Z axis slipping

[mattswensson]

I have a situation where (what is seemingly random) the z direction down sometimes drops farther than it should - almost like it is slipping. This results in my Z0 basically changing during the middle of a job.

I have manually gone up and down 20mm repeatedly and can sometimes reproduce but not always.

I’ve adjust the backlash numerous times thinking it might be coming loose but I don’t think that’s it.

I initially used a 3D printed backlash but then switched to one I bought off Amazon. The pitch and lead seems to be fine - the issue occurred with both the 3D printed and the purchased one.

I’ve swapped drivers from tb6600 to a dm542 but in watching the issue it seems more of a mechanical issue but can’t figure out what. It’s very frustrating.

Anyone else experienced something like this or have some advice?

Thanks
Matt

[HTheatre]

Hi Matt,

I initially used a 3D printed backlash but then switched to one I bought off Amazon. The pitch and lead seems to be fine - the issue occurred with both the 3D printed and the purchased one.

And what is about the TR8 screw itself ? Are you sure it has a 2 mm lead and 2 mm pitch ?
It's easy to check. Count the number of threads' starts, looking at the cross section from the top of the screw. Here are two pictures to help you to see what I want to mean.





See ya

[mattswensson]

Thanks I will double check in the morning.

Also I just remembered that when I swapped out the anti backlash I had some ball bearings fall out of the linear guides. I put them back but wonder if that could some how be related?

I did find also that my feed rate might have also been too high for the bit. When I slowed it down and made multiple passes it seemed to get me through a cut but in general I feel I have to be too delicate with the cuts - maybe that is just what it will be with the generic router

[mattswensson]

I just ran out there now for a picture. It looks like 2?

This is what I ordered (and believe is what I got)
3D Printer T8 screw THSL-200-8D Trapezoidal Lead Screw Dia 8MM Pitch 2mm Lead 2mm Length 200mm with Copper Nut
https://www.aliexpress.com/item/3271143 ... 4c4dkbWORj

This is the antibacklash nut i ordered (after my aliexpress order never arrived)
Befenybay 2PCS Anti-Backlash Nut 8mm Diameter Lead Screw Nut, Lead Screw Moves 2mm in One Turn for CNC and 3D Printer (2mm Pitch 2mm Lead)


I understand you don't always get what you ordered. The nut seemed to screw on with little to no play especially after putting the set screw in place.

Looks like 1 start on the left and one on the right

lead_screw.jpg

[HTheatre]

Hi Matt,

Also I just remembered that when I swapped out the anti backlash I had some ball bearings fall out of the linear guides. I put them back but wonder if that could some how be related?

I do not think it could be the reason of your issue, either.

I did find also that my feed rate might have also been too high for the bit. When I slowed it down and made multiple passes it seemed to get me through a cut but in general I feel I have to be too delicate with the cuts - maybe that is just what it will be with the generic router

In which material : wood, aluminum, other ?

I just ran out there now for a picture. It looks like 2?

No, I don't thin so. It's hard to say looking at your picture, but it seems you have the right TR8 screw. The members who didn't received the right screw (even if they had ordered the right one), usually received TR8 screws with a 8mm lead and a 2mm pitch, which are TR8 screws designed to use with our 3D printers. I have the 2 models in stock, so I will try to make pictures to compare.

This is the antibacklash nut i ordered (after my aliexpress order never arrived)
Befenybay 2PCS Anti-Backlash Nut 8mm Diameter Lead Screw Nut, Lead Screw Moves 2mm in One Turn for CNC and 3D Printer (2mm Pitch 2mm Lead)

As you also tried the printed version of the mstrens' anti-backlash nut, I think the TR8 screw and the anti-backlash nut, you purchased, are the right ones.

I am sure you already done, but if not, check the Z closed belt is properly stretched and that the screws of the Z motor are properly tighten.

We are agree you use NEMA32 motors and not NEMA17 ones, isn't it ?

See ya

[mattswensson]

In which material : wood, aluminum, other ?

I am cutting into Wood. Have yet to try metal. I am just trying to make some simple signs for christmas gifts.

I am sure you already done, but if not, check the Z closed belt is properly stretched and that the screws of the Z motor are properly tighten.

I will double check the motor is on tight and the belt is taught

We are agree you use NEMA32 motors and not NEMA17 ones, isn't it ?

I am using these NEMA 23 motors:
https://www.aliexpress.com/item/3250528 ... 4c4d1EAD41

are you using NEMA 32? (or did you mean 23 or possibly 34?)

Pretty much all the parts I ordered were from the PDF document.

Will see if I can get a good video of the situation.

Thank you again for your help on this.

[HTheatre]

We are agree you use NEMA32 motors and not NEMA17 ones, isn't it ?

are you using NEMA 32? (or did you mean 23 or possibly 34?)

Sorry, I inverted the 2 digits. I wanted to write NEMA23. Actually, I use these NEMA23, but I just received these new ones, which have more torque. I didn't install them on my RS-CNC32 yet.

See ya

[mattswensson]

Here is possibly a better picture of the TR8 screw.

Also, I noticed that it is possible for me to wiggle the whole assembly up and down - basically reproducing the issue manually. This would seem to rule out tension from the belt or motor and lead more to the antibacklash nut or screw.

I am able to turn the screw manually and then after a quarter turn or so, if I push down on the assembly, it 'catches up' to the position it should be at.

This would seem to indicate too much play with the antibacklash nut or possibly the wrong mix of screw and nut? Possibly not enough lubrication on the linear guides?

taking the z assembly apart to change the antibacklash nut is somewhat of a nightmare

How far in should the set screw of the antibacklash nut be screwed in? I've tried various depths although that is also very hard to get to with the assembly in the way.

[mattswensson]

Here is a video of the 'play' in the assembly.

[HTheatre]

Watching your video, it's clearly a problem of compatibility between the anti-backlash nut and the TR8 screw which have not the same lead.

Here is a TR8 with 2mm lead and 2 mm pitch (the right one). It counts 1 start of thread.





Here is a TR8 with 8mm lead and 2 mm pitch (used on our 3D printers - and not compatible with the RS-CNC32). It counts 4 starts of threads.







I am sorry, I no not have TR8 screw with 4mm lead and 2mm pitch, which counts 2 starts of threads, like you suppose your TR8 screw has.

Here is a video I made for a membrer I shipped a TR8 screw and its anti-backlash nut (lead: 2mm & pitch: 2mm), en Germany.



Moreover, I didn't tightened the screw of my anti-backlash nut assembly. Normally, you do not have to do it or just a little little bit.

You you want I ship you the right TR8 screw and the right anti-backlash nut ? I have 4 of each ones in stock. Here is all the information you need to know about this service. If you are interested in this service, semd me a private message.

See ya