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Why is an acme rod good?

Posted by jpan 
Re: Why is an acme rod good?
February 08, 2014 06:31PM

- akhlut

Just remember - Iterate, Iterate, Iterate!

Re: Why is an acme rod good?
February 08, 2014 07:42PM
This is the Nophead coupling.

Re: Why is acme rod good?
February 08, 2014 07:59PM
Still if you look closely at the print, you will see that the layers is not shifted sideways.

The above print was one of the first I printed on my all steel repstrap, with 16mm hardened smooth rods. The z leadscrews is only suspended in one end, so there is no way that they would be able to push the y carrige arount to cause that ammount banding.

At the time I struggled with the problem, the compresion effect was confirmed using a dial indicator, raising the z height 0.1mm at the time. This revealed travel between 0.08mm and 0.12mm, however every full revolution of the z leadscrews it measured spot on. Also there was no dectable lateral movement of the y carrige, when changing the z height.

Since you have probably constrained the x and y movement of the z nuts by not giving them lateral play, the only direction that the stress from the bent threaded rods can go is up and down. In the Ord Bot Hadron design, the z motor mounts have enough flex that this is what happens unless you give the z nuts lateral freedom. I did this using this thing without changing anything else.

Z banding similar to the one shown on your photo was eliminated.

By the way, if you completely eliminate the flex in the z direction in this design, then the bent threaded rods will probably get stuck.

Without seeing your printer, I'm guessing that the same thing was happening in your example.
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