[RnDmodder]

A really stupid question for most of you.............

In the process of full and proper conversion of cmd300 (sieg x2) with big steppers and ballscrews.

But I was asked a question and thought I needed other people to blame it on

For quality build and lots of accurate work.. the full rebuild is needed

BUT if only wanting to machine a few things EVER (not where the interests lie) why replace the leadscrews with ballscrews?

surely it would work, for the light useage, with motorising the existing bits ONLY.

malcolm

[truckeic]

A really stupid question for most of you.............

In the process of full and proper conversion of cmd300 (sieg x2) with big steppers and ballscrews.

But I was asked a question and thought I needed other people to blame it on

For quality build and lots of accurate work.. the full rebuild is needed

BUT if only wanting to machine a few things EVER (not where the interests lie) why replace the leadscrews with ballscrews?

surely it would work, for the light useage, with motorising the existing bits ONLY.

malcolm

There is a considerable amount of backlash with the leadscrews. Not too expensive or hard to change out..

Sent from my XT1635-01 using Tapatalk

[109jb]

When machining manually, you generally are only making linear X or Y moves and when moving in X, Y is locked and when moving in Y, X is locked. When running in CNC, the only thing that "lock" an axis is the motor not turning and relying on as little backlash as possible. If there is excessive backlash you will get chatter. If the acme screws are in good shape you could probably tighten the nuts and get acceptable results for a while, but if the machine is older and the nuts/screws worn, then you may wind up with spots too tight and others too loose. The acme screws also have a lot more drag than ballscrews and will cut possible travel speed down to about 1/4 of what ballscrews can achieve.

Going along with the above, anything requiring a reversal of direction will show up in the finished product. Something as simple as a interpolated circle will show marks at the 12, 3, 6, and 9 o'clock positions. Backlash compensation helps, but I've not had stellar luck with it and find that mechanically eliminating it works much better. With backlash, something simple like a bearing pocket can become difficult because of dealing with the backlash.

People have certainly done it. I currently have a little machine with acme screws but I replaced the cast iron nuts with acetal, nuts that were heat formed to the acme screws for no backlash. This means there is considerable drag though and it is not too long from getting ballscrews.

[shooter123456]

On the X2 that I had, the leadscrews were not accurate at all. Compared to an inexpensive DRO, the dials didn't even seem close. Even cheap $40 rolled ballscrews were miles ahead of the leadscrews on my machine.

[RnDmodder]

much as expected....

thanks to all of you

[dazp1976]

I have some of those Chinese C7 ballscrews in mine too. The stock acme are hopeless.
It has an acceptable backlash of around 0.05mm.

If you go down this route I strongly advise using angular bearings on the shaft. I used thrust bearings and they're nothing but grief as they don't sit well on the pre-machined screws. Gives huge screw wobble and causes premature wear.
I made parts manually for the X,Y. Used automated X,Y to make parts for the Z. Then re-did X,Y, parts more accurately

My new PM25 clone is being fitted out with AC bearings and the difference in fit compared to thrust is massive.
My X2 is making all the mountings.