turning ball screws

[Runner4404spd]

i'm getting ready to start machining my ball screws for my mill/drill conversion. does anyone have any tips on how to machine these? i have a 9x20 lathe and some carbide tooling. i've heard that i should heat the end and then try turning it after it cools. i also heard these were an air hardening steel. any tips would be greatly appreciated.

thanks
Jerry

[mxtras]

I would not heat it.

The carbide tooling should cut throught the hard surface (if it even is hard) just fine. Slow speed at first, medium depth of cut (maybe .004 - maybe more for your lathe I am guessing). If the carbide doesn't do it for some reason, I would suggest grinding the hardened portion off manually or with a die grinder mounted to the tool post. Spin it slowly until you are through the hard stuff.

Don't rely on the the chuck to be accurate - check the concentricity carefully after you get things roughed in - indicate on the nut if it is ground otherwise try to use the centers if they exist. You wouldn't want this thing wobbling after it's cut!

Scott

[kdoney]

When I did this on a 14X40 with a steady rest it started taking forever to cut through the first layers. I got through it in about 15 minutes with a tool post grinder. I would suggest that you get the ends down to a managable diameter with a grinder, toolpost or not. I had NO success with heat. I am able to work the ends on a 9X20 lathe easily for 5/8" ballscrew with the toolpost grinder and then carbide. I agree with the accuracy tip, keep checking and use a rest.

[widgitmaster]

I have a 9x20 lathe, and 5/8 rolled ball screws. When I turned mine down, I had to use several new carbide tool bits & brown threading oil to get through the case hardened surface.
After it was removed, the soft steel center was easily machined to fit my bearings!

I suggest a slow RPM, tighten all the slides on the lathe and hold the tool as short as possible to ensure regidity!

Its work, but its doable!

Eric

[Runner4404spd]

will i need to get a 4 jaw chuck for this operation? it seems like i do. i don't know if i'll be able to keep it concentric enough in a 3-jaw. i'm not opposed to working hard at it, but i would like to succeed in doing this. any other tips?

[widgitmaster]

Actually, I used a three jaw chuck, but first I made the chuck run true by holding a long dowel pin in the chuck and dialing it in with an indicator and soft hammer, tightening the bolts holding the chuck to its back plate when done!

Eric

[Zippi]

Are the screws rolled, or ground? If they are rolled, bear in mind that the outer ridges may not be concentric. If they're ground, they should be fine in a chuck.

Some 3 jaws are really accurate, but I'd go with a 4-jaw. I've had good luck on my 7 x 12 mini-lathe, the stock 3-jaw is pretty accurate. The way I set up my 3-jaw is to wipe the jaws and the part clean (no brush, too messy), rotate the part as I tighten up the jaws to just contacting, then I work the key for the chuck in each of the three key holes, rotating the chuck, and tightening bit by bit evenly. Then, I check for runout. If it's good enough, I continue, if not, I do it again. If I can't get it close enough for what I'm doing, I'll put on the 4-jaw. If I was turning a ballscrew, I'd set the carriage power feed to the screw pitch, and follow the groove with an indicator to measure runout.

I have always wondered- if you put too much pressure on the screw in the chuck, can you deform the edges enough to interfere with the ball movement?

[ViperTX]

I wrapped a wet cloth just below the level that I wanted to soften.....used a plummer's torch to heat the end....rotating it while it heated to an almost red state...let it air dry....wrapped a piece of aluminum from a beer can to cover the area where my 4 jaw chuck would squeeze the ballscrew.....used the blade of a putty knife (held by a tool holder on the tool post)....the putty knife blade was pressed against the ballscrew......the test indicator was centered on the putty knife blade and rested on it at the center of the ballscrew....centered the ballscrew, by adjusting each set of 2 jaws......On the end sticking out through the lathe spindle...I used a piece of wood with a hole in it....wrapped a rag around the ballscrew and stuck it in the hole....not a tight fit....just used as an anti-whip device.....moved a bench with a vise to hold the board....worked perfectly.

Used an indexable carbide cutter.....worked perfectly...followed by some emery cloth wrapped around some ground stock to finish the turned surface.

[mxtras]

A 4 jaw would be better, sure but if you don't have one you can use a 3 jaw - no problem. I would suggest indicating off the OD of the nut if you can - if the configuration allows it - if it's square then you may hve to go from the OD of the screw - maybe use Viper's method but I would try to go from the flank of the thread since that's where the nut runs and that's what will determine concentricity when in use - know what I am trying to say?

You have a few options for the truing. If you use a 3 jaw you can use shim between the part and the jaw. If your chuck runs really close, you can tap the 'high' jaw with a brass drift as you tighten to manipulate the grip a thou or so. You can also turn between centers using a drive dog if this is possible but it may be a weaker arrangement for turning and there's no telling if the centers are true or not for sure without checking them first. Another way would be to bore a sleeve in your chuck and use clamping screws on a known, good diameter but this would be my absolute last resort since it is the weakest method.

I wouldn't worry about accuracy until you get things roughed in and let the screw cool down before finishing. I think I would rough it all close, then take a break and get it running true for the finish cuts.

Scott

Scott

[ozzie34231]

I've done the ends of ball screws 5 times now using this method.
Get the screw running in the lathe as true as you can using any of the suggested methods. If it is a long screw make a plug or rig a simple chuuck for the back end of the spindle. Drill the ball screw 3/8" X 1-1/2", (drill, don't bother reaming). Machine a piece of stock large enogh for the end you need with a 3/8" tongue. Test fit it into the screw. You want a slightly sloppy fit. If the fit is tight, file a flat on the tongue. Coat the parts with silver solder flux, assemble and silver solder with the lathe running slowly.
I put the tail stock up to the end because if you have too much flux in there the end will blow right out. After it cools machine the end you need making certain the screw is still running true.

To get a true running rolled ball screw, I use a C5 collet that fits snugly. 5/8" is too big. You can also make a fairly thin walled tube from aluminum that fits snugly and indicate on that.

Jerry

[RotarySMP]

Swede has written up an excellent "how to" article here.

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

[ViperTX]

I've tried Swede's method....and it has some good points.....emery cloth to finish the journal....the rest was more work then my method....