.001 Z Axis Problem

[BlueFin]

I think I have backlash , I was having some problems using my mill as a lathe with a cut off tool on some brass and starting measuring things. A test indicator was put into the spindle, I brought the Z axis down to the vise until the needle moved, then zero the indicator dial and the DRO. holding the control key and stepping .001 it takes exactly 5 button pushes to move down .005 (this would be continuing down from a previous downward motion). Then when I start pushing the page up key the first push has no physical movement but you can hear the motor turn. It takes 6 pushes .006 to move the .005 distance back up to zero, then it takes another 6 pushes to get back down to .005 because again the first .001 of the direction reversal does nothing.

So, that sucks, how do I fix this? would it be the ball nut loose on the screw? or is it the thrust bearings on the end of the ball screw? At any rate the gibs are tight enough to allow this to happen otherwise there would be no backlash at all if the head was hanging from the screw like a bowling ball hanging from a rope (not that I am suggesting that as a fix only as an observation of current function).

[philbur]

Read your inspection certificate G7 c).

Phil

Originally Posted by BlueFin I think I have backlash , I was having some problems using my mill as a lathe with a cut off tool on some brass and starting measuring things. A test indicator was put into the spindle, I brought the Z axis down to the vise until the needle moved, then zero the indicator dial and the DRO. holding the control key and stepping .001 it takes exactly 5 button pushes to move down .005 (this would be continuing down from a previous downward motion). Then when I start pushing the page up key the first push has no physical movement but you can hear the motor turn. It takes 6 pushes .006 to move the .005 distance back up to zero, then it takes another 6 pushes to get back down to .005 because again the first .001 of the direction reversal does nothing. So, that sucks, how do I fix this? would it be the ball nut loose on the screw? or is it the thrust bearings on the end of the ball screw? At any rate the gibs are tight enough to allow this to happen otherwise there would be no backlash at all if the head was hanging from the screw like a bowling ball hanging from a rope (not that I am suggesting that as a fix only as an observation of current function).

[sharpshooter90]

I don't own a Tormach, but the principles for any machine are the same. With the weight of the head hanging on the ball screw, you will most likely not find backlash on the down stroke. However, if the thrust bearing adjustment is loose, then the screw will move upwards a bit before it bottoms on the bearing and moves the head- this would be your motor turning with no result. To test the screw for looseness, just put a dial indicator on the top of the screw and try to move the head upwards by hand or with a lever. If this shows no movement, then its probably in the ball nut itself. Good thing is that backlash compensation in your software should take care of this simple linear motion with no problem.

[MichaelHenry]

The values for the G7 parameter measured by the Tormach auditor for my mill are significantly better in all 3 axes than the acceptace criteria. I'm just curious whether or not others are seeing the same thing.

Mike

[seanreit]

My Tormach is scary accurate, sometimes I can not measure even .001 off of what I've cut. Serial number 115

[BlueFin]

Originally Posted by philbur Read your inspection certificate G7 c). Phil

Ok I see three values in MM and my machine at time of inspection was better than the limits of quality. However I don't understand what those numbers mean? I looked in the owners manual for backlash adjustment and they say the Z should be between .0006" and .001", I would like to have mine closer to the .0006" if possible. I don't see any documentation on adjusting the backlash at the ball nut so I wonder what you would do if you had slop there? I will try to tighten my ball screw angular contact bearings to see how that helps.

I was looking a Hoss's video of backlash compensation in Mach 3, but I do not see that option available for the Tormach Mach3. Was it removed at the factory? or is it hidden somewhere? it would be nice to get the .00025" out of the X and Y by cheating with the software

[philbur]

The ballnuts on the PCNC 1100 are not adjustable, at least not by us mere mortals. It would have to be performed by a specialist company.

All you can adjust is the preload on the thrust bearing. The procedure is very hit and miss. It's very easy to end up with to much preload without knowing it. Also if the gib is loose this can cause the head to "nod" slightly so you could also look there. The procedure here is also very hit and miss. However in my opinion chasing Z axis backlash down from 0.001" to 0.0006" will be a fruitless task. Spend a day getting it down to 0.0006" (maybe) then breath on it and it's back to 0.001". You are fiddling on the limit of the design. Why do you need those extra 4 tenths on the Z axis anyway? When milling there are many other issues that will result in your cutter not being within 4 tenths of where you thought it was.

I would call 0.001" good (it's in spec) and make chips.

Phil

Originally Posted by BlueFin Ok I see three values in MM and my machine at time of inspection was better than the limits of quality. However I don't understand what those numbers mean? I looked in the owners manual for backlash adjustment and they say the Z should be between .0006" and .001", I would like to have mine closer to the .0006" if possible. I don't see any documentation on adjusting the backlash at the ball nut so I wonder what you would do if you had slop there? I will try to tighten my ball screw angular contact bearings to see how that helps. I was looking a Hoss's video of backlash compensation in Mach 3, but I do not see that option available for the Tormach Mach3. Was it removed at the factory? or is it hidden somewhere? it would be nice to get the .00025" out of the X and Y by cheating with the software

[BlueFin]

Originally Posted by philbur I would call 0.001" good (it's in spec) and make chips. Phil

After reading the Internet today I guess I stand corrected. It seems as though .001" "reverse idle" is the normal mode of operation for a Tormach. I also learned that commercial machine shops generally are OK with a tolerance of .0005" - .0007" and that is for a Mazak or Mori Seiki, unless of course you are making jet engines or something.

