PGK's 1" Minnie

Tonights session was the drill and file the backhead firehole and test fit. Gratifying to have something go pretty well - perhaps I am learning .

I'm sure we all work differently. I'm not much for marking out and don't have surface gauges or a decent surface plate (to be organised) and prefer to work off the DRO but this time I did mark it out fairly accurately just as a visual check against dumbo moves 'cos it's not the time to screw up.

Self evidently the firedoor hinges/catch have to be relative to the firehole centre but I was concerned that the centre as drawn and mine may not be exactly the same place and the long stay bushes should be relative to the firebox roof/stays and the smokebox tubeplate stay bushes. So some simple sums to work out the distance of those bushes to barrel and work that out relative to the crown of the backhead. It was to find that this time I was within 1/32 of the drawn distances so blowdown bush hole can be drilled relative to the firehole centre. A nice suprise.

I've also done my usual scrawl doodle of all the offsets and converted to the mm I run the DRO in.

I don't see any way that I'd manage to cook-up backhead, manifold and foundation ring in one session. I've also had some thoughts about the many stays that have to go in later that I need to run past the experts after the backhead is in. That'll be a separate message in a few days when I've mulled it over.

Jason, Julian, anyone that wants to jump in, please, some questions:

Jason intimated earlier that there may be benefit to making the steam block larger? If so then now's the time, before I order bronze, and then a question of size/description.

Secondly.. assuming the backhead goes OK then I see an option before putting in the foundation ring... I'd still have access to the space between wrapper and firebox. Is there any benefit to sleeving the stays (it'd be a fiddle but doable I think). Again a matter of size. Mason suggests the small ones he used to keep water space but I could understand perhaps using 4 larger stays each side and 5 small ones and perhaps just 4 on the hornplates?? Again the debate then is re sizes. If sleeving with some tube then suggestions re wall thickness and s/s v bronze - would there be an electrolytic effect? And of course whether s/s thin walled tube of the sizes exists 303?

Lastly I guess that silver solder would be preferred to soft solder for the stays and if so then perhaps better to do that cook-up while access to the water space to blow the flame in and leave the foundation ring for last??

I'll admit I never expected to get this far

Comments appreciated

pgk

The reason for suggesting alterations to the steam block is that it is now prefered to have the steam passage to the top of the water gauge separate to the one going to the pressure gauge. If you are just going to play with yourself in the comfort of your own shed then it can remain as drawn. If getting it tested by an inspector then separate passages would be the way to go.

I would think adding an extra 1/8" to each end and letting it sit with 1/8" beyond the back of the wrapper would give enough length of block and still give some clearance to the 2nd shaft. Leaving out the "spare" outlet would also make life easier.(Make top water gauge fitting 1/8" shorter to suit)

My thought on firebox stays are to go with four large dia stays, one in each corner say 3/8" dia. You could avoid the need to use spacers if the wrapper and firebox side were drilled and tapped right through ( this is full size practice)with say 3/8" x40ME or 3/8" x 32ME. Which would stop them falling out and also maintain the gap between the two plates during soldering.

The remaining 5 stays could be 1/8" copper rivits, 1" long, Slip these in with the head inside the firebox then just bend the excess length on the outside enough to stop them falling out. Once soldered the excess can be cut off with nippers and tidied up with a file to leave a small bump with the intact fillet of solder around it.

When complete The boiler is laid on its side on the mill and the four thick stays milled back to the correct width. Then the horn plates can be offered up to the boiler and the hole position of the 4 holes spotted through onto the four large stays which are then drilled and tapped 4BA.

This is the way my Blackgates boiler was done though the thick stays were plain not tapped.

The stays are also just rods soldered into plain holes in the backhead and tubeplate.

I'll post a pic a bit later

J

Meant to say silver solder the stays, don't caulk with soft solder. Also not keen on stainless spacers better to make from brnze or copper tube if you go down that route.

Edited By JasonB on 06/12/2016 19:03:09

Jason,

I get the stay idea..makes sense although I'd worry that bending rivets on thoroughly annealed copper this gauge might leave dents. I'd be inclined to put the effort into threading those with something fine too. I'll dwell on that. Drilling at this stage allows me to slip ply or card into the water gap for support.

I accept I'm lazy and dense and haven't read far enough ahead: spare steam outlet.. which channel is that no longer to be drilled?

""If you are just going to play with yourself in the comfort of your own shed then it can remain as drawn.""

..made me chuckle

Thanks again,

pgk

There is an additional outlet on teh block on teh gear side of teh engine that is just blanked off with a plug, not much point in drilling it if not going to be used. You can just see teh hex plug in thsi shot.

Gotcha, ta Jason.

pgk

..spot/drilled/reamed the backhead holes yesterday and made up the bushes today. Also ordered more PB for the steam block etc and once that's made it'll be another solder session. I had to order more silver wire as well as flux. Those boiler tube ends got through almost 1.5 metres of 0.7 between them.

Hi pgk pgk,

If the firehole ring is turned accurately with registers/rebates and then squashed to shape this would usually be enough to keep the distances of the backplate ok on what is a relatively small boiler. Try a few dry runs first. I would silver solder the bushes to the backhead with J-M silverfo 24 first which saves a lot of angst and worry on the final stage, as there is otherwise too much to worry about, what with the rear foundation section as well.

If you can get some JM easyflo 2 for the final backhead stage you will not regret this. No longer 'sold' but there are a lot of fellow forum members who might have a stock of it to help you out. Unfortunately I have precious little left, and cannot help you out.

