Lead Screw Issue - Wobble

I reached out to Sienci for replacing this lead screw but i’m apparently out of warranty. I havent had this issue before, and ive diagnosed what I could. There is no slop on either end, it seems to be pulled through as tight as possible. Do these lead screws have the ability to bend over time? This is on the 30x30, 8 months old

It’s called “whip’ and is common on long lead screws driven at speed. One method that is used to reduce it is to put the lead screws under tension using tension nuts and thrust bearings.
This is my set-up - outer side of the plate with tension nut and thrust bearing

The inner side of the plate just uses a conventional locking collar

This problem is one of the reasons that the more expensive ball screws are used.

There are formulae online that you can use to calculate the maximum speed you can drive a lead screw of a certain length and root thickness. Thicker lead screws allow you to run your CNC faster and reduce “whip”.

In addition:
During normal operation ie. cutting, it shouldn’t be a problem as the lead screw speed is slow - you normally only see it when travelling at higher speeds.

@Chaosweaver Is it affecting your project accuracy at all?

Not that ive noticed, but it seems reasonable to assume it will wear the antibacklash prematurely in addition to vibrating the table.

Theres other items i need to order from the sienci store if yall change your mind on replacing the screw, save on shipping atleast.

How does the lead screw rotate with the locking collar attached? Edit: I think I understand, it butts up to the bearing.

@Chaosweaver Just an FYI, I don’t work for Sienci :grinning:

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Yes and there is a shim washer so the collar only contacts the inner bearing race.
I’m actually thinking about replacing the ball bearings with angular contact ball bearings but it means I will have to swap the gantry sides which is a PITA. Hmm - maybe not :sunglasses:

do you have links for those parts?

I bought mine here in Australia.
The Openbuilds store keeps them over there.
Thrust bearing

Tension nut

The only problems will be if your lead screws are cut to close lengths and if the stepper motor drive coupling is very close to the end plate
You need about an extra 30-40mm in lead screw length and I had to step my stepper motors further away using 9mm spacers - see photos.

All up I needed 3 longer lead screws plus 6 sets of washers and nuts - cost about $AU150

Thank you very much for taking the time to explain this, im sure there are others who would benefit from this as well!

The 30x30 has 530mm lead screws on the Y axis right?

Sorry. I don’t know. My CNC is a home built unit.

I have the same issue with whip on one of the lead screws as well. While checking the lock collars and antibacklash nut was tight, I did notice the antibacklash nut was a bit loose (probably from the whip). The whip doesn’t seem to affect the accuracy of the machine though since the gantry is usually moving short distances and at a slower rate than when jogging the machine (which is when I noticed the whip).

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