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Friday, February 13, 2009

Broke The Seat, Improved Chainline

Since it's been raining so much off and on lately, and I still want to sometimes test the bike on the neighborhood street for various changes here and there that can't really be tested any other way, I decided to at least temporarily cover the padding I was using, so it wouldn't get all wet and squooshy if it rained at an inopportune time.

It's a vinyl cover to some old footrest that no longer exists, and used to snap onto it. It's about 3-4" bigger than the seat itself in all directions, making it ideal for this. It's also been out in the weather for several months, accidentally forgotten about sitting on top of some stuff around the side of the house. There's no real sign of weather damage at all, which means it should do a *great* job of surviving on the bike itself, assuming it's not damaged in crashes or something. I just tossed in the wash with a blanket that happened to need washing, too, then in the dryer with it. Survived both fine, so again, oughta be a great seatcover.

For now, I just stapled it to the plywood, along the double-over/sewn edges, with a regular desk stapler and thin staples. I have a much better stapler and heavyduty staples, but it cannot be unfolded, and will only fit over something about 1/2" thick. With the padding, the cover won't squish down that far, so I will have to take the hinge-pin out of the stapler to use it for this, so it can be opened up wider. Or I will have to remove the padding, staple one side, then the other, then be able to stuff the padding in afterwards thru the top and bottom. Then I might be able to staple those two edges closed since the padding won't go right to the edges there. I'll worry about that when I get farther along in testing.

To fully clear my knees when pedalling at the top of the stroke during turns, I extended the steering tube in the rear headstock.

It's just the cut-off piece of the seattube from the rear half of this bike, turned upside down, and using it's former seatpost clamp to hold it to the actual steering tube in the headstock. That steering tube had to be changed, because there was not enough length in it to let this grab enough of it to be sure of a tightly-held joint (only about 3/4"). The original tube had come off the white Murray fork that is now the rear inter-frame brace/support/stiffener. I have an old bent and rusty-in-places Huffy Sportsman frame that someone else appears to have tried to modify but failed, which had a nice brazed-together flat-style fork I could use the steering tube from, since it was at least 1.5" longer than the Murray one.

I got another half-inch or more out of it by cutting the fork tubes away separately, leaving intact the base of the tube, then lathing away all the remaining bits (to ensure it remained round, which grinding/filing probably would not). Since I had to remove the original bearing-cone at the bottom, I had to weld a new one on (as there is no bottom piece to keep it from coming off now). However, it's a little more complex than that.

The tube's threads don't go down far enough to allow me to bolt it normally into this shorter headstock tube. I haven't any way of cutting threads onto the tube, as I don't have all the gears for the lathe to do screws/threads, and no tap/die set that goes even a quarter that large. Thus, I won't be able to bolt anything down at the top, to hold the tube in place or hold bearings in, etc.

The best fix for this is to use the tube upside down, threads on bottom end, and smooth end on top, so the extension I am making from the ex-seattube will go down onto it and fit properly and easily. Then I can weld a bearing cone just at the top part below the bars on the steering tube that will provide all the upper support for the tube. Doing this was a bit harder than I imagined, trying to get the cone lined up correctly--it's a hollow cone, instead of a solid one, so the edges of the thin hole in it don't keep it from wiggling around like a precessing top. None of the solid cones I have will fit it, so I'm forced to use this type instead.

Now the threaded parts go on from the bottom, but it turns out are not as easy to do that and get them to stay in place as they would be if they were on top, because I have the torque of the steering rod helping to unscrew it during one direction of turning. So, I will have to drill it for a bolt or weld it. Easy to fix, but annoying. If I had a way to thread the tube, it wouldn't be an issue, because this stuff would all be on top, and the steering pivot tab would be welded to the bottom end of the tube.

One thing I would like to do once I can bend tubing safely is to bend the ex-seattube that's now the steering tube extension, so that it angles back a little bit, bringing the bars closer to me. Flipping the stem around isn't an option, because then they're too far back and pointed downward, and interfere with knees again, during tight turns. Just a little bit more back would be more comfortable.

I had not yet done any hard pedalling with this seat, and still have not. But I still managed to break it at the supports, where the large hole for the hose clamp was drilled.

Apparently I'm an idiot, because it is obvious in hindsight that it is
A) A really bad spot to drill such a hole, where the seat begins to go from flat to upright, and thus could have a lot of tension on it during horizontal pushing
B) Dumb to not have a vertical rear support for the back of the seat, other than the seat's plywood supports/shapers.

I had planned on having one, but hadn't yet welded it on, because it would require bending some tubing in a way I can't yet do, to get from the seattube's top end (at toptube height) around the curved base of the seat and on up the back.

The crack is all the way thru the seat, and pretty bad. There's no way I'll be using *this* seat for final road use, but I will patch it and use it for more testing. Might as well totally destroy the prototype in testing rather than keep making new ones and break them all in different ways. ;-)

Since I can't do the bending of the tube needed for the support I *want*, I took the leftover forks from the headstock/steering tube extension and turned them into rear stabilizing supports.

I still have to drill the hole out a little larger (between the white reflective patch on the green ex-fork tube and it's brazed-on cap), to accomodate the bolt that will run all the way from one side to the other, thru both forks and the seat supports, including a block of wood between the supports. The forks are simply bolted down at the rear accessory hardpoint, and that makes them stiff enough that they have very little lateral movement even with lots of one-sided seat pressure. If I'd had them in place before, the seat wouldn't have cracked.

I improved the chainline by removing the top derailer that was being used as a tensioner, and replaced it with the entire axle/wheel assembly from one of those roller skates I got to use the wheels for the friction drive 2.x versions. Bolting it directly to the Magna frame's stand mounting point (using a bolt and nut from some of the Ford LTD engine bits I removed in a previous post, as the bolt that comes with the assembly is threaded only to go into the skate bottom, and no nuts I currently have will fit it) allows it to just align with the chain, but it doesn't provide enough support.

It needs to go at least far enough leftward to completely straddle the chainline, so that the chain will at the least ride within the groove cut in the wheel for it. I'll have to make a custom mount for it, with an angle bracket and the axle bolt out of the skate assembly, so that it will still use this mounting point but stick out farther to the left (adjustably, if possible).

Otherwise, it's *almost* perfect like this. If the skate axle was 1/2" longer, it *would* be perfect, since I could just put washers behind the wheel to push it out farther.

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