left corner of the left hand vice as that parts X0/Y0 location. The measured distance is then entered in the Work Offset table … both X and Y … under one of the Work Offset designations … we’ll use G54. The steps are repeated for the left hand vice … and the X and Y distances are entered in the G55 offset locations.

In our example, let’s imagine that the vises and the stock are the same height in the Z axis … just for simplicity … but the Z axis could have a value similar to X and Y if required.

How to use Work Offsets in the G Code Program?

Let’s say we have the scenario below …. the machines Zero Return position is the point on the top right designated with the purple circle :

Our Work Offset Table would look like :

Now for the programming part. Whenever the G code calls out a Work Coordinate System …. G54 thru G59 … that Work Coordinate System becomes the default and any X / Y / Z coordinates called out for in the G code will reflect the X/Y/Z coordinates from the offset table. So the programming line …

G00 G90 G54 X0 Y0

… would move the tool to the top left corner of the left hand vise. If we were to then command …

X3.100 Y-2.125

…. we would position to the top left hole of the left hand vise … because the G54 Work Coordinate System is the default. Similarly … the command lines :

G00 G90 G55 X0 Y0

X3.100 Y-2.125 

… would position the tool to first the top left corner of the right hand vise … then the top left hole of the right hand vise using the G55 Work Coordinate System.

So using the Work Coordinate Offsets and Work Coordinate System calls … it is very easy to switch between the left hand and right hand vise by simply commanding G54 or G55.

The Advantages of Work Offsets

As we outlined above … we are asking for problems when we don’t use the Work Offsets. How did we fix them?

  1. If we “bump” the vise … only the values in the Work Offset table will change … the G code program will not need any editing.
  2. If the vises were different heights …. we could easily use the Z value in the Offset Table to make that adjustment … again, no program editing.
  3. Next time we run the job … we only need to adjust the G54 and G55 Offset Table values … no program editing is required.
  4. and on and on and on. I’m sure you will see many more advantages on the shop floor.

As we progress through our Multi-Part Machining Series over the next posts … we’ll try to highlight some of the other programming Tips and Tricks that can be employed.

Stay Tuned …. and Happy Chip Making !!

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CNC Machine Maintenance – For The Not So Ordinary

cnc machine maintenance

Personnel who perform routine maintenance on their CNC equipment usually perform the same common checks and perform the same common tasks … those that I refer to as the “no-brainers”. Filling the way lube tank … greasing the hydraulic chuck … checking the spindle oil level … the common checks and tasks. Unfortunately they are usually the ones where the machine will generate an alarm to remind you … like when the way lube tank runs out.

In this post we wanted to spend a post and remind you of the not-so-common checks and tasks that also need to be performed … “stuff” you might either not be aware of or “stuff” you never really even think about. So we encourage all to jot these down on your CNC maintenance TO-DO LIST. What !!! What do you mean you don’t have a TO-DO LIST !!

One really good thing to do in regards to CNC maintenance and insuring your CNC machine is accurate and running at it’s top condition is to at least post a note on the machine that lists checks and tasks to be performed and at what interval they should be performed. Every day … once a week … once a month … etc, etc. The best method is to supply a log book at the machine that makes your personnel responsible for these tasks by requiring them to sign-in and confirm which tasks were completed and when. This will insure that the tasks are completed … handing responsibility off to either the operator or the programmer.

Estimating

Here is our list of the not-so-common tasks and checks that should also be included in your routine maintenance :

  • Check the hydraulic pressure to make sure it is at the manufacturers recommended setting.
  • Check the hydraulic oil to make sure it is filled to the manufacturers recommended level.
  • If your spindle to machine tool has a cooling system … check the cooling oil to make sure it is filled to the manufacturers recommended level.
  • Clean the chips out of the chip pan on a daily basis … not just when it’s overfilled. Oftentimes an overflowing chip bin will push the chips into areas such as the ball screw cavity and cause those chips to be forced into the ball screw covers. So while you think there is still room left in the chip bin … actually the chips are being forced into areas you do not want them to go.
  • If your machine has a chip conveyor … grease the chain at least once a month.
  • Clean the glass on the window of the door and the light inside the machine every morning. Waiting till you can’t see only makes the job that much tougher … and causes excessive downtime because the job takes twice as long.
  • Wipe down the stainless steel way covers at the end of the shift … and lubricate them with hydraulic oil. In the long run … this is a huge maintenance cost avoided.
  • Check the electrical cabinet fans and filters … these should be cleaned at least once a month.

