7/8" Scale Dinorwic Stub Point Chairs 1 in 8

A set of chairs for a Dinorwic Quarry stub or Fothergill turnout in 7/8" scale (1:13.7), also known as SE or 7/8n2 scale.

These chairs are intended to fit Cliff Barker code 250 bullhead rail for Gauge 3, being the nearest match I have found for Dinorwic Quarry 42 lb double head rail. They will not fit any other rail section.

This set contains 32 chairs of 11 different types (only 31 are needed), and they are laid out on the sprue in the correct sequence, to make it easier to work out which chair goes where. Some chairs are intended to sit on brass strip or sheet, of either 0.005" / 0.12 mm thickness or 1/32" / 0.8 mm thickness, and are correspondingly thinner below the rail foot, so that the tops of the sleepers can all be at the same height.

Fixed chairs have 3 mm diameter spigots to locate into the sleeper directly below the rail centres. Cliff Barker code 250 bullhead rail is 2.94 mm wide, meaning that sleepers should be drilled at 47.94 mm centres. In practice, 48 mm is fine. Block chairs have spigots under both rails (I recommend only one is used and the other is cut off), but check rail chairs do not have a spigot under the check rail. Slide and drive chairs have 1.5 mm diameter sprues which should be removed, and the crossing pivot chair has a 3.3 mm diameter pivot.

Block chairs give a clear gap between rail ends of about 3.6 mm. Check rail chairs give a flange gap of 3 mm.

Moving chairs are mounted in a number of different ways:

• Switch slide chairs are intended to sit on individual pads of 0.005" or 0.12 mm brass, somewhat longer and wider than the chair, to represent thin sheet steel. In the prototype, it seems that spigots were secured to the steel sheet and these stuck up through holes in the chairs. In this 3D print, dummy pins are modelled through the chair holes, and chairs can be glued to the brass pads, but there are also concentric indentations on the underside if you want to drill out the dummy pins and use real pins of about 1.2 mm or 3/64" diameter, at 10.6 mm centres.
• Both switch end chairs are intended to be mounted on 1/32" or 0.8 mm brass strip, which acts as a stretcher, transmitting the movement from the drive chair to the opposite switch rail. The point rod attaches to the drive chair with a clevis pinned through the top of the drive block, which has a nominal 1.2 mm diameter hole for the clevis pin, suitable for a 3/64" rivet (the hole will need to be opened out with a drill bit held in the fingers). Unlike the prototype, this hole continues into the bottom half of the block to give additional support. The opposite end of the drive chair has a dummy pin and indentation on the underside, the same as the switch slide chairs. Two chairs are included for the other switch rail: a second drive chair, and something similar to the switch slide chair, but with a thinner base to accommodate the thicker brass strip. Both have dummy pins and indentations (the drive chair has one and the slide chair has two). Photographs and remains of points within the quarry show both types of chair being used.
  Although the switch end chairs can be glued to the brass stretcher, it is better to use 1.2 mm or 3/64" diameter brass pins soldered through the stretcher, and to drill out the chair dummy pins.
• The entire moving crossing is mounted on a 1/32" or 0.8 mm thick piece of brass which is secured to the sleepers at either end of the crossing. The end chairs slide on this plate, and the pivot chair pivots in a hole in the plate. The drive chair has the same drive block and clevis arrangement as the switch drive chair, but neither this nor the slide chair have any pins or indentations.
• The crossing pivot chair has a 3.3 mm diameter boss as a pivot, which fits tightly inside 5/32" x 0.014" brass tube, to provide a more robust bearing surface.

Measurement of several surviving stub points in Dinorwic Quarry and comparison with old photographs show that crossing rails were 4' long and closure rails were 12' long. Closure rails were generally straight. Switch rails appear to be 7'6" long, but there is a set of points within the Gilfach Ddu museum that has switch rails about 4' long. Clearly, unless you are building a Y-point, one stock or switch rail (or both) will need to be a little shorter than the other. In my own point, I have used 12' for both stock rails, but made one switch rail 7'4", which seems to work well. I very strongly recommend you draw the point out full size before cutting rails to length.

12' stock rails produce an angle of 1 in 8, and this print is for a point where the diverging line continues straight beyond the crossing. If you want the diverging line to continue diverging beyond the crossing then I also offer a set of chairs with a 1 in 6 block chair immediately beyond the crossing.

If you are using a pivoted beam to drive the crossing (as shown in the photographs) note that although all four 1 in 8 chairs are identical, the switch rail ends need to travel further than the crossing rail end, because of the change in angle at the switch ends. The crossing drive beam pivot should therefore be on the crossing side of the mid-point. I recommend that you draw the turnout full size on paper before trying to build it.

Most points appear to have had check rails, on one or both stock rails opposite the crossing (one account says these were only for important routes, presumably ones used by locomotives). Even where a check rail wasn't fitted, some (but not all) points had check rail chairs. This print includes four check rail chairs. If you want to fit plain chairs, then these are available separately in sets of 18. If you omit a check rail but still use check rail chairs, you should cut out the keys, of course. Check rail chairs should be oriented so the keys are driven towards the rail ends.

Sleepers appear to be mostly 12" wide, but 9" or 10" wide sleepers appear to have been used where the extra width was not needed.

The chairs needed at each sleeper are as follows (numbers refer to the sleeper):
1: heel chair - heel chair (the rail joint is in the middle of the chair, and there is no fishplate)
2: switch slide chair - switch slide chair, both on thin sheet pads
3: switch slide chair - switch slide chair, both on thin sheet pads
4 (on sliding stretcher plate): switch drive chair - switch drive chair or switch end slide chair
4 (directly on the sleeper): 1 in 8 block chair - 1 in 8 block chair
5: plain chair - plain chair - plain chair - plain chair
6: plain chair - plain chair - plain chair - plain chair (this should be a long sleeper for mounting the crossing drive beam pivot)
7: plain chair - plain chair - plain chair - plain chair
8 (directly on the sleeper): check rail chair - 1 in 8 block chair - check rail chair
8 (on a plate spanning between sleeper 8 and sleeper 9): crossing drive chair
Mid-way between 8 and 9: pivot chair
9 (on plate): crossing slide chair
9 (directly on the sleeper): check rail chair - 1 in 8 block chair - check rail chair