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Post by atgordon on Feb 28, 2009 0:28:11 GMT
I am indebted to Dr John and Baggo for the discussion on the frame question ... and how one accommodates the blowdown valves.
I'm pretty close to cutting the frames in 3/16 (being in the US, I have got 1/8 as well, but I'm leaning to the heavier gauge to add weight). I noted Dr John's relief of the frames to allow the boiler with BD valves to be fitted ... on the SS drawings, Martin reduced the stretcher width ... if that width was restored to the standard Simplex width would that allow the BD valves to be installed without relief? Robin Smith has shared his thoughts and seems to think it might be possible to go back to the old dimensions.
If not, can the firebox be made a little narrower? Or am I missing something ...
Tony
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Post by drjohn on Feb 28, 2009 3:52:55 GMT
If I understand what you're saying Tony, by increasing the stretcher length, you will reduce/eliminate endfloat on the axles which will make cornering almost impossible, and I would also be disinclined to reduce the firebox width.
It might be possible to fit a "lower profile" blowdown bush as there is little need for the big lump of metal outside.
But to be honest, the additional weight is minimal and I think you will find it introduces so many other little problems it's not worth the hassle. The only reason I did it was because I couldn't get 1/8" steel at that time - I have since found a source of 3mm which is what I am using for the frames for the Black 5.
DJ
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Post by baggo on Feb 28, 2009 10:58:28 GMT
Hi Tony,
I hadn't noticed (until you mentioned it) that the frame spacing was different for the Simplex and the SS. According to the write up, Martin reduced the spacing on the SS to fall into line with the 'standard' of 4-1/8". To compensate for the narrower frames Martin just made the axle box flanges 1/32" thicker so the end float etc. will be the same.
You could increase the outside width of the frames to the same as the Simplex (4-7/16") and reduce the axlebox flange but this will still reduce the width between frames by 1/16" to 4-1/16". The firebox is shown as 3-7/8" wide over the wrapper so you could still fit a bush for the blowdown with a 3/32" (less a smidgen) thick flange which should be plenty strong enough.
As DJ suggests though, it might cause other problems if you use the 3/16". If you want a bit more weight it's easier to hide a few lumps of steel or lead between the frames ;D
John
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Post by atgordon on Feb 28, 2009 21:05:52 GMT
Many thanks Baggo & John, I think I will go for the 1/8" frames, although the early Simplex spacing is tempting since it gives a tad of extra clearance. And I think you are right on the BD bush ... 3/32 should be enough.
I might just leave the 4 lengths together in a pack held with the 1/4" UNC CSK head screws since it is fairly rigid unit and makes milling to width a lot easier Just stand them vertically in a Tee slot and clamp.
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