These are a few of the checks and tasks that should be performed frequently. They’re not always the “glory” items but are essential none the less.

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Way Lube System – Friend or Foe?

Your CNC machine is equipped with an automatic oiler system. Great ! You won’t have to think about oiling the machine and an alarm will tell you when the tank is dry. What a great device ? Right ?

Well, that is the design. Unfortunately, along with the “automatic” description of the system comes the “out of sight, out of mind” aspect of the system. Because many people know it is an automatic system, many people put it out of their minds and simply wait for the alarm to come up showing that the tank is empty and needs to be filled. But what if that alarm never comes on because the tank isn’t empty ? Why wouldn’t the tank be empty ?

As your machine gets older, the way lube system will require service just like any other mechanism. The main problem, which often gets overlooked, is that the “tank empty” alarm never comes on because the tank never drains and nobody ever notices it. Now your machine runs for months on end with no lubrication on the ways and when you finally notice a problem, it’s too late. Here is the “Rest of the Story …”

PROBLEM :  The machine’s ways are not receiving any way lube oil.

SYMPTOMS – IN ORDER OF SEVERITY :

  • Positioning / Repeatability Problems
  • Axis makes noise when moving
  • Axis Drive motor overload alarm coming when the axis is moving

POSSIBLE CAUSES :

  • Way Lube Pump burned out.
  • Way Lube Pump distribution flow set too low.
  • Way Lube Pump filter CLOGGED
  • Way Lube line BROKEN
  • Metering Units are CLOGGED

POSSIBLE CAUSES EXPLAINED :

(1) Way Lube Pump Burned Out : If the way lube pump is burned out, obviously there will not be any lube getting into the system. These pumps are usually set using a timer system. There is basically two types of timer systems used :

  • The pump is on a cam and the way it works is that the pump is always running. One gear turns another which acts like a step-down system and the second gear raises a “primer” lever. When the lever reaches the top of the stroke, the “primer” lever is released and the oil is pushed into the lines. This whole cycle can take 5-20 minutes meaning that even though the pump is always running, the lines get lube only every 5-20 minutes.
  • How to Check It : Take a flashlight and look in the tank or remove the oil tank. Once looking inside, you can see the main gear that should be constantly moving. It may be at a very slow pace, but you will see it moving.
  • The pump is set to an electrical timer set in the controls PC (programmable controller) or an actual physical electrical timer in the cabinet. This type of timer only supplies power to start the pump for every cycle.
  • How to Check It : On some pumps there is no primer lever but a light comes on on the tank when the pump is activated. Make sure this light comes on every 5-20 minutes or some other sign comes on to show the pump is activated every 5-20 minutes.

(2) Way Lube Pump distribution flow set too low : As stated above, the way lube pump usually is set using a timer system. The flow amount that gets distributed into the lines during every cycle is usually set and adjusted at the pump with a manual setting mechanism. This type of adjusting mechanism is usually a knob that can be turned higher or lower to set more or less flow. Also, just look at the primer lever. During the mentioned 5-20 minute cycle, you should see the primer lever raise slowly and then start to drop after reaching the top of the cycle. Check the stroke of the lever – short stroke, less flow.

  • How to Check It : The normal pump usage is in an 8 hour shift, you should fill the tank every 2-3 days. Also, you should see way lube flowing onto the ways. Always remember, the more flow the better. Yes, it may contaminate the coolant but that is better than ruining the ways and thus the machine just to save a couple of bucks.

 The photo above shows a way lube pump unit which includes a manual flow control device. Adjusting the white knob adjusts the amount of lube being distributed per one cycle of the lube pump. When this type of pump is working correctly, you can see the white knob rising slowly then retracting, pushing the lube into the lines. The amount of rise and fall, and therefore the amount of lube distributed, is determined by the flow adjustment.

