Dinorwic stub points

[MarcD]

Has anyone built any in any scale and if so do they have any tips on building them. Not sure if I'm going to build in O-14 or SM32 yet. It's going to depend on the availability of loco kits.

 

Marc

[pete_mcfarlane]

Have you seen the latest edition of the Narrow Gauge and Industrial Review? There's an article on stub points in there. 

[Jeremy Cumberland]

Hi, yes, in 45 mm gauge. It's dismantled at the moment for painting and landscaping, but I've put some pictures below. All the "castings" are 3D prints that I drew up myself, based on photographs and measurements I took at the quarry a few years ago. I neglected to measure some dimensions though, and I am not entirely sure about some of my guesses.

 

The quarry used more than one type of lever/actuation mechanism, with some points having the lever parallel to the rails and bell cranks going to the stubs and crossing. Also, most points didn't have check rails (at least one had just one, and some had check rail chairs but no check rails in them). It is difficult to see what purpose they serve, but I understand they were an attempt to stop locomotives pushing the crossing rail over. My flangeways are too wide for them to have any effect at all.

 

All the points I measured at Dinorwic were 1 in 8 (as far as I could tell), but I did find what appeared to be a 1 in 6 chair and something I saw (I forget whether it was a point in situ or a photograph) appeared to show the diverging line bending around the crossing, so in my point the chair at the far end of the crossing is 1 in 6, and the diverging stock rail has a kink in it.

 

By my reckoning, the actual rail lengths are 12 feet for the closure rails between the stubs and the crossing, 4 feet for the crossing rail and 7½ feet for the stubs, and this is what I have used, but my stubs are probably too long. 1 in 8 is a little over 7°, which if you are using straight rails through the points (which almost all stub points did, it seems) is a considerable angle to get your rolling stock to go round, in two sharp kinks. My 7½ feet stubs give an angle of 2.2° at the heel end, leaving nigh on 5° at the stub end, and my first attempts at double-flanged slate wagons couldn't get round the angle. I posted about it here:

 

Depending on what you intend building, both in terms of point geometry and wheel profile, this may or may not be a problem for you, but 5 foot stubs would even out the angles better.

 

The biggest single bit of advice I can give is to draw it out full size, using your actual rail head width. The separation you need at the four block chairs is at least as wide as you would allow for flangeways in whichever track standard you are using, remembering that single-flanged wheels are usually expected to make contact with check rails, but here you want to avoid contact (particularly if you are using track power, which I imagine you will be).

 

I don't know if you intend having a prototypical actuating mechanism, but if you are, you should include adjustment in the two "legs" (I have put in more adjustment points than necessary). Remember that nothing on this point self-adjusts; you have to ensure all four points of alignment in both positions yourself (the pivot position for the crossing rail is critical). This in turn may make actuation a problem in a model railway that is intended to be operated (mine is just for display, really, but I do want the point to work properly), and it might make sense to solder stops onto the fixed rails to control the travel of the moving rails. I expect you could also drive both the stubs and the crossing from underneath.

 

Finally, you might have to watch out for rails moving lengthways. In an earlier iteration, the rodding was at a slight angle to the stubs, and tended to pull them out of the joint chair so that the near one hit the stock and closure rails. The three moving rails are only held in position by friction against a single chair. I saw several chairs in the quarry with drilled holes in them, and I suspect that these were for pins to stop stubs and crossing rails from sliding.

 

 

 

 

[Jeremy Cumberland]

You might have come across this 1967 MRC article written by Keith Jaggers and posted on his website:

http://www.jaggers-heritage.com/resources/MRC%201967%20Padarn%20%26%20Penrhyn%20article.pdf

 

The illustrated (prototype) point has a different operating mechansim from mine. It is a shame the stub heels aren't shown, because the point appears to be set for the diverging line and there is almost no angle at the stub toes, so it must all be at the heel, pointing to something like 4 foot stubs, or even shorter (the point appears to be 1 in 8, the same as mine).

 

The proposed model stub point doesn't have any support for the ends of the crossing rail, which I cannot imagine working, but it shows using slide chairs for the stubs. This wasn't prototype practice (I like the way the stubs in the photograph don't have any chairs at all on the nearest  sleeper!) but it might work very well for a model, and if they are made double-ended (two half-chairs from Slaters, if you decide to model in SM32), then they could act as end-stops to limit travel in both positions. Using an ordinary model railway fishplate rather than a chair for the stub heels is probably a good idea too, if you want reliable operation, although I have no idea what movement they will allow, and whether they eventually work loose.

 

The proposed model stub point has a curved diverging rail, and the only working stub points I have ever seen on model railways share this feature, but to my eye this is too drastic a departure from the prototype. However, it would certainly make for more reliable operation. limiting the sudden bend to whatever you have at the stub heels.

[Ref44]

My experience in SM32 using Slaters locos is that 32mm gauge is too wide for the BtB setting if you want to keep the flangway gap at the crossing to near scale I think I closed the gauge to 31.3mm.

[jim.snowdon]

On 16/09/2021 at 18:50, Ref44 said:

My experience in SM32 using Slaters locos is that 32mm gauge is too wide for the BtB setting if you want to keep the flangway gap at the crossing to near scale I think I closed the gauge to 31.3mm.

Following either the 0-SF (31.25mm) or the 0-MF (31.5mm) standards. 32mm gauge is too wide for almost all 0-Fine wheelsets.