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  1. #1
    Join Date
    Oct 2018
    Posts
    79

    Could I machine ballscrews?

    Currently I don't a metal lathe but could be tempted to buy one, particularly if paying for machining of ballscrews would be expensive.

    But ballscrews are hardened, could I machine them? (and on a basic £500 lathe?)

  2. #2
    Join Date
    Jun 2011
    Posts
    692

    Re: Could I machine ballscrews?

    I've never tried it myself, but have thought about it as well. If you're thinking ground ball screws, forget about it, leave it to the pros. For cheap rolled screws it might be doable, but probably not worthwhile.
    It should be possible to anneal the part of the screw you need to cut. Wrap the screw in a wet rag where you don't want to cut it, and heat the part you do want to cut til dull red then let it cool on its own.
    With the right carbide inserts you can just cut through the hardened stuff. It's probably just case hardened, so you won't have to cut too much tough stuff.
    You could even try grinding through the hard skin.

    You're probably going to need more than a £500 lathe to do a decent job though. Typically in that price range lathes just don't have the rigidity to take accurate cuts in steel. I think a 10" swing would be a bare minimum.

  3. #3
    Join Date
    Apr 2015
    Posts
    170

    Re: Could I machine ballscrews?

    Quote Originally Posted by men8ifr View Post
    Currently I don't a metal lathe but could be tempted to buy one, particularly if paying for machining of ballscrews would be expensive.

    But ballscrews are hardened, could I machine them? (and on a basic £500 lathe?)
    You can easily machine ball screws if you soften the ends by heating the end to red heat and allow them to cool slowly. usually they are only case hardened to a depth of around 1.5 - 2mm so you can grind off the outer layer to expose the softer steel underneath.

  4. #4
    Join Date
    Mar 2015
    Posts
    409

    Re: Could I machine ballscrews?

    You're probably going to need more than a £500 lathe to do a decent job though. Typically in that price range lathes just don't have the rigidity to take accurate cuts in steel.
    I turn steel on my mini lathe lathe (300 mm) without any problems. Most times I use HSS tools but also CCMT060204 and CCGT060204 inserts. I have turned a hardened bike tool (crank shaft nut) to fit the crank shaft of my new bike. Its all a matter of cutting depth (Z and X) and speed. Just keep the cutting forces as low as possible. Normally i don't go beyond 0.15 mm in steel. I turned the hardened nut using 0.05 mm cutting depth and a new CCMT insert. Of course the (cheap eBay) insert didn't last long but it was doable. I also can't run the inserts on the mini lathe according to the manufactures settings but the finish is quite good. I must say that on the large lathe the finish is better, but who cares if the dimensions are within 0.01 mm.
    From another forum member I learned that you can use the CCGT inserts (polished inserts for aluminum) on steel like CK45 and Cr42Mo4. The polishing makes them very sharp and this makes it possible to use small cutting depth resulting in low cutting forces. With a new CCGT060204 insert I can go down to 0.001 mm on soft aluminum (still cutting not rubbing) and 0.02 mm on Cr42Mo4.
    On the dutch CNC forum members turn Titanium on their mini lathes!

  5. #5
    Join Date
    Oct 2018
    Posts
    7

    Re: Could I machine ballscrews?

    It is possible to machine the ends of ball screws. There are a few things to consider. How accurate will the lathe be as far as head and chuck run out? How sturdy is the lathe? Is the live center perfectly aligned with the chuck center? Things along this line.

    It might not be a good idea to heat the ends of ball screws to soften the case hardening, unless you are absolutely sure the ball nut will not enter this area of the screw. It would be difficult to gauge exactly how far down the screw that you are softening simply because of heat transfer. I have performed a lot of precision heat treating in the past, and when it comes to the drawing phase of the process, I know that on most metals a few degrees can make a big difference in the RC that you are left with.

    If you use a good quality carbide tool you should be able to carefully turn down past the depth of the case hardening, Typically this depth shouldn't be over 0.010 to 0.020" at most. This would hold true for both ground and rolled ball screws. But if you are using ball screws, go ahead and look into getting the ground screws. They are typically a lot better screw all the way around.

    Hope this helps.

  6. #6
    Join Date
    Mar 2015
    Posts
    409

    Re: Could I machine ballscrews?

    How accurate will the lathe be as far as head and chuck run out?
    Just put some mild steel in the chuck and turn a center on it. That way the run out at the headstock is zero.

    If you have a 500 mm ball screw and the tailstock is 0.1 mm misaligned, it would result in a 0.02 diameter difference when machined 50 mm. To align the tailstock, plate the ball screw between centers. Measure the distance to the ball screw, at the position of cutting tool tip. Place the measured ball screw end at the tailstock, move the carriage to the tailstock and measure the distance again. If the tailstock is aligned OK, you should find the same value. If not, adjust the tailstock until the values are the same. Doing it this way compensates for "all" tailstock and bed errors at the current tailstock (tip) position.

    If you have a 3 claw chuck on an adapter plate, turn down the register on the adapter plate a bit to adjust the run out of the clamped ball screw. When all is done, clamp a turned bar and adjust the chuck to reduce the run out. I have done it on my lathe and the run out of the (new) 3 claw chuck is reduced to 0.01 mm. I have done the same on my 4 claw chuck adapter plate to get the chuck aligned better to reduce vibrations.
    If you have a 4 claw chuck just keep adjusting until the run out is OK.

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