Machining/Turning the ends of ground ballscrews

[rodjava]

I plan to buy my ground ballscrews from Ebay. I doubt that they will be the exact length for my machine so I will buy them longer.

My question to the group is.

Will I be able to turn the ends on my South Bend 10 lathe if the ballscrews are hardened? I normally turn AL or some type of Hot/Cold rolled steel and havent turned anything that has been hardened.

If you say yes, then what lathe bits should I use? Carbide or HSS and what rake if any. Speed recommendations for both Carbide and HSS would be appreciated.

Thanks in advance,

Rod

[runchman]

My only comment would be good luck. I'm not an accomplished machinist by *any* means, though... I bought roton rolled screws which are supposedly not hardened very deeply, and they kicked my a** trying to machine them with my south bend 9". I ended up rigging up a grinder and grinding them.

I also bought a ground screw off of ebay, and just cut it to length using a cutoff blade in a dremel. The other end was already machined and useable as is.

Anyway that's my 2 cents worth, you'll hopefully get better answers from those truly in the know...

- John

[philbert]

rodjava,

Here is a great page describing exactly what you need to do: http://www.5bears.com/cnc16.htm



"This is a necessarily long instalment because it contains some good information, and will hopefully help a lot of guys with their own projects. In it, I will detail how to take a hardened and ground ballscrew, chop it to a shorter length, and finish it for a ball-bearing journal to standards as good as grinding, all with a lathe and some basic machinist's tools."

[rodjava]

Philbert,
I can't thank you enough for the link. It was exactly what I was looking for.

Runchman,
Thanks for your help too.

Rod

[fatal-exception]

I agree with 5bears about the sharp tool for 'sneaking' up to the final dim, but having turned several ball screws, I would never start with HSS (again) to take off the case hardening. In my experience, carbide tools work fine.

Paul

[alexccmeister]

I know this has been asked before, but can someone explain how you go about protecting the ball screw where its gripped by the jaws of the chuck? I know people use thin sheets of sheet metal. But some picture showing this would be great. Thanks.

[neilw20]

Put some strips of aluminum about 1mm thick between the jaws and the screw.
make sure they are the full length of the jaws. Nice soft comercial grade works best. Let it crush a little. You might need 1.6mm though.

Carbide or possibly ceramic tools are the only way to go.
You can get some low cost brazed on tips.
I machine ball race housings regularly. No problem. Not to fast, not to deep, but don't just scratch the surface. Take a real cut. Curly swarf can come off red hot. Beware. Amusing for wife when it catches fire. If it squeals too much, slow down. Then it just squeals a bit less. Once you get the right tool it is a breeze.
Practice on a shaft out of an old gearbox or whatever hard bar you can find.
If it stuffs the tool, find something better. It will work.

[chich2]

I used hot rolled Thomson ball screws. I used an angle grinder to grind the hard stuff off and then put the screw in the lathe and machined the soft stuff to size.

Easy!

Chich

[philbert]

Carbide or possibly ceramic tools are the only way to go.

I'm no expert, but again quoting from the 5bears link:

"I begin roughing with a TPG222 indexible carbide tool. Even with tailstock support, the lack of rake in this tool (like most indexible carbide tools) and the pressures, cause the work to spring away from the tool, up to .003" or more! Go ahead and hog, but remember this is not an accurate cut. Take it no further than final diameter of the journal, + 0.010" or 0.25mm."

[runchman]

I know this has been asked before, but can someone explain how you go about protecting the ball screw where its gripped by the jaws of the chuck? I know people use thin sheets of sheet metal. But some picture showing this would be great. Thanks.

Keep in mind too that this section of the ballscrew may never see any 'action' (i.e. ballnuts) when in use, since it is right next to the bearing. I didn't bother protecting mine and can't detect where my lathe jaws clamped it. And even if I could, on mine that area never comes in contact with anything anyway.

- John

[alexccmeister]

Put some strips of aluminum about 1mm thick between the jaws and the screw.
make sure they are the full length of the jaws. Nice soft comercial grade works best. Let it crush a little. You might need 1.6mm though.

Thanks for the tip.

Keep in mind too that this section of the ballscrew may never see any 'action' (i.e. ballnuts) when in use, since it is right next to the bearing. I didn't bother protecting mine and can't detect where my lathe jaws clamped it. And even if I could, on mine that area never comes in contact with anything anyway.
- John

Good point. This definitely helped in what I need to do. Thanks.

[Andre' B]

For production hard turning you want PCBN (polycrystalline cubic boron nitride) inserts at about 30 to 40 dollars per cutting edge, but for a one off you can get by with carbide and just accept the fact that the insert will not last long.

Some info on hard turning.
http://www.mmsonline.com/articles/049605.html