Annealing Ball Screw Ends

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Dave_C
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Annealing Ball Screw Ends

Post by Dave_C »

Question:

What is the proper procedure to anneal the ends of a rolled ball screw? (.750" diameter and .625" diameter)

I tried to turn down the end for the bearing with carbide inserts and it just broke the tip! These things are HARD!

All I know to do is to take a torch to the end, heat it till it is red and let it cool at room temp. I'll put a wet rag back about as far as I want the heat to go and keep the rag wet. Other than that, I need some advice from someone who knows what they are doing.

Dave C.
I learn something new every day! Problem is I forget two.
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DICKEYBIRD
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Re: Annealing Ball Screw Ends

Post by DICKEYBIRD »

Hi Dave, I ran across this:
http://www.cnczone.com/forums/general_m ... w_end.html

It's old but has some good info.
Milton in Tennessee

"Accuracy is the sum total of your compensating mistakes."
Richard_W
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Re: Annealing Ball Screw Ends

Post by Richard_W »

I use cermet inserts for the hard materials. You can even cut a bearing race with it. One job we kept getting was requiring 1045 welded to a HSS drill shank.The drill shanks are usually soft and easy to machine, but when welded to 1045 carbide alone wouldn't touch it at the weld. Cermet in the CNMG 432 style cut it just fine.

Richard W.
RET
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Re: Annealing Ball Screw Ends

Post by RET »

Hi Dave,

When I rebuilt the little CNC mill, I used machine tool quality ballscrews (5/8" dia. x 5 tpi.) from Thomson. I asked them to anneal the ends for me. I'm sure they use an induction heating coil to anneal the shaft ends. If you want to anneal yours, I would suggest you try putting the screw in the lathe with quite a bit sticking out, then start the lathe and bring an oxy-acetylene torch up to it. Heat the outside fairly quickly with the wash from the torch until it turns a dark blue or light brown, then take the heat away and let the rest of the shaft cool the heated area. You must have the shaft rotating to get the heat applied evenly. Try a scrap piece of steel to use as a test piece. Even if it isn't hard, it will still react to the air in much the same way.

Even when annealed, the Thomson shaft is still a bit hard but it machines not too badly. All you need is to soften the outside, I'm pretty sure the center isn't glass hard even in its original state. The first thing I did was to put a center hole in the ball screws I machined for support. I used standard high speed steel tool bits running at a slow speed and they worked fine, both for turning and for threading. Even when I got near the end of the annealed portion the tool bit still cut OK. You need a fairly substantial machine because the cutting forces are higher, but my 13" South Bend worked OK. Its old (made in 1942), but it still works.

Just my 2 cents worth.

Richard Trounce.
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Dave_C
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Re: Annealing Ball Screw Ends

Post by Dave_C »

Richard,

Thanks for the feedback!

I am concerned about the screw being a "rolled" screw as it has been work hardened by the rolling process. I noticed that when I took a lite pass the cutter hogged in and I could see the flexing of the whole tool support assembly. Which made it take too much material. NO way to get an accurate cut. (not good)

So I'm thinking I need to change the tool geometry to something that won't hog in hard material.

I think I can do the annealing process OK. I like the idea of putting it in the lathe and turning it!

Harold, I was hoping for some advice from you on this if you could.

Dave C.
I learn something new every day! Problem is I forget two.
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Dave_C
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Re: Annealing Ball Screw Ends

Post by Dave_C »

OK,

I followed the suggestion of putting the ball screw in the lathe and turning it as I heated it. I did just that, turned it at 200 RPM and heated 3" of it till it was between dark brown and dark red. I let it air cool and it machined like regular ole 1018 does.

So a lot of fuss over something because I had never done it. I just lacked the confidence and experience to put a torch to a ball screw.

So one end is done, all but the 1 x 15mm thread for the locknut. I should be able to handle that this afternoon!

Thanks again for the input and feedback!

Dave C.
I learn something new every day! Problem is I forget two.
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Dave_C
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Re: Annealing Ball Screw Ends

Post by Dave_C »

It's only fair to show the results of what I learned from this post! This turned out very nice and I polished it to within .00005" and I think that will be close enough.
Attachments
Finished ends. .500" x 1.000" for pulley and 15MM 1.675 for the bearing and nut.
Finished ends. .500" x 1.000" for pulley and 15MM 1.675 for the bearing and nut.
I learn something new every day! Problem is I forget two.
RET
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Re: Annealing Ball Screw Ends

Post by RET »

Hi,

Congratulations! I'm glad it turned out so well for you. I would have probably run the lathe at a slower speed, but hey it worked; that's the main thing. From the picture, I see you also did a good job on the threads too.

I used the ground thread machine tool screws because I wanted the accuracy, but even the rolled threads should be OK. Just make sure you set things up to keep the dirt and chips out. Even a little bit of dirt is enough to mess things up. I machined the y axis screw first and that worked just fine, but when I did the x axis, I made the mistake of forgetting to remove the burr at the end of the turned portion. When I put the nut on, some of the little bits of metal got into the ball races and messed everything up.

You aren't supposed to be able to take one of those apart. Actually, taking the nut apart is easy, the hard part is getting it back together again! I had to take the assembly apart and clean it 5 times before I got it clean enough to work the way its supposed to. The last time, I put everything in an ultrasonic cleaner with varsol and that finally did the trick. The nut I'm using has two separate ball tracks with a slightly different pitch to that of the screw and that supplies the preload. The things you learn when you make an "oops, what do I do now?"

Naturally, when I did the z axis, I was VERY careful to make sure all the burrs were removed before I tried to put it together.

My design has lip seals on the 1"Thomson support rails and wiper seals on the ball screws The y axis also has plastic covers to keep dirt and chips away from the shafts and screw and the x axis has an upside down assembly with the shafts and screw on the underside of the table to shield the working parts.

In the picture you can see the screen which shows a bit of the Sherline software which I continue to use with the new machine. The software is actually very good and quite user friendly. This is the only G code software I'm familiar with, but I would recommend it.

I hope the picture helps.

Richard Trounce.
Attachments
x & y assembly
x & y assembly
Last edited by RET on Tue Feb 11, 2014 7:40 pm, edited 3 times in total.
Marty_Escarcega
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Re: Annealing Ball Screw Ends

Post by Marty_Escarcega »

Thanks for taking the time to explain the process you went through and showing the results. Its those posts that serve as inspiration for the rest of us!
Marty
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Harold_V
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Re: Annealing Ball Screw Ends

Post by Harold_V »

DrDavo wrote:Harold, I was hoping for some advice from you on this if you could.
Well, DrDavo, indications are you handled the task admirably. Sorry I was not here to dispense my opinion, but today was our weekly trek to the "big city" for supplies.

If hogging is an issue, negative rake can be a solution (assuming you're using carbide). It's also somewhat better at interrupted cuts in that the edge tends to be more robust.

HSS? I'd use a slight lead, and take enough material to eliminate any interrupted cut, assuming that would leave enough material to then shoot for size. It's somewhat important to get down to a round surface before you attempt any degree of precision.

Depth and width of a chip breaker, rake angle, along with side relief, can all be used to limit the ability of a tool to hog. Positive rake increases the opportunity, especially in soft materials. Hard materials, not so much, but hard materials also tend to destroy thinned edges because they can't dissipate heat rapidly. All in all, you just have to call on all of the experience you've had when facing similar issues, and hit a balance that works for you and your particular machine, which you appear to have done nicely. I tip my hat to you, sir.

Harold
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