I had a chance to thread some 1/2 NPT pipes. The threader worked, however, the vise (Harbor Freight 4" vise) could not hold the pipe well, so the pipe would slip. I tightened the vise rather well. This is a vise with no special pipe holding provisions.
My question is, is the vise somenow not as good as it should be, or was it simply a wrong tool for the job? Do vises with pipe "slots" hold round objects better?
Ig, pipe threading requires an enormous amount of torque. Flat vice jaws haves too little surface contact. Try making this tool I have several sizes of. For 1/2" pipe (.840" OD) clamp two 3" pieces of 1" aluminum bar together with .015" shims between them. Drill thru the joint 27/32" long ways. With any luck this with make a saddle clamp with allmost 100% contact. Now put your pipe in this tool and into the 4" vise and try the threading die. This tool is also great for screwing/unscrewing nipples without damage. RichD, Atlanta
I've threaded pipe hundreds of times. Go to an auction of a closing electrical/plumbing contractor and get yourself an American-made trivise made for the deed. Don't worry how crappy and old it looks. The seat for the pipe has got to have teeth on it and then chain that you can then really crank tight.
Your vise can't hold 1/2"....hahahaha ! (not laughing at you)
I've threaded 2" ridgid conduit many times with these trivises. One usually needs to use a cheater bar out the end of the hand threader...and it helps to simply lay the weight of one's whole body across the bar to offset the torque.
You have to tighten the vise as hard as you can but it, amazingly, will hold even against those kinds of torques.
That will hold the pipe without marring it, but the surface area has little to do with the friction. The friction equals the psi * area * the coeficent of friction. If you double the area you halve the psi.
The jaws are supposed to dig into the pipe. If they are not sharp, or heat treated well enough, they will slip.
I just got done hanging 1100' of black pipe air lines. I have both an Oster pipe threader and the Rigid tripod vise for fitting work and so forth, and had to regrind the jaws twice to keep them from slipping
There are two main types of pipe vise. The chain vise, and the clamp vise. I actually prefer the clamp vise, given dull jaws in both. I will be rigging up the KO Lee tool cutter grinder to recut all the jaws now that the Project is winding down, in preperation for the next project.
Ive also learned to not skimp on pipe wrenches. While the $5 Harbor Freight wrenches are inexpensive, they tend to have soft jaws and after some use in a commercial application..dull quickly and stop holding. For home use, they are fine. So I scrounged up some beat up old Rigid pipe wrenches, and they, even beat up, held better than some new HF wrenchs
I'd never try to use a machinist's vise for holding pipe for threading. If you're doing a plumbing job, rent the right tool. I happened to inherit my granddad's pipe vise, this wraps around a post in the cellar and is tightened down with a wedge. The pipe holding part uses a chain to hold the pipe against a serrated V, the chain is tightened down with a jackscrew arrangement. There are free-standing vises using a tripod stand which are probably more useful than my vise, they can be used where there are no cellar posts. In either case, the pipe has to be rather firmly wedged into a number of serrations and they've got to bite into the surface or the torque of the die is going to spin the pipe, no matter how small. Use proper cutting oil and lots of it, too, the black stinky stuff, it reduces the torque needed considerably although it makes for a mess. Just lay a lot of newspapers down under the threading area.
My favorite emergency pipe vise is three pipe wrenches applied from under the pipe - the outer two to oppose the threading torque and the middle one opposed to them. The wrenches form a tripod, holding the pipe above the work surface, then you sit a moderately heavy load (child, wife,sack of potatoes) on top to hold the wrench handles in contact with the work surface. Gerry :-)} London, Canada