Switch blade spacing

[arthurbudd]

I'm building my first P4 track using Templot and I've reached the point where
I've got to fix the blades to a turnout operating device. I've decided, for the
sake of simplicity, to use Norman Soloman's method as describerd in MRJ 151.
This uses a 2.5mm wide strip of PCB material with brass lace pins soldered to
the blades. The spacing of the pins is given as 15.5mm for both EM and P4 but
having tried this, it gives a gap between the blade and the stock rail of about
2 mm which, to my untutored eye seems too big.

Many years ago I read an article by Iain Rice where he advocated cut down
"Dinky" hair grips Araldited together to give a joint clamp/gauge for setting
point blades. This device would give a gap of about 1.3 mm which would seem to
be much closer to the prototype gap of about 4 inches.

What do other people use as a blade/stock rail gap in P4?

Regards

Arthur

[Alan Turner]

The gap at the point tip is not inportant. It's the gap further along, which must as a minimum be the flangeway value. The gap at the point tip has to be sufficient to ensure the minimum is achieved.

Looking at GWR practice the gap at the point tips is shown as 4".

Alan

[grovenor-2685]

The standard point opening has been 4.25" for many years so as you say, 2mm is excessive and looks bad, similarly 1mm is not enough and also looks bad. There is no need to worry overly about measuring the flangeway in the heel area of the switch. I have never had any problem with this. We worry about it in the real thing as contact in this area under dense traffic or high speeds put a lot of stress on the point fittings leading to premature failures. Our models don't have this problem.
Keith

[Tim V]

I think Norman got the P4 dimension wrong, I too found it gave problems, I've amended the 15.5 to 16.00 with success.

[arthurbudd]

Many thanks all especially Tim; that's what I wanted to know.

Regards

Arthur

[Bilton Junction]

I used Normon Soloman's technique and did find 15.5mm was slightly too close but splaying the lace pin out slightly still seems to produce a reasonable joint and none have failed so far. I tried using a larger spacing but if it is surely better to have slightly too large a gap than too small, otherwise the flanges strike the switch and cause derailments. An offcut of 1.6mm PCB sleeper serves as a convenient spacer between the switch blade and the rail to hold it near enough the correct gap whilst soldering.
Carl

[martin goodall]

Sorry this comment is a bit late, but I have only just found this thread.

Like others, I have used Norman Solomons stretchers with complete success, following problems caused by using other types of stretcher rod (or tie-bar). So I would fully endorse the recommendation of the Norman Solomons design.

As to the setting of the switch blades, I have always used the set of sprung clips (with in-built spacers) which I bought from Studiolith about 35 years ago (!)

Out of curiosity, I have just been into the railway room to measure the spacings of the switch-blades on those points where I have fitted Norman Solomons units. The distance between the insides of the blades turns out to be 17mm, but I have joggled the stock rails. The joggles (if they were to scale) would be no more than 5-thou, but in practice mine are 20-thou - seriously over-scale, but they do the job they are designed to do. It is difficult to measure the centres at which I drilled the stretcher for the pins, but at a rough guess it would have been between 16mm and 16.5mm. I suppose that if I had relied on a 'set' in the stock rails instead of a joggle, the centres would have been drilled at about 15.5 to 16mm, which seems to be in line with what other people have suggested.

[arthurbudd]

Many thanks to you all for your suggestions. I've done a couple of turnouts now and centred the holes at a gnat's over 16mm which gives me a gap at the blade tip of about 1.4mm

Regards

Arthur