I never expected the machine to run down to .0001", but it's the damnest thing to pull the backlash out of the table, zero the indicator and watch the needle bump 10 times for each .001" of movement.

Still though, why no backlash compensation in the software? Hoss's machine had .006" or something in it and the software corrected all but about .0015" of it.

P.S. I made some chips this afternoon and was able to get my part with an intended Z height of .0600" to come out at .0595", I used a polished endmill shank at .1245" dia and slowly raised the spindle in .0001" increments until the shank would just slide under the tool tip. I typed .1245" into the DRO, bumped the head up to .125" and zeroed it. This would mean that on the down stroke the machine would always cut .001" too high because the first click would not move anything, however, when setting the z height in this manner you could still feel a very slight "tic" as you rolled the shank under the tool tip. So I would assume that "tic" would equal some cutting in aluminum if the spindle was on, so I figure the reverse stroke must have actually compensated for the acual Z hieght when the tool reached the metal.

At any rate, 1 month down and 19 years 11 months to go before I am one of those "been doing this for 20 years" machinists

[_swede]

Originally Posted by philbur Why do you need those extra 4 tenths on the Z axis anyway? When milling there are many other issues that will result in your cutter not being within 4 tenths of where you thought it was. I would call 0.001" good (it's in spec) and make chips. Phil

I agree with this to a certain extent. But, also playing the devil's advocate, I can appreciate how BlueFin wants to maximize the potential of his machine by striving for that extra accuracy.

I received Serial # 1333 and looking over all of my inspection measurements, I also received a machine that was well better than the allowed tollerances. (I haven't cut anything yet because I've been swamped at my day-job and haven't had time to finish my machine's installation )

However, I also realize that with time and use of the machine, many of these inspected values will grow. It's up to us as the machinist to know our tool and monitor the machine constantly. Worst case scenario: you cannot find a means to reduce this Z-axis backlash, but at least you are cognizant of it and can keep it in mind when setting up tooling / tool paths.

btw: This forum has some great discussions guys!

[_swede]

Originally Posted by BlueFin At any rate, 1 month down and 19 years 11 months to go before I am one of those "been doing this for 20 years" machinists

Hahah!

Hey, also I've been meaning to ask: any relation to Bluefin Robotics Corp. out of Boston?? Or just cooincidence? Perhaps you've answered this before.. I didn't bother to search.. Sorry!

[BlueFin]

Originally Posted by _swede I agree with this to a certain extent. But, also playing the devil's advocate, I can appreciate how BlueFin wants to maximize the potential of his machine by striving for that extra accuracy. I received Serial # 1333 and looking over all of my inspection measurements, I also received a machine that was well better than the allowed tollerances. (I haven't cut anything yet because I've been swamped at my day-job and haven't had time to finish my machine's installation ) However, I also realize that with time and use of the machine, many of these inspected values will grow. It's up to us as the machinist to know our tool and monitor the machine constantly. Worst case scenario: you cannot find a means to reduce this Z-axis backlash, but at least you are cognizant of it and can keep it in mind when setting up tooling / tool paths.

Welcome to new Tormach ownership, it takes a strange person to drop 10 grand on something that sits in your garage and when friends come over and ask what it is they walk away even more confused as to what your talking about when you try to explain it. Then when you show them a part you made they think that's the only thing it does! And yes, I am interested in making the machine be all that it can be, I do fully understand that it is not a 100K+ Mazak, but if the documentation indicates that .0006" is attainable and if it's within my limited capability then it's worth a try. Although I am not touching it yet for 2 reasons, I believe that the bearings will "wear in" and start to slow down somewhere so when the backlash is removed it will be more stable, and 2, I am still too chicken to mess with it yet! So for now I just keep checking the machine and when I hand write code I manually add backlash comp into it.

[BlueFin]

Originally Posted by _swede Hahah! Hey, also I've been meaning to ask: any relation to Bluefin Robotics Corp. out of Boston?? Or just cooincidence? Perhaps you've answered this before.. I didn't bother to search.. Sorry!

Nope, no relation. They were however the first ones to come up when I searched for anyone else who might be using that business name. Both the name and the fact that I am machining now are strange transitions. My real job for 20+ years now has been forestry related in timber harvesting and mechanized fire fighting. Mostly operating large dirty bulldozers smashing things into unrecognizable piles of debris, or felling timber down in some gawd-for-saken hole somewhere for a cable yarder to drag them out of. So now for me to stand in a clean, dry shop with the heater on and worry about .0004" is a far cry from anything I have ever done in my life.

As far as the name, I have only fished twice in my life, find it rather boring, but I became to admire the "Pelagic" lifestyle of the Bluefin Tuna and try to parallel it's habits with my own.