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mrchurchill
01-12-2005, 09:15 AM
Yes, I'm an idiot....8*)

With that out o the way, I do have a question I need to answer. Having never been overly endowed with smarts on tool grinding I've found the tool angles on boring tools to be a mystery.

What brings this to the fore is that I snapped my forged boring tool last night (a catch in a piece of CRS...).

Tonight's project is making a boring bar from a bit of 1/2" drill rod, with a drilled-through hole at a 45-degree angle to take a bit of 1/4" drill rod held in place and at angle by a setscrew from the front.

What should the business end of the cutting bit look like?

Thanks, Alan

Al Messer
01-12-2005, 09:34 AM
A left-handed turning tool.

SGW
01-12-2005, 09:44 AM
They're a mystery to me too!

But here's my approach. Maybe somebody who actually knows something can help.

One thing to watch out for is to have enough clearance on the end. Since the curvature of the hole "wraps under" the boring tool, especially in smaller-diameter holes, it's important to grind enough relief on the end of the tool so it doesn't rub.

Other than that, grind it pretty much as you would a lathe knife tool that's going to cut from left to right.

mrchurchill
01-12-2005, 09:51 AM
> Other than that, grind it pretty much as you would a lathe knife tool that's going to cut from left to right.

OK, now you've done it....8*)

Wouldn't I want a shape to cut from right to left, not the reverse? THis is not a trivial question - I'm left-handed, so these things oftentimes confuse me...

Near as I can tell, i'm cutting to the inside of a turning workpiece but the metal is still coming down to me, cutting on (the from the back, facing the work) left side of the tool.

I are so confused...

Alan

JCHannum
01-12-2005, 10:26 AM
It is not too mysterious. Forget that you are boring at all, and imagine that you are turning a piece on the back (wall) side of the lathe. The rotation would have to be reversed of course, but the cutting action is the same, and the cutter is ground the same.

Add extra relief as SGW suggests to clear the ID, take extra care to center the cutter, and have at it.

lynnl
01-12-2005, 10:47 AM
mrchurchill, your comment "....Near as I can tell, i'm cutting to the inside of a turning workpiece but the metal is still coming down to me, cutting on (the from the back, facing the work) left side of the tool...."

leads me to think you're viewing the cutting action with a boring tool as taking place on the radial periphery of the bore.
That's not how it's supposed to work. The cutting takes place axially. i.e. toward the headstock. What you want is 'clearance' between the tool bit and the cylindrical part of the bore. So you grind a relief on the tool bit surface that's toward you (the operator) both downward (to accomodate the curvature as SGW mentioned) and backward toward the tailstock). Only the leading edge of the corner of the tool does the cutting.

(My apologies if I've misinterpreted)



[This message has been edited by lynnl (edited 01-12-2005).]

mrchurchill
01-12-2005, 11:35 AM
Lynnl adds:

mrchurchill, your comment "....Near as I can tell, i'm cutting to the inside of a turning workpiece but the metal is still coming down to me, cutting on (the from the back, facing the work) left side of the tool...."

leads me to think you're viewing the cutting action with a boring tool as taking place on the radial periphery of the bore.

>>

Yes - i was having difficulty picturing the cutting action, hence my initial comments.

So effectively what i want is a point with clearance to the back and side, with a flat front (or raked which way?) which is the actual cutting surface?

ajr

lynnl
01-12-2005, 11:59 AM
Yes, that flat front will need some front clearance in order to cut. As for top rake, I don't have one to look at now, but I'd think some rake would help. Tho I've used tools with zero top rake that seemed to cut ok.

Paul Gauthier
01-12-2005, 12:46 PM
Does this help any, it's crude but I have only my left hand to use at the moment and I am not lefthanded. The wording says " clearance angle exagerated for clarity"

http://img.photobucket.com/albums/0603/PaulGauthier/boringbar.jpg

------------------
Paul G.


[This message has been edited by Paul Gauthier (edited 01-12-2005).]

mrchurchill
01-12-2005, 01:01 PM
YES. Thank you to all of you - the sketch just seals what I have been reading in all along.

Need to make some chips tonight...8*)

Alan

.RC.
01-12-2005, 03:46 PM
Just grind it like a boring bar.....It is the same principle as a boring bar except in boring head use the tool moves not the workpiece...