PM Research #1 Build

[kmanuele]

I've started on this, going ok with minor missteps so far. Maybe someone who has built this can answer a question:

I see the steam chest has ports labeled "1/4-40 tap 1/8" deep for model pipe". I'm confused, or blind.

Straight 1/4-40 taps I can find, though 1/8" deep is only about 5 threads. Maybe ok but how does it seal (tape?), and does "for model pipe" have a special meaning in the modeling world?

Thanks in advance

K

 

[EricB]

I use tapered threads "for model pipe." The tapered pipe in the tapered hole (with a bit of sealant) makes it steam tight.




Eric

 

[kmanuele]

I use tapered threads "for model pipe." The tapered pipe in the tapered hole (with a bit of sealant) makes it steam tight.

View attachment 458411
View attachment 458412

Eric

ok. looks like 1/8 NPT? which is what I plan to use. A 1/4-40 straight tap (per the drawing) is something I would not use again, so rather not spend the $$.

It turns out that the PM research catalog sells miniature "model pipe" fittings, which is what I suspect they were referencing.

Nice work, BTW. Is that a bronze casting in bottom pic?

 

[EricB]

ok. looks like 1/8 NPT? which is what I plan to use. A 1/4-40 straight tap (per the drawing) is something I would not use again, so rather not spend the $$.

It turns out that the PM research catalog sells miniature "model pipe" fittings, which is what I suspect they were referencing.

Nice work, BTW. Is that a bronze casting in bottom pic?

A 1/4-40 MPT tap uses a 13/64" pilot drill (0.2031"), where the 1/8-27 NPT tap uses an R pilot drill (0.339"). It would probably work but it won't look right for the model. I would suggest a 1/4-28. It's at least close to the correct size and widely available.

The prices for model size taps have skyrocketed!

Yes, It's a PM Research #5 that I built during the lockdown. It was my first model engine attempt. It taught me humility. I still need to put the lagging around the cylinder, and paint it, and mount it to a board, etc...

Eric

 

[kmanuele]

Thanks again;

Agree there may be some visual mismatch with 1/8 NPT.

My confusion was drawing says "... for model pipe." I assumed it meant for the piping on the rest of the model

Apparently they meant 1/4-40 model pipe thread (MPT), not a 1/4-40 straight tap. Getting the MPT tap probably means getting the mating die too.

I'll have to ponder this. There's no hurry in doing those ports until ready for assembly.

K