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GWR Buffalo (1076 Class) in 2FS (Part 2)

Ian Smith

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After a few months of doing other things, I have once again started work on my 3rd loco. Previously, I had formed the saddle tank (http://www.rmweb.co.uk/community/index.php?/blog/1009/entry-16413-gwr-buffalo-1076-class-in-2fs/) and there the project had stalled for no other reason than I wanted to progress Modbury for the 2mm Association's Supermeet last month.

 

Picking up the reigns again, I have made a start on the chassis. Once again I have decided to provide the engine with a milled solid brass (albeit split framed) chassis. To achieve this, a length of 1mm thick brass is bolted to a main chassis block some 6mm thick the bolts being secured in insulating material in the main block. Once the pair are united at their extremities (outside the finished size of the chassis), the various holes for fixing bolts, axles and gear shafts are drilled through before the shape of the chassis is milled away.

 

For this loco, I will be using some etched coupling rods of 14.5mm x 16.5mm wheelbase that I have done my own artwork for (they are of the "fish bellied" profile which unfortunately the Association do not provide). Until my own rods are ready I will be using Association ones as a jig to drill the axle holes and to test the final chassis build.

 

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Axle centre line and chassis extremities marked, first axle hole spotted with 0.5mm drill and peg inserted

 

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Coupling rods being used as jig to drill other 2 axle holes 0.5mm spaced from the peg of the first axle

 

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All 3 axle holes drilled. They are subsequently opened up to 2.4mm to house Association phosphor bronze bearings

 

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Axle holes for the gears drilled, chassis block milled to shape, and Association phosphor bronze bearings soldered in place

 

​Because the Buffalo class had outside frames, Association wheels with extended axles were purchased, unfortunately the wheels do not come with Fly Cranks so these had to be manufactured. A sheet of 0.018" nickel silver was used to fabricate the cranks, a 0.7mm hole drilled in a piece of the material for the spigot on the extended axle, and a 0.5mm hole was drilled 0.080" (about 2mm) from that hole. A little jig was made with a 0.7mm peg in it onto which the piece of nickel silver sheet was hung and the 0.5mm hole drilled 0.080" away from it. The crank was then filed around these two holes.

 

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First crank made and a start made on filing out second one

 

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First crank being used as a pattern to finish off the filing of the subsequent cranks

 

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Full set of 6 cranks

 

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Wheel, fabricated fly crank and Association flanged crankpin

 

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Set of wheels complete with their fly cranks and crankpins and remainder of spigot filed off

 

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Completed chassis, albeit with the extensions still in place - these will be cut off once all of the machining has been complete (the worm housing still needs to be made and bolt holes drilled and tapped)

 

Finally a short video of the chassis being pushed along

 

There is still a bit to do, not least of which will be a full strip down so that it can be painted!

 

Ian

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Guest Simon Dunkley

Posted

Serious work, there.

And in such a small scale.

 

How well does it roll without being pushed?

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wow excellent work as always   :locomotive:

 

what do you insulate the bolts with and how is it secured ?

 

wish even one of my attempts at a steamer would roll as well  :resent:

 

Nick

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That's very good workmanship Ian. I do like the heavy chassis idea. I am assuming there is a thin layer of insulant between the two halves of the chassis. I presume you will not be fitting Simpson springs. Do you ream the axle bushes to 1.5mm or do you drill them at 1.6 (i.e as for the Simpson springs) to give a litlle clearance. I am assuming something like tufnol plugs in the thick chassis side tapped to take the bolts. Presumably you would drill and fit the plugs before drill the holes for the bolts.

If you are etching the rods could you not etch the fly cranks too?

 

Don

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Thank you all for your positive comments!!

 

Serious work, there. And in such a small scale. How well does it roll without being pushed?

Simon, it's not too bad.  There is a very slight tight spot which I will address when I rebuild the chassis after it's been broken down for painting.

 

 

what do you insulate the bolts with and how is it secured ?

 

Nick, the bolts are held in tufnol plugs in the main chassis block.  The fixing points are drilled 1mm, the 1mm thick section of chassis removed and the 1mm holes in the main block opened out to 2.3mm.  Tufnol plugs are turned up and araldited in those holes, and when secure the 1mm section of chassis is bolted back on (hence the fixings outside the extremities of the finished chassis).  The 1mm holes in the 1mm section are used to drill the tufnol plugs 12BA tapping size and the plugs tapped 12BA.  The 1mm section is again temporarily removed which it has its holes opened out to 12BA clearance and countersunk.

 

 

That's very good workmanship Ian. I do like the heavy chassis idea. I am assuming there is a thin layer of insulant between the two halves of the chassis. I presume you will not be fitting Simpson springs. Do you ream the axle bushes to 1.5mm or do you drill them at 1.6 (i.e as for the Simpson springs) to give a litlle clearance. I am assuming something like tufnol plugs in the thick chassis side tapped to take the bolts. Presumably you would drill and fit the plugs before drill the holes for the bolts.

If you are etching the rods could you not etch the fly cranks too?

 

Don

 

Don, not my idea, just copying what Nigel Ashton did for his Manor chassis and his Cambrian 0-6-0 that was detailed in the Association magazine a few years back.  I won't be fitting Simpson springs on this one, the centre axle has a little bit of vertical play introduced by filing the bottom/top of the bush.  Because the loco will have outside frames, I was concerned about the extended axles potentially shorting on those if too much play was given to the axles so the bushes are all as purchased - I haven't opened any of them out by drilling or reaming as they were all a good running fit on the wheel axles and axle steel that the gears are on.

I did think about doing the artwork for the fly cranks but decided that it would hold up the build and they are such simple things to make anyway.

 

 

Very impressive Ian, those cranks must be seriously tiny!

 

Dave, thanks.  They are quite small an indication can be seen in one of the photos of them with a ruler.  But then to you 7mm boys even my workshop would seem tiny :-)

 

 

Ian, Inspirational work. Duncan

 

Duncan, thank you.

 

Ian

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Excellent work Ian. Given me some good pointers for how I might progress my next loco chassis which is going to need as much weight as possible. Thanks!

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