Tuesday, 15 January 2013

Saddle Rails

The next part of the saddle to get my attention is the rails, the front to back members that bolt to the neck at the front and the cantle plate at the rear. I cross checked measurements of the original facile saddle with a couple of original Brooks of the period and the wire is 9/32" or very close to 7mm, if you prefer. This is quite a substantial gauge to have to bend by hand, even more so when you consider that the rails are made from spring steel which must be bent cold. Spring steel is hard to shape since it is designed to bend back (obviously), it is tough stuff.

A quick trip around the corner to CMI Springs and I was able to get some straight lengths of 9/32" spring steel wire. They don't normally sell small volumes to the public but I chatted the receptionist up and she caught the boss on a good day. This was just before Christmas and they were all looking forward to the holiday. I bought a few spare lengths at the same time.

Most of the bends are very straightforward, the hard one is the eye loop at the rear of the rail which bolts to the cantle plate. I don't like hitting things, I prefer to use measured force so I made a little jig to assist in the process.

First make a loop in the wire as tight as possible by gripping the end very firmly
 in a large vice and bending back on itself so that it forms a coil. 

This was about the limit of my physical strength and I ended up 
on my arse a few times as the wire slipped in the vice. 

When the basic loop has been formed, the vice can be 
used to decrease the size of the loop and also to flatten it. 

Then carefully cut off the end that has been gripped and 
again squish it in the vice to flatten as much as possible. 

I needed to use various spacers to push the coil too far the other way so that when it sprung back it was flat. Cutting spring steel is also a bit of a mission, hacksaw blades will dull very quickly. An abrasive cut off wheel is probably the best option.

The basic loop can now be squished into the jig...

... and bolted up so that it can't move. 

This is then held in the vice and the return bend completed. 

The jig lends a certain amount of uniformity to the shape of the eye.

With the eyes completed, the remaining bends seemed easy in comparison. The only difficulties were ensuring that both sides remained identical mirrors of each other and that the straight, front section of both rails were parallel to each other. This is where the saddle tensioning hardware slides back and forth.

According to the head guy at CMI, all I need to do now is soak in my oven for an hour at 200 degrees Celsigrade to remove the residual stresses from bending. No other heat treatment is needed. I'll have to be a bit careful about when I do this, I don't particularly want my lovely wife to find out.

I have been slightly surprised by the length of the saddle on this bike, from the front tip of the rails to the back of the cantle plate is 16.5". This is much longer than the usual Brooks B70s found on contemporary penny farthings. The reason becomes clear when you consider the rationale behind the bike, the whole idea being to get the rider lower and further back as a safety feature to help prevent headers. Remember that the bike was in direct competition to Starley's new rear driving safety and of course we know which design became dominant. Over the course of the 6 years that the geared facile was in production, the bikes became less upright and the rider was placed further back. It is very fortunate that the original I am copying is so complete, even down to the saddle leather. Had I not had an original saddle to copy I would have made it to the same dimensions as a conventional Brooks B70 International saddle.

The original saddle from the geared facile.

Next week I'll make the front clamps that bolt the rails to the neck, the ones on a facile being particularly complex (of course).

In other news we've been having more weather this week, we had 38 degrees Celsigrade in my garden on Saturday, it was so hot that we all went down to a local swimming hole at the river and messed around for a couple of hours. The braided rivers in our part of the world are excellent for making dams and other contrived hydraulic civil engineering projects. Much fun can be had diverting the river about. Of course after the next big rain, all our efforts will be washed away as the river shifts again.

It has also been too hot to do much machining, but after seeing Tweed Pete's spotless shed a few days ago, I have forced myself to have a tidy up in mine. I've found all sorts of things that I'd forgotten I had, hidden under several feet of swarf. I may have to do it more regularly.

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