Switch blade planing length - how close to the ideal is possible?

Discuss the prototype and how to model it.
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Triode
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Switch blade planing length - how close to the ideal is possible?

Postby Triode » Tue Oct 04, 2022 10:16 am

Hi All,

I've been referring to the following very helpful and often-linked page on the Templot forum for my turnout building: https://85a.uk/templot/archive/topics/topic_491.php

As I prepare to tackle switch blades, can anyone advise whether it is practically possible to actually achieve the ideal planed length of, say, 29.3mm for a B switch? Does this value need to be reduced to allow an adequately strong tip for the switch in practice?

Cheers,

Liam

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Will L
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Re: Switch blade planing length - how close to the ideal is possible?

Postby Will L » Tue Oct 04, 2022 11:48 am

Triode wrote:H...As I prepare to tackle switch blades, can anyone advise whether it is practically possible to actually achieve the ideal planed length of, say, 29.3mm for a B switch?
Never heard any suggestion you cant, and as to avoid going under gauge the blade has to fit against the angle of the stock rail, you don't really have any choice.

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Martin Wynne
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Re: Switch blade planing length - how close to the ideal is possible?

Postby Martin Wynne » Tue Oct 04, 2022 12:10 pm

Triode wrote:As I prepare to tackle switch blades, can anyone advise whether it is practically possible to actually achieve the ideal planed length of, say, 29.3mm for a B switch? Does this value need to be reduced to allow an adequately strong tip for the switch in practice?

Hi Liam,

At the planing angle it's not going to make much difference provided it is somewhere between 29 and 30mm. Mark the rail with a felt-tip pen so that you can see and measure where the planing runs out.

The tip will be adequately strong because the knife edge applies only at the top. This is the end view of the blade for model purposes:

Image

To get the knife edge, after filing clip it to the stock rail and then work over it with abrasive paper. The tip will drop slightly below the stock rail so that it serves only to deflect the wheel flange and does not bear any load for the first few mm.

Lots more about all this on this page:

https://85a.uk/templot/companion/real_track.php

Scroll about half-way down for the blade planing detiails.

cheers,

Martin.
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Winander
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Re: Switch blade planing length - how close to the ideal is possible?

Postby Winander » Tue Oct 04, 2022 12:33 pm

Martin Wynne wrote:Mark the rail with a felt-tip pen so that you can see and measure where the planing runs out.

Make it a witness mark, plenty of Sharpie or whatever so that you know if you (accidentally) file too far. Another important requirement is to keep the filing straight, even verge marginally on concave rather than convex. I find it easier to rub the rail on the file; I also mark along the filed bit to highlight where I'm cutting and find it helpful to ensure it is straight.
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Triode
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Re: Switch blade planing length - how close to the ideal is possible?

Postby Triode » Tue Oct 04, 2022 12:53 pm

Thanks All.

My reason for asking is that I've received some pre-made B blades and the planed length is only about 19-20mm by my measurement. The manufacturer has advised that this is to avoid having a weak tip and that the actual angle of the planing is correct even if the length is short.

Cheers,

Liam

Tony Wilkins
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Re: Switch blade planing length - how close to the ideal is possible?

Postby Tony Wilkins » Tue Oct 04, 2022 1:11 pm

Hi Liam.
Something wrong there as that planing length is too short even for an A switch blade.
Regards
Tony.
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Julian Roberts
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Re: Switch blade planing length - how close to the ideal is possible?

Postby Julian Roberts » Tue Oct 04, 2022 2:21 pm

Hi Liam

If you got these blades from Wayne, I've had the same experience and just posted my correspondence with him. It's perfectly possible to get the blades the same length as the prototype without gauge narrowing. As Martin says above, the last few mm to the tip will be below the rail gauge level acting on the flange only. The tip will look like this.

Capture 2.PNG


Or else with a thicker blade tip you have to joggle BOTH stock rails. I explained all this in the download here -



https://scalefour.org/forum/viewtopic.php?f=39&t=7452

There is also far more erudite instruction from Tony here viewtopic.php?f=5&t=5727

Wayne's blades are for mass produced turnouts and I assume neither of the above approaches are suitable at readily affordable prices for the mass market. I would expect his Vs and assembled crossings to be perfectly suitable.
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Tony Wilkins
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Re: Switch blade planing length - how close to the ideal is possible?

