Machining ballscrews

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WJH
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Machining ballscrews

Post by WJH »

Hello, my 5mm pitch, 20mm diameter ballscrew came in the mail from China. As I understand it, it’s very hard. So I have two issues to deal with. One is machining it with interrupted cuts and carbide. Thinking that I should use my tool post grinder to remove the ridges and valleys, then tackle it with carbide or cermet.
The other issue is indicating the screw in the 4-jaw chuck with no smooth reference surface. Thinking I will make a tight fitting sleeve out of bronze, brass, or aluminum that is machined in a single chucking that slides over the ballscrew to serve as that reference surface.
Thoughts? This is for the CNC conversion of my 8” lathe.


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Harold_V
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Re: Machining ballscrews

Post by Harold_V »

This is an excellent place to use soft jaws, which, with care, will provide runout of less than a half thou, and virtually dead parallelism. That's a hard to beat deal! It likely would be easier than trying to accomplish the task using a four jaw, where you have to get the shaft not only running true, but dead parallel with the spindle as well. That can be challenging, especially if the jaws of the chuck are not dead parallel. The time you'd spend messing with a sleeve would be spent boring the jaws, with time left over. As an added bonus, you'd then be able to remove and replace the part if necessary, quickly, with no concern for it's relative attitude.

You would likely enjoy success grinding. Just pay attention to taper, and allow the part to cool to ambient temperature before making any critical measurements. A jet of air will chill things relatively quickly, assuming you have air in your shop.

Before you put a wheel to a part that would be expensive or difficult to replace, I highly recommend you do some practice grinding, so you understand the quirks of your setup. Pay strict attention to surface speed of the wheel----do not exceed the speed marked. Ring the wheel before mounting, and stand aside while it spools up.

H
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WJH
Posts: 1417
Joined: Sat Jan 16, 2010 9:29 pm
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Re: Machining ballscrews

Post by WJH »

Harold_V wrote:This is an excellent place to use soft jaws, which, with care, will provide runout of less than a half thou, and virtually dead parallelism. That's a hard to beat deal! It likely would be easier than trying to accomplish the task using a four jaw, where you have to get the shaft not only running true, but dead parallel with the spindle as well. That can be challenging, especially if the jaws of the chuck are not dead parallel. The time you'd spend messing with a sleeve would be spent boring the jaws, with time left over. As an added bonus, you'd then be able to remove and replace the part if necessary, quickly, with no concern for it's relative attitude.

You would likely enjoy success grinding. Just pay attention to taper, and allow the part to cool to ambient temperature before making any critical measurements. A jet of air will chill things relatively quickly, assuming you have air in your shop.

Before you put a wheel to a part that would be expensive or difficult to replace, I highly recommend you do some practice grinding, so you understand the quirks of your setup. Pay strict attention to surface speed of the wheel----do not exceed the speed marked. Ring the wheel before mounting, and stand aside while it spools up.

H
Hi Harold, I think I should invest in a nice 3 jaw chuck that has two piece jaws so I can utilize soft jaws. I currently don’t have this capability.


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Harold_V
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Re: Machining ballscrews

Post by Harold_V »

I recommend soft jaws highly. They solve too many problems, even for one-off projects, to not be at one's disposal, assuming they are available in your given chuck size.

I've not seen small chucks so equipped, although I expect they are finally gaining in popularity. If, when purchasing a chuck, one has the option for two piece jaws, that would be the logical choice. I can think of no reason to choose otherwise.

H
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tornitore45
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Re: Machining ballscrews

Post by tornitore45 »

Lacking soft jaws in similar cases I have interposed a thin leaf of steel from a banding strip and set the indicator on it. The leaf is held by a tool holder in the QCTP riding with spring on the top of the part.
Mauro Gaetano
in Austin TX
WJH
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Re: Machining ballscrews

Post by WJH »

I’ve seen them as small as 5”. Just ordered a Shars cast steel 6” 3 jaw with 2 piece jaws, and a set of steel soft jaws. Uses American standard.


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jpfalt
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Re: Machining ballscrews

Post by jpfalt »

You might want to consider drawing the temper on the end of the shaft you are machining. If drawn past purple to gray, the hardness will come down enough to cut fairly easily with standard HSS or carbide tooling. Also, most ballscrews have an exterior surface that is cylindrical and can be held in a collet chuck if you have one. Your idea of turning a close fitting sleeve or even a wringing fit should work well enough for what you are doing. The last time I did something like what you are doing, I made a shoulder sleeve that shouldered out on the top of the chuck jaws and went back into the chuck jaws. It was turned for a slip fit and closing the chuck jaws on it deformed it enough to grab the acme thread I was doing end work on.
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WesHowe
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Re: Machining ballscrews

Post by WesHowe »

I didn't have much trouble machining a 12mm ball screw (shortened and reformed the slack end). I used a 4-jaw chuck and copper pads, carefully dialed it in, and a carbide parting blade and lathe bit. It seemed the steel core is not all that hard, although the chrome plating over it is. Once under that, machining was routine.
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SteveHGraham
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Re: Machining ballscrews

Post by SteveHGraham »

Will all of the threads be used when the screw is in operation? Maybe you can use soft shims and grip it by an area which will never touch the nut.
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SteveM
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Re: Machining ballscrews

Post by SteveM »

WJH wrote: Sat Mar 31, 2018 8:19 amI think I should invest in a nice 3 jaw chuck that has two piece jaws so I can utilize soft jaws. I currently don’t have this capability.
You can find chucks that use 2-piece jaws and get them for cheap on ebay or at machinery dealers, because a new set of hard jaws is very expensive, so the chuck can go for cheap.

Then get some soft jaws from US Shop Tools and you're all set.

Steve
John Hasler
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Re: Machining ballscrews

Post by John Hasler »

Do you use a spider when boring soft jaws?

There's got to be a way to make soft jaws that will work with one-piece jaws. Another project...
SteveM
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Re: Machining ballscrews

Post by SteveM »

John Hasler wrote: Mon Apr 02, 2018 12:29 pm Do you use a spider when boring soft jaws?
I used to, but now I have one of these:
41BmS2KYBVL._SX342_.jpg
41BmS2KYBVL._SX342_.jpg (12.66 KiB) Viewed 5867 times
John Hasler wrote: Mon Apr 02, 2018 12:29 pm There's got to be a way to make soft jaws that will work with one-piece jaws. Another project...
There is:
Image
but this is only good for gripping at the face, not the full depth of the jaws, which is what you need.

Steve
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