FB base plate assembly - Brimsdown

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proto87stores

FB base plate assembly - Brimsdown

Postby proto87stores » Tue Feb 16, 2021 5:26 pm

The effect is magnificent, but it seems to me the double layers of the base plates are being unnecessarily soldered together twice. Once "for rigidity" and once again when soldering the rail to the plate and sleeper.

I'm also wondering how thin the base plate material is for the half etch step to give an reasonably accurate 1:40 cant when the rail base is only 0.082" wide?

Here in the USA, we are fortunate to have true wooden ties (sleepers) . So we are able to use pre-shaped scale spikes through the base plate holes to fix the rail to the plate and tie in one pass without soldering steps.

Andy

Tony Wilkins
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Joined: Tue Mar 20, 2012 3:57 pm

Re: FB base plate assembly - Brimsdown

Postby Tony Wilkins » Wed Feb 17, 2021 5:13 pm

Hi Andy.

The double hit of solder is needed as the scheme is to get the solder to flow first around the base of the spikes to make them more rigid prior to forming. Believe me, you soon know if it hasn't as the resistance to bending is noticeably less and tends to bend from the half etch fold line and not bend the protruding piece of the spike. Any solder that flows between the two layers of the base plate is incidental at this stage.

The etch fret is 0.01" so the half etch is 0.005" allowing for tolerances. The cant angle is 1 in 20 and although I haven't checked the sums, it does cant the rail significantly.

Regards
Tony.
Inspiration from the past. Dreams for the future.

Tony Wilkins
Posts: 493
Joined: Tue Mar 20, 2012 3:57 pm

Re: FB base plate assembly - Brimsdown

Postby Tony Wilkins » Thu Feb 18, 2021 10:20 pm

Having now thought about it, assuming the 0.005" difference is across 0.080" of the width of the foot this will give a cant of 1:16.
0.004" divided into 0.08" gives 1:20, so if anything its slightly over what it should be to represent our peculiarly British way of doing things.

Regards
Tony.
Inspiration from the past. Dreams for the future.

Terry Bendall
Forum Team
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Re: FB base plate assembly - Brimsdown

Postby Terry Bendall » Fri Feb 19, 2021 7:47 am

I haven't measured the cant angle but it is certainly noticeable when a length of track is viewed end on. The information that Colin Craig supplies states that the system is designed to give a 1 in 20 cant angle and knowing how Colin works, I would have thought this would have been achieved.

Terry Bendall

Tony Wilkins
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Joined: Tue Mar 20, 2012 3:57 pm

Re: FB base plate assembly - Brimsdown

Postby Tony Wilkins » Fri Feb 19, 2021 1:07 pm

Terry Bendall wrote:I haven't measured the cant angle but it is certainly noticeable when a length of track is viewed end on. The information that Colin Craig supplies states that the system is designed to give a 1 in 20 cant angle and knowing how Colin works, I would have thought this would have been achieved.

Terry Bendall

And his track gauges are designed to ensure this is so.
Regards
Tony.
Inspiration from the past. Dreams for the future.

proto87stores

Re: FB base plate assembly - Brimsdown

Postby proto87stores » Fri Feb 19, 2021 5:08 pm

Sorry I goofed on the rail base width earlier. Getting to have too many senior moments nowadays :?

The base width of modern code 82 is actually 0.068 +/-0.002" (All the other US originated model FB profiles are the same width as their heights).

That means for the nominal 0.068" rail base the least slope for a 0.005" step is in 13.6 . However, a step must extend a few thou under the rail edge and the half etch depth obviously has to be a thou or so greater that 50%. So say 0.006" tilt in 0.062" and the slope easily increases to 1 in 10, or twice too much.

Using the canted track gauge can obviously force things right, but does mean the rail is then partly supported on a solder blob wedge, rather than the two resting points of the brass plate.

Andy

Proto87stores

Re: FB base plate assembly - Brimsdown

Postby Proto87stores » Sun Feb 21, 2021 6:50 pm

One further point. If the rail head tilt exceeds the model wheel profile angle, the wheel tread will then switch over to bear and run on the far side of the rail head. Depending on how much the excess is, there will be a corresponding lifting of the wheel flange above the normal flange root / rail head interface.

Given the importance of the flange root / rail head integrity to good P4 (and P87) running, I'd be reluctant to cant the rails at all in a model environment. Models have no need to spread the vehicle weight evenly over the width of the rail head, as the prototype does. And a higher tread bearing pressure on the rail is better for model electrical pick-up.

Andy

Tony Wilkins
Posts: 493
Joined: Tue Mar 20, 2012 3:57 pm

Re: FB base plate assembly - Brimsdown

Postby Tony Wilkins » Tue Feb 23, 2021 4:03 pm

Hi Andy.
I can't fault your logic and I have just measured the foot width of my rail as 0.069". When I originally bought my etches from Colin, he asked what rail I was going to be using as it was most important to have the correct track gauge to suit the rail and assure a good fit. So I assume that it is the gauge that ensures the correct angle of cant is achieved. The design of the baseplates are such that there is room for the rail to be held where needed as the solder flows into the joint and thereafter hold the rail permanently. When the solder has cooled each baseplate / rail interface becomes a solid unit, much like ply and rivet track construction does. The spikes are then purely cosmetic.
Regards
Tony.
Inspiration from the past. Dreams for the future.

Proto87stores

Re: FB base plate assembly - Brimsdown

Postby Proto87stores » Tue Feb 23, 2021 4:42 pm

Tony,

Thanks for checking. Model canted rail is an ultimate realism issue that I decided long ago I couldn't find a simple technical modeling solution for. (see my earlier missing post).

Apart from the potential mismatching of the wheel and rail cants, possibly throwing the contact weight onto the outer surface of the rail head, I've also realised that on a perfect match, the tiny progressive outward decrease in the supported model wheel diameter introduces an extra tiny form of wheel slip friction. Something P4 and P87 model lightweight locos don't need.

Andy


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