Monday, 28 May 2012


After the successful experiments of last shedweek, I can now do something about the current invertebrate nature of my geared facile. Time to make the backbone.

I'd been recommended to go and see Ron at Sherlock Rings & Flanges about bending my chromoly tubing for me. After explaining what I wanted and providing a drawing of the exact radius I required I left the tubes with him, he told me to come back the next day. Now, carrying a length of 1 3/8" tubing around on a motorbike is not easiest thing in the world and everyday I ride the motorbike to work is a day I don't cycle. I was a little sceptical about the promised time frame but I took the motorbike again the next day and turned up as requested. Well Ron was a man of his word and had already bent the tubing to my exact measurements. I think the project had tickled his fancy a little, we have several acquaintances in common and chatted for ages before I had to leave. If you ever need tube accurately bending, I recommend that you go and see Ron. As it turns out I asked Ron to bend the 7/8" tubing for the rear forks at the same time.

Bent round tubing before rolling.

My elliptical rolling mill needs to be bolted down the the deck and with the dark evenings now, I had to wait until the weekend to use it. The rear forks got rolled first, everything went smoothly and by cutting the tube in the middle of the bend I can produce both fork legs.

The elliptical fork legs, over length at this stage.

Next came the backbone, and time to see if my calculations are correct. I'd had the tube bent to an inner radius of 475mm (18.7"). This radius is too tight to follow the 40" front wheel, I'm expecting it to open out to a radius of 20.75" when I roll it to the correct elliptical profile.

Rolling the backbone elliptical.

Conforming to the rollers.

The much larger tube, actually the largest I have rolled, was physically very hard to manipulate. The process went well and the final shape is spot on, an accurate ellipse and the radius is perfect. Mathematics is your friend.

The next job is to trim the straight part of the backbone to the correct length so I can taper it. I've created a little jig that sits the wheels at the correct wheel base, I can then offer the backbone up and jiggle around with angles and clearances etc.

The front forks have just been rotated out of the way to allow clearance for the too long backbone.

The taper on the backbone is quite slight compared to a penny farthing, the final dimension being 1 1/8" at the rear fork crown.

Once again a little calculation on how much of a sliver
 to remove and then get busy with the hacksaw. 

Where the backbone meets the rear fork crown, the tube has to be round.

This shape has to be corrected from the elliptical shape 
before it is welded, after welding the 4130 is too hard. 

The tube went into Christchurch on the motorbike to get welded up and as before I took it to Pete who again did a first class job on Tigging it up.

This weld bead still needs to be dressed off a little.

I confess to have a minor concern about durability of these split and welded 4130 tubes, I'm unsure if the welds will crack with flexing. Time will tell I suppose.

My next shedweek will be spent making the rear fork crown from a billet of hot rolled 1045 steel.

In other news, my lovely wife has purchased a new pair of winter boots. This time I accompanied her so she had no need to hide them in the wardrobe. She was going to buy a ghastly pair until I suggested an alternative at twice the price, immediately earning myself bonus family credits. Family credits are hard won and I'll need to think carefully about how and when to cash them in.

In more other news we've had a nasty little flurry of aftershocks this weekend, starting with a magnitude 5.2 on Friday afternoon that almost had me clearing my nether throat [1]. After getting shaken out of bed twice last night by the house getting all jiggy with it, I gave up and read a book instead of trying to sleep.

Also, I've munted my back again. I have a long term disc injury and it's bloody well popped again. I wasn't even doing anything heroic at the time, merely emptying the washing machine. Based upon previous experience, My family have now got between two weeks and two years of extra grumpiness ahead. Ironic really when you consider what I've been making this week.

[1] apologies to Sir Walter Raleigh c/o Mark Twain

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