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Rolled ballscrews, are not made straight and will always need some amount of straightening to make perfectly straight. If you machine is rigid enough it should be able to take some bend in the screw. It is good practice to have all ballscrews staightened before use. For hobby use this is impractical but if you were buying your screws pre machined from a professional company straightening should be included in the price.
Personally I'd have a go at straightening them. Whilst the machine will probably 'work' with bent screws, the life of the system (particularly the ballnut) will clearly be lower. How much lower is hard to say, but why take that chance? It's a similar reason for why you shouldn't exceed the critical speed of the screw - whilst sometimes it can look OK as the nut guides the screw, it's still putting larger than normal radial forces on the nut which the nut isn't designed to tolerate.
I straightened a RM1204 ballscrew a while ago. It wasn't challenging.
Just remember not to use steel V-blocks as you could damage the threads on the screw.Quote:
Originally Posted by JAZZCNC
Guys thanks very much for your comments.
You really help me understand that i an go on with my build as this is not a disaster.
Regards this straighten process i have some questions
Yesterday i borrow a dial indicator from a friend
Question 1
If i try to follow the straighten process as described here
Screw Shaft Straightness
and measure the TIR where should the node of the indicator touch ?
I am asking because if i put the node in the lower spot of the thread, as i turn the ball screw and have the indicator stable, the node of the indicator will pass from the lower spot to the higher spot of the thread( as the screw turns). I don’t know if i make my self clear.
Is ti logical to put the indicator node on the ballnut that has a cylindrical outer surface so i can capture the TIR.
Question 2
what is a logical distance for the V blocs
Question 3
How much pressure should i apply? I mean if i have a bend like that ) 1mm from the rotation center, i should apply a force to bend the the ballscrew to the opposite dimension so the screw take temporarily this shape (, and after i stop applying the opposite force the screw become straight | . This temporary opposite force is it logical to bend the screw 1mm ( temporarily ) or more? Again i don’t know if i make my self clear.
Anyway thanks for your patience.
Vagelis
Vagelis.
Q1 You can't use the Node of the indicator directly on the screw you need something flat between the screw and the indicator node.
Q2 For measureing then you want over the full length of the screw. For straightening then it depends on the bend amount and where on screw it's bent. Often just moving blocks slightly in ward of ends and light pressure is enough to straighten.
Q3 Trial and error I'm afraid.? . . . How longs a piece of string.? Often just a little more than the amount of bend will do it but could require more depending on where the bend is on the screw.?
If you go too far then just tweak it back but often you'll creep up on straight. It's honestly not difficult to straighten screws just time patience needed. Don't be afraid you would have to be Very rough to destroy the screw. Just protect the threads while applying bending force and you won't have any problems and you'll be surprised how little it takes to straighten them.( Or bend them.!!)
So Dean putting the ballnut on the screw and touch the indicator to the nut i think will work right?
NO I wouldn't do that, while in theory it could work I wouldn't do that it may lead to inaccuracy's and make it harder to straighten.Quote:
Originally Posted by ba99297
Would you not use a flat tip probe - like the one 2nd from the right in the pic..?Quote:
Originally Posted by ba99297
Attachment 12540
Wal.
Yep them's what's needed Wal but like finding Hen's Teeth unless your prepared to splashout on expensive dial gauges and then they are expensive for a one off job.!Quote:
Originally Posted by Wal
Edit: I retract that statement I've just found this set at Arc eurotrade (bottom of page).!!. . . http://www.arceurotrade.co.uk/Catalo...nt/Dial-Gauges
Vagelis, look at your video No 4 see how much wobble there is on the of the drill. That will only make the screw vibrate the ball nut, even holding it in your hand it will still act like a vibration unit. Once it's bolted securely to the frame 99.99% of the vibration will go. Like Dean says the chances are it will be ok.
Longy the wobble that you mention isn’t on the drill. That dancing movement of the drill is cause of the ballscrew bending. I can say that because the same drill turn the other 3 ballscrews and the wobble wasn’t so much.. In video #4 is the 500mm 1605 ballscrew that I think that is bended at the edge ( where the drill attach the screw.) and not at the middle.Quote:
Originally Posted by longy