(3) Way Lube Pump filter CLOGGED : The way lube tank usually has a filter between the tank itself and the oil line that starts the distribution. This filter is usually in the tank itself at the bottom of the primer lever or in-line right after the main distribution line leaves the tank. It will get clogged over time, especially if there is no filter at the oil fill hole or if someone takes off the filter when filling the tank.

  • How to Check It : Disconnect the main lube line where it exits the tank to feed the system or after the in-line filter if so equipped. When the cycle reaches the pump stage as outlined above, oil should flow through this connection. The flow should be strong at this point. If not, remove the oil tank and search out the filter or remove the in-line filter. They can often be cleaned with a cleaner but the best remedy is to replace it.

(4) Way Lube line BROKEN : Oftentimes a lube line in the system gets crimped or broken during machining or during service. These way lube systems are usually “pressurized” so to speak and if the pressure is released at one point, say at the broken line, the oil will flow all to that point, depriving all the other lines of fluid.

  • How to Check It : When the pump is in the pumping stage, the primer lever should fall slowly. This is due to the fact that it is pushing the oil into the system. If a line is broken, the primer lever will fall quickly as all oil is funneled to the broken line area only. On systems without a primer lever, the pump may have a pressure gauge on the pump. During the pumping cycle, the pressure should register for a couple of seconds as the oil is pumped into the lines. If the pressure is low or does not come up at all during the pumping cycle, a line in the system may be broken.

(5) Metering Units are CLOGGED : In order to create the “pressure” of the system needed for even distribution, each oil line leads to a “metering unit” where the flow is lowered and the oil is discharged. When the pump forces oil into the lines, they all fill and flow to the metering units where the flow is stopped. Each metering unit is set to discharge the desired amount or “drops” of oil and perform their individual duties. Since some areas require more lube, the metering units can be different for each line or area. Since these metering units have actual valve type components in their very small bodies, over time these units can be become clogged or the inner workings can become stuck.

  • How to Check It : This is a much harder area to check. The best remedy and prevention is to change these units every year as part of a yearly maintenance program. Because these units allow only drops to flow through, they are harder to see when troubleshooting. These metering units are usually located in “clumps” around the machine. Several lines lead to these central areas and lube lines are branched out from here to the various areas of the machine. Replacement metering valves should be obtained from the machine tool builder or dealer to insure that you are getting the correct replacement part. When changing these units, pay close attention to the flow arrow that is commonly marked on the units themselves. This arrow shows the direction of installation and flow. Check the original unit before removal and replace accordingly.

 The photo above shows an example of some metering units. These individual fittings are usually located in one or two main terminal blocks that feed certain areas of the machine such as the axis and ball screws. As the system fills with pressure and lube, these fittings discharge the lube at their pre-set flow rate into their lube lines. Over time, like cholesterol in the arteries, these units become clogged and no longer allow lube to exit and thus deny vital areas of the machine the way lube they require. As part of a yearly maintenance program, metering units in the machine should be replaced as a precautionary measure.

Due diligence and a little tracking will insure your Happy ( and ACCURATE ) Chip Making for years to come !!

Estimating

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CNC Machine Warm-Up — How? Why? When?

As former field service engineers … one of the items we always stressed to our CNC customers was the importance of performing a machine warm-up routine. Below are answers to some of their most frequently asked questions … which pretty much tell the whole tale about this activity.

WHY?

A machine warm-up routine benefits both the machine and the machining in a number of areas :

  • Running the spindle and moving the axis give the oils in the machine … spindle oil and way lube … an opportunity to distribute and do their jobs. Especially in a colder environment … start of the day when perhaps the heat in the shop was reduced for the night … running the spindle and moving the axis gives the oils a chance to warm up to their appropriate temperature and “work” the way they were intended. The end result is improved machine life, operation and reduced down time due to break downs.
  • It stands to reason also that when the oils are working as they were intended … the accuracy of the machine can more easily be maintained. It is an unreal expectation to assume that you can walk in in the morning and start the machining and hold a tolerance of .0005″ … perhaps when the machine is brand new … but not in the “real world”. Starting your day like this will most likely result in offset adjustments being made due to the machine’s “cold” condition … and will begin the process of “chasing” size for quite a while. I heard countless times from customers how they spend 1-2 hours in the morning “chasing” size. Hello? Did you warm up the machine?

WHEN?

