Saturday, 30 October 2010

Not the end, but a place from where you can see the end.

I'd like to announce that the whole on-going seat catch scenario has reached a resolution. Rather amazingly, the resolution it has reached is one of completion as opposed to one of the far more sensible file under "B" for "binned" variety. As you may know, the actual catch part of the equation was made some time ago and seemed to function admirably, and the metal base for the seat has been knocking around for a while too. What was lacking was a means of operating the catch to effect the release of the seat base.

The major part of that problem, at least as far as I was concerned, was the bracket. A few  moments thought should make it clear why. Essentially, the bracket has to attach the number plate to the seat hump, which in itself is a simple enough thing to achieve. The Construction and Use regulations (and the M.O.T) also require that the number plate be illuminated by a white light, and that that light shall not be visible from the rear of the vehicle. So, the bracket has to carry the number plate, and the number plate light, right? Well, yes, but....

The idea, as you may recall was to have a concealed seat release mechanism, with the operating lever concealed behind the number plate. That tends to imply that the bracket would also have to support the operating lever.

It doesn't end there though, as not only does the bracket have to support the lever, it has to provide a cable stop so that the lever has something to operate against, and while it's at it, it has to provide for routing the cable in a fashion that's discrete and doesn't force the cable through any overly tight bends which would impair its operation. On top of which, it would be nice if this masterpiece of design was as near to completely innocuous as possible. Oh, and it has to position all of the a fore mentioned items in a region of space that the rear wheel isn't going to occupy at any point in the proceedings.

If you stop and take stock of all that, it's actually quite a complex design brief, but for a moment let's just consider the operating lever. Clearly it has to operate the seat catch, and it's going to have to do it through the medium of a Bowden cable as do many other things on a motorcycle, what's not stated in the "design brief" is that it's really quite important that the lever doesn't rattle. At the same time, it would be nice if the effort required to operate the lever was such that you knew you were operating a lever without it being a struggle to operate.
This is where the elusive concept of "build quality" slips in. It needs to be pointed out that build quality is not a conspicuous feature of many thoroughly enjoyable, exotic, and (it has to said) Italian cars. So, by the same token, it ought to be perfectly possible to build a motorcycle which was complete rubbish, but, at the same time, fun. Since, almost by definition, that wouldn't involve spending four weeks of your life making a seat release mechanism, it certainly has a lot to recommend it. On the other hand, there is something to be said for the satisfaction of a job well done, or even a ludicrous target set and met. The target I set myself for this particular motorcycle was that it ought to have an air of "factory" about it, more suggestive of low volume production than of a one off built in a shed.
Literally on the other hand though, the more observant will have noticed that the release mechanism is "left handed". This is because, I am.

When I've been prototyping things in the past, I've made left handed prototypes so that I could assess how easy they were to use, and then mirror imaged them for the production version. Strictly speaking, I suppose that means that there never was an actual pre-production prototype, but it seems to have worked out quite well on the whole.

While it's easy enough to sit here and pontificate on the merits of design philosophy and assert that one's seat release mechanism was a success, I suppose we live in an age which is a little more "show me" than that. So in keeping with the spirit of the times, here's a rather gloomy video of it all in action...


Hopefully that should mean that some far more interesting frame related things are next on the agenda.

Sunday, 24 October 2010

Last time, I mentioned that some sort of workshop tidy up was in order. The agenda also turned out to contain some "crashy" FJ1200 forks and another heavy cold. Marvellous.

However, driven by a deep seated guilt at having failed to do anything of note last week, I did batter away at it and make quite a lot of progress on Friday and Saturday. I say quite a lot of progress, but to the casual, or even interested, observer, with it parked in the workshop the motorcycle appears not to have changed very much. That sadly, is the nature of having a concealed seat release mechanism, very few, if any, observers are going to spot it if it's any good. People queueing up next to the motorcycle and exclaiming, "I say, take a look at this chap's cunningly contrived concealed seat release..." tends to indicate that the level of concealment, may leave something to be desired. 

