I need to cut an acme thread in a steel block. Roughly 5/8" X 6. I forget what I measured! Is that done with a tap or a boring bar? Friends have not heard of an acme tap. Thought someone might know.
Thanks,
Bill A
yes
There are such taps. I have one, 1/2" x 10 Acme.
Boring a female Acme thread is something I've never tried. I still scratch my head over single-point turning of *external* Acme threads. Some of the old books tell you to cut both flanks at once, but I've never figured out why. I made a couple of Acme threaded shafts in 1/2" x 10, and cutting on one flank, just scraping the other, seemed to work Ok.
On Fri, 25 Jun 2010 10:44:27 -0400, BillMe wrote the following:
Sure it's ACME and 'Murrican?
UNC is 5/8-11, UNF is 5/8-18.
-- Pain makes man think. Thought makes man wise. Wisdom makes life endurable. -- John Patrick
ACME taps are readily available but are expensive. They also are often in sets for roughing and finishing, though some are multi stage with a roughing section followed by a finishing stage and are even more expensive. A quick look on the McMaster site shows a number of ACME taps, including the tandem ones, ranging from $60 to $300.
Typically unless you need to make a bunch of parts, it's cheaper to buy a ready made ACME nut assembly and install it in your part. McMaster lists a lot of precision ACME nuts, but the typical bronze thread in ACME nut that you thread into your part and secure with a setscrew, locktite, etc. runs $20-$30. These also make the nut readily replaceable for wear.
That worry kinda goes away if you grind an accurate Acme profile and feed straight in, slowly.
There are such taps. I have one, 1/2" x 10 Acme.
Boring a female Acme thread is something I've never tried. I still scratch my head over single-point turning of *external* Acme threads. Some of the old books tell you to cut both flanks at once, but I've never figured out why. I made a couple of Acme threaded shafts in 1/2" x 10, and cutting on one flank, just scraping the other, seemed to work Ok.
I've never seen an explanation of what you do that, Bob. Why plunge straight in, nearly doubling the chip load, rather than feeding in on an angle and cutting on one flank, as with conventional threads?
There must be some simple reason that I've just never come across.
ACME taps are very common and easy to buy in any size, if you have the money of course. McMaster has them. I may have a tap in that size.
i
McMaster-Carr: Google for machinists.
On 06/25/2010 08:12 AM, Robert Swinney wrote: (top posting fixed)
Doesn't that mean then that you need a different threading bit for each diameter and pitch of Acme thread you'll ever do? Or do you just need a different bit for each pitch, with enough clearance for the smaller diameters?
I have seen ACME taps for sale on Ebay. Probably some of the better on-line machine parts sellers will have them.
============ Given the cost of the taps [Acme usually has two, roughing and finishing] you may want to consider a threaded insert. This makes the thread easly renewable. Also if a replacement part, left hand acme threads are frequently used for adjustment. Be sure which one you have. There is also a metric trapizoidal thread with a 30 degree thread angle rather than the 29 degree acme.
mother lode of information on Acme threaded products
Serial tap. A series of taps that work you up to an agressive thread form.
Wes
Why wouldn't you set the compound at 14.5 degrees and make your infeeds via the compound?
Wes
That's the question I'm asking. And that's what I did. But that's not what Bob is saying -- and what Bob is saying is the same thing said by every source I've ever seen.
Plunge straight in, they say. Why?, I ask. It nearly doubles the chip load, and I can't see a good reason for it. There probably is one, but I don't get it.
Maybe it's to keep the tool tip from bending left/right? The tip isn't as well supported as a 60 degree tool would be.
I'll wait to have it explained. Now if we were using cnc's we could get creative in how we cut the profile. I seem to remember reading in the Sandvik book a technique for alternating between both flanks to reduce cutting forces.
Google is my bud.
D. Alternating flank infeed
This method alternately feeds the insert along both thread flanks, and therefore it uses both flanks of the insert to form the thread. The method delivers longer tool life because both sides of the insert nose are used. However, the method also can result in chip flow problems that can affect surface finish and tool life. This method is usually only used for very large pitches and for such thread forms as Acme and Trapeze.
Wes
Acme taps do exist, and the better ones are longer with a roughing and a finishing section separated by very little.
Looking through MSC's on-line catalog, 5/8" typically has 8 TPI, and 7/8" has 6 TPI.
The 5/8-8 goes for $81.59 for the combination tap.
The 7/8-6 goes for $221.25 for the combination tap.
Be sure to order the correct one. Leadscrews turned by handwheels often have left-hand threads so clockwise advances the nut.
As for single-pointing it with a lathe and a boring bar -- I think that it is unusually coarse for that, though I guess that it could be done by someone sufficiently skilled.
Good Luck, DoN.
I've single-point turned an Acme thread in a bronze nut (for a friend's log splitter). I think that it was something like a 1-1/4" major diameter or so. There was enough room for a reasonable boring bar to hold the tool, and I used a sine plate and some other tricks to grind the tool itself. But if he really is working with a 5/8" major diameter, and 6 TPI, that does not leave much room for a rigid enough boring bar.
Enjoy, DoN.
[ ... ]
I fed in at an angle of 14 degrees (a little less than the half-way point). But I ground a bit specifically for the thread I was cutting, including side clearance angles calculated for 5 degree clearance with the pitch and diameter I was working with for maximum strength. A more general tip (more clearance to adopt to various diameters and thus different thread angles) would have to be weaker.
And yes -- you make (or buy) a separate tool for each pitch you cut. My 12x24" Clausing can handle insert tools for above 10 TPI, but not up to the big bronze nut I was making -- so I had to make my own tool bit from HSS there.
Enjoy, DoN.
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