Hello everyone, I have a problem with my “MPCNC”. The Z axis is skewed sideways. It’s not the XY frame. The four corners / tubes are all at the same height. The tubes are at an angle to the front and back. I tried a little to fix the problem by making adjustments to the screws of the middle section. Unfortunately without success. Do you have any ideas about what else I could do?
That is just a matter of getting the tension fairly equal on all four of the 2.5" bolts. I bet you will find two opposites are fairly loose and two are tight.
Thanks for your quick response, Ryan! Today i tried to fix it with equal and different tensions on the four screws (for example like shown on the pic). Sadly it wasn‘t the solution. Maybe i have to try it just with one tube on the left and the right side without the printed toolmount and z parts, to see where the problem is. 
Start by making things more loose instead of making the loose things tight.
I have exactly the same Issue and a few more details i might be able to add for the OP to check and someone else to comment on if such behavior is “acceptable”:
Unless mentioned otherwise all of these issues arise even if all tension bolts als loose to the point of “barely touching the plastic”. So “more loose” is not really an option.
- Initially not all bearings make contact to the tubes. Tightening the tension bolts fixes that ofc.
- If the 130mm center bolt is loose the spacers can freely rotate around the bolt (guessing around .3-.5mm of play) if no leadscrew is inserted. Should those make contact already? Shimming them would be easy.
- Z-Axis tubes are not parallel when mounting the toolholder. -.2mm difference in width top to bottom. Everything else is straigt and square until the Z axis tubes are inserted. Then Stuff shifts. Shim toolholder? Add any kind of reinforcement at the bottom?
Maybe the op can confirm, if anyone knows any places to look for further errors that would be great.
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Everything is an interference fit. All bearings should always touch, so if they are not have a look at the FAQ. Take it apart and do it again, that almost always fixes it. Too tight can 100% cause this.
3- It should be parallel. When assembling take note of this and do not let it happen.
It would be best to star your own topic if that does not fix it. With no reply in 2 weeks I have to assume the OP issue is fixed.
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I was on vacation the holidays. The problem has not yet been solved. I have adjusted my Ender 3 more precisely and will reprint the middle section completely. Maybe that will solve my problem. I’ve already tried every option regarding the screws. This means that the Z axis cannot be set at right angles. My guess is that especially not perfectly angular XYZ parts lead to the skew. Since the upper and lower parts are mounted the other way around, this could possibly lead to this. I will get back to you as soon as I have finished printing and assembling. (And sorry for my bad Google translated english 
)
Hey Ryan,
i will come up with a complete buildlog eventually. “Lessons learned” and “Ongoing issues” will be part of that. Is there any “proper” way to contribute to the assembly instructions? I have some suggestions on my list that i feel like it would make life easier for some ppl if it was in there right from the start. Would love to share them.
But back to topic…the Z-Axis parallelity issue ist almost fixed. Disassembled the entire thing, noticed screw-marks on the holes in the pipes, widened the holes to 6mm and reassembled. Have it parallel to < .1mm now and the twisting after insertion is gone. I assume the remaining error is just in the printed parts itself and will be shimmed or parts will be reprinted…we’ll see.
Just one thing that is not yet perfectly clear to me: The “center block” spacers are also supposed to be an interference fit? They never were for me cause i never tightenend the bolt much (my gantry was pretty square an I didn’t want to f that up). I could image them being designed to be a little loose to make room for adjustments so it would be great to have a clear answer on that.
As with the other issues…if reprinting helps the OP I might just do that as well. As for now i will try to get better bearing contact through reassembly, then tighten everything as good as i can, get the spoliboard done to have a “better” surface to measure against (although the frame itself came out pretty straight, square and level and running a dial-indicator across the baseplate didnt reveal anything completly terrible) and see if toolmarks tell me anything i dont know yet.
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The docs have a pencil on every page that will lead you to a page for editing their content. You will need a github account, and the changes will result in a “pull request”, which just means Ryan and others can comment, or change your changes before keeping them. So far, we haven’t had many contributions, but we are hoping for more community contributions.
So, yes, please!
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Full teardown and reassembly helped quite a bit. Also just slightly sanded down the layermarks on the bearing-“standoffs” to improve the contact surface and cleaned up the holes. Should have done that right after printing. And i realized that my “square” is not a square but just some random non-90° angle. Need to get some precision stuff. A least to know how far off my other stuff is.
For me the issue has improve enough to call it done for now.
Now lets get that github thing rolling…
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Hi there,
@Jansetsfire
is there any progress or findings on the loose spacers and how they affect the tilt z-axis?
As i posted in another thread already today, my spindle is quiet heavy and leads to more tilt on my z-axis than my lighter proxxon tool.
I do think if i minimize that play using shims oder reprint that spacers it will help to carry or distribute the spindle weight over the parts.
Reassembling my z-axis again is not an option at the moment cause i already did that a couple of times to get my mpcnc squared. At the end, i decided to use the dual endstop solution which improves my build much.
Regrads Thomas
Hey Thomas,
sorry for the late reply. The actual mpcnc build is somewhat on hold at the moment. Was on vacation mid january and after that I had to almost completly rebuild my entire basement to make the machine go in the right place and not obstucting my other work area (yep, it a small basement ;)). I will move the machine today or tomorrow. Then i will be able to do some dirkty work without my wife killing me (Milling mdf in the living room is never a good idea).
This however will hopefully get me a solid baseline on machine performance and some better understanding on the areas that require the most attention. The drawings i did gave me some insight on dimensional accuracy in x and y but apart from that i know nothing yet. And all i know will most likely change as cutting forces become a factor.
Hi Jan,
no problem! I know about the “Woman Acceptance Factor”, believe me 
At the moment i do the final wiring of my spindle, vfd and the rest.
A water cooler/chiller arrived last week so i can start milling after i get my vacuum done.
Otherwise i get in trouble with my wife too…LOL
I also think the tilt and play get’s more worse when starting to mill sheets of mdf or aluminum.
Maybe i will change dimensions so it get’s more rigid and use a double or bigger belt as show in another post.
But this will be a project for next winter 
I also consider to sell mine as it is and build something complete different. I will see when the time has come …
Until then i will update this thread from time to time if there are new findings.