Check out my Y-Axis Assembly!

[Bird_E]

This is for my X3 mill

[CNCadmin]

What's your gearing?

[Bird_E]

It is 2.5:1
XL 20groove and 50 groove
Bob

[Swede]

Looks very nice! I like the fact that you finished off the aluminum blocks. What secures the motor in place? A split clamp?

[Bird_E]

Yes, the motor is secured by a split in the clamp under the motor. A single 1/4-20 cap screw tightens it up real nice.
Thanks!
Bob

[Bird_E]

well, it all looks good until I mounted it and tried it out.... Something went wrong when I turned the bearing journal on the ball screw. It has a bunch or runout! CRAP!

[Halfnutz]

Wow, that scares the ^%$^% out of me. Im getting ready to buy ballscrews and hope I can handle machining the ends myself. I have a lathe and a torch for anealing, but my turning skills are limited. I talked to someone today from a local ballscrew shop and they said they get 350.00 plus parts to machine each screw. I sure cant go that route. Fortunately the screw is only about 10.00 a foot. Any advice with maching the ends would be appreciated.

[Bird_E]

Come to find out it wasn't that my turning job got screwed up, the ball nut mount wasn't mounted square... I only had it loosely titghten... All is good!

As far as turning the ballscrew, I tried a few different methods. I turned my X screw by grinding down the majority material with a bench grinder and then turned the rest with brazed on carbide tooling. It worked ok. My second attempt on the y screw was turning the bare screw with carbide tooling. it worked , but my lathe didn't like it very much and it took awhile. My third attempt on the z screw, I took my propane plumbing torch and heated up the end till it was almost glowing red, took a while to get it there, I gave it about 30 minutes to cool down, and then it turned much easier!

I would recommend the last method, all though each one will work, just don't rush!

By the way, I turned the ballscrews in my Harbor Freight 9X20 Lathe.
Bob

[Swede]

Bob, I'm glad your assembly is working properly. It is NO fun to find that a lot of work might be for nothing, and a LOT of fun when it finally turns out that it is good to go!

Guys, I'm glad you've found various methods that work. Turning down a carbon steel ball screw on a home lathe can be a real pain. I've done quite a few, and have developed a technique which yields very nice results.

The typical 5/8" or 3/4" rolled Thomson type of screw is one of the easier metals I've tried. My impression is that these screws are surface hardened, while the core is still relatively soft... soft being defined as annealed, high-carbon steel like 4340, which, while turnable, sure isn't 12L14.

I think the secret is twofold. First, brazed carbide (or indexible carbide) tooling usually does not have the best geometry for a 10" home lathe. Their geometry is based upon high HP, very rigid machines, for the fastest possible removal of metal, and to heck with high cutting forces. This is due to the lack of rake. Think of rake like a wood chisel. When you apply a wood chisel for a clean cut, the angle is relatively acute, and this allows you to cut cleanly and with minimal force. Carbide tooling is akin to keeping the chisel perpendicular, and dragging it across the wood. You can remove wood, but imagine the forces required to keep the tip of the chisel 1/16" below the wood surface.

This is kind of a lame analogy, but it leads into turning these screws with light equipment. First, carbide is used to cut through the hard portions of the screw. The cut will be interrupted and the tool will be abused, but carbide can excel in this environment. Once through into softer metal, you can rough to within 0.010" or so with carbide, but don't expect high finish and accuracy. Then, try a ground HSS tool with a very aggressive rake, and a miniscule tip radius. A tool like this is good for no more than a few thousandths, but will cleanly remove metal with accuracy. Too heavy a feed will break the tiny tip or dull it quickly. I recommend honing this tool prior to each use with a fine diamond stone or hard Arkansas. Definitely give it something better than what it will have coming off a bench grinder.

Once within 0.0006" or so, break out the abrasive paper and sneak up on the final dimension. You can create a journal in this fashion that looks like it was ground, and it will perform as well.

See http://www.5bears.com/cnc16.htm for details. I've posted this link a few times, but the turning of ballscrew journals seems to come up fairly often, and I think this is worth repeating.

Pic of high-rake finish tool in HSS: