Tuesday, 18 June 2013

Things get interestinger

Apart from optional extras such as the rear mudguard and a few other minor parts, I only need to make the driving gear to complete the bike. I've been looking forward to this bit for ages, most of the hard stuff is behind me and the bulk of the remainder is straightforward machining, I even have most of the steel I need. The only parts I'm still trying to work out how to make are the levers. Being hollow, elliptical, tapered and bent, they present an interesting challenge to make strong enough and yet still reasonably light. They will be the last parts to get made, I may as well finish on a high. But all in due course.

First I'm going to make the cranks and planet gear assembly. These parts are the heart of this wonderful little machine. I've had a good long think about this assembly over recent months and I've planned the order of machining so that that everything fits properly, the gears line up, are correctly spaced and both sides are equidistant from the centre line. This isn't trivial as I'll try to illustrate over the next few weeks.

One of the things I still need to determine is how I'm going to attach my cranks to the live axle. This is another case where every example I have seen has used a different method. The original I am copying has both cranks screwed to the live axle and then locked in position with taper pins. Others I have seen use Renouf's patent wedge, modern cotter pins and taper pins with a split axle. I need to investigate taper pins to see if I can get hold of a suitable reamer. Taper pins were extensively used to secure collars and pulleys to shafts back in the day, properly made and installed, they do not come free. More later.

The first part is to make the adjustable bearing cones for the live axle and the planet gear.

When I measured and photographed the original bike I didn't realise that these are interchangeable and I diligently measured each one separately. These will be made from 4140 chromoly and nitrided as with all the other bearing surfaces. As usual here is a pictorial list of the various machining processes to make them.

First drill and bore the hole to the tapping size for 5/8" cycle thread.

Then tap the bore. My father gave me a full set of cycle thread taps and dies some years ago. 
It's his fault that I've ended up like this.

Machine the bearing surface at 45 degrees to start with...

...before using a form tool to complete the shape.
Polish and part off. Repeat.

Then make a small threaded arbor for the next job. 
I used a collet chuck for this so I could ensure easy concentricity when taken off and remounted on the dividing head.
 I only have two collets, I wish I had a full imperial set, they are jolly useful.

Using the same highly contrived setup as before  when machining the locking slots.

In other news, work on my lovely wife's deck is progressing. I've called in a few favours this weekend to get the post holes dug. I simply can't do hard manual digging any more, my back lets me know very firmly that it is not happy and it wants me to stop. Unfortunately the rain has been persisting down again and work has had to stop. We got 11 out of the 15 holes dug, these are now full of water and dangerously hidden. The deluge has caused a lot of damage locally and nationally and one landslip proved fatal when it destroyed a house. My lovely wife failed to get to work as the flood has removed a necessary bridge and I've restricted myself to riding the motorbike in daylight hours as many roads are flooded and unlit. We are due for an Antarctic blast later this week. If it snows and I can't get to work I'll be forced to work from home <cough> shed </cough>.

Also, Tweed Pete's new saddle is coming along, I've worked out a quicker method of making the laminated wooden block. Pete has lots of useful contacts and I recently had a riveting conversation with him. I've run out of genuine Brooks rivets so I needed a local supply. I gave Pete the important dimensions and asked him to see what he could do.

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.