Bent Acme Rod

Would a bent acme rod cause movement in the bit? I notice when it the bit raises and lowers it almost makes a circle pattern at the tip. I’m assuming this isn’t normal?

Yes and no.

I had a bent rod that caused my bit to deflect. INVENTABLES quickly replaced it. I only noticed the issue when the Delrin nut was on a certain location on the acme Rod. There was a little deflection and movement of the bit in this area but I did not notice a circular pattern.

It almost sounds as if you have an issue with your spindle having severe runout.

If you move the Z axis up and down, Do you see the bit moving in this circular pattern when the spindle is OFF? If so then it could very well be, that acme Rod is throwing you this curve.

But if it does not perform this circular rotation when the spindle is off, then most likely it is an issue with your spindle.

Thanks for your insight Michael. I actually can only notice it when the spindle is off. My eyes aren’t good enough to notice it when it’s actually spinning up. I’m going to take a video of it tonight to post.

I notice my Acme rod the top nut has a great deal of wobble in it when the Z axis is moving up and down. Been planning on taking it apart and rolling it on a table to see exactly where the bend is. It was not noticeable during install but I didn’t check it out closely. I’ll have to check to see if the bit moves any once it warms up.

Just an FYI. When I first installed my a me Rod, I tested it for flatness. The bend was so subtle that I did not see it. So the Rod was installed with the bend unnoticed at first. It was not until I started raising and lowering the Z axis did I start to see this deflection. So I dismantled and check it again, paying closer attention. This is when I found the issue.

The bend was very subtle but it still caused the deflection in the bit.

If you are seeing the nut go out of round on top of the Zaxis, also verify that your bearing is good. Even with a bent Rod, the bearing should still hold the nut in place bc the nut and pulley are tightened down to the Z Plate. If the Rod extended past the z plate several inches, I could then see the Rod being the culprit. But it should be unlikely for there to be that much circular motion above the plate unless you have a Rod that was poorly manufactured/machined or a bad bearing. Check to make sure where your pulley attaches and where the Locknut attaches to the Rod, that this area was properly machined and not machined off center.

With this design of the Z axis, if the Rod is bent, having the bottom of the Rod uncaptured by a bearing, the bottom of the Rod should be where the most deflection or circular motion should be while testing just the Rod.

It turns out my rod is bent and has been from the beginning. I wish I knew enough when I started to notice it so maybe inventibles would have been able to replace it.

Send a message to INVENTABLES support. I have found that they are more than reasonable to work with. Worth a try