The Home Machinist!

I just received my first handful of MTP pipe fittings for my shay from Eccentric Engineer. They're really nice looking fittings! But I cant seem to get a grip on them to tap them. The first ones Im trying to tap at 1/4" 45 degree regular elbows. I tried holding the elbow in a small smooth drill vice with marginal success but Im afraid putting much torque on that setup with bend the casting slightly out of round, not a big deal for no pressure oil lines but definitely a problem for pressure lines.
So my question is how do you hold these little fittings to tap them? I also purchased a handful of street elbows to play with so I will need a setup to hold them steady while I run a die over the male ends. Thoughts?

I made some split - round holders, held together with two SHCS.

I'll take some pictures of them and post them.

Karl

Tristan,
You'll need to make a 'pocket' holder of aluminum (or even hard wood) with an appropriate sized ball end mill to make a mold type two piece clamping device - like a mold to fit and clamp the fittings solid. (It's like doing more work on the fixture than doing the whole job.)

The valve castings definitely need a fixture like this. That's the only 'safe' way to tap the 45° elbow since as you have found; there is no way to hold them from rotating without damaging them - the street ell too. There's a series on the forum about this....memory fails who did it.

Found it: machining+valve+bodies#p333252 He's a Bill C too - but not a Clemens though.
BC

Karl beat me to it!

Here's a link to the 2 minute video I posted showing the finished jig for the globe valve:

http://youtu.be/63FNuddqkzM

I got the idea from some photos and posts on a separate discussion board (either Home Model Engine Machinist or Hobby Machinist). I found those posts by simple google searches for PM Research fittings.

Hope that helps!

Bill "the other" C.

Here a photos I saved from the other thread referenced above. Like I said, credit goes to others for the idea and these jigs.

Bill C.

I just did a set of PM fittings last month - my FIST time ever doing fine machine work! I used Tubalcain's video as a guide https://youtu.be/2E-cqeWWsTU

I screwed up a couple of pieces learning but most came out okay. I had fairly good luck using the milling machine vice and a piece of threaded rod as a guide for the fitting angle.

The one thing I learned to machine a good fitting is to do all operations for each end of the fitting in a single clamp - i.e. machine the end flat, centre drill, tap drill to depth, then tap. It means a lot of tool changes but it works. The 45 degree elbows are the most challenging!

The MayJune 2004 issue of Live Steam deals with this also in an article entitled "Machine Your Own Model Pipe Fittings" by Paul J. Smeltzer.

Mine look like Bills - nice job.

Karl

The discussion motivated me to start on some of my fitting castings, I mulled the different techniques and like Mr. Pete started with the simplest fitting, the coupling. I ran my MPT tap into the coupling 4 complete turns after it took a bite, then to see how it would make up with a pipe, I threaded the end of a 1/4" piece of copper tubing (6threads). To my surprise, when I tried to turn the pipe out of the fitting, it tore along the helix of the thread and came out like a cork screw! Any thoughts on what happened? John

Your copper tube is thin walled from Home Depot or... You need thick wall copper from a refrigeration supply house if you plan to thread it.
Fred v

If these are the taps and dies from PM research, they work best with heavy wall brass tubing. The taps and dies works great with the brass tube they sell. It is heavy wall, unlike the K & S tubing.

David

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