how to radius an opening edge on a large weldment

I have a large weldment that is too big to fit on any mill we have. I need to machine, file or grind a .125 radius on the corners of a 4" x
60" opening. Does anybody have any ideas how to mechanize the operation? The outside surface is critical and cannot be damaged.
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Mark Cram wrote:

You might be able to route it.
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John R. Carroll
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John R. Carroll wrote:

I second that idea, especially if it's alum.
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Regards,
Steve Saling
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Garlicdude wrote:

I third it. I use a router fairly often for radiusing or chamfering edges on aluminum.
Jon
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Hmmm...perchance you've a mill that's small enough to fit on the weldment instead ?
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Perhaps something like this: http://www.sliber.dk/sliber-dansk/produkter.htm
The page is in Danish, but you'll get the idea from the picture. (or use Google translate http://translate.google.com/translate_t# )
We ground the inserts for the prototype. It will cut up to a .2" radius or a .25"chamfer on steel plates in a single cut.
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http://www.hydratight.com/en/products/machining/milling-machines/mini-mill
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Bipolar Bear wrote:

BPB:
    Now that device looks trick, expensive, but trick.
    I think Robin's die grinder suggestion is the cat's meow, in this case.
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weldment
http://www.hydratight.com/en/products/machining/milling-machines/mini-mill
Odd that--I do seem to be missing quite a few posts lately...

Yeah a .125r edge break really isn't all that heavy when it comes down to it I'd probly first knock off a appx .08 chamfer using a 3in flat dotco type angle or even a welder's disc grinder and then follow up with cartridge rolls using any garden variety 1/4in straight burr gun.
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Router won't likely work in the case of steel, although you might find a carbide radius cutting bit and a very low-speed router.
Anyway, you can certainly do this with a disc grinder and a die grinder by hand. Not trivial work though. You'd need to do a bit of practice, but I've done this extensively on large stamping dies and it's certainly fast and effective. This is the option I'd take if you've only got one piece to do. If you've got lots to do, it does get arduous.
Regards,
Robin
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On Fri, 12 Sep 2008 12:37:10 -0700 (PDT), Mark Cram

I tried the LFK200 on 304 stainless 1/4" plate.
We used it for chamfering, they do have radius inserts.
http://www.csunitec.com/magneticdrills/beveler.html
I didn't really think it was good enough for stainless but it was worth a try. Worked out great, it's inexpensive (IMO) especially since it saved about $50,000 labor on first job.
Tom
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Just to clarify things a little. I work with the original poster and know of this part. It's made of 304 ss and was fabricated with the radius on it but after they ground the flange flat it removed a lot of the radius. The radius needs to be brought back to full radius now. The first one was done by file and sanding block and came out nice but was very time consuming. There are two more to be done. Thanks for any advice. Steve
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snipped-for-privacy@mail.com wrote:

Steve:
    You might try grinding a .125 radius on a 1/2 square HSS lathe tool bit, then hold it in a small vise and "scrape" most of the material off, then finish with 1" strips of abrasive cloth, like you were polishing shoes. That's quick and dirty, but might give consistent results. (try it on a piece of scrap first)
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Bob, Something like that had crossed my mind but I haven't really gotten involved with working on that part yet. If I do then I think I just might try it. With the right relief and rake angles it just might work. That is some tough stuff though. I'll post the results either way. Thanks Steve
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