PGK's 1" Minnie

I'm planning on this thread being picture heavy and as much a diary of an inexperienced guy feeling his way through the build. Hopefully I'll find some more pointers along the way for the next guy following and hopefully not too many 'in hindsight'.

Everyone has their own way of working. I'm going to have to plod. I don't have the mindset to duck and dive on different bits so I'm just plodding through the build book and this report is while I'm sitting waiting for the saw to cut a large piece of scrap rusty hot-roll for my first former.

The boiler barrel first. This was a 12" piece of tube cut to the required length. I chose to cut that on the bandsaw and that really sliced through fast.

Two wooden plugs spaced by all-thread are to be fixed inside temporarily. I have some pieces of silver birch from my woodland that has sat in the shed for 4 years. It turned beautifully.. almost a waste to use it for this but i have plenty.

I centre drilled and drilled these through and actually threaded them M8 before parting off 25mm wide pieces. I had to over-drill one threaded hole to 8mm when i realised that a firm fit couldn't be twisted into place but had to be tapped down the all-thread. All-thread centre-drilled at one end for tailstock support.

Back in the lathe for squaring the ends and marking out. It was only when marking out i realised i had been a bit rash in assuming the 3-jaw would centre and hold this parallel to the axis without checking and i suppose I was lucky that there was less than 1mm deviation at the tailstock end when marking out from the viewpoint of the toolholder scribe touching the work.

If I ever make another then I must remember to dial and bump it in. Bt i got away with it.

The cut out was hand-sawn and filed. I left the corners curved as suggested for final fitting later and sawed leaving the scribe line intact again for possible adjustment.

The throatplate is next but it's going to take a while to turn this hot-roll into a nice former. I have a large supply by way of local scrappy and I'm in no rush so we'll save pennies where possible.

Off to a good start. Before you get too far think about the manifold and water gauge feed as the prefered method now is not to have the gauge off the manifold. Also the threaded and nutted stays to the sides of the firebox and not used much now, solid stays are more common that can be tapped for fixings or drilled right through for nuts on the inside.

Jason,

I'm hoping some of this becomes clear to me as i build the thing!

I've read some of your comments before about these matters. The side stays presumably are just solid short rods soldered in instead? But does one place one or two threaded ones to help hold things or thin them to a shoulder and pean over?

As to the water gauge.. that's from the steam block to the bulkhead. I've again read your recommendation for a separate water feed but not clear where this goes. An additional bushing? You've also commented about location of water pump....

Otherwise little to report today.. just working on the flanging former and it's taking a lot longer to saw up and square up the lump of hot-rolled than i expected..mostly 'cos I failed to adjust the horizontal bandsaw weight tension properly and the blade kept jamming and it couldn't self cut 6" height straight so i had to make a good safety margin on width. I tried it in it's vertical position but again the blade kept jamming (probably not the best tooth count) so had to go back to horizontal. Sides and one flat surface faced off so far...

Stays. You can thin each end of the solid rod so it won't slip out or use a plain rod and put a couple of punch marks in the sides deep enough to raise a burr to stop them falling out while you solder. Peining over could expand the stays and fill any gap that the solder needs to flow into. Leave the stays a bit over length on teh outside and then set the completed boiler up on the mill and true the barrel then skim the tops off the stays which gives a nice level surface for the hornplates. Probably 3/8" stays with 5BA fixings to hold horns would work. As with any alterations run them past who will inspect the boiler first.

I would keep the water gauge mounting as is. But make the manifold wider so you can put in a separate hole down into the boiler for the pressure gauge as there is not much room for a bush.

Small pump down on the side of teh hornplate is an option with just a clack (one way) valve where the pump would have mounted. This is only really needed if you are going to steam it a lot as the pump body can become hot and then the pump does not work so well.

Thanks yet again... and I guess I'll be writing that a lot and leaning on you

Reality here is that there will be no boiler inspector involved and indeed even if it does run at the end then it'll be just to prove it works... that's assuming I have the tenacity to actually finish the thing and enough luck/skill/your and others advice to not screw it all up along the way...

It's about building it to learn the skills involved and if still interested in the hobby at the end (and still looking like I might live long enough) then perhaps build one of a useful size...

