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Backlash compensation
« on: July 28, 2012, 01:15:31 PM »
Over time I have noticed if I leave the Taig fairly sloppy it tends to stay close to the same amount of sloppy for much longer than if I adjust and tighten it up to reduce mechanical backlash.  One of Hoss's videos inspired me to try leaving it that way and instead using backlash compensation.  At his settings the machine would lose position and walk across the face of the work piece fairly quickly.   I used very conservative settings compared to what He had used and it seemed to work ok.  I cut a 1" register pocket with a .250" end mill and I was modestly satisfied with the results.  It was within .003" total tolerance of round.  Then I tried to cut some parts.  With a 1/4" ball end mill the 3D pocket I was cutting seemed to rough out very nicely, but when I tried to do a "finish" pass with tighter resolution and percentage of step over it seemed to drift a little on each pass.  No machine settings where changed between passes. 

I was cutting in constant velocity mode, but with a very small rounding number. 

Offline Hal

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Re: Backlash compensation
« Reply #1 on: July 28, 2012, 01:48:31 PM »
Yep backlash issues.

The heavy cuts force the axis to one side. The lighter cuts allow the float of the axis to show up. You need to get machanial backlash out of the mill as possible. This may include the lead screw and nut. Check the gibs. Slop there could show up as backlash in the other axis. Sloppy will give you greater speed.  Any flex in the Z axis?

Try a circle cut. Is it round. Is it round?
Re: Backlash compensation
« Reply #2 on: July 28, 2012, 02:12:03 PM »
Over time I have noticed if I leave the Taig fairly sloppy it tends to stay close to the same amount of sloppy for much longer than if I adjust and tighten it up to reduce mechanical backlash.  One of Hoss's videos inspired me to try leaving it that way and instead using backlash compensation.  At his settings the machine would lose position and walk across the face of the work piece fairly quickly.   I used very conservative settings compared to what He had used and it seemed to work ok.  I cut a 1" register pocket with a .250" end mill and I was modestly satisfied with the results.  It was within .003" total tolerance of round.  Then I tried to cut some parts.  With a 1/4" ball end mill the 3D pocket I was cutting seemed to rough out very nicely, but when I tried to do a "finish" pass with tighter resolution and percentage of step over it seemed to drift a little on each pass.  No machine settings where changed between passes.  

I was cutting in constant velocity mode, but with a very small rounding number.  

I can adjust to about to about .002 backlash per axis.  Unfortunately if I do that the machine exhibits excessive wear and loss of consistency within a few hours of machine time.  If I leave the backlash at about .005 to .01 excessive wear or change in backlash takes a about 20 hours of machine time.  I was hoping backlash compensation would work so that I coule leave the machine in that sloppier range and be able to actually complete a longer job between machine adjustments.  Your reply tends to indicate to me that backlash compensation CAN NOT BE USED for this purpose. 

Yes I do know how to adjust the machine. 

Perhaps another member might be able to suggest actual settings for backlash compensation that might work, but thank you for your feedback. 
« Last Edit: July 28, 2012, 02:14:45 PM by Bob La Londe »

Offline Jeff_Birt

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Re: Backlash compensation
« Reply #3 on: July 28, 2012, 02:42:48 PM »
Quote
Unfortunately if I do that the machine exhibits excessive wear and loss of consistency within a few hours of machine time.  If I leave the backlash at about .005 to .01 excessive wear or change in backlash takes a about 20 hours of machine time. 


Then you are doing 'something' wrong. I set my Taigs so the backlash is under 0.001" and it will stay that way for hundreds of hours. I do have a tendency of moving my fixtures and vise around so that I use the entire length of the screw, not just a few inches in the center. How often are you lubricating things and what type of lubrication do you use?

You are never going to get 0.005"~0.010" of backlash out with open loop software compensation it will just not work as the table is pushed around by the cutting forces.
Happy machining , Jeff Birt
 
Re: Backlash compensation
« Reply #4 on: July 28, 2012, 03:11:10 PM »
Yes, Jeff.  Whatever you say.  I suspect the answer to this is going to be like your answer to 250IPM rapids for a Taig, but I am willing to play.  

How much cutting force can it stand to stay within .001" for hundreds of hours?
How often do you lubricate the machine to stay within .001" for hundreds of hours?
What kind of lubricant do you use to stay within .001" for hundreds of hours?  
What rapid speed, cutting speed, and acceleration do you set your machine at to stay within .001" for hundreds of hours?  

