- West of the Severn UK
@AndyBI had a similar thought. Why not just put circular holes in the sleepers to accept a cylindrical pip on the bottom of the chair and let the rail align the direction of the chair?
I'm pretty sure Martin will have considered this and abandoned it for several good reasons
(Crossing chairs would probably need two pips)
I've been asked this several times, but no-one has explained what benefit accrues by discarding information which Templot already knows (the angle of the chair on the timber) and leaving it to be determined by the rail? And if you then say two pips that argument is destroyed anyway.
The intention is that the plug chairs are a firm press fit in the sockets, in most cases not requiring any adhesive, and setting the gauge in the process. Once pressed home it wouldn't be possible for the rail to rotate the chair into alignment. So with a cylindrical plug you would be relying on the chair being aligned by means of the ungauged loose rail before pressing it home. The chances of getting some misaligned chairs strikes me as very high.
Having a rectangular plug makes it much easier to adjust the tolerances for a good press fit. In comparison two cylindrical plugs would be very difficult to tolerance.
As far as I can see the only advantage to a cylindrical plug is that you could drill the holes in home-made timbers. But because they also set the gauge, it would be necessary to do the drilling on a CNC miller or jig borer for sufficient accuracy.
The edge of the chair base is very thin and fragile, so adding a rectangular plug provides support as close the the edge as possible.
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