well, the title says it all, i needed to cut some pipe threads for my new bed (yet another pipe bed) and i didn't wan't to invest money in a new vise with a pipe holding jaw, mainly because i alredy have a pretty heavy vise which suits most of my needs.
so, i proceded to find a way. tried pieces of cloth on the vise to have a better grip, then tried adding shellac to the cloth to make it 'stickier', then i made rubber jaws for my vise. none worked. finally i devised a simple method with tools most people alredy have lying around, and if they don't they really should make/buy (i often make even though it costs more, because it's fun!)
you'll need a heavy vise ideally, you could do around that using a fulcrum of some sort but if the pipe keeps sliping that will bother you to death, cutting threads is alredy hard enough.
the second tool is a pipe wrench. yes! a pipe wrench! turns out an instrument used to apply huge ammounts of torque is also the ideal instrument to resist applied torque. and really, the hard part of cutting pipe threads is the torque which causes the pipe to slip in the vise.
third tool is the threading die. this one is pretty straightforward, you need a die to cut the threads unless you want to file them (not since maudslay we don't!). you need to buy/make/rent a die and a threading kit (the turning thingy). mine is 1/2".
fourth tool is cutting oil. i use lard. that may sound retrograde but it actually has great adhering and lubricating properties. in fact, some machining oils still use lard in the mix even today. i advocate it's use because
1º it's enviromentaly friendly, lard is a byproduct and it is completely biodegradable and relatively non-toxic, unlike many cutting oils
2º it's cheap. the small cup you'll see me using in this instructable was made by myself and it cost me almost nothing
3º acessible to the hobbyist and still provides great, just as good, results as anything else.
well, let's get to it!
Step 1: Setting Things Up
measure twice, cut once. (that saved me today while i was cutting these)
be sure you are cutting square, you don't have to be absolute about it but some care makes the threads come out better and makes work easier.
i like to lubricate the blade of the hacksaw (guess i didn't mention this tool, duh) it makes it MUCH easier to cut, the lard beatifully adheres and doesn't drip (try finding a cutting oil which will do that). also , the lard won't stay solid as people may think, it sort of liquefies on contact with metal (my guess is that the metal's ability to transfer heat fast is the responsible, but i digress)
after you cut, take down the edges with a file and make up for any imperfections in the cut.
i know most of you all know this, but bear with me, someone might not know that so i'm including every step except the stuff you can figure by yourself(not going to take all of the fun out).
lube it up and it is ready to tap!
Step 2: Actual Significant Part of All This
with the pipe secure on the vise (not tight yet) put the pipe wrench on it as it is in the picture, move it around until you get that 'bite', then turn the pipe so that the handle of the pipe wrench rests on the table, this will ensure it keeps 'bit' and the torque will flow to the handle, which will keep things in place. then tighten the vise.
beware that there's a right way to put in the wrench(as if you were turning to the opposite direction that you are tapping), if you put it the wrong way there will be MAYHEM! (lol), actually, it'll just fall of because the rotating pressure will cause it to 'unbite' the pipe. but do beware there are extreme pressures going on as with any tapping and things can jump at you if you aren't careful.
lube things up. the pipe and the die. enough lube prevents wear on the die and these are expensive, lard is cheap.
proceed to tap. just turn ir clockwise while keep pressure forward on the first turns, then it'll become VERY hard to turn, this is a sign things are going well ( you're not striping the threads.). then keep going until your arms fall off, or until the thread protrudes just a bit out of the tap. you're done! turn things counter-clockwise until the tap slides off. you might have to replace the wrench the 'wrong way' because torque now is to the other side.
clean your threads and you're done. if you leave the lard in there it'll go rancid and stink. soap will take it right off.
Step 3: Ta-da!
i had a lot of fun making this instructable and finally i feel a little useful doing something back for the community instead of just lurking.
i did this short instructable because i didn't find anything on google that was a good, cheap solution to this problem. so i thought other folks might see some use in it. if you have a better solution please share! if you like the article, please let me know!
Step 4: Addendum
firstly, you can also use locking pliers to resist the torque, perhaps that's a better alternative because it will stay still.
second, while 'cheating' i had some stripped threads, nothing that i couldn't chase back with the die but be warned it can happen.
third, when pushing forward on the first few turns on this kind of die you want to make pressure as in the picture, right on the die, with a cloth on your palm (it gets hot and can burn you).