Templot Club Archive 2007-2020
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posted: 1 Oct 2010 14:28 from: Glen Suckling
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Hi Martin, This post is probably going to demonstrate my stupidity to everybody, but here goes ..... A black and orange thing appeared recently at the top of each forum page called a "handy hint". It looks like a plan view of a piece of flatbottom rail that has been partially filed away (part of the head and web missing). I cannot figure out why I would want a square end on a blade.  Can you enlighten me?Regards, Glen |
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posted: 1 Oct 2010 14:37 from: Bill_Lobb
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Glen Suckling wrote: Hi Martin,I thought exactly the same. It took several days to twig that it is a side view, rather than a plan view. (Or am I showing my stupidity?) Bill |
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posted: 1 Oct 2010 14:42 from: Bill_Lobb
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Bill_Lobb wrote: I thought exactly the same. It took several days to twig that it is a side view, rather than a plan view. (Or am I showing my stupidity?)On reflection that did not really mean much. Am I right in thinking that if you ink the rail, then file it so that the shiny bit looks like the orange part of the diagram, you will have filed half way through the rail at the tip? Bill |
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posted: 1 Oct 2010 14:45 from: wcampbell23
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It's not a plan view but elevation - where it is labelled "inked rail" is the web of bullhead rail. Bill Campbell |
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posted: 1 Oct 2010 15:57 from: Nigel Brown click the date to link to this post click member name to view archived images |
So the idea is that the bit at the end where you are filing through the web is equal in length to the next bit where you are filing the top and bottom but not the web. Couple of thoughts:- a) Is this correct? Only if the web is half the width of top and bottom. No idea if this is true on the prototype, but do wonder if it's always true on model bullhead rail. b) Does it matter? I file to somewhere in the web, enough to know that I've hit the web, then attack the other side, leaving the bottom bit as is. The less you file into the web initially then the more bottom bit you have on the other side to discourage the planed bit from flexing too much. Cheers Nigel |
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posted: 1 Oct 2010 16:25 from: Martin Wynne
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Oh dear, do we need a handy hint to explain the handy hint?  I thought the site header looked a bit "texty" and an occasional image or diagram relevant to our subject might make it more interesting: 2_190931_260000000.gif  Bill_Lobb wrote: Am I right in thinking that if you ink the rail, then file it so that the shiny bit looks like the orange part of the diagram, you will have filed half way through the rail at the tip?Hi Bill, That's correct. It's a side view of model bullhead rail. Most such rail has an over-scale* web thickness approximately half the overall rail width. So if you ink the rail and then file the planing length (shown orange) on the back of the switch blade to match the diagram, you will be half-way through the rail at the tip. Planing lengths are marked on the Templot templates and also given at: http://www.templot.com/martweb/gs_realtrack.htm#split_switch You then turn the blade over and file the same planing length on the front of the blade, but this time at an angle, so that only the rail head is removed. The result is a knife edge at the tip, but with half the web thickness remaining below the tip and still providing sufficient strength for proper flexing of the whole switch rail. This diagram shows the resulting end view of the switch blade: cranked_switch_dropper.gif  The final task is to put a set in the rail where the planing runs out, so that the top corner of the gauge face is returned to a straight line. With the blade then clamped against its stock rail, the deflection angle can be checked, and a rub with abrasive paper will radius the tip corner from a knife edge to something comparable with the prototype which will be robust enough in service. I originally prepared this diagram for use in a much longer write-up somewhere, but at present I can't find it.  It was to demonstrate that filing switch rails is quite straightforward and doesn't need expensive jigs. *prototype web thickness is 3/4" against an overall width of 2.3/4". But that would scale to less than 10 thou in 4mm scale and I don't believe such rail would be practical. All code 75 bullhead rail I have measured has a web thickness around 18 to 20 thou, i.e. approximately half the overall width of 36 thou. In the larger scales the rail section may be nearer to exact scale, in which case the diagram would not apply. regards, Martin. |
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posted: 1 Oct 2010 17:11 from: Bill_Lobb
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Martin Wynne wrote: Oh dear, do we need a handy hint to explain the handy hint?The handy hint is a good idea. While it took me a while to work it out, it was worth it for the 'Eureka' moment when the penny dropped. Little things please li...... Bill |
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posted: 1 Oct 2010 18:02 from: Glen Suckling
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Martin Wynne wrote: Oh dear, do we need a handy hint to explain the handy hint? Hi Martin (and Bill, Bill and Nigel), Thanks for the speedy replies. As soon as I realized that it was a side elevation everything became clear. I just tried it out on a piece of Code 125 BH rail and it works well. Previously I had just filed away until it looked OK. I like the idea of the handy hints - although you may need a little patience with people like me who are slow on the uptake. Regards, Glen |
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posted: 3 Oct 2010 09:06 from: David Higgs
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Must admit, I didn't understand the Switch Blade 'Handy Hint' although the Transition Curve is something that I feel is a 'Handy Hint'. David |
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| Last edited on 3 Oct 2010 09:07 by David Higgs |
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posted: 3 Oct 2010 20:47 from: phileakins
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As the Handy Hint has now been superseded in the header, can the diagram be reprinted here please Martin, otherwise the posts above don't make a lot of sense. Thanks. Phil |
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posted: 3 Oct 2010 21:00 from: Martin Wynne
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phileakins wrote: As the Handy Hint has now been superseded in the header, can the diagram be reprinted here please Martin, otherwise the posts above don't make a lot of sense.Hi Phil, er, it is reprinted here, for that very reason -- message 7718 Martin. |
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posted: 4 Oct 2010 14:07 from: David R
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Martin Wynne wrote: ... file the planing length (shown orange) on the back of the switch blade to match the diagram, you will be half-way through the rail at the tip.Why do you want to be "half-way through the rail"? According to the NER Permanent Way Standards (available from http://www.ner.org.uk/ ) only one-sixteenth of an inch of the web was removed (not very much even in 7mm scale) although the black ink on the side of the rail will show even this amount. http://homepages.tesco.net/~david.r.rayner/lumpy/track.html#switches shows how scale straight-cut blades can be made. Unfortunately I ran out of words at step 3 but the bevelled planing angle should be about the same as the angle on the wheel flange and the depth of the bevel enough to clear the flange (presumably with an allowance for tread wear). Step 4 shows the 2 stages of top-planing (essential for smooth running); the longer length is 70% of the side-planing, and the GWR replaced the short top-planing with a 2 inch radius. Step 5 is rounding and smoothing followed by drilling all the holes. It works for me in both 4mm and 7mm scales despite the rail webs being overscale in both cases; which has something to do with it being impossible (or just too expensive?) to roll the rail with a scale thickness web. David http://www.shapeways.com/shops/otr for Off The Rails |
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posted: 4 Oct 2010 14:31 from: Martin Wynne
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David R wrote:Why do you want to be "half-way through the rail"?Hi David, So that the end view of the blade looks reasonably prototypical. If you leave the full overscale web thickness, the end of the blade looks too stubby. It also means that a flatter angle is needed on the front of the blade to remove the head part only, which again looks too stubby and may not clear all flange profiles. Also, by having the tip on the rail centre-line, the required set angle where the planing runs out can be exactly specified as half the planing angle. On the other hand, if you are getting good results the other way, that's great. An excellent set of pictures on your site, thanks for the link.  Years ago I made a wooden demo model about 2ft long of a prepared switch blade tip. I used to have it on my stand at shows when selling 85A pointwork kits and components. It came in handy for hitting awkward customers. If I can find it I will take a picture and post it here.regards, Martin. |
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