Sunday, 13 May 2012

Jiggy wit it

The jig is proving somewhat problematic...

Not being the sort of man to spunk actual cash on the real thing when I can get a reasonably functional facsimile by doing it myself, I am going to build my own jig to hold framey things in place. My first idea was to make something up out of bits of not too heavy structural steel - I already own a MIG welder and so throwing something together should be a doddle. To this end I purchased a length of second hand 80x40mm channel (probably the start of my failure right there as it looked as though it had been salvaged from a beach somewhere, and prior to that had been coated with some form of rust preventative substance that could only have been sourced from a 1980's Italian car factory). Adding to my woes was that the channel web was not very flat at all, in fact 'ribbed for pleasure' was the phrase that came to mind. Certainly good for preventing conception anyway, I should have got wood.

An hour or so on Saturday morning was spent creating this;

As soon as I started marking out the centerlines of the frame and such, it became immediately apparent that this just wasn't going to be good enough, a finger push was enough to twist the frame a few mm out of whack. I could brace everything with more steel but it is already a heavy little bugger. This, coupled with the actual impossibility of getting the bits even roughly flat to each other in the first place due the built in Mariana trench on the steel meant I needed to come up with something better.

Now, I have recently designed a test rig for one of the local tech companies and the basic frame of the rig was made out of stuff called Minitec. Using this can get kind of expensive but it is an extremely flexible way of building framework for things - proper jigs commonly use very similar stuff, although it is usually their own custom profile.

Sod the cost I said to myself, it is clearly the way forward... and in a trice I had come up with this;

Actually I came up with something very similar to that pic, but then I found this, which caused some tweaking to take place. Sincerest form of flattery and all that...

Anyways, tomorrow I will get a quote from the local supplier for the bits that I need, and assuming I need not sell a kidney to pay for it I think this will be the way forward. It certainly simplifies manufacture of the other bits that actually hold the frame, so we shall see.

In other news, these last few weeks I have been pondering using a Gates belt drive with the Alfine when it gets put into the frame. This makes a lot of sense, particularly after a blowout I had a week or so ago, the fixing of which left my hands looking like I had lost a contact lens while inspecting the inside of an oil tanker. This episode eventually resulted in some quite fetching Ramboesque face camo so not all bad really.

There is no need to lubricate the belts on the Gates system so it would be much nicer to handle...but the issue is that the belts cannot be split like a chain, and so you need to have a way of splitting the rear triangle to fit it all in. There are a few ways of doing this but the least invasive is to put a joint in the seat stay like so, and this is probably what I will be doing. I may put this in anyway so I can go down the belt drive path later even if I don't now...

All of this has caused me to rethink the dropouts - for a start you need a pretty robust tensioning method for the belt which isn't that easy to get with the dropouts I ordered, plus it turned out that the angles on these dropouts are a fair way off optimal for my geometry. This could all be dealt with without too much issue, but I thought it would be nice to make up something proper for the task. I am not 100% happy with the design yet but I will first see what the manufacturing cost comes in at with this version that I have had quoted. I can always make them from scratch anyway as they are not too complicated...

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