Help Z noise

[Albert Nix]

I am still fighting a noise as the table raises and lowers It is so bad at time s that it cause the table to shake. I can put a little pressure on one corner of the table and it stop shaking. also I can tighten the belt ans it helps but not a fix. I have taken the belt off and all of the lead screws turn very free and seems to be no loose play or no noise. I check the table for level and if it is off any it is a few thousandths. The only thing I noticed that seem strange was when I turned the stepper motor it felt like it had detents on regular intevals around it axis. There is a resistance at each detent and if you try to turn it fast you can hear it. Almost reminds me of a bearing with tight spots. The servos on the x & y axis turn smooth but I know nothing about either so I do not know if stepper should feel this way or not.
Any input would be apprecaited. Thanks

[Jim Reinhard]

Hi .Not sure if you seen my earlyer reply.My mercury did the same thing.Check that your table is square with the post screws.Loosen the table from the supports under the table.run the table up and down a few times and then re tighten the cap screws.Also if you had something at any time that wedged between the table and wall you may have a bent jack screw.My table would vibrate so bad the parts I had on there would bounce around.

[Richard Rumancik]

The stepper is probably working the way it is supposed to. There are usually 200 "detent" positions in a normal stepper motor. When you turn a stepper by hand you will feel the cogging as the permanent magnet poles line up with the coils.

Stepper motors can have a tendency to generate vibrations due to the cogging. It can excite any resonances in the table assembly which unfortunately seem to be in the same order of magnitude. I have the same problem as Jim mentioned with my Mercury . If I raise the table a small amount at a time it does not go into resonance but if I raise a lot in one step it will initiate resonance.

I have not really spent much time fixing it, but I thought at one time of getting a separate microstepping motor controller and making my own separate circuit for the z-axis. (My other motivation is that in my Mercury the smallest amount I can raise with the button is too much - it is hard to get fine adjustment of the z-height without overshooting). So a separate motor controller might solve both problems. But I can't say for sure that microstepping the z-axis will solve your problem or not.

I would need to add some pushbuttons or a rocker switch beside the control panel. It would take a bit of work and time to do this and like a lot of projects it hasn't got to the front of the list.

I don't know if there are any mechanical ways of solving it. You might change to a different viscocity lubrication (I'd probably try lighter first - maybe oil instead of grease or graphite or silicone-based oil?) on the screws and see if you can reduce any slip-stick that is involved. Slip-stick in the screws can cause a vibration to occur.

http://www.bornemann-gewindetechnik.de/en/press/how-to-avoid-stick-slip-effect.html

The problem should have been identified in the design phase of the machine and you are limited to what you can do now to fix it. The quality of the lead screw surface finish and the nut, as well as the materials, could also have an effect. If you can find a different set of nuts that match your screw (say nylon or teflon), that might fix it but again there are no guarantees.

[Albert Nix]

Jim I quess I missed your other post. I haven't been on the creek as much as I like lately. So did loosening and retightening the screws solve your issues?

[Albert Nix]

Got my fingers crossed Jim, but I think you hit the nail on the head. I ended up loosening the two screws underneath
the table on the right side where the single lead screw is that holds the table to the lead screw nut mounting plate, it has slotted hole in it. I had to shift it back and forth a couple of times and tighten them a little at a time. It works fine with the screws loose so I figured there was a happy medium some where. Thanks again

[Jim Reinhard]

Hi, Yes it did fix my problem also.Have not had the vibration since I adjuste it.