Postby Tony Wilkins » Tue Oct 04, 2022 2:39 pm

If the planing angle is correct then the blade tips must be too thick and thinning the top edge at the tip will not resolve the length problem. The resultant blade will have too sharp an angle and not match the angle of the stock rail resulting in the the switch area being under gauge.
Regards
Tony.
Inspiration from the past. Dreams for the future.

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John Donnelly
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Re: Switch blade planing length - how close to the ideal is possible?

Postby John Donnelly » Thu Oct 06, 2022 5:48 pm

Would be heretical to admit that I didn't measure the planing length on any of the 40+ switch blades I've made and fitted so far and that they all work as intended...

John

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Julian Roberts
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Re: Switch blade planing length - how close to the ideal is possible?

Postby Julian Roberts » Fri Oct 07, 2022 9:38 am

You must be a born natural John :) For us who aren't so gifted :? here is a table from Templot of the huge variation of planing lengths. Of course accuracy to 1mm isn't an issue as Martin said above, but there's not going to be very successful running with a 30mm planing in an F turnout!
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John Donnelly
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Re: Switch blade planing length - how close to the ideal is possible?

Postby John Donnelly » Fri Oct 07, 2022 9:41 am

Julian Roberts wrote:You must be a born natural John :) For us who aren't so gifted :?


I'm going to go with beginner's luck :mrgreen:

I think most of my turnouts are Bs or Cs so I suspect that I've got lucky in that my planing is probably slightly longer than the values given in that table.

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Rod Cameron
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Re: Switch blade planing length - how close to the ideal is possible?

Postby Rod Cameron » Fri Oct 07, 2022 10:34 am

Is it more important not to forget the very slight bend in the stock rail to accommodate the planing?
Rod

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Martin Wynne
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Re: Switch blade planing length - how close to the ideal is possible?

Postby Martin Wynne » Fri Oct 07, 2022 11:08 am

Rod Cameron wrote:Is it more important not to forget the very slight bend in the stock rail to accommodate the planing?

Hi Rod,

Indeed -- illustrated here in your own photo, which you kindly gave me permission to use about 20 years ago: :)

Image

cheers,

Martin.
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Philip Hall
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Re: Switch blade planing length - how close to the ideal is possible?

Postby Philip Hall » Fri Oct 07, 2022 12:49 pm

These technical ideals are all very well, but what matters in the context of a reliable working railway is that settings and parameters are not exceeded. I have absolutely no idea whether my switch blade planing is the correct length, although I guess that Eddie Bourne, who made most of my pointwork, did. What has seemed to be most important is that the blades fit snugly against the stock rail, and if a bit of a joggle is required to ensure this (and to maintain the track gauge) then so be it.

The railway has to work, reliably, at all times, without fail. If that means we have to occasionally drift away from the theoretical ideal, even if that means it doesn’t look perfect in prototypical matters, again, so be it.

The thing has got to work otherwise it’s just a source of frustration. I suppose I ought to mention that I think we have on ‘Mellstock’. Thanks to Eddie!

Philip

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Hardwicke
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Re: Switch blade planing length - how close to the ideal is possible?

Postby Hardwicke » Tue Oct 18, 2022 11:33 am

Julian Roberts wrote:You must be a born natural John :) For us who aren't so gifted :? here is a table from Templot of the huge variation of planing lengths. Of course accuracy to 1mm isn't an issue as Martin said above, but there's not going to be very successful running with a 30mm planing in an F turnout!

Excellent info. At some stage I need to make 2 large possibly F blades.
Ordsall Road (BR(E)), Forge Mill Sidings (BR(M)), Kirkcliffe Coking Plant (BR(E)), Swanage (BR (S)) and Heaby (LMS/MR). Acquired Thorneywood (GNR). Still trying to "Keep the Balance".


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