Plug dimensions

[SimonD]

Morning all,

Apologies if I am being dim, but I can’t find the nominal dimensions of the plug & socket for plain track chairs.

I’ve just modelled a GW 1895 chair, and need to model the plug, so need length, width, and relation to gauge face.

Is there a published standard?

Tia
Simon

 

[Martin Wynne]

Morning all,

Apologies if I am being dim, but I can’t find the nominal dimensions of the plug & socket for plain track chairs.

I’ve just modelled a GW 1895 chair, and need to model the plug, so need length, width, and relation to gauge face.

Is there a published standard?

Tia
Simon

@SimonD

Hi Simon,

The plug size is determined by the chair size. Generally 1" all round inside the chair base dimensions. i.e. dimension X here is 1" :

For the REA S1 chairs those plug dimensions are:

plug outer length: 8.25" from gauge-face
plug inner length 4.25" from gauge-face
plug width: 6"

In 4mm/ft scale that means the plug is 4.17mm x 2mm.

Those dimension apply immediately below the chair base. There is a short parallel section and then an inset taper. The corners need a generous relief and the plug sides need a flexible tang to clip into the sockets.

If you need to create sockets for some other plug size, you can change each chair type from S1 to SC in the chair heaving, and then click the SC size... button for the chair. You are setting the chair base dimensions, so add 1" all round to your plug size. The socket clearances can be set on the DXF dialog chairs plugs/sockets tab.

If you use Templot to create the SC chair, you could export it to CAD and then copy the plug from the DXF and paste into your own chair design. See this post for more info:

https://85a.uk/templot/club/index.p...-plug-track-up-to-version-244c.220/post-10752

n.b. this project is experimental. The above dimensions may change in future program updates. If you are plugging your own chair design into a Templot socket, check carefully that the resulting track gauge is correct.

cheers,

Martin.

 

[SimonD]

Good morning, Martin,

Thanks for your rapid reply.

If I’ve understood correctly, you’re sizing the plug from the chair, so the plug (and therefore sleepers/timbers) will vary according to the chosen prototype? Or is it always 4.17 x 2mm (7.3 x 3.5)?

I hesitate to offer suggestions, but might it be easier to define a nominal hole (eg 6” x 12”, with 1.5” corner rads) and define the inner face of the hole a given distance (eg 4.25”) inboard of the gauge face? Obviously that would work for plain track but might be more difficult to implement on pointwork.
Thanks again
Simon

 

[Martin Wynne]

Good morning, Martin,

Thanks for your rapid reply.

If I’ve understood correctly, you’re sizing the plug from the chair, so the plug (and therefore sleepers/timbers) will vary according to the chosen prototype? Or is it always 4.17 x 2mm (7.3 x 3.5)?

I hesitate to offer suggestions, but might it be easier to define a nominal hole (eg 6” x 12”, with 1.5” corner rads) and define the inner face of the hole a given distance (eg 4.25”) inboard of the gauge face? Obviously that would work for plain track but might be more difficult to implement on pointwork.
Thanks again
Simon

@SimonD

Hi Simon,

Yes. Everything is derived from the outline dimensions for each chair.

The reason is that the dimension X in the above screenshot is critical. If it is significantly more than about 0.5mm at each end it will not 3D resin-print reliably without additional supports, or redesigning the chair rafts with chairs tipped at an angle.

More explanation and options here:

https://85a.uk/templot/club/index.php?threads/3d-plug-track-version-244c-and-beyond.891/post-10973

Obviously if you design your own plug track you can do whatever you want. But the defaults in Templot plug track have been arrived at after a lot of testing over the last few years.

cheers,

Martin.

 

[SimonD]

Thanks Martin, no desire to re-invent the wheel, and yes, I understand that overhangs are an issue in printing. Just feels to me that a standard offset from the gauge face to the inner edge of the plug would be “a good thing” . I guess it depends how much different companies’ chairs differed in baseplate dimensions.

So, as you’ll see on WT, I’ve done CAD for some 1895 GWR 2-bolt chairs. I’m planning to put the STLs on the WT Resources sub-forum. Do you want / could you use a copy? Happy to share. Native Solidworks, or IGES/STEP if useful.

Cheers
Simon

 

[SimonD]

Oh yes, I also discovered “vigorous plunge washing” is helpful!

 

[Martin Wynne]

Just feels to me that a standard offset from the gauge face to the inner edge of the plug would be “a good thing”

@SimonD

Hi Simon,

Well in practice we already have that -- 4.25" from the gauge-face to the inner end of the plug.

But this makes sense only for ordinary plain track chairs -- S1 and S1J.

It's no help for L1 and M1 bridge chairs, or S1O half-bolted chairs, because the plug would be longer than the chair base dimensions.

For P slide chairs the overhang from the plug end would be too great for successful 3D printing.

For all other chairs there is more than one rail through them, so the same applies, and which gauge-face do you choose?

It seems to me that the existing plug track dimensions are working fine, and I'm not clear what you are trying to gain by changing them?

The one which is causing me some grief at present is a loose-jaw option for the slab & bracket chairs. I'm confident I can get there in the end.

cheers,

Martin.

 

[Martin Wynne]

scan for use on Western Thunder.

GWR / BR(W) plain track chairs. Paddington R.3798A drawing -- Nov. 1948, amended 1958.

GWR / BR(W) 2-bolt versions of REA chairs on the left (for use with BS-95R rail.)

GWR chairs on the right (for use with GWR 00 rail).

Click twice for hi-res scan:

Martin.