The Home Machinist!

jscarmozza wrote:Kinda figured that the pipe wall was too thin, Fred this was refrigeration tubing, I guess that's out for threaded piping material.
Do you know the proper number of internal and external MPT threads to cut into pipe and fittings, so they make up properly?
John

You want hard copper for threading as well. As far as number of threads, Ive found its just trial and error. Run the die over the pipe till the end of the pipe is flush with the back of the die. Then start with the tap and play with the depth till you get a fit you like. I have American Model Engineering Supply taps and dies and have found I need to leave about 2 threads of the tap sticking out of the hole.

Thanks for the tips, my taps and dies came from PM Research, so a little experimentation is required in order to get the proper fit. Thanks again, John

jscarmozza wrote:Thanks for the tips, my taps and dies came from PM Research, so a little experimentation is required in order to get the proper fit. Thanks again, John

John, do you like the PM taps and dies? Are they sharp, etc. ?

I need to get a couple of sizes and don't want to QC all the offerings out there!!

Thanks,
Pete

Hi Pete, P M Research was a pleasure to deal with and their products appear to be first class. The taps and dies are sharp and produce a clean thread, excellent on brass and very good on copper.

Happy Thanksgiving, John

As a general rule, when working with any taper pipe thread die - you work to flush and call it quits...no point in going any further.

as already described, run the tap in, then perhaps wrap it with some tape for a reference for the next time when you don't remember

the bad thing about all of this is you generally need two taps....one to get started and one, with the end ground off, so that you can work blind holes - or 90 or 45 ells.

jscarmozza wrote:Hi Pete, P M Research was a pleasure to deal with and their products appear to be first class. The taps and dies are sharp and produce a clean thread, excellent on brass and very good on copper.

Happy Thanksgiving, John

And you as well!! Thanks for the review.

Pete

Bill Shields wrote: the bad thing about all of this is you generally need two taps....one to get started and one, with the end ground off, so that you can work blind holes - or 90 or 45 ells.

Same in full size work... which means buying two of everything eventually. Not a big deal 'cause they'll out last me...

Pete

This turned out to be a timely discussion for me as I begin to overhaul and retrofit my engine over winter. I found most of the existing fittings and pipes on my engine to be threaded 1/4" x 32 TPI, and I'm wondering if I should redo everything in MPT or UST. After everyone went home yesterday I relaxed and read through the P M Research catalog that came with my order, lots of good information. One thing I discovered is that MPT threads have a smaller root diameter then UST or straight threads, that may be why my external pipe threads nearly cut through the pipe wall, coupled with threading the tubing too long. According to PMR an MPT tap will cut their proprietary UST if turned in 3 turns deeper. Since I have a 1/4"x40 MPT tap and die set, I think I'm going to get a 1/4" UST die and see if that produces stronger threads on copper tubing. I'll go with hard tubing where I can, but there are a few places where I'm going to have to use bendable. Good discussion, thanks for the input. John

Thanks for all the info guys! I tried a wooden jig with limited success. Will make a metal one from some scrap aluminum flat bar I’ve got when I get home from thanksgiving

Drilling and tapping these little things is challenging to say the least, I ruin one for every one I complete. Today I tried to make an angle boiler check valve from a PM Reasearch globe valve body, after figuring out what I needed to do, I had to figure out how to do it. The valve body had hex ends so I figured I'd hold it in a three jaw chuck and drill it in the lathe...I couldn't hold it centered and on line, so I went to my vertical mill. To make sure the hex ends of the valve body were all uniform I used a 5/16" Allen head cap screw as a broach and pressed it on to each valve body hex end, then carefully squared up the ends of the body so I could securely hold it on parallels in a vise. Everything was square, plumb marked out, center punched and secure, but I couldn't get the exact center, then it dawned on me, I drilled through the 5/16" Allen cap screw with a 7/32" drill (tap drill for a 1/4 X 40 thread), I then let the drilled Allen screw float on the drill bit, fit it over the hex end of the valve body and drilled the body on center. If the body is square and plumb, you get a drill hole on center. It may not be the best way, but it's a way.
John

Don’t know if this would be useful or not for small fittings. But I use a set of v blocks clamped in a vice to hold pipe and pipe assemblies. Sometimes the v blocks will hold the valves and unions as well.

Glenn

I've found for pipe threads, it's pretty much mandatory to have something to keep the tap aligned, like having the part clamped in a vise, and a center in the chuck on the drill press to keep the tap straight. In a pinch, I've put the tap in the chuck, and just given it a blip of power to start the threads, then loosen the chuck and tap the hole to finish depth by hand.
If I had a mill and was tapping brass or aluminum, I might be inclined to power tap on the lowest speed:)