Weird Shank on Boring Head

[SteveHGraham]

I found a neat deal on a Flynn boring head. It has a weird shank, however. It's a straight 5/8" shank with a tapered bit at the bottom, and it has threads inside it. It almost looks like someone cut out part of an R8 shank.

My question: if I tried to run this in a 5/8" collet, would I be inviting destruction? I think I would. It's pretty long.

A new R8 shank would only be about $250.

[SteveM]

Besides the downside of the huge overhang, you are at the mercy of the skill of whoever turned that down.

$250 for a shank? You're almost as big a cheapskate as I am. There must be an alternative.

Can you turn something between centers with a 3/4" shank to work in a collet?

What are the threads?

Can you use something like this:
http://littlemachineshop.com/products/p ... &category=

Steve

[SteveHGraham]

It's hard to get info on the threads, but I believe the thread attaching the shank to the head is 2"-20. Not sure why the shanks cost so much. I suppose they must be super-precise. I could make a straight shank with a 2"-20 thread myself. Or I could take this one out of the head and turn the fat part to fit in the collet. Not sure how well that would work. If I couldn't match the diameter of the existing shank, I would have to make it a couple of thousandths smaller.

[SteveHGraham]

I think this is the part it should have.

http://www.pts-canada.com/cgi/CGP2SRIM? ... 0text/html

[leeko]

Forgive my ignorance, but why would it be a problem? Boring heads are designed to run eccentric, so even if the PO was blind drunk when he turned it down, it shouldn't matter. If the length of the shank is excessive, chop off the excess down to the length that is grippable in the collet. I think 5/8" should be plenty of meat for the type of cuts you'd likely be making with a boring head. The only issue i can see is if the turned shank has a significant taper, limiting the surface contact in the collet.

Lee

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[SteveM]

Boring heads are designed to run eccentric, so even if the PO was blind drunk when he turned it down, it shouldn't matter.

Yes, they run eccentric (otherwise, they wouldn't do anything), but you don't want a wobble that would cause the bottom edge of a bored hold to not be square to the hole.

If I were turning the shank down. I would turn it to the size of the largest collet I had, which in the case of R8 is 3/4".

For my Bridgeport M, I have tools on 1/2" shanks, because that's the largest.

Steve

[leeko]

Boring heads are designed to run eccentric, so even if the PO was blind drunk when he turned it down, it shouldn't matter.

Yes, they run eccentric (otherwise, they wouldn't do anything), but you don't want a wobble that would cause the bottom edge of a bored hold to not be square to the hole.

If I were turning the shank down. I would turn it to the size of the largest collet I had, which in the case of R8 is 3/4".

For my Bridgeport M, I have tools on 1/2" shanks, because that's the largest.

Steve

Steve,

That's a fair point, and one i hadn't considered. I still wouldn't think twice about throwing it in the spindle and seeing how good it runs. If it's off, press a sleeve onto the shank and turn it back down yourself. I wouldn't spend $250 on a shank - much more important things to downs money on

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[SteveHGraham]

Sadly, the shank is 5/8" right now, so that's the smallest I could hope to go. Again, I wonder why I couldn't make my own shank. There must be a reason why people pay $250 for them.

[leeko]

Sadly, the shank is 5/8" right now, so that's the smallest I could hope to go. Again, I wonder why I couldn't make my own shank. There must be a reason why people pay $250 for them.

Steve, see my post above. Press a sleeve onto the 5/8 shank, then turn it to whatever size you want

Lee

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[rudd]

It may be made to fit a Clarkson collet chuck - British make. Without dimensions that is speculation, but it looks about right . I have the Clarkson set-up on my CVA miller. The collet chuck is visible in the black and white illustration. I have looked hard, but not found any literature on this particular Clarkson product.
http://www.lathes.co.uk/cvamiller/

[GlennW]

I could make a straight shank with a 2"-20 thread myself. .

That's a winner right there.

[GlennW]

Yes, they run eccentric (otherwise, they wouldn't do anything), but you don't want a wobble that would cause the bottom edge of a bored hold to not be square to the hole.

I'm not sure I follow what you are referring to there.

It's a single point tool and the tool tip will always run concentric with the spindle axis regardless of shank error.

You can mount your DTI in the spindle and bend it any position you want and it will always give an true reading. (well, to the accuracy of the DTI itself)