ball screws and backlash

for those who know about these things
would I get any backlash on ball screws if so what sort of amount
Thanks Andrew
Reply to
Andrew Bishop
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What type of ball screw, ground or rolled?
What type of nut, single or preloaded?
What tolerence is the ball screw C0 etc..
Reply to
Stephen Woolhead
good Question the reason I ask is I'm fitting a dro to a Bridgeport clone and the scales aren't cheep but I plan to fit steppers(Bridgeport) in the future so I wondered rather than fit scales go for a rotary encoder and ball screws on the x axis Which by the sound of it have got to be chosen carefully I think that for the time being I will fit Chinese scales to y and z axis
Thanks Andrew
Reply to
Andrew Bishop
The short answer is that you will always get some amount of backlash in a mechanical system, regardless of the type of screws and nuts that you use, simply because stuff flexes. The question is always about how much it will be, not whether/if it will be present.
The long answer is that you should be able to get backlash down to reasonable levels with any type of screw, if you take appropriate measures ("anti-backlash" nuts, double pre-loaded nuts, ground vs rolled threads, etc. etc.), so it is basically down to how much money you are prepared to throw at the problem.
The X3 conversion that Dick Stephen serialised in MEW recently (and which I have just finished a variant of) uses rolled 2mm pitch ballscrews with single, non-preloaded nuts & he reckons that the worst backlash he has on any axis is about a thou. I haven't measured mine yet. You can probably do better than that with ground ballscrews with preloaded or doubled nuts, or with a good quality conventional thread with antibacklash nuts. However, you have to know where the backlash is coming from in order to improve on it - depending on how you put the drive system together, the screw/nut backlash may not be the dominant factor. For example, badly adjusted toothed belt drives can introduce a significant amount of backlash through flexing of the belt.
Also, bearing in mind that screw systems can generate significant forces (I measured about 130 Kilows of downforce on the Z axis of my X3 before I decided that I was about to wreck the bathroom scales!), stretch/compression in the leadscrew may be significant!
Regards, Tony
Reply to
Tony Jeffree
This guy:
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has a fair bit to say about ball-screws and backlash. The link is to a CNC mill project, contains a lot of info & things.
Have fun
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