What answer for all of the above questions at the same time allows you to stay within .001 for hundreds of hours?  


And bear in mind I am not running that overweight chuck of lead Taig calls a spindle.  I am running a spindle that turns 28000 RPM currently and making cuts in aluminum that a 28000 RPM spindle is capable of.  Actually conservative cuts at that speed, but far above what the stock spindle is capable of.  

If I could get the machine to stay within .001" for hundreds of hours (and not babying it at 10% of its "capacity") I would not even need backlash compensation.  

Bear in mind that the roughing pass with much more aggressive (more cutting load) cuts seemed to cut beautifully, but the finish pass with very light cutting loads was the one that wandered out into left field.  

In the long run if I continue to run this machine its going to get ball screws on all axis and probably a totally redesigned Z.  The nuts, and screws have been recently replaced and were broken in from limit to limit for about 2 hours with grease (as recommended by Taig - the grease not the breakin).  My typical job uses from 40-100% of the X and Y working envelope.  Often parts use nearly 100% of both for the over all part, and about 60-90% for intensive machining.  The gibbs are fine, and all the axis bearings were replaced when the screws were replaced.  Since the axis bearings are just cheap Chinese skate bearings I am really impressed that you can keep your machine running at high rapids, and adjusted to under .001" for hundreds of hours just because of the bearings.  


Yes, Jeff.  Whatever you say.  I suspect the answer to this is going to be like your answer to 250IPM rapids for a Taig, but I am willing to play. 

How much cutting force can it stand to stay within .001" for hundreds of hours?
How often do you lubricate the machine to stay within .001" for hundreds of hours?
What kind of lubricant do you use to stay within .001" for hundreds of hours? 
What rapid speed, cutting speed, and acceleration do you set your machine at to stay within .001" for hundreds of hours? 

What answer for all of the above questions at the same time allows you to stay within .001 for hundreds of hours? 


And bear in mind I am not running that overweight chuck of lead Taig calls a spindle.  I am running a spindle that turns 28000 RPM currently and making cuts in aluminum that a 28000 RPM spindle is capable of.  Actually conservative cuts at that speed, but far above what the stock spindle is capable of. 

If I could get the machine to stay within .001" for hundreds of hours (and not babying it at 10% of its "capacity") I would not even need backlash compensation. 

Bear in mind that the roughing pass with much more aggressive (more cutting load) cuts seemed to cut beautifully, but the finish pass with very light cutting loads was the one that wandered out into left field. 

In the long run if I continue to run this machine its going to get ball screws on all axis and probably a totally redesigned Z.  The nuts, and screws have been recently replaced and were broken in from limit to limit for about 2 hours with grease (as recommended by Taig - the grease not the breakin).  My typical job uses from 40-100% of the X and Y working envelope.  Often parts use nearly 100% of both for the over all part, and about 60-90% for intensive machining.  The gibbs are fine, and all the axis bearings were replaced when the screws were replaced.  Since the axis bearings are just cheap Chinese skate bearings I am really impressed that you can keep your machine running at high rapids, and adjusted to under .001" for hundreds of hours just because of the bearings. 


Yes, Jeff.  Whatever you say.  I suspect the answer to this is going to be like your answer to 250IPM rapids for a Taig, but I am willing to play. 

How much cutting force can it stand to stay within .001" for hundreds of hours?
How often do you lubricate the machine to stay within .001" for hundreds of hours?
What kind of lubricant do you use to stay within .001" for hundreds of hours? 
What rapid speed, cutting speed, and acceleration do you set your machine at to stay within .001" for hundreds of hours? 

What answer for all of the above questions at the same time allows you to stay within .001 for hundreds of hours? 


And bear in mind I am not running that overweight chuck of lead Taig calls a spindle.  I am running a spindle that turns 28000 RPM currently and making cuts in aluminum that a 28000 RPM spindle is capable of.  Actually conservative cuts at that speed, but far above what the stock spindle is capable of. 

If I could get the machine to stay within .001" for hundreds of hours (and not babying it at 10% of its "capacity") I would not even need backlash compensation. 

Bear in mind that the roughing pass with much more aggressive (more cutting load) cuts seemed to cut beautifully, but the finish pass with very light cutting loads was the one that wandered out into left field. 