A lot of people assume that performing a machine warm-up routine is only appropriate after an extended “vacation” period … either by the personnel or by lack of work flowing to the machine. While a longer warm-up period is recommended after an extended break … an everyday warm-up routine is still recommended for the reasons listed above. Here are a couple of options for when to perform a machine warm-up routine :

  • Start of the Day … whether that’s at the shop opening or the start of the 1st shift.
  • After the machine has been idle for a time period of over 4 hours.
  • After an extended vacation period.
  • If the shop temperature is cold during the winter months … a short warm-up should be performed even after lunch  / dinner breaks.
  • If the machining requires holding a tight tolerance … a warm-up routine should be left executing during ANY breaks in the machining … inspection time, bathroom break, at machine deburring process, etc..

Estimating

HOW?

Matching the situations above requires an assortment of warm-up routines. No matter what the length of time … the warm-up routine should always include the following :

  • Spindle running
  • Axis moving along the full stroke of each axis.

The beauty part is that the various warm-up programs can be left in the CNC control and called up anytime as needed. Or in the case of just keeping the spindle warm … it may be a case of just manually starting the spindle and leaving it running while you walk away and attend to something else.

Spindle Warm-Up

After an extended break the spindle should be run through all the speed ranges with substantial dwell times in between speed changes. Start slow and work your way up with at least 15-30 minutes between increases. An example of a Fanuc style program might be :

  • G97 S100 M03
  • G04 X1200.0 ( dwell for 1200 seconds or 20 minutes )
  • S300
  • G04 X1200.0 ( dwell for 1200 seconds or 20 minutes )
  • S500
  • G04 X1200.0 ( dwell for 1200 seconds or 20 minutes )
  • etc. etc. etc. until a speed of at least 3500 RPM is obtained.

You can create a program like the above to be run after extended breaks … and a program with less dwell time to be run after shorter breaks.

As mentioned above … to maintain the spindle temperature during the course of the workday … manually starting the spindle at say 2500 RPM and leaving it running while you leave the machine can also be quite beneficial in maintaining machining accuracy.

Axis Warm-Up

After an extended break  ALL the machine axis should be made traverse the complete length of each axis … or if fixturing / workpieces are in the way the maximum length of the stroke that is possible … using various speeds. You don’t want to start the movement under full rapid traverse speeds … but rather work your way up during the warm-up cycle. The easiest way to accomplish this is to utilize the RAPID OVERRIDE feature on the machine. The G code warm-up program will call for G00 / rapid … but start the program with the RAPID OVERRIDE switch at it’s lowest percentage …. then work it up manually as the routine runs. A sample Fanuc style axis warm-up program might look like this :

  • G00G91G28Z0
  • G00G91G28X0Y0
  • G00G91Z- ***** …. incrementally move the Z axis as close to the table as possible.
  • G00G91G28Z0
  • G00G91X ***** …. incrementally move the X axis to the opposite end of it’s stroke
  • G00G91Y ***** …. incrementally move the Y axis to the opposite end of it’s stroke
  • G00G91G28X0 …… move the X axis back to the zero return / home position
  • G00G91G28Y0 …… move the Y axis back to the zero return / home position
  • G00G91X ***** Y ***** …. incrementally move both axis at the same time to their stroke end
  • G00G91G28X0Y0 …. move X and Y back to their zero return / home position.

The above routine gives you an idea … and feel free to make additions as you see fit. The main idea is to move ALL the axis along as much of their stroke as possible. Not just a “square” pattern … try to make “fancy” moves that can move all the axis through as much of the strokes as possible.

 If you don’t like or don’t have a RAPID OVERRIDE option … you can simple make a longer program using FAST feedrates … such as :
  • G00G91X ***** F100.00
  • etc.
  • etc.
  • G00G91 X**** F200.00

You can get the idea … repeat the program and alter the feedrates as the program progresses. Again … the good part is that once it is written, you can maintain the program in the machines memory and recall it as needed. No need to re-create it each time.

 Spending some time creating these warm-up routine programs … and instituting a policy of when and how they are to be run … can go a long way to improving your machine’s life … as well as your machining efficiency and accuracy.
 

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Happy Chip Making … and may you Make Chips and Prosper !!