Thursday, 27 September 2012


Here is a lesson in quality control.

Some months ago I purchased some tapered 4130 tubing from which to make my handlebars. The tubing was exactly the right gauge and tapered from 0.75" to 0.6" over exactly the same distance as the original handlebars I am copying. In short they were perfect. There was however a drawback, the pair of tubes were in the States and there were only two of them left. Ever.

Tapered 4130 tubes.

I bought them and imported them at a reasonably high cost and this week I started to think about bending them to shape. Now, I have bent 4130 tapered tube before and it is not easy. The last time I did it I used a special alloy that melts in hot water and filled the tubes before bending them, It was still not easy. The alloy is known as Woods metal in the UK and as Cerrobend in the States. It is also horrible stuff, containing cadmium amongst other things. I have a small amount and I dislike using it. So I decided to outsource the bending to a professional tube bending shop. I made an accurate drawing of the bend I required and took the tubes around for a discussion. I spent considerable time explaining what I wanted and why I thought it would be a difficult bend, the tapered aspect making it an order of magnitude harder. The professional airily dismissed my concerns and said he would ring me when they were ready.

I later received a timid phone call, suggesting that I might like to call in.

A professionally bent tube, yesterday.

So the lesson here is that when you outsource something you instantly loose all control over quality.

I'm not sure how to proceed here, I can get thinner gauge tapered tube of a similar taper but I don't think it will be strong enough as a handlebar, I need to have a think about this. When I'm a little calmer.

Whatever I decide to do, I'll be doing it myself.

Wednesday, 19 September 2012

Salami Warning

As suggested last week, I've spent my shedweek machining the lever pivot castings or ankles as Mr. Middleton would probably refer to them. Recall that these are cast from p20 and then annealed to make machining easier. Actually, they machined quite well with carbide, but drilling with HSS is out of the question.

The first job is to machine the bore straight through the casting. I used a Keats angle bracket/plate. This mounts to the faceplate and is very useful when boring holes in round objects that can't otherwise be easily held. It's the perfect tool for these castings. When the casting is flipped around in the bracket, the bore will still be concentric, which means that both bearing surfaces can be easily machined into either end.

The Keats Angle Bracket - perfect for this job.

Both bearing races can be machined concentrically.

Testing that my formula works

The fork ends were not quite round after the cut and shut welding technique used to produce the tapered tube. To remedy this, I made a split clamping die with the appropriate tapered bore. Clamping this around the ends of the fork legs has cold set the first half inch of the tips to be perfectly round with the correct taper.

The split clamping die

Squeezing the fork ends to a the correct round taper took considerable force.
I used a long lever to tighten the vice.

Remount in the 4 jaw and centre.

Machine a plain bore the same ID as the through bore and 
then machine the tapered socket to match the fork ends.

Then drill and thread the holes for the oilers and then drill the holes with the unknown use. These holes are a bit of a mystery, they are either for lamp brackets or foot rests. Some bikes have them and some don't, it's also not an early versus late model thing either as I've seen early and late versions both with and without them. The versions without use simpler, symmetrical castings. I have woodcuts of faciles with twin lamps down in this location, one per leg. Also note the photo at the top of this page, it has footrests, although not sprouting from this location. The example I am copying has the holes and a lamp bracket on the head. As I said, a bit of a puzzle. Does anybody know the answer?

The castings are now more hole than casting, the weight for the pair before machining being 1lb 3/4oz (~ 0.475 kg). They are now a Svelte 7oz (~ 0.2 kg)

Finally, clean up some of the casting seams and roughness from the outside. They are now ready to be nitrided before brazing on, although I do need to make a suitable jig to hold everything square whilst I apply the heat.

In other news, on Sunday we all went for a bike ride, the route selected being the Tuhaitara track between Woodend Beach and Waikuku Beach with a detour to the cafe at Pegasus for a coffee. As usual my daughter was on the tandem with me.