In the long run if I continue to run this machine its going to get ball screws on all axis and probably a totally redesigned Z.  The nuts, and screws have been recently replaced and were broken in from limit to limit for about 2 hours with grease (as recommended by Taig - the grease not the breakin).  My typical job uses from 40-100% of the X and Y working envelope.  Often parts use nearly 100% of both for the over all part, and about 60-90% for intensive machining.  The gibbs are fine, and all the axis bearings were replaced when the screws were replaced.  Since the axis bearings are just cheap Chinese skate bearings I am really impressed that you can keep your machine running at high rapids, and adjusted to under .001" for hundreds of hours just because of the bearings. 
Yes, Jeff.  Whatever you say.  I suspect the answer to this is going to be like your answer to 250IPM rapids for a Taig, but I am willing to play. 

How much cutting force can it stand to stay within .001" for hundreds of hours?
How often do you lubricate the machine to stay within .001" for hundreds of hours?
What kind of lubricant do you use to stay within .001" for hundreds of hours? 
What rapid speed, cutting speed, and acceleration do you set your machine at to stay within .001" for hundreds of hours? 

What answer for all of the above questions at the same time allows you to stay within .001 for hundreds of hours? 


And bear in mind I am not running that overweight chuck of lead Taig calls a spindle.  I am running a spindle that turns 28000 RPM currently and making cuts in aluminum that a 28000 RPM spindle is capable of.  Actually conservative cuts at that speed, but far above what the stock spindle is capable of. 

If I could get the machine to stay within .001" for hundreds of hours (and not babying it at 10% of its "capacity") I would not even need backlash compensation. 

Bear in mind that the roughing pass with much more aggressive (more cutting load) cuts seemed to cut beautifully, but the finish pass with very light cutting loads was the one that wandered out into left field. 

In the long run if I continue to run this machine its going to get ball screws on all axis and probably a totally redesigned Z.  The nuts, and screws have been recently replaced and were broken in from limit to limit for about 2 hours with grease (as recommended by Taig - the grease not the breakin).  My typical job uses from 40-100% of the X and Y working envelope.  Often parts use nearly 100% of both for the over all part, and about 60-90% for intensive machining.  The gibbs are fine, and all the axis bearings were replaced when the screws were replaced.  Since the axis bearings are just cheap Chinese skate bearings I am really impressed that you can keep your machine running at high rapids, and adjusted to under .001" for hundreds of hours just because of the bearings. 


Yes, Jeff.  Whatever you say.  I suspect the answer to this is going to be like your answer to 250IPM rapids for a Taig, but I am willing to play. 

How much cutting force can it stand to stay within .001" for hundreds of hours?
How often do you lubricate the machine to stay within .001" for hundreds of hours?
What kind of lubricant do you use to stay within .001" for hundreds of hours? 
What rapid speed, cutting speed, and acceleration do you set your machine at to stay within .001" for hundreds of hours? 

What answer for all of the above questions at the same time allows you to stay within .001 for hundreds of hours? 


And bear in mind I am not running that overweight chuck of lead Taig calls a spindle.  I am running a spindle that turns 28000 RPM currently and making cuts in aluminum that a 28000 RPM spindle is capable of.  Actually conservative cuts at that speed, but far above what the stock spindle is capable of. 

If I could get the machine to stay within .001" for hundreds of hours (and not babying it at 10% of its "capacity") I would not even need backlash compensation. 

Bear in mind that the roughing pass with much more aggressive (more cutting load) cuts seemed to cut beautifully, but the finish pass with very light cutting loads was the one that wandered out into left field. 

In the long run if I continue to run this machine its going to get ball screws on all axis and probably a totally redesigned Z.  The nuts, and screws have been recently replaced and were broken in from limit to limit for about 2 hours with grease (as recommended by Taig - the grease not the breakin).  My typical job uses from 40-100% of the X and Y working envelope.  Often parts use nearly 100% of both for the over all part, and about 60-90% for intensive machining.  The gibbs are fine, and all the axis bearings were replaced when the screws were replaced.  Since the axis bearings are just cheap Chinese skate bearings I am really impressed that you can keep your machine running at high rapids, and adjusted to under .001" for hundreds of hours just because of the bearings. 

Yes, Jeff.  Whatever you say.  I suspect the answer to this is going to be like your answer to 250IPM rapids for a Taig, but I am willing to play. 

How much cutting force can it stand to stay within .001" for hundreds of hours?
How often do you lubricate the machine to stay within .001" for hundreds of hours?
What kind of lubricant do you use to stay within .001" for hundreds of hours? 
What rapid speed, cutting speed, and acceleration do you set your machine at to stay within .001" for hundreds of hours? 

