Bent ACME Lead screw

X-Carve Assembly
23

Yes.

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24

Thank you Justin

25

Your fine. I was going to ask the same thing… I’m going to look into that later. Maybe santa can bring me one :smile:

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26

I should clarify my answer a little. Most of the linear Z axis don’t use the ACME screw. I think the Z plunge from Kyle does use it. The CNC4Newbie slides that most are getting definitely don’t use the stock ACME screw.

27

Thanks for that @JustinBusby. I screwed it to the spindle mount and it doesn’t seem too bad now. I’ll have to see how it cuts to be sure . Going to look at a few upgrades around the new year . I tried contacting suckit about but they have nit replied to emails or messenger on facebook:frowning:

28

I’m a year late, but I am having this issue with a bent lead screw.
It is straight when rolled on a flat surface.
However, I noticed the Delrin nut doesn’t fit quite right–it seems too deep along the y-axis when in place. When the spindle carriage is screwed to the z-axis, it forces the screw/delrin nut slightly out of vertical, which is even more noticeable during the z-axis test.
I am going to try to sand down one side of the Delrin nut so it’s not noticeably pushing the ACME screw out of vertical, but is still snug in place and doesn’t have backlash when the z-axis changes direction.
In addition, I’m going to double-check the plumbness of the bearing assembly.
Any thoughts on this?

29

The lead screw is not bent. Where the screw is machined to fit thru the bearing, it creates a partial shoulder that seats against the bearing. When the assembly is pulled tight by the nut at the top, it causes the screw to pitch to the unsupported side of this partial shoulder, causing the runout condition that many assume is a bent lead screw. It’s more or less self-correcting at the lower end of the travel due to available flex, however it can cause bind near the top. Loosening up & reseating the assembly may help this condition. This top nut doesn’t need to be very tight, just pull the play out of the assembly with it. Tightening this nut is what causes the apparent runout condition.

If assembling spindle carriage actually forces the screw out of vertical as you claim, then something isn’t assembled correctly. Sanding down the Delrin nut would be a mistake, as there is nothing wrong with the dimensional stack-up of the components if assembled correctly.

30

I just experienced this myself, after upgrading to 9 mm 3GT3 belting on the Z-axis (the bigger pulley doesn’t leave much threading at the top of the ACME screw for the top nut). The Z-axis worked fine unless I was at the top ~0.5" of travel (i.e. homing). I greased up the washer that fits between the bearing and pulley and kicked the drive current for the Z-axis up just a smidge, and it solved the problem for me.