Chimney machining

[Speedy Builder5Participant @speedybuilder5]

Machining of cast loco chimney

[Speedy Builder5Participant @speedybuilder5]

One (of many) outstanding jobs on my 5" SPEEDY is to machine the bronze chimney casting. Are there any links as to how to do this. My first idea is to bore the inside to size, then make some sort of blind expanding mandrel to go inside the chimney and hold this in the milling vice horizontally, and use the vertical boring head to machine the smokebox flange end of the chimney.

Any other ideas out there ?
BobH

[Martin ConnellyParticipant @martinconnelly55370]

Why not thread the hole and screw it on to a carrier bar of suitable size. Once the flange is machined you can loctite the casting to a bar with the correct diameter to machine the rest of it. Add jubilee clips for extra holding if needed.

Martin

[Speedy Builder5Participant @speedybuilder5]

Hi Martin, I get the idea, but the bore of the casting is not far off finished size, and no room for a thread I think, also the saddle (Boiler diameter is 5&quot would need a big bit of scrap to mount it on. Getting the bore of the chimney right can be done with a 4 jaw chuck on my Boxford, its probably the saddle that I am looking to overcome.

[Tim StevensParticipant @timstevens64731]

Here is an idea: Turn a piece of wood to the diameter of your boiler (where the chimney is to fit). Wrap it with a spiral of emery held with a drawing pin at both ends, leaving a section of a few inches between the pins. File the inside of the chimney face to remove rough casting flash etc, and attach it to a handle where the chimney proper will fit. The thread idea above seems sound to me for this. Then offer it carefully to the rotating emery, and with care this should produce a radius to match your boiler.

You might find it helpful as an alternative to slot the wood lengthwise, and use a full sheet of emery held in the slot. And wet & dry works as well as emery, as will garnet paper if your chimney base is brass.

This should give a good enough fit for soft or silver solder – but do be sure to remove every speck of emery or the solder might not run so well.

Regards, Tim

[Clive HartlandParticipant @clivehartland94829]

What is the normal method of fitting a chimney to the smoke box, screws or silver solder?

Clive

[Michael ToppingParticipant @michaeltopping17870]

I have always done as you suggested, finish turn the bore and make an expanding mandrel long enough so you can hold it in the vice on a mill and use a fly cutter or boring head to finish the smoke box radius. You can then transfer to the lathe to finish turn the outside. I have given up using castings for chimneys as there never seems to be material left on where you need it and it is cheaper to buy a piece of continuous cast iron bar and use that.

Clive chimneys are usually attached with 6 or so small hex head screws.

Michael

[NJHParticipant @njh]

Bob

I did pretty much what you suggest. Having bored out the inside I turned up a scrap piece of ( as it happened) hex bar to fit and fixed it with loctite. At that time I had access to a big horizontal mill and, holding the hex in the vice, cut the required shape (gently!) with a side& face cutter of the same diameter. Your idea using the boring head should work just as well. When completed just heat up with a torch to break the bond.

This was a total success but the loco languishes 1/2 made in my workshop ! We moved to the depths of the country some years ago and the nearest club track is a way away. Not likely to get finished now.

Norman

[Speedy Builder5Participant @speedybuilder5]

Thanks for the ideas, at least I know what I need to look out for, never used loctite like that before, but seen it recommended several times. There is always a first time for everything.
NJH – try not to give up – my nearest track is about 50 miles (80Km) away and I am not even sure how I would get the loco into the car. Thinking of an overhead monorail just for moving it around in the workshop !
BobH

[julian atkinsParticipant @julianatkins58923]

hi Bob,

there is a problem with the original Speedy draughting.

i have re-done it using Jos Koopmans' formula, and if you PM me will gladly send you the details.

for machining the chimney, do the inside to the corrected dimensions, then fit on a mandrel to suit to do top and middle and part of the base. the rest of the base is best done with a sharp half round file putting the mandrel plus chimney in the bench vice.

note that for a GWR copper capped chimney gunmetal is the wrong colour, and you may like to consider a separate copper cap or hard drawn bronze copper cap.

cheers,

julian

Edited By julian atkins on 24/12/2015 23:03:56

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