Weird Shank on Boring Head

[SteveHGraham]

That's a winner right there.

Any idea why a factory shank costs $250?

[GlennW]

Because they can!

Kind of like metric change gears for a Clausing...

[SteveHGraham]

So there's no mystical reason why a shank made on a lathe (non-Clausing) would make the boring head explode or give off gamma rays or anything.

[GlennW]

Not even a chance of cooties.

[GlennW]

Not sure from the pic, but if the existing shank is solid, the remainder may possibly be turned down to 3/4" and still be equal to the grip length of a 3/4" collet, and then the 5/8 part just shortened up.

I don't know what size head it is, or what size bores you plan to work with as far as rigidity/stability goes.

[SteveHGraham]

It's about 3". I don't have any plans. I just feel like it would be fun to upgrade from my Indian boring head.

I saw the price on the new shank, and I thought, "There HAS to be a reason why I can't make that for five dollars."

I wonder if this is one more example of the kind of price structuring that helped kill the American manufacturing base.

[spro]

It is likely the original was a B&S 9 or 10. It looks like an attempt was made to use it for an R-8 or similar taper nose. I can only imagine how that worked if the taper wasn't perfect. It could have been machined closer to the head but the length would be too long. If he cut it, he would lose the threads. I don't know the size of the boring head but the old mills with that taper had at least 4-5" of contact inside the spindle, of a "locking" taper. It was like the spindle and the boring head became one unit. It is difficult to achieve the same work by a smaller collet.

[johnfreese]

Buy a chuck arbor for R8. Weld on a puck big enough to make the threaded end to fit the boring head. Turn and thread to fit.

[Harold_V]

Not sure why the shanks cost so much. I suppose they must be super-precise.

Nope. The only real requirement is that it holds the head securely, and does not permit any motion between the head and shank.
If you had a shank that had runout, one that even mounted the head such that it had a distinct wobble, the boring bar, assuming it would fit within the hole you'd bore, would still generate a true circle, and bore just as straight as a head with no run-out. The precision is not reliant on the head, but on the spindle and quill.

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.

Get to it! Use the boring head as the thread gauge, and achieve a snug fit for the thread. Remember, all it has to do is mount the head. Once mounted and tightened, pretty good chance the thread will never again be undone. Make sure the face of the shank is perpendicular to the thread pitch, so it shoulders properly. You do that by facing and threading without removing the part from the setup, or by running between centers.

The only critical thing, in my opinion, is the diameter of the shank. If you pursue the logic of keeping shanks short and of a common size, you'd shoot for a 3/4" shank, nominal in diameter, and about an inch long. No big deal, really. Just make sure you hold the .750" diameter, and it has a decent finish. If you can't achieve a good finish when machining, shoot for a half thou oversized, then size it by polishing. The first half thou goes pretty quickly, and will improve the finish considerably.

Best scenario, though, is to grind the shank. There's nothing like the finish one achieves by precision grinding.

Harold

[GlennW]

Now, if it is a boring/facing head, shank accuracy may play a part, as the dovetail slide needs to be perpendicular to the axis of the shank or a faced part may technically end up slightly conical.

[GlennW]

My first choice for making a new shank would be pre-hard 4140. (Although, I don't believe that $5.00 will quite cover it!)

[SteveHGraham]

The next time I see someone complaining about people about buying Chinese I will remind them how much a boring head shank made in America costs.