Mayner Posted July 23 Posted July 23 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. 2 Quote
Tullygrainey Posted July 23 Author Posted July 23 All you've ever wanted to know about building chassis but were afraid to ask... 1 1 1 Quote
Tullygrainey Posted July 23 Author Posted July 23 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! Quote
Tullygrainey Posted Sunday at 14:57 Author Posted Sunday at 14:57 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. IMG_2986.MOV 4 1 Quote
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