Dom's Minnie Boiler Build

Hi all,

The time has come to take on the challenge of building Minnie’s boiler – so I thought I would start a thread in which to post what I suspect will be numerous questions.

I successfully completed the ME vertical boiler last year as a practice project for this, but there is no doubt the extra complexity of a traction engine boiler is intimidating – compounded by the fact that the consensus seems to be that the instructions are far from perfect.

I’ve studied some of the old threads and I think I understand the main issues with Mason’s method – but will consult here with the wise heads of the forum at each stage to make sure my approach is sensible.

I don’t intend to get the boiler tested - I am not a member of a club, and my work commitments mean that it is not practical for me to join one. I fully appreciate that there are considerable benefits in having an inspector check your work at each stage of the build – but in this case I will have to manage without.

So in terms of deviations from Mason’s instructions, I will be silver soldering the stays – so will change the build order so that the back plates go on after the stays are in place. For stays I will be using bronze for the horn plate stays and copper rivits for the rest. Since I am not going to get the boiler tested I think I will leave the steam block as is. I also noted that some members recommended soldering the front foundation ring early on.

In terms of kit – I have a vermiculite hearth from CupAlloys and some fireblanket for extra insulation for the job when needed. My torch is a Sievert with a 7.7 and 26kw and cyclone burners. For solder I intend to use 438 and 455, flux easy flow and HT5.

So – I’m fast approaching my first cook-up: I have the tube pads, pump pads, barrel and throat plate prepped. (The boiler kit has come from Blackgates – so the plates are already flanged.)

Whilst Mason recommends doing all of this in one hit, my current thinking is:

1. Solder on the barrel pads and pump pad first with 438 / HT5. 26kw burner
2. Solder on the front foundation ring to the throat plate with 438/HT5. Foundation ring to be wider than the water space and profiled around the flanged firebox frontplate. 7.7 kw burner
3. Solder the barrel to the throat plate and wrapper with 438 / HT5. 26kw burner

Any thoughts and advice would be appreciated. The front foundation is the main departure here so any comment on that in particular would be welcome. Will this cause any problems soldering the front stays for example? Also is solder / flux /burner choice sensible?

Cheers

Dom

Practise with 438 first you might might find it too difficult, I would only use it for the bushes in the front and rear plates. Though to re-melt the solder the temperature increases and it doesn't really flow that well so stuff should stay put anyway.

Make sure the cylinder pad fits properly. if you fail to get capillary flow you increase the chances of a leak through the bolts.

Make sure it's all dead square and parallel and use 1/2" rivets to secure the joints, don't use a hammer, just bend them. 

You need the front foundation in anyway to give you two location points for the fire box

Judging the cool off period before dunking it is difficult. Too soon and you get stress cracks in the solder. Too late and the copper remains in the black oxidised state.

As you do the back head last the boiler tubes can launch pickle at you if the boiler is too hot 

Don't drop it, 

Edited By Dave Halford on 14/03/2021 19:06:44

Edited By Dave Halford on 14/03/2021 19:13:41

Edited By Dave Halford on 14/03/2021 19:18:58

Edited By Dave Halford on 14/03/2021 19:21:13

Edited By Dave Halford on 14/03/2021 19:24:57

Edited By Dave Halford on 14/03/2021 19:28:09

Thanks Dave,

I formed the cylinder pad over an aluminium bar turned to diameter so I think it is pretty close - I will double check it to be sure though.

Think I need to consider when to use 438 - I used it a fair bit on the ME boiler, so have some experience, but suspect getting Minnie up to temperature will be more of a challenge. I haven't used the HT5 flux before either - so some practice is probably sensible.

With regard to bushes on the front plate - when is the most sensible time to add the blow down bush - at the same time as the front stays? If so is it just as well to wait until then to drill the hole - or would this be sensible to drill it before attaching the throat plate to the barrel?

Cheers

Dom

You might find some Rockwool roof insulation is better as a blanket to cover the boiler end you are not working on. Just wave the blowlamp at it first or chuck some red hot scrap copper on, it shouldn't melt. It worked for me.

Do the bush at the same time as the front foundation, they are nearly touching. BTW there is no location for the bush in the drawings and just a photo in the book.