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

Friday, 18 May 2012

Elliptical tube rolling - part 2

I need to make some more elliptical tubing. You may recall my initial success with the front fork legs some months ago. I've now started thinking about how I'm going to make the backbone and rear forks, both of which are elliptical. However, the backbone and the rear forks are bent elliptical tubing which adds a new dimension to the problem. Do I roll the round tubing into it's final elliptical shape and then attempt to bend it or do I do it the other way around and bend the round tubing and then roll it into an ellipse. Well, the answer is obvious when you consider why the tubing is elliptical in the first place, to increase the resistance to bending in the plane of the major axis. So I need to bend the tubing and then roll it to profile. This sounds simple but consider what will happen to the radius of the bend when it is slightly flattened, it will tend to straighten out, but how much?

I've developed a simple mathematical model to predict how the radius will change with increasing eccentricity from round to squashed flat. I'm pretty confident that it will be reasonably accurate for relatively low eccentricity and then become less accurate as more metal distortion takes place at high eccentricity. Theory is all well and good but I also want to test it with a real world example. I want to see if it possible to roll a bent tube without it bending in another plane for example.

I'm going to coin a new word at this point. The word is 'Shedweek'. A shedweek is the amount of time a person can spend happily occupied in a shed during the course of a week before other family members begin to pass unkind comments. Shedweeks are clearly variable in nature. I would strongly suggest experimenting in the lower range before venturing into the more advanced upper reaches.

I've spent my shedweek making some new rollers for my rolling mill, I have one pair for the backbone that roll from 1 3/8" tubing and another pair for the rear forks that roll from 7/8" tubing.

Rear fork blade rollers on the left and backbone rollers on the right.

Let the testing begin.

Start with a bent length of 7/8" bicycle frame, in this case the "loop" from an old ladies loop frame. 
The frame had no merit other than as a donor for some suitable bent tubing.
It died for a good cause.

Then progressively squish the tube in the rollers, in practise I found that 
the bend in the tube just followed the rollers beautifully, it wasn't an issue at all.

Frequently remove the tube, measure the major axis and draw along the radius to measure later. 
This will enable me to see how well my mathematical model behaves at different values of squishedness.

The final shape is a nice even, flat ellipse. 

There is a very slight twist, as before, in the straight section, but I'm not worried about that. 

As it turns out my model was accurate to 98% for the eccentricity I require in the backbone. This means I can calculate the initial bend I need, which works out to an inner radius of 18.7" (475mm). Then when I roll the backbone elliptical, it should straighten out to a final radius of 20.75" (527mm). I'll cut some of my remaining tubing, after Mr. Middleton helped himself, and take it to a company that specialises in rolling large tubes next week.

The rear forks are mostly straight with a sharp bend at the very end, I have a simple tube bender that can cope with this size so I may do this bend myself. 4130 is so tough though that I may reconsider.

In other news, last Sunday was Mothers day here in NZ. This had a seriously negative effect on my shedweek but I'm not about to complain. The children had made various shoddy cards and paintings of the sort that make mothers all misty eyed and emotional, but no presents. We have a rule in our house regarding presents to each other. As a normal man, I don't really do hints or observe subtle suggestions. Instead I ask for a clear, concise, written list of possible presents stuck prominently on the fridge door well in advance. I know that this may possibly remove a certain amount of surprise and romance from these occasions but it also dramatically reduces errors and improves efficiency.

So I took the list and the kids shopping late on Saturday afternoon because I'd forgotten all about it until then. We managed to get all the items including the lingerie which I'm also not going to complain about. These lists always feature marzipan. I should know this by now, but marzipan, real marzipan is hard to get in NZ. It is sometimes available in some supermarkets and I generally stock up when I see it for future list fulfilment purposes. Sadly, this time, my magic cupboard could not help and we had to run around like idiots to find some.

In more other news, I failed to complete a bike ride for the first time in years this week. I was riding home from work and had got to the road works where the new development is being built to the west of Kaiapoi, the one near the cemetery (the dead centre of town). The excellent road workers had left an unmarked, unlit trench across the shoulder. The night was dark and wet with thunder and lightning (very, very frightening) in the distance and I only saw it at the last second. I got the front wheel over it but the back wheel slammed into the far edge and popped the tube and dented the rim. Of course at this point the heavens opened and my wimp glands came up again. My lovely wife came and picked me up after I'd telephoned her on one of these new electric "mobile phone" things. They may catch on you know.

Wednesday, 9 May 2012

Tyres, Teeth & Tuhoe

I've haven't had much time to actually do much this week although I have spent time working out how to make the backbone, more on this later.

The tyres are red, they are not pink darling.

I've had the tyres fitted to my wheels, or more accurately, the tires since I've used the American system rather than the English one. The English system uses a spiral of wire moulded within the rubber. The tyre is cut too short for the rim and and inch or so of the spiral exposed on either end of the length. Then by twisting the rubber the wrong way for the same number of revolutions as coils are exposed on the spiral, the tyre can be joined and the spiral screws into itself and the gap is closed. The loop is then stretched over the rim and is held in place by tension only. This is usually OK for normal use but recent batches from the UK have been a bit crap. This is what can happen when crap rubber is used, the Rider is Jack Castor from California, he was quite seriously injured but is now fully recovered. This happened on an NZ tour a few years ago, Jack was descending from the Otematata saddle between Omarama and Kurow, notice the 'loop' forming in front of the wheel before it all goes pear shaped.

In contrast the American system uses a rubber extrusion with an empty hole through the middle, the rubber is cut too long for the rim and wire fed through the hole. The wire is tensioned on a special machine in such a way that the excess rubber gets bunched up evenly around the wheel whilst leaving a short section of each end exposed. The two ends are trimmed and silver soldered together. When the jig is removed the gap closes up tightly. The rubber used has been sourced directly from the states and is of very high quality, it wears well on our rough roads but is still grippy enough to be safe in the wet.

I painted a couple of pinstripes on the rims before the rubber was mounted. I've been collecting images of original Victorian pinstripes for years now. Every time an original machine gets restored another unique reference point gets lost. But don't get me started on that. It is surprising how gaudy some of the Victorian machines were. We tend to think of the Victorians as very straight laced with stiff upper lips and little skirts around table legs lest the men think unseemly thoughts etc.. Actually, I'm not sure that the table legs thing is true but it's a good story. The point remains though, that to our modern eyes, some of the pinstriping and painted decoration seems way over the top. The double pinstripe on each rim is common, I've seen it on many original machines.

Tax free teeth?

Also this week, I've got the gears back from the gear cutter, he has done a fantastic job and I'm very pleased with the result. I will not say if he waived the GST when I waved cash, that would be rude. They need to be lapped to polish the faces but there is also a lot of machining to be done on both gears anyway. I'll oil these and set them aside for the time being as I focus on the rest of the frame so I can get the bike sitting on it's wheels.

This week I'm going to make some more rollers for my elliptical tube rolling mill, I need to make two sets. One for the elliptical backbone and one for the rear forks. The facile I am copying is a later model and has fully tubular fork blades either side rather than the half open style of earlier machines.

In other news, the family was at a loose end on Saturday so we took a trip on the MV Tuhoe moored at Kaiapoi.
MV Tuhoe.

It was fantastic in that old fashioned, slightly naff way. Sunday's trip coincided with the 'Super Moon' so the tidal river was very high.
Oh, that's super.

I particularly liked the way we were allowed free access to the engine room. If you find yourself at a loose end, I can highly recommend it, just wrap up well if an Easterly is blowing.

The engine room complete with engineer complete with engineer's cap.