Substitute Stuart taps?

[Nick WelburnParticipant @nickwelburn]

I think this is a daft question, but the wisdom here is greater than mine. I’m making (slowly) a Stuart 10v. This needs a number of small BA taps and some larger BSW taps (I think they are BSW). I don’t have the relevant BSW taps. But I do have a full set of BA taps. Is there any sound reason why I cannot just use the larger BA taps and dies here?
After all I am making both the threads?

[Nick WelburnParticipant @nickwelburn]

[JasonBModerator @jasonb]

The threads are ME series 1/4" x 32, 3/16" x 32 and 5/32 x 40 if fitting drain cocks and 1/4" x 32 & 5/16" x 26 for teh glands

You can tap what you like unless you intend to use commercial steam fittings which will have an ME thread if sourced in the UK. If you want to make your own fittings then no problem as you will be doing both male and female threads.

valve gland could be done with 0BA but you would need something larger for the piston rod gland M8 x 1 metric or the specified 5/16 x 26 or 5/16 x 32ME is another option.

[Howard LewisParticipant @howardlewis46836]

You should be able to find BA threads that APPROXIMATE to Imperial sizes. The determining factors are sufficient wall thickness for an oversize thread, and thread strength. The thread form will be different, 47.5 vs 55 degrees.

The only other factor is whether the different hexagon sizes will be sufficiently different to spoil the look of the engine.

Those have to be your decisions.

The pitches will be finer than BSW. (!/4 BSW is 20 tpi, 0 BA is 1 mm pitch so roughly 25 tpi 3/16 BSW is 24 tpi, 2 BA is 31.4 tpi, 5/32 BSW is 32 tpi 3 BA is 34.8 tpi 1/8 BSW is 40 tpi ,5 BA is 43.1 tpi )

0 BA is undersize for 1/4", 2 BA is undersize for 3/ 16, 3BA is oversize for 5/32, while 4 BA is undersize.

5BA is close to 1/8,, 7 BA is oversize for 3/32, while 8 BA is undersize

HTH

Howard

[John OlsenParticipant @johnolsen79199]

When I purchased my Unimat 3 nearly 40 years ago, it came with a set of Stuart 10 castings without screws and fasteners, and with a booklet giving all fasteners and dimensions as metric sizes. It all worked fine. So it is certainly feasible to change any or all of the threads to different systems, within reason.

John

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