The silver soldering on the smokebox tubeplate looks very good. This is the last bit I do before the backhead.

Cheers,

Julian

Edited By julian atkins on 07/12/2016 23:53:28

The firehole indeed has a rebate/register and the instructions state to pean over the firehole. It sits fine on that and looks square to the wrapper. I did plan to cook in one session ... I'm finding that for me laying the solder down in heavy flux and cooking up until it runs works best. I intend to use 0.5 wire as two hoopsaround each bush, a ring of 1.5 around the firehole countersink I put in and the same around the outer edge and likely wire around the steam block... then insulate upto and including the firebox and its inside, warm up and then blow into the firebox/wrapper waterspace to try and cook the backhead from behind and then around the steam block.

I've been far less tidy whenever I've tried to use the rods hand held although i obviously have one and flux on standby. If you think there's serious risk of the bushes coming out while cooking the foundation ring then I'd rather hold them in with fireblock and wire than use 24% or even my 38% at this stage 'cos I'll likely make a mess .

I've also got a cookup before that for the firebox/wrapper stays and those in the backhead will also be a risk.. Again I hope to blow into the water spaces for all those in one hit....

Firehole reister below

Edited By pgk pgk on 08/12/2016 00:13:46

Do not peen over the lip of the firebox hole ring. It negates the 2 to 4 thou clearance required for silver solder penetration.

Cheers,

Julian

Point noted, Julian, and thanks. I'll try to just roll/flare the edge a tad so that backhead can't fall off if I overcook it later.

pgk

A simple update.. I've been turning out the threaded studs I intend to use as firebox stays.. took longer than I'd have thought and I did run out of PB 1/8 so waiting on some more. Steam block also done although I bogged up the first one with stupidly working out a depth for the bevel cuts and then using the wrong number..Doh!.

I'm also suffering from Boiler-makers Angst. The backhead will be slightly further aft than intended and there's all sorts of concerns in my head about how square it all is. I bit the bullet and finally invested in a height gauge..yeah i could have managed without but it's time to own one. I'll be spending some time checking dimensions and relative planes working on the assumption that all that really matters is that the boiler tube is horizontal and central and everything can get shimmed to fit- assuming the boiler holds pressure when finished. At some time in the distant future it might need some high temp filler to patch dings and scratches before painting to hide a novice's mess. Heck it's my first boiler - well if we ignore the 1/4 boiler of practice I wrecked....

There's nothing more than basics to these studs and the steam block apart from which way one might cut the radius beneath it. I used the mill and the easy technique of setting the boring head the radius away from the part and opening the cutter until it just scratched the surface.. then using the table to bring it in progressively until the edges of the part just became involved. It's a nice fit.

Check the core dia of those studs as by threading them you have reduced the cross sectional area. Original drawing is for 4BA which I suggested 1/8" solid rivits for.

The small studs are 1/8th PB threaded 5BA. The larger ones are 1/4 PB threaded 40T.

Darn, you're right. Good catch (I said i needed watching)........

threaded 1/4" may also be a bit on the thin sid eby the time you have poked a 4BA hole down it espacially as you will be spotting through from the hornplates and the boiler stays may be a bit off so you could end up drilling to one side thats why I suggested 3/8", you can see how the screw holes are not centred on mine

You should not need any shims, they stays can be over length then milled back to be 1/16" proud of the sides of the boiler barrel as I said earlier.

Brainf@rt, sorry. They are 3/8th x 40. As to shims was referring more to my need to shim other elements attached to barrel to square such as whether pump pad will end up perpendicular etc. I've got some 1/4PB so will start to make new 4BA studs and that was in my head when i replied earlier, though 5/32 would be less wasteful.

I have a new acronym BMA or BoilerMakers Angst.

I have made the 4BA studs and also got around to making a flycutter with a circular insert tool..I've meant to for some time just to see how it compares

OK lots of folk will ask why bother when HSS can do the job. the answer is simply that i can run this at 4xRPM of HSS which is a boon for manual table winding. I'm quite impressed with the result on a piece of my large stock of rusty hot-roll. It's a blurry piccy but the finish is darned good:

And made up the stud template out of scrap rather than bought sheet

The BMA is another matter. With lots of fiddling I've concluded that the barrel has a bow along it's length.. not surprising with all the heat cycles and rivetting etc. as best i can level it under the mill head it's about 3, perhaps 4 thou along it's length dipping in the middle.

More fiddling (and I'm not finished with the fiddling yet) suggests one side of the outer wrapper is about 2 mm short of the drawing and the other side about 1/2 mm short . courtesy of my new and expensive height gauge.

I also need a way better camera but money is haemorrhaging out of me at the moment.

It was my intention to drill the stud holes before the foundation ring soldering and try and solder more in one hit but if so then I need to adjust the size of the template and mark new reference points.

The further issue is that I finally discovered the cost of gears and/or gear cutters... that's another debate.

The drawn distance of bottom of outer wrapper to barrel is 1&15/16 or 49.21mm My worst distance is 47.38mm so just under 2mm short. I've scored lines at 46mm both sides and will adjust the template accordingly.

It also looks as though the firebox position is such that the firehole ring prevents the backhead from sitting as deeply as shown.. there's plenty of flange but total barrel length to backhead is about 4mm over the drawing and adjustments to the hornplate dimensions will have to be made.

I don't believe there's anything that can't be worked around.