What answer for all of the above questions at the same time allows you to stay within .001 for hundreds of hours? 


And bear in mind I am not running that overweight chuck of lead Taig calls a spindle.  I am running a spindle that turns 28000 RPM currently and making cuts in aluminum that a 28000 RPM spindle is capable of.  Actually conservative cuts at that speed, but far above what the stock spindle is capable of. 

If I could get the machine to stay within .001" for hundreds of hours (and not babying it at 10% of its "capacity") I would not even need backlash compensation. 

Bear in mind that the roughing pass with much more aggressive (more cutting load) cuts seemed to cut beautifully, but the finish pass with very light cutting loads was the one that wandered out into left field. 

In the long run if I continue to run this machine its going to get ball screws on all axis and probably a totally redesigned Z.  The nuts, and screws have been recently replaced and were broken in from limit to limit for about 2 hours with grease (as recommended by Taig - the grease not the breakin).  My typical job uses from 40-100% of the X and Y working envelope.  Often parts use nearly 100% of both for the over all part, and about 60-90% for intensive machining.  The gibbs are fine, and all the axis bearings were replaced when the screws were replaced.  Since the axis bearings are just cheap Chinese skate bearings I am really impressed that you can keep your machine running at high rapids, and adjusted to under .001" for hundreds of hours just because of the bearings. 

As to backlash....  it wasn't just a matter of eliminating backlash by software, but the fact that the cut drifted and continued to drift on every cut pass.  The net result would have been satisfactory if turning backlash compensation on had not caused the machine to drift out of position.  Every single cut pass was off from the previous one by a small amount.  The cumulative loss of position was pretty bad.  With backlash compensation turned off this does not happen. 




« Last Edit: July 28, 2012, 03:29:44 PM by Bob La Londe »
Re: Backlash compensation
« Reply #5 on: July 28, 2012, 03:33:29 PM »
Oops.  Not sure how that happened, but here:  


Yes, Jeff.  Whatever you say.  I suspect the answer to this is going to be like your answer to 250IPM rapids for a Taig, but I am willing to play.  

How much cutting force can it stand to stay within .001" for hundreds of hours?
How often do you lubricate the machine to stay within .001" for hundreds of hours?
What kind of lubricant do you use to stay within .001" for hundreds of hours?  
What rapid speed, cutting speed, and acceleration do you set your machine at to stay within .001" for hundreds of hours?  

What answer for all of the above questions at the same time allows you to stay within .001 for hundreds of hours?  


And bear in mind I am not running that overweight chuck of lead Taig calls a spindle.  I am running a spindle that turns 28000 RPM currently and making cuts in aluminum that a 28000 RPM spindle is capable of.  Actually conservative cuts at that speed, but far above what the stock spindle is capable of.  

If I could get the machine to stay within .001" for hundreds of hours (and not babying it at 10% of its "capacity") I would not even need backlash compensation.  

Bear in mind that the roughing pass with much more aggressive (more cutting load) cuts seemed to cut beautifully, but the finish pass with very light cutting loads was the one that wandered out into left field.  

In the long run if I continue to run this machine its going to get ball screws on all axis and probably a totally redesigned Z.  The nuts, and screws have been recently replaced and were broken in from limit to limit for about 2 hours with grease (as recommended by Taig - the grease not the breakin).  My typical job uses from 40-100% of the X and Y working envelope.  Often parts use nearly 100% of both for the over all part, and about 60-90% for intensive machining.  The gibbs are fine, and all the axis bearings were replaced when the screws were replaced.  Since the axis bearings are just cheap Chinese skate bearings I am really impressed that you can keep your machine running at high rapids, and adjusted to under .001" for hundreds of hours just because of the bearings.  

As to backlash....  it wasn't just a matter of eliminating backlash by software, but the fact that the cut drifted and continued to drift on every cut pass.  The net result would have been satisfactory if turning backlash compensation on had not caused the machine to drift out of position.  Every single cut pass was off from the previous one by a small amount.  The cumulative loss of position was pretty bad.  With backlash compensation turned off this does not happen.  
Re: Backlash compensation
« Reply #6 on: July 28, 2012, 03:36:54 PM »
P.S.  When I say hours I mean hours of run time cutting parts.  Currently I think I have over 20,000 hours of run time on this Taig.  
« Last Edit: July 28, 2012, 03:39:53 PM by Bob La Londe »

Offline Jeff_Birt

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Re: Backlash compensation
« Reply #7 on: July 28, 2012, 05:14:14 PM »
Bob there is no need to be snide. I'm trying to help and by saying "you doing 'something' wrong" I'm meaning to imply that your results are not typical. (I was not trying to be rude.)

