Alan's Workbench

[Mayner]

Mike Sharman explained seems to have introduced the concept of square cuts outs in the frames in conjunction with what he termed "Sub Hornblocks" in his "Flexchas" booklet 1st published 1982. Written from a scratchbuilding perspective writed about machining V groved axle brushes to slide in the subhornblocks and filing up & individually matching the subhornblock and brush. 

While Mike Sharman did not specify frame cut out or hornblock sizes he noted "allow Brushes to move approx 1mm above and below axle centre line"

The square frame cut out and individual hornblock is similar in concept from prototype practice.

My first compensated loco assembled 84-5 was a TMD Midland tank the original TMD (brass chassis) had rectangular frame cut outs suitable for use with a compensated frame bush (I used Sharman), my second a scratchbuilt 0-6-0 with "Perseverence" etched hornblocks and compensated brushes (I was not happy with the 0-6-0 and scrapped/dismantled the loco about 30 years ago, hopefully I will get round to building a replacement!)

I usually assemble my compensated locos with all driving axles running in hornblocks (including fixed axle) as I like to treat the wheelsets as separate sub assemblies for painting/maintenance.  I try and ensure that the upper edge of the floating (sub) hornblocks are level and usually mount the fixed hornblock 1mm lower & eliminate vertical travel by mounting the keeper wire higher.

I usually assemble chassis on a flat surface (hardboard or MDF) with a piece of rectangular stripwood to ensure angles are at 90°, I have always found a coupling rod jig similar in principal to the "London Road" jig in Alan's photo perfectly adequately, one of the most improtant factors in assembling a compensated chassis is to ensure that the hornblocks are truly vertical before soldering in place, otherwise a chassis will bind when the floating axles move up and down.

 

 

 

[Tullygrainey]

All you've ever wanted to know about building chassis but were afraid to ask...

[Tullygrainey]

33 minutes ago, Mayner said:

one of the most improtant factors in assembling a compensated chassis is to ensure that the hornblocks are truly vertical before soldering in place, otherwise a chassis will bind when the floating axles move up and down.

Very important. A lesson I learned the hard way!

[Tullygrainey]

Some more progress on a chassis for the Countess of Antrim. Frames separated and ready to be assembled. Those funny triangles of brass shim are representations of the firebox, visible through the cutouts in the frames.

 

I find getting the first frame spacer in straight and square is always a challenge requiring a number of goes and I haven't settled on a good way of doing it yet. It's all set squares and clothes pegs and verbal blandishments. Etched kits often have tabs and slots to help the parts go together accurately. No such refinement with these hand hacked bits!

 

Spacers in, front, back and middle. Guard irons added. Ready for hornblocks. Poppy's jig does its stuff.

 

Hornblocks in. Compensation beam fitted. A chassis sitting nice and level. Yay!

 

The gearbox I chose for this one is a High Level HiFlier+. The etch is up to High Level's usual high standard - beautifully crisp - and goes together nicely, given bit of patience and care.

 

The articulated final drive carriage means the motor can be pushed forward into the Countess's boiler leaving the cab free.

 

A little jewel.

 

 

[David Holman]

Magic!

[Tullygrainey]

The Countess's chassis got  a coat of paint before the wheels went on. It rolls nicely under finger pressure with no tight spots.

 

Rods next, then an hour or two spent chasing a tight spot which predictably appeared when the last crankpin nut was tightened down. Just when I thought I was home free!

 

The outside cylinders/slidebars/crossheads are probably the trickiest part of this build, both making them and getting them to work properly. I'm half way through that battle.

Each crosshead was cut from two thicknesses of 16 thou nickel silver to get front and back matching. 

 

This is the kit of parts half way through the process. Cylinders from 8mm outside diameter brass tube, slidebars from 1mm square brass rod. The bits of scrap etch soldered to the slidebars are there to keep them equidistant until they're soldered into the cylinders. 

 

Connecting rods have a 14BA bolt soldered into one end. These go through the crossheads.

 

Piston rods are 1mm brass. they'll be trimmed to length eventually.

 

Now to unite cylinders with chassis and get the whole caboodle working. If I recall, it needs three hands.

Alan

 

[Tullygrainey]

Since posting the above I've had a rethink about the crossheads, or maybe that should be I actually gave it some thought.

Instead of bolting the connecting rod behind the crosshead, the end is now slotted into the space between the front and rear faces of the crosshead and a 14BA bolt run through both, thus creating a bit more clearance and making it less likely that the con rods will clout the crankpins on the front wheels. 

Got there in the end.

[Galteemore]

Fabulous work as ever Alan. Reminds me how grateful I am to model railways which eschewed external valve gear….

[Tullygrainey]

24 minutes ago, Galteemore said:

Fabulous work as ever Alan. Reminds me how grateful I am to model railways which eschewed external valve gear….

Yes David. One of the attractions of modelling the BCDR too!

[Galteemore]

2 minutes ago, Tullygrainey said:

Yes David. One of the attractions of modelling the BCDR too!

Yes. If you stray away from the cosy world of all those inside cylinders on the County Down it’s Baltic out there…

[David Holman]

Great work, but which brought back painful memories of my own attempts at such alchemy!

[Patrick Davey]

Alan you will be ready for this in no time:

 

[Killian Keane]

Thank goodness outside cylinders are almost entirely confined to the Narrow gauge on Irish railways, and that Walschaerts only appears on a portion of those!

[Tullygrainey]

55 minutes ago, Patrick Davey said:

Alan you will be ready for this in no time:

 

[Horsetan]

1 hour ago, Patrick Davey said:

Alan you will be ready for this in no time:

 

Outside admission valves. That's very similar to the arrangement used by the Great Western Steam Railmotors.

[David Holman]

The saving grace of outside valve gear on a model is that while it looks complicated, most of it doesn't do much, other than rock to an fro a bit. Outside cylinders, with their piston and conrods, do a fair bit more. Add in brake and sanding gear and it all starts to look a bit scary, with lots of opportunities for electrical shorts - which I'm sure our man is well aware of!