minnie 1" scaled to 2"

I knew julian favoured thermalite type blocks but wasn't aware of the anti-using firebricks inside. Indeed as Rod points out they are used /sold as brazing hearths and in the woodburner industry commenst such as needing them to act as liners to prevent the ast or steel becoming too hot.

BUT stirred into thinklng about it.. Yes, they do get hot so they aren't acting that well as insulation and therefore adding to the mass of heatsink one is pouring the therms into. That could have some benefits in terms of storing heat and keeping the item towards temperature but equally the extra time involved has to add to flux exhaustion and leads on to some other thoughts I'd had the other day when working just on one part of my boiler as to whether there may be benefit in heating from the end I had totally enclosed (as in open a window there) so one can raise basic temp of the item without directing the high temp at the flux until necessary....

...I suspect that's what they call experience...

pgk

I began my Minnie boiler in back in the 80's using the book of words. Not wanting to use coke as insulation I thought I'd be clever and get some fire bricks. Being a child of the 50's, fire bricks to me are heavy grey hard things that protect the side of the hearth from too much damaging heat from a coal fire. I can confirm they are medium rubbish at insulation when compared to a bit of Rockwool. They are not made of vermiculite and you can get them to glow eventually, but it takes ages.

Dave,

These are vermiculite wood-burner type liner blocks cut from vermiculite board.. not the same as the sort of stuff old pizza ovens are built from that can just cope with the heat cycles without cracking like ordinary house bricks. However I have no doubt that spun as rockwool is way better

Hi Rod,

I think the particular problem here is the wide range of vermiculite blocks available. Some are very light and reflect heat rather than absorb it. I bought a batch off ebay thinking they would be the light type, but they were heavy and absorb heat.

Cheers,

Julian

Fair enough. Mine came from CuP. Actually, I think the biggest boon to boiler making is the insulation blanket they sell - definitely worth a tenner.

Cheers,

Rod

So im thinking of starting the 2" project off with the rear wheels followed by the front wheels. i have just seen the price of the rear rim castings!!!!!

Can you make the rear wheels in two seperate parts and then braze them together?or can you make them from the solid?

250+ is a lot of money for 2 12" rims

What are other good things to machine starting off, while i get my head around a 2" boiler design that will surfice?

boiler bushes?

smoke box?

maybe the making up the formers for parts of the boiler?

also i remember someone saying about being careful about doubling everything up, otherwise i will end up with a very chunky looking engine. i can totally understand where there coming from, and now am very aware of how i can get around this.

thanks

james

Options for your rims are:

Find some suitable thick wall tube and machine from that if you can swing 12" on the lathe.

Turn from 12" dia bar, the front rims can be trepanned out so you won't be wasting all the metal in the middle, need to swing 12"

Make from two "Tees" which could be flame or laser cut from plate, again need to be able to swing 12". The originals were two tees and the strakes held them together with possibly some additional plates or a band on the inside.

Have two strips of 3mm steel rolled and weld it into the outer rim, get some more 3mm material laser or plasma cut into flat rings and weld into the rims, this is usual practice for the larger models. No lathe work needed but you need to be able to weld or get them done by someone like Ashbys.

Use the cast ones from Blackgates that need turning

Use the cast Fowler ones from MJ Engineering which are finish cast so no turning needed.

I would suggest the easier front wheels first, a lot easier to get at the rivits, simpler to bend spokes as they are all the same.

As I said by message get the boiler design sorted before you start bying or cutting metal, no point in making formers until you know what thickness metal you will be working with.

Most people tend to build the front end first as that is not dependant on boiler on most designs, so thats smokebox, chimney, perch bracket, axle.

Edited By JasonB on 10/01/2017 07:37:05

I found it quite a shock on the 1" version when I looked at those rear wheels. 6" isn't particularly large but finished at 1&3/8 means that a solid chunk of bar is still quite heavy. I'm hoping to get those rims flame cut from plate with the centres then usable for the front wheels. Us knackered old geezers have to worry about lifting this stuff - well actually more about dropping it. On the 2" I can see a lot of reason to consider finished cast ally although my nature makes me daft enough that i'd still have a go from solid... and probably making two of everything before i get one right..

Hi James and welcome,

I'm also building a 2" Minnie , albeit slowly ,I have a set of drawings for the boiler which were very kindly done by Fizzy and were passed by our boiler inspector if you would like a copy let me know,

regards

bob

Think of it like parting off on the face of the work, you you have a narrow cut which produces a ring from the outside and leaves the centre intact.