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Acme Tap Question

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kev74

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#1
I'm working on making a small drill press vise form a kit consisting of cast iron castings. I want to use a piece of 1/2-10 Acme threaded rod for the screw.

I'm shopping for a 1/2-10 Acme tap and see 3 types of taps available - a regular tapered single pass tap, a tandem type tap, and a two piece set consisting of roughing and finishing taps.

Is there much difference in the quality of the threads each can cut? And would the cheaper single pass tapered tap be likely to thread a hole in cast iron that would be good enough to tighten a vise? Thanks!
 

MrWhoopee

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#2
I believe it's mostly a matter of how much horsepower it takes to drive the tap. If you are a manly man, a single pass tap will be fine. It's only a vise, not a lathe.
 

mmcmdl

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#3
I have some 1/2-10 acme taps on hand ! Shoot me a pm . Dave .
 

P. Waller

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#4
A tandem tap is very long and has 2 sections on the same tool, roughing and finishing.
This will allow you to tap the parts in one set up saving a good deal of time, much like a nut tap they may accumulate parts on the shank so you do not have to back it.
 

kev74

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Is it unreasonable to try and tap Acme threads through about .8 inch of cast iron? It seems like I'd be removing a lot of metal at once.

This is going to be a one-off project. If I could get it done with a single pass tap and get good results, I'd prefer to go that way. Otherwise I might try to fixture it in the lathe and single point cut the threads.
 

P. Waller

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Is it unreasonable to try and tap Acme threads through about .8 inch of cast iron? It seems like I'd be removing a lot of metal at once.

This is going to be a one-off project. If I could get it done with a single pass tap and get good results, I'd prefer to go that way. Otherwise I might try to fixture it in the lathe and single point cut the threads.
If few parts are required by all means single point them, however producing such a small diameter acme thread will prove arduous with a manual machine. If there is no time constraint then have at it and you will surely learn a good deal.
 

benmychree

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#7
You probably do not have enough length between the boss and the vise jaw to use a tandem tap, it would likely strike the jaw before getting to full depth; there are sets of "serial hand taps" that are short and each taps the thread deeper than the previous one; When I made my drill press vice in high school (class of '63) they would borrow a set from the local Navy Yard.. They were guided by a drill chuck in the radial drill, each in turn, there were three in the set. When we made ours, we did not rely on acme thread rod, we made our own screws from material large enough to make the hub and we made the ends of the tightening lever; there is so much more satisfaction in doing it ALL by one's own self.
Yes, I still have and use the vise in my home shop. The teacher of the class visited my shop downtown once and saw the vise on the welding table; I was embarrassed to have him see it in use in that way and location, but he was not at all put off, and said "you still have it and you still use it" or something to that effect.
 

kev74

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#8
I wound up using a single pass tap. Every couple of turns I blew out the chips and it went through a lot easier than I thought it would.
 

Rooster

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#9
I used a single pass acme tap for the cross slide nut i made out of C954 aluminum bronze, worked great.
 
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