I do have to doubt your 20,000 hour estimate though, that would be 833 days of use 24 hours a day. So unless you have run your machine for more than 2.5 years non stop, or five years twelve hours a day then your estimate is a bit high. I think though that your point is that you run your machine a lot and judging my all the neat molds I have seen pictures of I would guess you do run it many hours.

I'm also not sure what your getting on about with your 250 IPM quip, again rudeness is not required. As is clearly stated in the video and in what I have written about it is that the point was to show big stepper motors are not required to obtain high speeds. As I said in the video it is not recommended.

For the last six months I've had my machine set for 85IPM rapids and generally cut anywhere from 4~30IPM in aluminum. I work mostly with aluminum but do plastics, steels and PCBs on occasion. Acceleration is about 10 i/s/s. Before that, for the last three years or so, it has been set to rapid around 50 IPM. I raised it to 85IPM when helping a customer tune his machine for best performance when doing lithopanes. With this machine I lube the leadscrews and ways about every 8 hours with automatic transmission fluid. On occasion I'll run an exercise program to run each axis from limit to limit to make sure the lubrication is well distributed.

I have another Taig with the MM2000 controller that is not capable of the high rapids but its cuttings speeds are similar. It is set up with flood cooling so it gets lubricated about twice as often. Both machines use the stock spindle motor and spindle. Both machines use bits from teeny-tiny sizes to 3/8"

As I recall Bob you do a lot of 3D profile work which can take many hours of continuous running. If your running these long sessions you would want to stop every now and again to lube things up or fit your machine with an automatic oiler. This is what I was getting at asking about how often you lubricate the machine and with what sort of lubrication. Lack of lubrication will wear things out in a hurry and this would be my first guess as to a cause. Cutting a small aluminum mold could take 20-30 hours and if your not stopping to relube every 4-5 hours you will wear things out quickly.

Large stepper motors can put more strain on drive components. Some folks have problems on some small machines breaking stepper couplers that were designed for 150oz-motor because they are using much larger motors. If your spindle motor is much more powerful than the stock Taig unit and your combining that with large stepper motors to get fast cutting rates with a large cutter than you could just be applying more force to the leadscrew/nut than they were designed to handle. This may be a contributing factor but I'm still guessing that it is lack of lubrication.

You could fit an automatic oiler to your machine but it is sounding like you might be growing out of it. A small Haas or similar machine might be better suited to the type of work you are doing and your need for a stronger spindle.

Good luck...
Happy machining , Jeff Birt
 
Re: Backlash compensation
« Reply #8 on: July 28, 2012, 05:43:21 PM »
20,000 is a guess, but at one point I had the log in Mach showing over 13,000 hours.  That was the second computer on the machine.  Its now on its third computer.  I have had the machine for about 4+ years.  I'ld have to go back into my accounting software and see when I purchased the machine.  I have definitely outgrown the machine, but I just can't afford a Haas.  I am considering a Syil X5 Speedmaster (with the optional 35K spindle) though.  I would have to give up a little X axis, but the design is definitely a lot more robust than a Taig.  I did talk with some of the guys at Syil (China) and I might be able to tweak the machine by running dual limits or disabling limits for certain jobs to maintain the 12" X limit I really need.  The Syils now have auto oiling built in to all mills so that's a plus. 

I was also considered a Tormach 770, but I would have to back off on production (10K max spindle) or plan on buying a couple of their speeders to go with it.  Their lack of concentricty is not an issue since I probably wouldn't do both low and high speed machining on the same part.

Anyway, the practical answer is probably that I just can't get any more out of the Taig, and I have probably gotten a lot more out of it than most folks. 

In this case though, I just want to know why it started losing position incrementally when backlash compensation was turned on (with some pretty conservative settings).  Also why it did not lose position with the first very aggressive roughing MOP.  Full depth (less roughing clearance) in one depth increment with a 1/4" ball mill.

I run flood transmission fluid for coolant and cutting oil on aluminum by the way.  Even if it washes away my grease its a lubricant in its own right. 
Re: Backlash compensation
« Reply #9 on: July 28, 2012, 05:55:46 PM »
The radical change just blew me away...