lathe turning a ball screw end

[margni74]

I need to get a 34"x1" diameter ball screw end turned.

I have no documentation as this was an ebay purchase (dumb me), so I don't know if it is hardened steel. Is there an easy way to tell? I dragged a mill file over the end, and made a bit of a dent, but it took some effort.

The NSK website list the hardness for their screws anywhere from 55-60. Can something like this be turned easily on a lathe?

[Oldmanandhistoy]

Take a look here.

http://www.5bears.com/cnc16.htm

[Splint]

It will be hardened. What you'd best do is use a 4 jaw chuck so you can true it up accuritely. To do this you will need to use something like a feeler guage blade (a thick one so it wont flex and cause false readings) between the thread and the tip of the dial indicators plunger, so to have a surface to measure from rather than the threads of the screw. When you have worked out the cutting details, use a grinder (unless you have a tip for hardened steel) and grind through the hardened metal on the surface down to the normal metal and then finish it with the lathe. Depending on the length of the leadscrew you may need to use something to support the other end of the leadscrew to minimise the whiping effect as the chuck spins. This may be as simple as jaming rags tightly up the end of the spindle around the screw. You could also turn up a sleeve which fits neatly over the leadscrew and neatly inside the end of the spindle, make it stepped so it cant work it's way up the spindle and stop at the back of the chuck, and use a clamp (maybe hose clamp) to keep it from moving out of the spindle. If that is insufficient you may need to locate the bush further outboard with an external means of securing it, put some grease in the bush if that's the case.

Good Luck
Splint

[One of Many]

Other than getting past the screws ball paths, it should turn fine with carbide. The ball paths may be flame hardened and that is an interrupted cut, so keep the rpm under blue chips. Best if your shaft/bearing ID is below where the ball paths are and the flame hardening ends. If your turned ends do not end up round, the bearing may suffer if the press fit is excessive.

If you had to, you could use a tool post grinder to get past the hard stuff and maybe finish it off after turning if need be. Then spend a week cleaning the lathe of grit, but do what ya gotta do!

DC

[Glacern]

All ballscrews are hardened (hopefully). You can turn them with just about any lathe, but the heavier the better. I find that high DOC and very low SFM are best for roughing. I set my DOC deeper than the case hardening (taking as much as .150" off the radius). SFM and feed rate are low enough such that my machine doesn't complain and the chips are silver.

[margni74]

Originally Posted by Splint It will be hardened. What you'd best do is use a 4 jaw chuck so you can true it up accuritely. To do this you will need to use something like a feeler guage blade (a thick one so it wont flex and cause false readings) between the thread and the tip of the dial indicators plunger, so to have a surface to measure from rather than the threads of the screw. When you have worked out the cutting details, use a grinder (unless you have a tip for hardened steel) and grind through the hardened metal on the surface down to the normal metal and then finish it with the lathe. Depending on the length of the leadscrew you may need to use something to support the other end of the leadscrew to minimise the whiping effect as the chuck spins. This may be as simple as jaming rags tightly up the end of the spindle around the screw. You could also turn up a sleeve which fits neatly over the leadscrew and neatly inside the end of the spindle, make it stepped so it cant work it's way up the spindle and stop at the back of the chuck, and use a clamp (maybe hose clamp) to keep it from moving out of the spindle. If that is insufficient you may need to locate the bush further outboard with an external means of securing it, put some grease in the bush if that's the case. Good Luck Splint

My knowledge of lathes is limited, Im going to try to find someone local to do the job, hopefully they know what the heck they are doing. Im also looking for a lathe myself to learn on, and ive been reading various things on the web.

I don't understand something though (actually many things), forgive my ignorance.

"Depending on the length of the leadscrew you may need to use something to support the other end of the leadscrew to minimise the whiping effect as the chuck spins. This may be as simple as jaming rags tightly up the end of the spindle around the screw."

What do you mean by other end of the screw? both end are anchored to something are they not? how is jamming rags going to do anything? is the halfway point of the lead screw going to actually try and oscillate? The length of the screw is 34" long, and one end has already been turned. I would imagine that this is the end that is going to be fastened in the chuck, and the other end will be anchored by the tailstock, right?

[margni74]

Originally Posted by Oldmanandhistoy Take a look here. http://www.5bears.com/cnc16.htm

thanks, i read through this, still trying to wrap my head around the explanation.

[One of Many]

If the ballscrew were sticking through the spindle out the back end, you would need to support it somehow from whipping around. Tail stock support via a center may not be strong enough, given the hardness and interrupted cut. Keeping the end being cut nearest the spindle is best for rigidity.

Using the tail stock up close to the chuck can be a good plan if you can verify the ball paths are on spindle centerline before center drilling the end for live(or dead) center support. A bad job of center drilling will cause the screw runout in the bearing if that were used as reference in machining.

DC

[margni74]

Originally Posted by One of Many If the ballscrew were sticking through the spindle out the back end, you would need to support it somehow from whipping around. Tail stock support via a center may not be strong enough, given the hardness and interrupted cut. Keeping the end being cut nearest the spindle is best for rigidity. Using the tail stock up close to the chuck can be a good plan if you can verify the ball paths are on spindle centerline before center drilling the end for live(or dead) center support. A bad job of center drilling will cause the screw runout in the bearing if that were used as reference in machining. DC

OK, so actually it is possible to turn this screw with a lathe that is much shorter in length than the 34" length of the ballscrew?? Apparently you are saying you can actually feed the screw through the back of the chuck? im trying to find some more info on this process. so far my exposure to lathes is via google image search, ahah.

[Splint]

Originally Posted by margni74 Apparently you are saying you can actually feed the screw through the back of the chuck?

Yes , thats correct. and there will be a need to support the other 20 something inches of leadscrew which is hanging in mid air through the spindle. Jamming rags between the spindle and the leadscrew (keeping the leadscrew on the centerline of the spindle) is a primitive way of doing it but it works. Some lathes have screws in the end of the spindle which can be screwed in to locate the stock in the desired position, sort of like the jaws on a chuck.

[Fastrip]

I don't know about screws that are that small but the screws we make are induction hardened in the area of the grooves only. Even at that rate once through the case things would cut like any steel pretreated to 28-32Rc.

[Horsedorf]

Originally Posted by Oldmanandhistoy Take a look here. http://www.5bears.com/cnc16.htm

That was an excellent article, though I don't understand that last cutting bit he used, what was it made of? just HSS? didn't look dark like carbidem, and I'm assuming that's a tool you can buy? or can it be made?

Thanks for that pointer! Nice find.