I've a used 1/2" MT2 end mill holder that I'd like to bore out to 3/4". The problem is that the holder seems to be hardened throughout. A small file won't scratch the bore of the holder. It seems that my options would be to bore it out as-is with carbide or anneal it and bore. I suspect that grinding would take forever and am not real thrilled with the idea of grinding on the lathe, though I do have a decent toolpost grinder.For annealing, I have available a toaster oven (500 °F) or gas barbecue, a propane torch, or a 1-hour round trip to a friend with a small heat treating oven. If scale is likely to be a problem with annealing, what is the best way to deal with that? I don't much care about the appearance of the end mill holder end, but don't want to screw up the MT2 end.Does anyone have any thoughts on the best approach?

I'm not familiar with that particular holder, Mike, but I'd be cautiousabout opening it up for a larger shank unless the exterior is fairly largediameter. If it compares favorably with the typical 3/4" holder, Iwouldn't hesitate, but it could prove a mistake if you put it to work with aslender body. Screws may not hold, and it may offer chatter that a morerobust one wouldn't. I'm assuming it looks similar to a cat 30,40 or 50holder.Assuming there's no good reason to not open it up, the first thing you needto determine is if it is hardened through. It may be induction hardened,which often controls heat treat depth. If that be the case, you may getthrough the hard layer and it will machine better, although you would thenbe faced with a soft interior when finished. Regardless of how hard itmay be, I think I'd hesitate to anneal it in any way, not being able tocontrol where to stop, and scaling.Grinding the size larger would be the ideal way to go, assuming it ishardened,...

Boring out hardened MT2 EM holder?

Feb 25, 2005 22 Replies

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Harold and Susan Vordos 21 years ago

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Very cool, Mike. That means the idea is manageable, and the purchased one is likely to have thicker walls, which was one of my concerns. Great solution.

Harold

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Mike Henry 21 years ago

I'd have been fired long ago if I did this for a living. It's mostly just a hobby for me, though some parts are made for work in an R&D environment.

The flycutter can be seen here, in the second picture down from the top:

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It's got center holes on each end, so I suppose it could be turned between centers. Getting a dog leg on the flycutter end might be a problem given the radius on that end, so it might be better to hold it in a 4-jaw chuck. From an engineering standpoint, though, it seems that a 3/4" EM holder is simpler and at least as cheap a solution if machining time is considered. Then too, I'd also like to use (or at least try out) the Tree boring head and I'm not about to try turning it's 3/4" shank down to 1/2".

Mike

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Mike Henry 21 years ago

Thanks - that's just what I did. They are out of stock, but this is has been a long-standing need so waiting a little longer is not an issue.

Mike

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