Whilst at Waikuku playpark, somebody decided to test the tsunami warning system. Which is right next to the playpark. And very loud.

Instead of sirens, the system uses large speakers. The following text is followed by a series of unpleasant, raucous squawks.

This is a tsunami siren test.
This is a tsunami siren test.
It is only a test.
Do not be alarmed.

Repeat until deaf.

Actually, it was good to hear. There was some talk when the system was built that it wouldn't be loud enough. I beg to differ. My daughter then spent the tandem ride home happily chattering about the new Salami Warning System.

Also this week my lovely wife and I celebrate a significant wedding anniversary. Which reminds me

What's the longest sentence in the world?

"I do"

It's a good job that she doesn't read this nonsense.

Wednesday, 12 September 2012

Very Hot Glue Gun.

Including the 20 ball bearings, there are 33 distinct components that comprise the backbone assembly. Coincidentally, there are also 33 vertebrae in your own backbone, some of which are fused together. This shedweek I've been fusing some of my backbone pieces together. Except I used silver solder and oxy-acetylene rather than icky gooey stuff.

Here is the sequence of steps I used to stick the bits together.

Cleanliness is definitely next to Godliness when brazing joints together, all surfaces that are to be brazed need to be freshly cleaned and degreased before assembly. I tend to give the surfaces a good rub with some emery cloth and then a wipe down with a rag soaked in a suitable solvent. I used mineral turps. In my case this includes the inside of the tubes which are somewhat tricky to see into but it pays to be thorough. You need to get back to clean, fresh, shiny steel, no paint, rust or other coatings.

Shite and Briny, ready for brazing.

Then liberally apply a suitable flux for the type of braze you are using, I'm using 40% silver and I used a flux for Easy-flo No. 2 even though the solder wasn't Easy-flo. I don't know if Easy-flo is still widely available, I certainly can't get it here in NZ, I'm pretty certain that it contained cadmium and was discontinued. I would recommend staying away from solders containing cadmium. It's really not good for you. My flux came as an innocuous pot of white powder, mix this with water into a thick paste, making as much as you will use. I then just steal one of my children's paint brushes and daub the stubs and inside of the tubes and assemble.

I am going to braze the backbone into two main assemblies, the bottom half and the top half and then join the two, I'll explain why later.

I made a simple jig to hold the fork legs, rear fork crown
and fork ends in place, this is the bottom assembly.

The brazing process works by capillary action, as the joint is heated up to the melting point of the filler rod, it will suck the molten filler into the gap, A reasonably snug fit is required for this to happen, but even so, the braze can only creep so far. On the joints that have deep stubs, such as the neck/backbone, I have drilled some small (1.5mm) holes in the middle of the joint. These holes will allow me to introduce the braze farther into the joint and ensure that the joint is fully penetrated. The holes are then filled afterwards.

Silver solder melts at a much lower temperature than brass or bronze, this is important when you are joining alloy steels like chromoly that are damaged if you over cook them. When I applied the heat, I tried to keep the heat off the tube as much as possible and heated the fork end or crown instead, the tube being heated by conduction. You'll know when the joint is at temperature because the rod will just melt and flow right into the joint, if it is a large joint you can feed a whole rod in very quickly. It can be helpful to dip the end of the rod into the pot of flux. When you get near to the end of the rod and your fingers start to get hot, it is possibly to stick the remnant to the end of the new rod and carry on. With the price of silver solder only going one way, this is a skill well worth acquiring fairly early on.

I don't tend to use goggles when silver soldering since the tubes never actually get red hot only a dull red. If they are bright red then you've over cooked them, I find it easier to see this without dark goggles. It is important to keep the torch moving to prevent overheating one spot, it's a little like rubbing your tummy and patting your head at the same time. Brazing isn't rocket science but it does need practise.

