Acme thread

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 Dan
The sine of 14.5 degrees is 1/4, so a patternmaker can accurately construct the angle by linear measurement.
jsw
Reply to
Jim Wilkins
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Reply to
Phil Kangas
"Phil Kangas" wrote in news:i0anrm$pih$1 @news.eternal-september.org:
Someplace I saw a similar setup using a small boring head. Even gave calibrated offsets on the dial. Not sure if the tang on the taper had been cutoff, of carefully aligned so that the axis of the head was horizontal.
I actually found a web site with a description of such a device, but he doesn't address how you make sure it's horizontal:
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Doug White
Reply to
Doug White
"Doug White" wrote in message
I can see how that would work but it's a bit bulky for a 9" SB. I have two sizes of Flynn boring heads but they're on an R-8 mount that I'd rather not monkey with. I'd have room on my 13x40 turn-pro but can't justify the cost of another head, yet. A boring head on a 3MT is kinda useless other than for a tailstock center, eih? Making this thing was a good schoolhouse lesson for me ...;>)) And you get to use trig to set it up too! phil
Reply to
Phil Kangas
There is usually two opposed parallel flat surfaces on a boring head. The part that holds the boring tool. You indicate that. Insert the boring head in the tailstock loosely, set the indicator on the cross slide, tram, tap, indicate, tap, then wack it in place for use when you have it horizontal to the ways.
Wes
Reply to
Wes
You're correct in your earlier posts that this doubles the chip load, but the cutting forces oppose each other and cancel out, and moreso with the narrow Acme angle versus the 60 degree thread form. This cancellation means that the tool rigidity can handle a lot more pressure than if you were making just a one-sided cut. It is like drilling a center hole, where two cutting edges oppose each other and allow you to use a lot more pressure and feed than if you were boring a center hole with one cutting edge.
Reply to
Richard J Kinch
That could be it; the resistance of the tool and toolholding pieces are a lot more rigid when resisting loads perpendicular to the bed.
I've never doubted that there must be some reason for it. The thing that's always bugged me is that I don't recall ever reading or hearing an explanation. The reason that's curious is that I immersed myself in old machining books when I was an editor at _American Machinist_. And we had what probably was the best collection of them in the world.
It will have to remain one of those mysteries of the universe.
Reply to
Ed Huntress

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