Power for Turning 3/4-6 Acme Tap?

[SteveM]

That is a 1 1/2-8 tap and there is no way I could have turned it in a drilled hole.Back plate tapping.JPG The 4 jaw is held in a bench vise.

If you had tried, the part would have slipped in the chuck, the chuck would have slipped in the vise, or the workbench would have spun.

I had to make some 1-1/2x8 threads in a 1/4" plate and the threads didn't need to be a tight fit, so I overbored the hole. Even then, it was a bear to turn the tap.

Steve

[SteveHGraham]

I'm afraid people have the impression that it was nearly impossible to turn the Acme tap. It wasn't. It was just very slow.

[Harold_V]

The reason I would like to get a tap wrench is that you can grab both handles, so you're not pushing the tap off center as badly, and it's easier to apply force.

That's not an advantage when tapping in a lathe, although there may be exceptions. It's usually clumsy, and you can't keep the center in contact, as that requires a hand on the tailstock handle, so you can't use both hands (on the tap wrench), anyway. The center used to follow the tap compensates for side thrust, so a single lever (Crescent wrench) works just fine. Plus, it offers the advantage of not getting in the way, the way a long handled tap wrench would (hits the bed). That limits the amount you can turn the tap, and is VERY inconvenient to relocate, unlike an adjustable wrench.

Without following a tap, you're risking misalignment. The center serves more than one purpose, in other words.

H

[tornitore45]

The advantage of a two handles wrench is that it generate twice the torque all thing being equal
BUT most important it generate a true torque without a resulting radial force.

A one handle wrench generate a torque but also a resulting radial force acting against the axis.

If the set up is such like Harold described, where the tail stock center resist any radial force generated by a single arm wrench then you can use as long a lever you need to generate the necessary torque, without fear of de-axing the tap. Still the tail stock must be snugged up constantly to keep the tap on axis. Basically a two hand operation with your right hand doing the lesser work and your left arm (presumably the weaker) doing the heavy pulling.

[SteveHGraham]

The problem for me is that it's not possible to move the ram and turn the wrench at the same time, so you might as well have a wrench that deflects the tap as little as possible between ram bumps.

[BadDog]

Use a (purchased or made) spring loaded center. Then you don't have to follow it with the quill. One of my earlier projects was a relatively long travel spring loaded center for guiding a manual tap. It is straight shank to mount in collet or drill chuck for use on mill, lathe or drill press. I don't use it much since I got a good selection of machine taps, but sometimes it still comes in handy.

And by using a single wrench you can follow relatively easy with the quill, unless you need 2 hands to generate the torque needed, but then you can just get a longer lever. I have some larger 2 handle tap wrenches (2 that won't rotate on my 17" lathe), but only use them when not tapping on the machine, usually just when cleaning/repairing damaged large threads. The most I remember using them was with weld in pipe bungs that distort from the welding and need to be recut to seal, or when I had to clean up a bunch of damaged threads on my tractor.

[tornitore45]

I am not sure a spring loaded center is strong enough. Steve is handling a stubborn tap that requires a force at his comfort limits. There is also to consider that if the wrench does not swing around it (or the chuck) has to be re-positioned by 1/4 turns.

[BadDog]

Sure, but at least a wrench can be repositioned easily where a tap-wrench cannot. The center I made has a pretty long shaft guiding the floating point, so it resists side forces pretty well as long as you don't overcome the spring, which could be made stronger I suppose. But mine was really made for just guiding, not locking in place. I've used it for running some fairly large taps (that I don't have machine taps for) and found it to work. But that was on a drill press with the big handles, don't recall doing it on the lathe with a wrench. But even so I think it would work with some care to minimized deflection using the off hand. Then again,if I didn't have sequential taps I think I would probably have roughed a hole before tapping with a large acme.

[SteveHGraham]

I am not sure a spring loaded center is strong enough. Steve is handling a stubborn tap that requires a force at his comfort limits. There is also to consider that if the wrench does not swing around it (or the chuck) has to be re-positioned by 1/4 turns.

This is what occurred to me. It would have to be an incredible spring.

I guess I should mention what I do when I tap on the drill press and mill. Much of the time, I use a Walton piloted spindle tapper, which is a sort of chuck with a T-handle built in. It has a rod that runs through it axially, and you can put the rod in a drill chuck (loosely) or, I suppose, a loose collet. It helps keep things on track. For smaller taps, I often use an ordinary cheap T-style tap wrench. They are round at the upper end, so you can put the upper part in a loose chuck, and it will keep you lined up. The Walton tool is too small for the 3/4 tap, and they don't make a bigger one.

I couldn't put the 3/4 tap in my drill chuck, because it would have covered the square end, and I would not have been able to turn it.

Just thinking about it, I believe it would be useful to have an extra-large T-style tap wrench. I could insert the round rear part in my drill chuck to hold the tap in place and use the T handles to turn the tap.

I wonder how tight my steady rest will close. It would definitely hold a big tap on center.

[SteveHGraham]

Another option: bore a hole in a piece of scrap and mount it in a tool holder. Center the hole and run the tap through it. The tool holder would probably interfere with the wrench, though.

[tornitore45]

Steve, I get it that you are in battle of pride with your tool. You are determined (nice word for stubborn ) to show the damn tap who is the owner and who is the tool. I get this and on occasion I am guilty of the same determined mind.
But this thread has exposed all the problem of tapping such a hefty thread and alluded at the joy of a single point approach.
You already have the Acme bit, why not relax and let the motor do the turning.

[SteveHGraham]

You have to know the history. I bought the tap to replace a single-point tool which was a complete pain to use. The tap was a joy compared to the single-point tool.