The neck/backbone joint is a big one and even though I had removed all that material from inside the casting it is still a big chunk of steel to warm up. I mounted this in the vice and just waved the torch until I had the whole joint warm but not too hot and then I could focus on one part at a time to get the braze to fully penetrate, the four little holes were invaluable to get the braze right to the end of the casting.

The top assembly, the tube was left too long deliberately to
make the brazing process easier.

With the two assemblies now complete, I put the rear wheel in place and assembled the backbone into the head. Using line of sight I could then rotate the rear fork crown until I had the two wheels perfectly aligned. Mark this and drill a small hole right through the crown and the backbone. A suitable pin (a nail) is then tapped in to hold the two assemblies in the correct orientation relative to each other. This is the final joint to braze.

Pinned, Fluxed and ready for the heat...

Note how the silver solder has flowed out of the pinned hole
indicating very good penetration of the joint.
The fork legs didn't come undone as the heat didn't have time to
conduct down the legs and the remelt temperature is a little higher anyway.

Then when everything is cool, it is simply a matter of cleaning up all the joints with files and emery cloth.

 The original neck...

... and my facsimile.

 Note how the neck contours nicely against the 
shoulder of the fork as per the original patent.

Top view. Note the filled holes along the joint, there are two visible here.

The step minus the top of the screw and the fork ends.

I can now trundle the machine around the garden and I'm pleased to report that it seems to handle like a bicycle. That may sound obvious but it means I've got the trail about right and it should have decent road manners when complete.

I had set myself a goal of having the bike sat on it's wheels inside of a year from when I started. Well, it's taken me 13 1/2 months including the 6 week museum leave, so I'm not going to complain and anyway I have no deadline since I'm only building it for myself. I don't like deadlines, apparently I get extra grumpy according to my lovely wife.

I need to have a little think about what to work on next, probably machining the lever pivot castings. Decisions, decisions.

In other news, we've had a lot of wind lately. Where I live they make a special variety of wind known locally as the Nor'Wester. It is a Foehn wind and is hot and strong, so strong that you often have to pedal downhill when riding into one. One of my favourite routes goes from my house up to Whiterock and back, it is a dead end road (unless on an MTB) and is slightly uphill all the way, it also heads off in a general N/W direction. At the weekend we had almost no wind at the house and a howling Nor'Wester just 10km up the road. The ride out was 52 minutes of grovelling into the teeth of the gale and then flying home like superman in 36 minutes. Riding uphill at 50kph is a magic feeling...

My children often come into the workshop and "borrow" my hot glue gun. When I explained what I was doing on Saturday morning, my daughter asked if the oxy-acetylene torch was a hot glue gun. Very perceptive of her really since I suppose it is a very hot glue gun.

Wednesday, 5 September 2012

The Step

As I thought, I've not had a big shedweek. Only just enough time to fashion a step from some scrap steel. The scrap steel being the original handlebars off my Honda motorcycle that I commute on. The bike was stored in a garage when we had the earthquake. The bike got thrown around a bit and the bars bent into interesting shapes. I find it rather fitting that this week is the 2 year anniversary of the original magnitude 7.1 that started all this and I've incorporated a piece of the damage into my latest project.

I'm not terribly good at bending steel around and it took me a long time to get something that resembled a step.

 First cut a suitable bent section from the handlebar.

Bend it roughly into shape. A little heat helps here.

Then make a female pattern to hammer the step shape into.

Some careful filing to make it a good fit against the fork leg

File the serrations.

The step is screwed to the fork leg while it is brazed, the screw head will be filed off after brazing.

I've also drilled and tapped the holes for the mudguard mount on the rear fork crown.

I've now completed all the components for the backbone and now just need to make a suitable jig to hold the bits together while I braze it up.

In other news, we had a glorious weekend and I was able to dismantle the old deck in one go. I have a design in my head for the new deck but it's going to be complicated, nothing new there then...

We were treated to an amazing electrical storm last night with almost continual lightning and then later hailstones the size of golf balls. It doesn't happen too often but when it does it is most spectacular.