Sunday, 10 October 2010

I could have made a simple tag from 1" x 1/8" and a knurled thumb wheel, and just used those to locate the seat base on the motorcycle, but I'd decided I wanted something a little more "factory". It's taken me a while to get around to it, and you might be wondering what the big deal is, after all, how hard can it be to mount a seat? Well, if you've decided you want a concealed, cable operated, spring loaded catch and can't find a suitable ready made one, then quite hard enough would seem to be the answer.

The first problem was finding a spring, but since this is a perennial problem (in the past, I've ended up winding my own...) I bought a box of assorted compression springs from Screw-Fix for a shade under £9. These ones in fact. While rummaging around would undoubtedly turn up a suitable spring in the workshop, one piece of revealed wisdom that I am privy too is that in the course of this sort of exercise, the spring will inevitably go flying off. The question is whether you manage to find it exactly the same number of times it does this,  or one less. Since most of the other components will tend to be sized to suit the spring, losing it, is a bit of a disaster. Unless you have a box full of them.

This is what I made. It's basically a couple of pieces of bent sheet steel and some 8mm square section steel. It all looks simple enough, until you start thinking about how to bend the steel to make the section in which the "bolt" runs back and forth and the spring is housed. The simpler piece was easy enough to bend as I have a box and pan folder, a crush folder, and a vice and a largish hammer, any or all of which would suffice to manufacture the easy bit. Making the other part by bending it, when there are four bends that are 8mm apart, would have been something of a challenge. Luckily, while I may get a little carried away in the design complexity department on a fairly regular basis, I'm not overly fond of making hard work for myself, so instead of jury rigging some sort of arrangement to bend the required section, I cut a couple of squares of 1/4" plate and welded on a length of the square section steel to one side of one of those, and a short length of 25mm bar to the other side of it, and a further two pieces of the 8mm square section, spaced apart by 8mm plus two thicknesses of the sheet steel I was using to make the catch body. As well as the folders, I have a fly press, and pressing the section out was going to be a lot easier.

In the first picture you may notice that the "tongue" of the catch has a rather pleasing chamfer to it. Sadly, I managed to snap a drill off in that one, so the tongue in this picture is another one that I decided to drill for the cable nipple and thread for the stop before I got Trevor to file another pleasing chamfer. The components are (from the top left, going clockwise) the easy bit of the catch body, the bit of the catch body I made the press tool for after it had been drilled for the BA bolts that hold the catch together and the slot for the travel limiting slot filed out, the spring, the new tongue drilled for a cable nipple and the M4 stop screw, the stop screw itself with the silly little spacer that keeps it from tightening up onto the catch body, and the four BA screws and nuts that hold the whole thing together. The spacer under the stop screw was cut from a piece of 6mm OD 1mm wall aluminium tube that I bought from B&Q (think Home Depot if you're American) to make some grilles for the side panels on my GS550 chopper, which look a lot better than they sound. Cutting 2mm off of the end of a piece of flimsy aluminium tube was quite an interesting experience...

With all of the fiddly bits made and working properly, I marked and drilled the seat hump to accept the catch. I used pop rivets to locate it because I didn't want the fasteners to protrude any further from the mounting face than they absolutely had too, and frankly, I was getting a bit pissed off with all the fiddling around and wasn't really in the mood to make some dies to press countersink dimples into everything. Once I'd filed a square hole in the seat hump and the catch was riveted in place and working correctly, I marked the seat base and drilled some 1/8" holes in that which were definitely in the vicinity of the tongue of the catch. Once I had a hole and could see where the tongue of the catch was than it was simple a matter of finessing the hole in the right direction until it was both square and aligned with the tongue of the catch.

That still leaves me needing to make a cable, a handle to operate the cable, some sort of locating arrangement for the front of the seat base, and file (or get Trevor to file) a chamfer on the tongue of the catch, but since it all works after as fashion already, I don't see that as a huge problem.

Though, I may need an extension spring for the release handle.....

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