Lead screw tension, board & LCD mounting and more!

My MPCNC is coming together nicely…just dropped the middle assembly onto the rails and put the steppers on. Time for the electronics. A few things have popped up so I thought I’d ask.

when I slid the Z assembly into place the leadscrew didn’t want to thread into the brass nut (which is at the bottom of the assembly - might as well check that that is correct too). I removed the nut, drooped the leadscrew down, threaded the nut on the end and slid it all back up. Now with the nut resecured in place the leadscrew is HARD to turn. I suspect something isn’t aligned but not sure what to check / adjust.

The boards - should they be enclosed in something to keep them out of dust and accidental harm?

Nope top. It should line up very well though and be very smooth to operate by hand for the full range.

I like to. I have made cases on Thingiverse open to heat transfer but should keep debris out as well as a bunch of other ones.

Ha. Thanks. Now imagine the head scratching trying to figure out AFTER I’d removed a stepper from each rail to pull it apart and flip the middle assembly only to wonder why I didn’t just take the nut off and put it on the other side…hahaha

There’s still something that doesn’t seem quite right though. If I force the nut into the hole it pushes the lead screw outward from it’s natural happy place. Hopefully you can make it out in the pic - this is with the nut pulled out of the component just resting where the lead screw wants to rest naturally (and where it spins freely). You’ll see the hole offset below the nut. As soon as I force the nut to drop into the hole the lead screw binds and is very hard to turn. Everything was square and parallel when it went together. If I measure the leadscrew distance from the z rails it’s dead parallel without the nut in the hole.

I tried to deduce where I might be able to make any sort of adjustment to get the lead screw to shift over that 1/16-1/8 but it just looks like it won’t no matter what. Can I drill out the hole in the middle assembly a bit so the brass nut drops in without binding the lead screw? It’s the only thing I can think if as a fix unless I’ve really mucked something up somewhere here.

Tough to diagnose, Usually I say just take the center apart and try again but…here are a few checks.

Are all of the tension bolts nice and loose?

On the Z axis is it flat when you put it on a table, a twist can do this. Also try taking the Z axis off, loosen all the screws, slide the lower Z mount to the top of the tool mount before snugging it up. It can get pinched.

Is your coupler on straight?

I saw the assembly note as far as adjusting things using the tension bolts (A or B) but to be honest I have no idea which are the tension bolts. Anywhere in the assembly instructions it said “snug it up” I snugged it up. Anywhere it said nice and loose I left things nice and loose.

I assume the coupler is straight? There aren’t many ways to make it not straight are there? One thing I will check is the stepper to the mount. I noticed when putting the rail steppers on that if I didn’t thread all four screws evenly and gradually that the stepper would twist a hair. Like less than a 32nd of an inch. But over the distance of the lead screw that could magnify. I’ll check that and report back with answers to the rest.

I have some carvings drying right now in the shop and the stuff is toxic to me so I’ll check it over tomorrow. Thanks for helping me in terms of where to look. There’s no hold up because of this - I had to order more belt and it won’t arrive until tomorrow afternoon anyway. Ditto for the wire sleeves and rubber end caps. They come Wednesday.

Any bearing that has plastic on both sides of it is s pinch tensioning bolt running through it. All the bearings that only have plastic on one side should be snug.


Usually it is pretty easy to see. Holding it as it would be in the machine does the leadscrew favor one side at the end furthest from the coupler. Also try the above suggestion to slide the lower Z mount down, or measure the rail distances to make sure they are not pinched. Also makes sure the long 5" bolt is extremely loose.

If none of these show anything or are not making sense, take the center and Z all the way apart swap a few pieces and put it back together, most people get it right the second time for some reason.

If you printed the parts yourself you may need to verify your printers calibration, and verify you used all the correct parts.

Would you mind taking a lot more pictures? Of the assembly from the front where the z axis slides in, the bottom with the leadscrew still in it, and any other angle?

Don’t mind at all. I’ll start top down here and if it’s not lining up right will snap a pile of photos.

Look closely to check that stepper motor is mounted flush and straight on top mounting bracket.

I think we’ve got it. It appears that the Z-Lower bracket needed to be twisted just ever so slightly when tightening it down to keep everything straight. If I just snugged it up it would kick the lead screw off to one side just enough to cause the binding. All back together and smooth as silk.

Thanks so much for all the troubleshooting gang! I received my “guaranteed ship by” Amazon emails today - the belt, wire sleeve, caps and 660 arrive tomorrow!

1 Like