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Old 02-13-2012, 11:32 AM
Corm Corm is offline
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Default Lathe turning question

I am contemplating making a new die for my tubing bender. When I bought the plans for the bender (from <gottrikes.com>), die plans were included.

I want to make the die for 1.5" tubing. It involves turning a 7" diameter x 2" thick hunk of steel in my lathe, with a 1.5" round bottom groove in the middle around the circumference.

I'm wondering how to go about machining that 1.5" round bottom groove. I've made two other dies for the bender, and used ball end mills in my BP for those, but this one wants a round die turned in a lathe.

I can envision making a series of cuts with a regular bit, each cut going a little deeper towards the middle of the groove, from each side of the groove, and then maybe finishing it with some (a lot of) filing to smooth out the steps between the cuts. I believe that process is called 'Kellering'. I'm not real confident that I could do a real precise job using this method.

Is there another/better way to do this? I have a Craftsman 12x36 lathe, so please keep that in mind. The lathe is capable of doing this job, but it's not a huge honking lathe that weighs tons...

In case anyone is having a hard time trying to envision what this will look like, here is a URL that will take you to a picture of one that is close to what I need - http://www.northerntool.com/shop/too...9564_200389564

Thanks in advance for any machining suggestions any of you may have

Corm
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Old 02-13-2012, 11:41 AM
PixMan PixMan is offline
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That's a tough one for a lathe that size, but it can be done. The BEST way is by using a carbide insert groove tool to rough it out and a ball turner tool (working to the outside of the center-of-rotation) to finish it. You can of course do the whole thing with a ball turner, it just takes longer.

Another way I thought of (because I haven't made and don't own a ball turner either) would be to fasten it to the horizontal/vertical rotary table a I have (in vertical position) and use a 1-1/2" end mill to plunge the groove while I crank the rotary table.
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Old 02-13-2012, 11:52 AM
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nctox nctox is offline
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The ball turner is what I first thought of, though I don't have one either.
It might be difficult to find/make one that will cut an inside radius that small.
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Old 02-13-2012, 12:10 PM
Corm Corm is offline
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Hi Pixman.

I don't own a ball turning tool for my lathe either, although it has been on my list for a while.

I also thought about putting it on my rotary table and using a ball end mill as you suggested. I'd have to buy a 1.5" ball end mill, and an end mill holder, which would run a little over $100 (using the Enco catalog as a base for my prices). After buying the steel I'll have well over half the price of what I would need to just buy a die.

I made my other two dies using my rotab. It was slow going, but it got the job done. I did however already have the ball end mills and end mill holder I needed, so I didn't have to buy anything special to do those jobs.

Corm
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Old 02-13-2012, 12:14 PM
Corm Corm is offline
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Quote:
Originally Posted by nctox View Post
The ball turner is what I first thought of, though I don't have one either.
It might be difficult to find/make one that will cut an inside radius that small.
I'm beginning to think that might be the best thing for me to do - make a ball turner. I've probably got enough stuff around here to make one.

Corm
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Old 02-13-2012, 12:31 PM
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rickairmedic rickairmedic is offline
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Corm there are alot of Ball turner plans on the internet that should get you headed in the right direction .


Rick
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Old 02-13-2012, 12:36 PM
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LKeithR LKeithR is offline
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Just to be clear, what you need is an internal radius cutter, not a ball turner. Some tools can be adjusted to do both but I have seen some that will only cut spheres and can't do an inside radius...
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Old 02-13-2012, 01:29 PM
Corm Corm is offline
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Quote:
Originally Posted by LKeithR View Post
Just to be clear, what you need is an internal radius cutter, not a ball turner. Some tools can be adjusted to do both but I have seen some that will only cut spheres and can't do an inside radius...
You are correct of course. I had an inside radius cutter in mind, while thinking about ball cutters that can do both. I'm thinking that in my case, where I need a pretty small inside radius, I'll most likely make a single purpose inside radius tool, one that I can hang from my Aloris toolpost.

Thank you for the clarification

Corm
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Old 02-13-2012, 01:57 PM
PixMan PixMan is offline
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I wasn't thinking of using a ball end mill, but a regular 1-1/2" end mill as side cutting. It may require a long holder, but a 1-1/2" end mill with a 1-1/4" Weldon shank in a holder might be long enough.

If you don't have the stuff, throw the part into your car and come on down to MA and we'll do it up in about an hour.
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Old 02-13-2012, 02:07 PM
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GWIZ GWIZ is offline
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As in Pixman post,
If you want to be slow and cheap, a fly-cutter set at 1.5 dia.

Do the 'Kellering' in the lathe first, may get away with making a 3/4" radius (not a full ball) on a tool-bit ( slowest spindle rpm). finish in the mill if needed.
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Last edited by GWIZ; 02-13-2012 at 02:23 PM.
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