Saturday, December 05, 2015

The Dark Art Of Solid Tyre Mounting- Part 2

The late 19th Century jig used to wire tires on with.
Earlier in the week I mentioned that the shop where I work at had a job to do that required some really old knowledge. The job involved two old wheel chair wheels that needed new rubber wired on to their rims. These rims were simple "U" shaped hoops of sheet steel that had no mechanical connection to the tire, like our current day "clincher" wheels do. These also weren't "tubular" tire rims either, where a pneumatic tire is glued to a rim.

The way these treads were held on the rims was by a wire which runs through the center of the rubber tread. The "tires" are really "hoses" with really thick walls, or you can also say that they are solid rubber "ropes" with a hole molded in the center running the length of the "rope" which a wire is strung through. Either way you want to describe this, it is not a circular tire. Nope. These are coiled rubber lengths of a certain diameter that are cut to a specific length, then strung with wire. The wire holds the section of rubber to the specified rim.

The length that you need for a specific rim is done by a formula which requires a certain amount of rubber "rope" be added to the overall rim circumference. (It's not too complicated to figure out, by the way.) If this is done correctly, the tread, or "rope" of rubber actually will overlap itself by about three inches or so when you string it around the rim. The wire extends out from the ends of the tread a significant amount more. Now, I will attempt to give you all an overview of how this is done.

There is a lot going on here! Read below! 

Okay, I have this image which shows a lot of things. I want to break it down and walk you- the reader- through all of what is going on here. I'll start out with the objects shown in the upper, center part of this image. Let's dive in!
  •  Coiled Rubber: In the upper center part of the image you see the coiled rubber "tread" and by looking carefully you will note the silver colored steel wire sticking out of each end of the tread. This wire runs the length of the tread. 
  • Bundle Of Wire: Next to the tread, in the upper right hand side on a white piece of paper, you can see a bundle of wire. That is actually silver soldering wire which I used to braze the wire in the tread together. The jar is the special flux I used for brazing. You'll see what I mean later........
  •  No. 500 Tire Setter: Here you can see in the center of the image the jig shown up above. I affixed it directly to the work bench with two dry wall screws and a "C" clamp. 
  • Wheel and Tread: In the lower part of the image you see the gold colored wheel chair rim, spokes, hand rail, and hub. The tread is laced around the rim, and the central wire can be seen here as it was affixed to the jig and drawn tightly up by the hand crank and worm gear arrangement. The tread is held apart here by a cast metal jig, which the wires are running over the top of here. The tension on the wires will be held when I cut the excess ends off by two needle nosed "Vice Grip" adjustable jaw pliers. All will be explained below. 
Remember I said that the tread overlapped the circumference of rim by a specified amount? Well, when the wires are threaded into the jig, those blocks on the worm gear are close together at the center of the jig. The hand crank is turned clockwise which then starts the blocks on their outward journey on the worm gear. This pulls the wire which in turn begins to draw up the rubber to the rim. Once the tread settles into the "U" shaped channel of the rim, enough tension is applied that the ends of the tread are butting right up against the jig which the wires are running over. When do you know when to stop cranking? Well, that was a guess on my part, but it seemed reasonable to stop at the point where the tread was deforming against the jig block.

A close up look at the jig block, wires, and how my pliers were positioned to hold the tension of the wires once cut. 

A look with wires cut, aligned alongside each other, and fluxed in preparation for brazing. 

Again, I will walk you through what you see in the image above which was taken just before I brazed the wire ends together.
  • Jig Block: This was my first attempt at this ever, and I wasn't 100% pleased with how the jig shifted after I cut the wires which exposed a bit of the tire in the center. I made a slight change when I did the second wheel which worked perfectly. 
  • Wire Prep: The exposed length of wire was clipped, which then allowed me to move the wheel away from the tire setter jig. The tension cranked into the wire was being maintained at this point by the two carefully positioned Vice Grip pliers. Then I had to get into that tight space the block jig created between the tread ends and maneuver those wire ends alongside each other close enough that the silver solder would adhere and bind them together. Once that was done, a paste of flux was applied with a small bush. A piece of tin bent over the rim to protect it from heat is also seen above. 
  • Brazing: I used to be a bench jeweler for 10 years and I have done a lot of soldering and brazing work. It had been some years since I had handled a torch, but I managed and this was done using a frame brazing torch fueled by oxygen and acetylene. 
Like I said, it had been awhile since I had operated a torch and I went straight into this with zero practice, so I was taking a risk, but relying on my years of experience. The torch was a bigger one than I was used to and it hadn't been in regular use either. All in all, looking back on the first attempt, I was so lucky it worked out. The flame was too hot, for starters, and how I didn't atomize the whole deal into a gaseous cloud, I don't know. I was a bit taken back by the heat the flame I had generated. The thing was, due to the tip being contaminated/dirty/underused, I couldn't dial it down at first. Well, anyway, it brazed up like a champ, amazingly, and that one was done. The second wheel was much smoother due to the torch having been cleared out and I was able to set it much cooler on that pass so everything went with much more control and a lot less luck!

Finished product.
Once the thing had been cooled down by spraying down the block jig and brazing area with water, I could remove the tin heat shield, jig, and Vice Grip pliers. This takes the tension off the tread, and since the tread wants to creep in toward the center to release that energy that was put into it by the setting jig, the tread butts up against its ends and that's that. You have a rideable wheel.

The process itself isn't too complex, but there are, as in anything you do, nuances and tricks which you don't see, or have described in an article or from a YouTube video. Like I said above, I changed a couple of things on the second wheel attempt and it went a lot smoother than the first one did. I wasn't 100% stoked on how it was afterward, but for a first attempt at a 120 year old process, I was pretty pleased overall. It worked! We got the job done.

Besides the little tricks and processes, there are two major things here without which I would never have been able to accomplish this job. The first and foremost was having the setting jig. The other was having the skill of brazing that I have learned from my years as a jeweler. I was reminded how things like torches kind of freak some people out when my coworker was acting skittish around the torch and jumped when I popped the torch a couple of times at first because I was having an issue with the touchy acetylene valve. I know I get freaked out sometimes by things folks do with regularity and I am not familiar with how what they are doing works. So, I suppose it shouldn't surprise me that a few of the guys hanging around the shop were awed by what I had done. That said, I couldn't have done it without that decade of experience around a torch and without that jig. Then there were the internet videos and articles I found explaining the process. Those were the missing links I needed to understand it all.

Well, I am glad we got that job done. Am I going to be doing this again? Who knows? But if so, I will have some invaluable experience to draw upon. I was glad to have had the chance to set my hand to this task.


Chris K said...

Nicely done & well written up. A lot of things that had to work right to get the job done.

Wally said...

Very cool. I was hoping you would post the how to on this job. Thanks!

john said...

Nice post - I had no idea

50voltphantom said...

Great post. Very interesting read.

Unknown said...

Wow! Very cool. I'd not really given any thought to how one replaces one of those "solid" pennyfarthing tires. Who knew that it was a trick tubeless setup?