Taig Z axis stepper screaming!

[Andy Fritz]

Hi folks!
I have a Taig CNC mill I haven't used much as the Z axis movement get's stuck traveling in the minus, (down) direction. Moving up is never a problem. What happens is that when rapid moves are done in the minus direction I can first hear a vibrating sound and a second later the stepper seems to get stuck and gives up this screaming sound. I first thought that the gibs were too loose and that caused the vibration to start. Tightening did not make it any better and loosening did not fix it either. Did anyone have the same problem and how did you fix it?

Any help is appreciated!

Andy

[cartertool]

Remember that you are not so much loosening and tightening as you are positioning the tapered gib - it sounds as though it is loose in the tapered pocket and when it feeds down is sliding and becoming tight, and when feeding up is becoming loose again.
When done adjusting both screws should be tight, top and bottom...

See here:
http://www.cartertools.com/millset.html
and
http://www.cartertools.com/millset2.html

[Andy Fritz]

Hi Nick,

Thanks for your advise and your fantastic web site. Adjusting the z gib is clearly the issue. I have tried just about every imaginable setting. Yesteday I spent 3 hours and the closest I got was to elliminated the pinching moving down, but it would still pinch when moving from the lowest point upwards.
I could never manage to totally get rid of the problem. BTW:
1 Is the top screw the "A" or the "B" screw?
2 When you write that they both have to be tight after adjustment, exatly how tight do you mean? It would seem to me that the actual adjustment is made in the tightness of both A and B as once they are tight and I have the pinch nearly elliminated only a 1/8 additional turn on the top screw tighter will casue more errors.

If a screw is loose so that you can rotate it with your fingers, then finger tighten it. After this point you can still tighten it a lot more with the hex key. How much additional tightening with the hex key would you recommend? As tightening the A also tightens the B, would you recommend alternating between A and B while tightening, (like you would while changing a car tire)?

It seems to be a very sensitive adjustment as I get big variation with these settings and NEVER manage a setting that totally and repeatably eradicates the problem!

Andy

Originally Posted by cartertool Remember that you are not so much loosening and tightening as you are positioning the tapered gib - it sounds as though it is loose in the tapered pocket and when it feeds down is sliding and becoming tight, and when feeding up is becoming loose again. When done adjusting both screws should be tight, top and bottom... See here: http://www.cartertools.com/millset.html and http://www.cartertools.com/millset2.html

[cartertool]

Originally Posted by Andy Fritz Adjusting the z gib is clearly the issue. BTW: 1 Is the top screw the "A" or the "B" screw?

It would be considered the top screw. Tighteing the top screw/loosening the lower screw tightens the gib, as it travels in the tapered pocket.

Originally Posted by Andy Fritz 2 When you write that they both have to be tight after adjustment, exatly how tight do you mean? It would seem to me that the actual adjustment is made in the tightness of both A and B as once they are tight and I have the pinch nearly elliminated only a 1/8 additional turn on the top screw tighter will casue more errors.

It's one of those "feel" things. Make sure the gib is loose - the last moves you made should be in the upwards direction. Once you get it adjusted, try using it - don't tighten the screws further. If they end up vibrating loose then readjust and as you suggest, tighten each a tiny bit at a time. Too much will obviously throw everything off...but I found that I needed to become comfortable with the process experimentally - after a while you will sense the feel better. Also it is better too loose than too tight...
But very loose will cause other binding issues...
As I note in my setup articles, it can cause you to go insane. Once it works, leave it alone...I haven't adjusted the z-axis in months now that I have it working right...

[phil burman]

The technique (or at least mine) for making the final adjustments of a gib that has two opposing screws is the same as the final adjustments when centring with an independent four jaw chuck on a lathe. Adjustment of the last couple of tenths is only about changing the distribution of strain between the four jaws. If a jaw gets slack then you are way past losing it. Just the absolute minimum nip on the “high side” jaw is all that is needed. If that jaw is reaching it limit then just the absolute smallest reduction in compression on the opposite jaw will finish the job.

Regards
Phil

[Andy Fritz]

Thanks Nick,

I got it working by adjusting the gib until it only got stuck at on point of traveling upwards. After that I dropped the z speed a bit in the Mach 2 motor tuning and this seemed to do the trick.

Andy

Originally Posted by cartertool It would be considered the top screw. Tighteing the top screw/loosening the lower screw tightens the gib, as it travels in the tapered pocket. It's one of those "feel" things. Make sure the gib is loose - the last moves you made should be in the upwards direction. Once you get it adjusted, try using it - don't tighten the screws further. If they end up vibrating loose then readjust and as you suggest, tighten each a tiny bit at a time. Too much will obviously throw everything off...but I found that I needed to become comfortable with the process experimentally - after a while you will sense the feel better. Also it is better too loose than too tight... But very loose will cause other binding issues... As I note in my setup articles, it can cause you to go insane. Once it works, leave it alone...I haven't adjusted the z-axis in months now that I have it working right...

