Stuart S50 – choice of thread

[GaryMParticipant @garym]

Hi,

I'm gradually making a Stuart S50 engine. I've drilled and tapped the steam pipe inlet and exhaust ports 1/4" x 32 as stated on the drawings. I now find that most of the pipe unions available are threaded 1/4" x 40. If 1/4" x 32 unions are available then they are about double the price (in one example £8.40 for one). Does anyone know why this is the case and why Stuart chose to use a different thread than what appears to be the norm. I realise I should have checked first as then I could have drilled and tapped 1/4" x 40. Obviously I will just buy one but I'm curious why.

Thanks for any ideas.

Gary

[GaryMParticipant @garym]

[NJHParticipant @njh]

This is just a guess Gary – so i may well be shot down in flames!

The Stuart S50 is an old design – it has been around for years as has much of the Stuart range. Nothing wrong with that I hasten to add and generations of model engineers have been introduced to the hobby by the Stuart brand. At the time of their introduction pretty much all "stuff " was imperial and threading equipment was plentiful and relatively cheap. That is not the case now and my suspicion is that you are paying a premium for the unusual size.

I guess you know that both1/4 x 32 and 1/4×40 are available from Stuart see HERE or Tap & Die HERE or even cheaper! Tracy Tools HERE

Good luck!

Norman

[JasonBModerator @jasonb]

Norman its not the taps & dies Gary is asking about its the cost of unions threaded with a less common thread. 1/4×40 unions can be had for less than £2, and Poly and Stuarts want the above mentioned £8.40 for the 32tpi version

Can't say why Stuarts use a different one to most but unions are not that hard to make so before buying it may be worth doing the sums to see of a suitable die and length of brass hex work out better

 

Edited By JasonB on 11/10/2013 16:22:13

[NJHParticipant @njh]

Thank you Jason – I apologize . **(Note to self –  in future engage brain before posting !) 

As you say though pretty easy to make so, with a 1/4 x 32 CS die from Tracy at £3, that's maybe a cheaper option.

Norman

 

Edited By NJH on 11/10/2013 17:58:48

[GaryMParticipant @garym]

Thanks for the reply Norman, but as Jason has pointed out I've already got the taps and die, I was just curious why they had chosen that size. I'll probably buy one anyway at the Midlands show next week. I'm not sure my machining skills are up to making one at the moment but I might give it a go if I can figure out the dimensions or find a drawing of one.

Gary

[Geoff StevensonParticipant @geoffstevenson56049]

Hi Gary.. The Stuart S50 is a lovely engine. I first made one back in the 60's when the machined kit was 5 Pounds..!! Still, as a young apprentice, that was about a weeks pay. I still have it. The sliding valve block is quite loose and depends on steam pressure to keep it seated. This means you need more pressure than the engine really requires to run it. I filled most of the fingers of the block with soft solder and then filed it out until the block was reasonably snug against the port face. The innocence of youth.. haha.. The engine, once hot , will tick over at only a couple of psi with this modification. As for the threading, I prefer the older 32 tpi pitch. The finer the thread, the more likely it is to strip. And the fittings..? Don't make anything you can buy. Cheers from downunder.

[GaryMParticipant @garym]

Thanks for the input, Geoff.

[LambtonParticipant @lambton]

Gary,

I have checked some old drawings for a Stuart No 10 engine from about 1963 when I first made one. The threads in the cylinder and valve chest cover are both 1/4" x 32. I guess the reason is that the courser thread will be less likely to strip when tightening up the steam pipes/unions. I cannot explain the difference in price – have you tried asking the current owners of Stuart Models?

Eric

[GaryMParticipant @garym]

Posted by Lambton on 12/10/2013 12:23:17:

… I guess the reason is that the courser thread will be less likely to strip when tightening up the steam pipes/unions….

Eric

Thanks Eric. As Geoff suggested, that is probably the reason. I might ask Polly Models why they are much dearer but buy one from Reeves as they are half the price.

On a separate note, can anyone recommend a book that covers steam pipes and fittings. None of the books I've bought since starting model engineering seem to cover this area. K. N. Harris's book 'Model Boilers and Boilermaking' is on my shopping list for next week, so that might be the one to buy.

Gary

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