you will need a decent sized tap wrench..

you will need a decent sized tap wrench..

About 6 feet long, a 3/4 inch thick bar, one man on each end and the job will be a doddle

Definitely screwcut on the lathe first, accuracy is essential, then use the tap as a chaser

I used to watch heating engineers, assembling school heating systems, putting threads on 1.5 & 2 inch steel pipe & they did not seem to have any trouble. The more senior in years among us may well remember the heating pipes running round changing rooms & classrooms with reducers at the old CI radiators. Not allowed now for fear of scalding kids

So how come a tap is harder to use than a die?

I saw them at work too, up to 4 inches from memory, It is probable, the first cut was with the die open, seem to remember that they used two part "square" dies that slide up and down in the die stock.

Frank

That sized tap will be hard work in anything other than free machining. As been suggested, screw cut to size, but with a full form threading insert makes internal thread cutting that size quite a simple operation. It will take quite a bit to even run the tap through to clean up the thread to size. Buying a 1.5mm internal threading insert and holder will be worth while if you are making quite a few accessories. The advantage of screwcutting is that the thread will then be true to the faced reference and location diameter.

Neil

I get this out when the hit & miss engine models need a large pipe thread.

Holding the part is usually more of a problem as our plumbing friends don't think twice about using a pipe vice with its heavily grooved jaws which would chew up our sort of work.

Edited By JasonB on 04/02/2016 19:02:12

And having screwed 2" pipe by hand as an apprentice ISTR it can be darn hard work. Was the cause of much mirth among the very large middle-aged tradesmen as my 75kg frame struggled to get the darn dies started and then keep going.

Thank goodness for Rigid pipe threading machines, like a mobile lathe that grips the pipe and has the dies mounted on a toolpost sort of arrangement and you just press the button and go. Had to wait a few years before I got to use one of them though.

For your puposes, +1 on screwcut in the lathe and then use your tap for a very final clean up, just to remove tool marks etc. Be sure to bore your hole a little oversize before starting to screwcut, otherwise you make a lot of work for yourself getting that final fit. Most taps will not be made to give 100 per cent thread engagement. More like 90 per cent or less.

Don't forget, the bore size can be a little larger than theoretical as you probably only need 70% or so engagement on the thread – Others will correct me on the percentage engagement required.
BobH