[Andy Fritz]

Well put,

The only difference is that with the 4 jaw you have an indicator to help you!

Andy

Originally Posted by phil burman The technique (or at least mine) for making the final adjustments of a gib that has two opposing screws is the same as the final adjustments when centring with an independent four jaw chuck on a lathe. Adjustment of the last couple of tenths is only about changing the distribution of strain between the four jaws. If a jaw gets slack then you are way past losing it. Just the absolute minimum nip on the “high side” jaw is all that is needed. If that jaw is reaching it limit then just the absolute smallest reduction in compression on the opposite jaw will finish the job. Regards Phil

[phil burman]

You are right Andy but then again with the gib you are not trying to achieve a measured alignment with anything, just a feel. Just keep lots of compression on both screws at all times as you make the final adjustments.

Regards
Phil

Originally Posted by Andy Fritz Well put, The only difference is that with the 4 jaw you have an indicator to help you! Andy

[Andy Fritz]

Slowing doen the motor speed worked fined for a while. Now I have the same problem again. My guess is that it is caused by vibrations and slowing the motor just shifted the frequency a bit. Now I made an interesting discovery. First i tightened the gib just to the point the force over came the weight of the spindle and motor. Then you could see the backlash was huge. Then I removed the gib and I still have binding and stepper screaming on the upward move. Maybe if I adjust out the backlash the gib adjustment will not be so sensitive?

Andy

[cartertool]

First off you want the z-axis to hang by it's own weight - this is the mechanism that Taig uses to take up the backlash in the z-axis. If the z-axis is too tight then you will have backlash.

Have you played with the shoes on the side of the z-axis that clamps it to the slide back to front? You may find you need to adjust those as well.


What controller are you using? The Taig one or an aftermarket controller?
What are your rapid speeds set at?

[Andy Fritz]

Ok here is easy way to adjust the Z gib:

1 Loosen both top and bottom gib scew and unscrew them completely.

2 Remove the gib by pushing it upwards by a small hex key or similar.

3 Clean and oil it.

4 Traverse the Z axis down all the way.

5 Clean and oil the ways. Dont forget the ways behind the column.

6 Drop the gib back in place.

7 Jog the Z axis a tiny bit up and down so it settles.

8 Replace the bottom screw first. Use your fingers only.

9 As you approach the point where the bottom screw start pushing up the gib, screw in and out a few times so that you feel exactly the touch point.

10 Tighten another quarter turn.

11 Replace the top screw and hand tighten it so it feels as tight as the bottom screw.

12 Alternate tightening top and bottom screws further with a hex wrench one 1/8 turn each until both screws are tight.

13 Jog the Z axis up and down on a higher rapid. The idea is that the gib adjustment is more sensitive at a higher traverse speed and you will detect any binding quickly.

14 If the Z axis binds on the up ward travel, (+), tighten the bottom screw 1/8 turn and try again. If it still binds on the upward travel, tighen the bottom screw another 1/8 turn and repeat. If it binds of the downward travel,
do the opposite.

15 Adjust your z motor back to its normal speed setting.

The important thing is to think a bit before turning the screws. A good idea is to always go back to the previous setting if you go to far. If you tighten and want to go back, remember the backlash. Loosen further and tighten back to where you want it.

Andy

[Andy Fritz]

Hi Nick,

Yes, I did adjust the side screws with out the spindle motor, clamping it by hand force like recommended. I think the problem might be that either the ways or the gib is not ground right. Now it works, but running a program you can hear an emerging vibration when the spindle is really low on the axis. It can bind at random. I just went through a long program getting ready to jump in a lower the feed if needed. I had a few problem with the Y binding as well. The nasty thing is that it is not easy to get the off set back again as I only have soft limits which depend on the machine coordinates.

I tought I could use the Taig to free up my Bridge port and keep both running in the same time. It appears the Taig is too time consuming as I have to watch it all the time, or lose offsets all the time.

The control is from Deepgrove in NYC. The steppers are 253 Oz and the program is Mach 2.

Thanks for all you help!

Andy

Originally Posted by cartertool First off you want the z-axis to hang by it's own weight - this is the mechanism that Taig uses to take up the backlash in the z-axis. If the z-axis is too tight then you will have backlash. Have you played with the shoes on the side of the z-axis that clamps it to the slide back to front? You may find you need to adjust those as well. What controller are you using? The Taig one or an aftermarket controller? What are your rapid speeds set at?