I'm also thinking in terms of closest metric size for threads rather than buy a whole additional set of taps/dies.. I assume one can buy a pressure gauge with metric threads. By manifold again i assume you mean what Les calls the steam block? When you suggest wider then by how much?

IF I understand correctly then I quite like that idea of a thin groove around the stays' ends to hold them for brazing.

I'm quite prepared to destroy a couple of boiler-worths of copper and silver to learn enough to get a working one. Even nicer to get ti right first time.

I'll sketch something out for the stays & manifold/block/turret later.

"I assume one can buy a pressure gauge with metric threads"

Yes But, no but. If you go to one of the european ME suppliers they have steam fittings with metric threads BUT they are metric fine not the usual metric coarse so unless you have a set of fine metric tackle you are going to have to invest in taps and dies either way weather ME or Metric Fine. You will also need these for a lot of the fittings.

Also a lot of the BA threads suggested fit nicely onto imperial size stock eg 5BA will thread nicely onto 1/8" bar and 7BA onto 3/32" bar. If you want to go metric you will then need to start thinking of changing to using metric bar stock too so 1/8" would come down to 3mm dia and 3/32" upto 2.5mm.

You have also drawn me into the metric fasteners debate. Off the shelf mass produced metric nuts and bolt/hex screw heads are stamped out to ISO sizes which can look very large on a small model and may not even fit in some of the tight spaces on the Minnie. You can buy machine cut fixings again from the European suppliers and also Bruce Engineering in the UK which are a smaller hex, taller and with only one side chamfered which look so much better but they do cost more. Or make your own. Alternative is to use BA which are the right sort of size and can be had from any of the ME suppliers.

There is a "Metric" minnie drawing set on the net if you want pointing that way but some of the conversions are a bit iffy

I'm aware of metric minnie and some of your comments here and elsewhere regarding it. It is however a useful reference for those of us with poor visualisation to see the exploded view and alignments.

It's an excuse to buy imperial stuff then I like accumulating tools (just hate paying for them). As it happens I do have metric fine taps and dies in some sizes... came in a really cheap set that I've had for years and still mostly works albeit I've had to replace a couple of dies I abused. For taps I find generally it's way easier to use machne taps by hand.

..Off to window shop some imperial drills etc...

If its visualisation that you want then this is good provided you can run te 3D pdf which needs flash, move it about and zoom in etc.

If you are not having it inspected then you may as well stick with the same steam block as per the original.

For the 4 stays each side that take the hornplate fixings I would go for something like this, length of 5/16" bronze turned down at the ends to say 7.5mm, 3/32" long on the inside & 3/16" lg on the outside to allow for machining back, central section 3/16" long at 5/16" dia. If the holes are drilled 7.5 you can pop the stays into place as the wrapper is placed around the firebox and they won't go anywhere.

For the remaining stays I would just drill 1/8" and poke a copper rivit through the hole, give it a slight bend to stop it comming out and then when its all soldered trim off the excess length just proud of the boiler.

All stay joints silver slodered not soft soldered like Mason's

J

Edited By JasonB on 28/03/2016 17:11:26

Once again you're a star.

However the link to the 3D pdf image only goes to a jpeg. It must have lost it's link to the original file.

Goes to a PDF for me. here it is again

When you get that up click somewhere on the image, as you move the mouse over the image it will say "click to activate"

You may get a yellow bar along the top, go to options and trust the document and the OK the next box, finally click the image again.

J

Got it this time. I think it was some firefox bypass just loading the link image. Immensely helpful and certainly shows your suggestion of the pressure gauge position..probably worth doing.

All I achieved today was finishing the former. the 3/32 radius is close enough to 5mm that i made a quick simple radius gauge by cutting a 5mm endmill into the edge of some scrap. Radiused the plate mostly on my bench belt sander then a little draw-filing. The time wasting was over milling the plate to size..it started as 10mm rusty plate and it has to be the 1/4" for finishing the flanges. A length of bar would have saved 2 sessions.

I'll cut copper tomorrow. I'll see if my bandsaw can do that in it's vertical mode without snagging or it'll be the slow way. I really need to think about some different tooth count blades in stock.

Run a bit of scrap ply or MDF under the copper as you push it through, 1/4" will do. cutting both helps stop the blade gullet catching the thin metal

After mulling things over I decide the easiest solution would be to cut it on the mill. That avoids all the issues of wobbly saw lines and leads to a nice easy rectangle. yeah, the setup is more of a pain but I don't have a fence on my bandsaw when vertical and overall this might have been as quick..plus it's hopefully easier to align with the templates with right angle sides.

