Saturday, 8 June 2013

The Brake Lever

I was supposed to be working on the new deck for my lovely wife this week. However rain stopped play so I've been forced to take shelter in my shed and inconvenience some bits of steel. Sigh.

As appears to be usual with the surviving examples of these bikes, of those that still have their original brakes, they all differ slightly. This shedweek I've been fabricating the brake lever based upon photos of originals and the tracing of a casting taken from an original.

As with the spoon last week, the lever is made from Bisalloy 80, first job is to mark the plate based upon the outline of the tracing from the casting. The lever is quite  broad, something that I would not necessarily have picked up on from photos alone.

Then chop out the shape and rough file it, also drill the two holes at this point. 

I forgot to mention last time, but when I was drilling the spoon pivot, I didn't clamp the work to the drill table. I just held it with my fingers. Bisalloy 80 is relatively tough to drill and it picked up and spun the blank around. I got some reasonably good cuts from that experience. I didn't repeat it this week.

The next job is to bend the lever to match the handlebar profile. 

I used a round form tool and a G clamp to apply measured pressure until I had the shape I wanted. It required considerable force to bend which is reassuring given it's purpose.

The next bit to fangle is the thumb grip at the end of the lever. Brake levers on bike with T grips are often designed to be operated with the thumb only. This is the case with the geared facile, so I made a little wooden mock up to work out the correct placement for the lever and my right thumb. That's the beauty of bespoking a bike for yourself, you get to make it a very good fit.

Wooden mockup to get the correct placement of the thumb grip.

Then I need to bend a section of bar stock to approximate the 3D shape of the grip. I happened to have a piece of square section that was roughly the right size. This was clamped firmly in the vice and then twisted and pulled with a long length of tube until I could see the lever contained inside it.

Long thick wall pipes are your friend when bending stuff.

Then get busy with the files. First the outer profile...

... and then the inner profile. 
I actually used a carbide burr in an air die grinder to remove the bulk of the material. 
The curve inside the lever made it tricky to file.

Then mount on a suitable jig and take it to Tweed Pete to weld on for me. 

At the same time I asked him to build up a blob of steel for the return spring screw bulge.

Then clean up the lever to grip transition and make the bulge look presentable.
(Gets harder to do this as you get older)

the rear side of the bulge is machined to locate a spring and screw, it's quite elegant really.

Next make the return spring. A good tip if you need to buy a small amount of spring steel is to go to your local hardware shop and harvest a suitably sized paint scraper. You do get a few odd looks when you take a micrometer in and measure the thickness of the steel. This particular one has a tapered blade as an added bonus. Unless you want to go down the anneal, cut, re harden and temper route you need to grind the blade to shape and that includes the hole. I used my Dremel, I love my Dremel. Finally bend around a mandrel by hand to achieve the desired profile and spring rate.

I can recycle the handle for a file.

The screw is made to fit neatly into the recess so that there are no sharp edges 
to catch clothing when bent over, slogging up a steep hill.

In other news, I've received my first commission for a new saddle top. It's in return for all the welding that Pete has been doing for me. He's building a spiffy new 27" double top tube racer and he needs a suitably old fashioned saddle. Foolishly he's given me free rein to do as I please. I'm going for a late 1890's look based on a much more recent Wrights frame. I'll be sure to let you know how it works out. I'm going to do two at the same time as I have a need for a saddle of the same era.

No comments:

Post a Comment