The ACME rod doesn't want to slide into the bearing

There was a brief period where they were shipping the wrong nut. Check this thread:

And if that looks like your problem, contact and they’ll get you sorted right quick.

Thanks PJ, but I don’t seem to have a problem with the delrin nut, fits fine. The rod itself won’t go into the bearing on top.

Whoops, sorry about that, it’s what I get for skimming. I seem to recall that it should just slide right through. Any chance you have some calipers handy? I went to the schematic and measured that opening, it looks like it should be 8mm across:

The diagram shows the ACME, so that should be the right bearing. I couldn’t find a schematic with the other threaded rod to compare, so I don’t know if it’s the same bearing for both or not.

Wow, I really appreciate you investigating this for me. Unfortunately, I don’t own calipers. It’s awful close though, seems like I could force it but I’m pretty sure I shouldn’t. I’m wondering if I got the flanged bearing for the threaded rod instead of the ACME. Have a great weekend - appreciate your assistance.

You really need a good digital caliper. $18 at Amazon

@WilliamNagel email help@ and they will get you fixed up.

Can you post a picture of the parts you got so we can see if they are out of tolerance or the wrong parts?

Thanks Zach,

Here’s the ACME with the Delrin nut.

A closer picture.

The flanged bearing.

Attempting to fit the rod into the bearing.

The numbers on the bearing are small, but it looks like they might be “609LHV”

I’ll email help with a reference to this post, thanks.

The flanged bearing should be - 8mm x 22mm x 7mm

Mine didn’t go in either at first. I thought it was going to be a problem but after some more wiggling it suddenly slide right on in.

I seem to have the proper 8mm bearing - I borrowed calipers from work, the rod is slightly larger at the top then seems to be right on 8mm at the base. I’m going to have the engineers at work check it for me tomorrow - but it looks to me as if the ACME was just not milled exactly in the reduced area that “fits” into the bearing. I’ll update again tomorrow - in the mean time CS is sending a new bearing just in case. Thanks everyone

OH & Allen: I ordered the calipers, good advise!

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If the ACME is out of tolerance the new bearing won’t solve the problem.

Zach, I figured that too. Our engineers confirmed my measurements & were able to reduce the milled area of the shaft so that the ACME would slip into the bearing. It seems to be good to go now, I’ll be putting it back together this evening - just to be sure, what is the tolerance on the ACME? It doesn’t seem loose to me but wanted to be sure they didn’t take too much off. I appreciate all the support, you’ve got a great team.

That makes me think it might just be a machining error on the rod itself? Maybe there’s a small burr where it was cut that needs to be lightly sanded off.

I actually had the same problem. The ACME leadscrew was the right diameter to fit in the bearing, but when I slid on the Z carriage the lead screw was about 1mm offset towards the gantry side. If the delrin nut was near the bottom of it’s travel, then I could fit the rod in the bearing, but as I brought the nut up, it would bind. Seems like some dimension was off. I ended up putting the Z-axis motor plate on a mill and extending the mounting holes for the makerslide an additional 1mm and then everything fit well.

I am seeing the same type of issue, My Z axis works very well as long as it is moving along the bottom 60% of the ACME rod. Any time it moves higher it begins to bind a bit and make an odd noise.

I was not sure how to correct it, but since 99.9% of the work I am doing keeps the Z axis in that bottom 60% I have not worried to much about it.

Can you describe exactly what you did to correct it? Did you just change the two mounting holes in the motor plate from holes to slots, then adjust by hand till it was aligned?

Yes, I just extended the holes connecting the motor plate to the makerslide to turn them into slots. The plate needed to be moved approximately 1 mm (I didn’t try to be exact) so that’s how far I extended the holes. I just pulled the plate to the new end of the slot inserted the ACME in the bearing and tightened down the screws. The fit was close enough with that extension that I didn’t have binding afterwards.

I used a mill to modify the plate, but one could also potentially thin down the delrin nut or add spacers to the V-groove bearings to make up the difference. The 1 mm thick washers might do the trick.

Thanks for the information, I may try sanding the delrin to gain a mm.

I also had the same problem of being unable to slide my ACME rod through the bearing. I measured with calipers on both rod and bearing and it was just a few hundreds of a mm that might have been off. I solved it by inserting the rod into my screwdriver and sanding it a little before trying to fit it into the bearing again. Did this 3 or 4 times and then it fit perfectly.


I had this problem as well. The measurements that I got for the bearing are .310" while the rod is at .312". Sanded a bit and it fit.

I just received my xcarve yesterday and had a similar issue. The ID of the bearing measures 0.310" and the OD of the ACME rod measures 0.312". I followed the advice in this thread and mounted the smaller diameter end of the rod into my drill and pressed a file to the ACME rod to remove the 0.002" excess diameter. The rod inserted into the bearing with a small bit of force after that and seems to be doing fine.