I chose to use a 3mm 2 flute because my last play with a 1.5mm cutter was --- well the cutter wasn't around long. I also cut in 3 passes to avoid any risk of the cutter pushing itself sideways. the actual cuts didn't take long.. more time was in juggling hold-downs so there were always at least 2 clamps in place.

Cutting this with 3mm slots out of a 12" square means that the width ends up 2.25mm less than drawn but a) a saw kerf would take some up as would filing straight and b) that's on the flanges which can't be critical and get tidied up for neatness anyway.

I've got other commitments tonight so my first flanging goes happen tomorrow when I've dug out the emergency gas cooker

gratuitous pics follow:

Hi pgk pgk,

There is a lot to be said for getting your Minnie boiler approved during construction by your local club and certified.

You will get a wealth of advice plus updates on the boiler design, and at the very least if you decide to sell at a later date all your efforts will be worth considerably more than an uncertified 'lone hand' boiler that most would regard as scrap - which is probably more serious in the case of a small traction engine than in the case of a miniature loco as all the other bits are attached to a traction engine boiler.

I wish you all the very best with your project! I am sure JasonB (who is extremely generous with his advice and help) will keep you on the straight and narrow! I enjoy boiler making and bashing copper and silver soldering, but I am a bit odd in this respect!

Cheers,

Julian

Julian,

If this was a larger machine then I'd find a way to deal with certification but i live in rural wales and the nearest club only meets once a month and is a goodly plod away.

And while I shall do my best to go about making this boiler with the right tools and supplies i'm by no means confident that I'll succeed..

Another experienced boiler basher keeping an eye on this thread can't hurt (hint)

This evening's efforts:

I annealed the throatplate blank on a camping gas ring. I expected a slowish change to plum and red since I've never annealed copper before. It turned plum where the ring flame hit it very fast with a pale center then seemed to suddenly flash-over a sort of silver colour?? Grabbed and dropped in a bucket of water.

I used a rubber mallet to flange it and with the benefit of hindsight that plate could have been way thicker..or the copper piece narrower and where it overhung the mallet rippled it a touch and i had to beat it back flat - no biggie as it goes and I was gratified to find the radius sat a 5mm rod neatly in it - close enough to the imperial target. and the flanges measured square.

It would have been nice to have a fretsaw to cut the circle out..i had to make do and hack with a large saw and then lots of filing

the instructions then require filing the boiler tube tabs to a sharp edge and bending the flange ears of the plate to fit inside them. Its a lot of fiddling and there's no precise approach apart from eyeballs and juggle. I didn't find that very satisfying to do and there's inherent spring in the junction so it's hard to hold and measure.

I trimmed the flange to match the tube using the mill with very light cuts and several passes. The end result looks OK to me... we'll find out in time.

Hi pgk pgk,

That silver flash you saw whilst annealing is way lower than dull red of the copper. Do not be beguiled by the surface colour of the oxide. You need to concentrate on the base colour of the copper in subdued light. When you get to silver soldering up the bits you will see what I mean. You get to that silver flash and you keep going till the whole lot glows dull red! It goes black oxide after the silver flash. Then it starts to heat up properly and gets dull red.

Try out a test piece of decent sized copper and take up to glowing red and note the oxide colours during the process.

Cheers,

Julian

Edited By julian atkins on 30/03/2016 23:12:30

Thanks for that info. Fortunately I had no trouble flanging.

I do intend to solder a few test pieces before tacking the boiler bits.. once I've sourced and built my brazing hearth, burners and supplies.

I've done a fair bit of reading but never noticed mention of the silver flash-over... cool.. at least i wasn't imagining it.

You have quite abright workshop which will make it harder to see the colours of teh metal, I often turn of some of my lights when soldering inside.

The straight flanges (just a bend really)  will be a lot easier than when you come to do the curved ones and start needing to loose metal, they may even need a couple of heats as the metal will start to work harden and become more difficult to manipulate.

If your formers are a bit thin then add a piece of wood to the back to thicken them up a bit.

Edited By JasonB on 31/03/2016 07:54:00