Having cut a couple of pieces of 1" by 1/4" strap steel to make the hooks for the front of the seat base, I drilled a series of holes n the seat hump, which I suppose would be more accurately referred to as the seat base base, but I feel calling it the seat hump, is a little clearer. After I'd drilled the series of pilot holes out to something like six and a half millimetres, I filed the resulting gash it it more nearly resembled a hole. The idea being the the pieces I'd cut that were going to form the hooks for the front of the seat base would be drilled and tapped with an M6 x 1.0mm thread, and the seat hump drilled to allow them to be bolted to the seat humps inner face. With the three holes drilled in each of the "hooks" (two for the fixing screws, on for the "hook") I transfer drilled the seat hump, and then opened everything out to the right size, and tapped the threads in the hooks. That let me assemble the whole thing, and with the seat base fitted to the hump, I could turn whole assembly upside down, and drill through the holes that were going to form the eyes of the hooks into the seat base and locate the holes for the pins that were going to attach to that and locate it on the hooks.

 That all worked out according to plan, except for the bit where I was meant to take some photographs of it all to illustrate this ramble with. I blame the head cold for that. As a consequence, this last picture is of a block of aluminium I drilled to make a mould for casting the nipples for the seat release cable, directly onto the cable. The round thing at the right of the picture is a ferrule I machined from stainless steel for the cable I was thinking of using. I've decided that the job requires something a little less heavy duty though, so I'm thinking of acquiring a bicycle brake cable to do the job.

Rather than just have the seat release cable dangling under the hump, I think it makes more sense to incorporate some sort of a handle into the number plate mounting bracket. Between my desire for the bracket to incorporate a handle, and the Construction and Use Regulations requiring the number plate itself to be illuminated by a white light that isn't visible from the rear of the vehicle, that's starting to look like quite a complicated bracket.

Sunday, 17 October 2010

Once again, another week has slipped by without me getting anything done on the Beemer. Frankly this would be a disgrace if it weren't for the other projects I've got on the go. It has to be borne in mind that I'm also building a tricycle with an Alfa Romeo engine, a GS 550 chopper, and usually something else as well, of late, making a Mustang fuel tank from some sheet metal and a tree trunk.

Next week isn't looking too great either as I need to tidy up behind myself.

I'll endeavour to squeeze some Beemer Werken in between the tidying up.


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.....

Monday, 4 October 2010

Well, Wales was nice, my Dad seemed quite pleased with his present, and I borrowed a few books off of my Mum relating to my house building aspirations. Didn't actually do any BMW though.

I did poke a few pieces of steel in a desultory fashion, and wander around looking for the springs that I'm sure I've seen in the last couple of weeks, and even got as far as sawing off a length of 10mm square bar with the idea of making the tongue for the seat catch, only to discover that the compression spring I had was 12mm in diameter. It wasn't an insoluble problem, but it would have meant a lot more work for a less efficient finished product. The idea of expending extra effort to make something that works less well because I haven't tracked down either a spring to match the metal, or some metal to match the spring, seems fundamentally stupid to me. As I had some other things that needed working on to meet a real world deadline (as opposed to a self impoosed, blog related one) I didn't manage to find the time to run around, source and acquire what I needed. I suppose I could have made a start on the frame braces, but I find that having a motorcycle project with too many unfinished jobs on it is depressing. You reach a point where you feel there's not much left to do, and remember that there are in fact lots of little things left to do, so not only is it a long list but it's all the jobs that you couldn't muster the enthusiasm to do at the time.

On the other hand, if you stick to getting the irritating, fiddly little jobs done instead of rushing ahead and doing something you're looking forward to doing, then you (or at least I) are more highly motivated to get the job at hand finished.

With that in mind, I'll leave you there and hope to have the seat base sorted out in time for next week.