Author Topic: Limerick Boilermenís Union model steam engine  (Read 1435 times)

Offline TGD

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Re: Limerick Boilermenís Union model steam engine
« Reply #15 on: January 20, 2021, 07:25:33 PM »
I see that the excentric and strap are stamped with 11. Does this imply that there were a series of the engines made not just one?

I would expect so as a few of the components have that 11 stamped on them. So, I expect the engine at least came from a kit of some kind.

Offline TGD

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Re: Limerick Boilermenís Union model steam engine
« Reply #16 on: January 20, 2021, 07:33:48 PM »
I think you have gland nuts on both the piston and valve rods hiding under the paint ....

Drain on the watergauge will need to be made to suite the tapered hole or the taper recut with a homemade reamer.

Yes, it looked like it had very neat packing glands when I stripped the paint but they were 'seized' - I spent ages with heat, penetrating oil etc etc trying to coax them off and then I eventually ralized they are just cast as one piece! It's going to be a leaky engine!

I think I'll just lapp a new draincock plug into the existing body. Anybody go an idea of the taper of those plugs? I can do triall tapers but it would be at least good to have an idea where to start.
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Offline gary.a.ayres

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Re: Limerick Boilermenís Union model steam engine
« Reply #17 on: January 20, 2021, 07:37:47 PM »
The parts of this engine have a lovely patina of age about them. It's going to be very handsome when it's all in working order... :popcorn:

Offline TGD

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Re: Limerick Boilermen’s Union model steam engine
« Reply #18 on: January 28, 2021, 01:54:33 PM »
The main shaft of this engine is badly bent and I have to make a new one but I am having a problem with the thread (it is crewed into a crank). Also, I have a question about the whistle.

The thread is 6.8 mm and .75mm pitch. The nearest thread I can find corresponding to this is 7mm UNF, or am I missing something?
If this is correct I could try to source a die but I'd prefer to cut it.
However, the next problem is that I don't have the option of .75 pitch on my little Chinese lathe - just .7 or .8. I can't find any work-around for this on-line: any ideas (the lathe has a 1.5mm leadscrew).
(I got the 'metric UNF' details from this page - https://lightningboltandsupply.com/metric-bolt-thread-pitch-chart.html  )

The whistle: it has this line of holes between the boiler and valve and it doesn't seem to seal. What am I missing here?
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« Last Edit: January 28, 2021, 02:13:08 PM by TGD »

Offline cnr6400

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Re: Limerick Boilermenís Union model steam engine
« Reply #19 on: January 28, 2021, 02:50:21 PM »
It sounds closer to 5/16-22 BSF thread (6.75mm dia  x 1.15mm), but the pitch is a little large for BSF. I am sure it is not UNF , there is no 7 mm UNF thread and 5/16-24 UNF is .312" or 7.92mm  OD and 1.05 mm pitch.

Might also be M7 x 0.75 metric fine.

 Is the thread flank angle 55 degrees or 60 degrees? If 60 degrees, I'd bet it was or is very close to M7 x 0.75. You can get taps and dies for this size, amazon and a few tool companies do list them, but they may be harder than usual to find as this is a listed size but is not commonly used. I have seen it a couple of places on older Japanese motorcycles.
« Last Edit: January 28, 2021, 02:54:15 PM by cnr6400 »

Offline Jasonb

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Re: Limerick Boilermenís Union model steam engine
« Reply #20 on: January 28, 2021, 04:12:01 PM »
M7 x 0.75 would seem to be the closest but odd if it's an old engine, Have you got a 32tpi leaf on your gauge as it may be 9/32" x 32tpi ME

Offline TGD

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Re: Limerick Boilermenís Union model steam engine
« Reply #21 on: January 28, 2021, 06:52:33 PM »
Thanks for the input.
Yes, M7 x 0.75 metric fine seemed to make sense (even though 'strange' given the age and history as pointed out).
However, I happed to have an M7 x .75 die but it wouldn't run through it - wouldn't even start on it. That's strange also, because it 'should' given the dimensions - maybe it's the thread form?
Even with a magnifying glass, I'm afraid I wasn't able to see whether it was 55 or 60 degrees.
Yes, I have 32TPI gauge and that wasn't right either.
I did a bit more Googling of thread conversons etc and one chart shows .747mm equals 34TPI. However, 34TPI is a very odd imperial thread for reasons beyond me, explained here -  www.practicalmachinist.com ("...if I had a 58T change gear on my chinese lathe (lead screw pitch 1.5mm) I could cut a 33.997 TPI thread, actually better than you can do on a lathe with an imperial leadscrew").
I guess I could just re-cut threads with in the eccentric with an M7 x .75mm tap?? (even though I would have to use a die to cut the shaft rather than turn it on the lathe).