27 May 2006

       Marcel spent a grand total of about 8 to 10 hours making the funky wooden, molded seat pictured to the right.  It's about ¼" thick and made from 3 layers of thin, shaped veneer that he pressed into a plywood mold he made, and then glued with water activated glue.  Holes were cut in it to both ventilate and lighten it, then he painted it gloss black.

     The front forks are off a small 16" bike and he carefully spread the forks using a scissors style car jack.  It worked perfectly and spread the forks very easily, and most importantly, evenly.  .  The front wheel fits fine, but it still needs to be dished to the right some more to get it center-line on the forks.  Not sure if the little pink forks will be strong enough, but we'll find out, I guess. :)  The rear yellow fork is an old 20" that you might notice from the mishaps of the Bowden Baron.  We cut the remainder of the broken steerer tube off, and welded it onto the end of the backbone.  Seat stays will be added later.

     The frame is made out of 1¼" x .049" steel box tube.  The middle and rear sections of the frame are cut and welded to exactly match the wood seat, which is about 55 degrees.  The head tube, stem and handle bars are standard bike issue off of salvaged bikes.  Six 1" x .049" sections of box tube were welded to the sides of the backbone to support the seat, and ¼" holes will be drilled in the ends of the seat supports to accept large head carriage bolts.  The frame was laid out and tack welded together in about 3 hours.  We did plan to draw out a full size plan on big pieces of paper, and then build a jig but we just sort of went "freestyle" on it instead :)

     About 6 hours build time on the frame so far.

30 May 2006

     A boom was made out of 1¼" x .064" steel box tube, with the outer boom being made from a 6" piece of 1½" x .100" steel box tube.  We slit the thicker tube 4" along the seam and welded two ¼" connector nuts on it to act as pinch bolts.  Marcel sat in it and we marked the height and length of the BB making sure the cranks cleared the front tire.  He's planning to use possibly a single 60 tooth chainring on it, with 150 or 140mm cranks, but right now, it's got a 52 tooth Biopace on it with 170mm cranks.  We made up a power side pulley using 3 pieces of phenolic sheet running on a 12mm sealed bearing and mounted with a 5/16" bolt to a small piece of 1" x ¼" plate steel that is welded to the side of the downtube just behind the head tube. We drilled a bunch of holes in the phenolic both to lighten it, and to make it look cool :)  The 12mm bearing rides on an aluminum adapter that allows about ½" of sideways movement just in case the pulley wants to move during turning or gear changes.  A small return side pulley is mounted to a small ¼" thick tab and has about ¾" of sideways movement on it so that there is less torque on the derailleur . . . hopefully :)  A small 1" x ¼" tab was drilled, tapped and shaped and then welded to the front of the right side fork drop-out to mount the XT derailleur on.  We linked up some old bits and pieces of 7 speed Z-51 KMC chain to temporarily get the bent mobile.  Cool thing about this, is the chain can be removed from the bike even without a master link.  Test drive time!

     Marcel can be seen zipping down the street on its first test ride.  It handled (to me) much like the Bowden Baron, but it pulled to the right when you pedal due, I think, to the fact that the front drive wheel is still offset to the left in the front fork.  The handle bars need to be trimmed and the stem needs to be lengthened to get into a more "praying hamster" position, but aside from that, it felt good.  It also turns like crazy!  The turning circle is about 7 or 8 feet.  It's a fairly comfy ride and we're not sure about the handling or head tube angle and trail until we get the front wheel dished over.  So far though, we're pretty happy with our first twist chain FWD.  At one point while it was clamped on the bench, the front wheel was completely sideways and still you could pedal with nothing more than a little increased noise.  It's very cool how much the chain can twist and still function properly.

     During setup, we made sure that the power side of the chain cleared the rear of the right fork blade by enough to be able to turn fairly sharply.  Unless at very low speed and sawing the bars back and forth, there's no problem with chain clearance but we're going to put a layer or two of teflon tape on it just in case once the paint job is finished.  Also, the sliding return side pulley worked flawlessly and I would highly recommend making the return pulley so it can slide, because while shifting gears and/or turning, it DOES slide.  Only at extreme wheel angles does it sound like it's pulling the derailleur hard enough to be trying to make it shift gears.

     Next, seat stays, modify the bars/stem, and true the front wheel.  We're at a total of about 8 hours now.

31 May 2006

     Seat stays off an old chopped up frame were trimmed down and welded from the front of the rear forks, to the back of the frame.  This was to make sure the rear forks didn't twist (because it corners SO hard) and also to stiffen up the rear end a little.  The frame still flexes a little at the bottom joints in front of and just behind the seat.  May have to stiffen these up, but Marcel is a light guy and there shouldn't be a problem . . . hopefully.  Marcel popped the front wheel on the truing stand and did a masterful job of truing and shifting the wheel over (almost ¾") and now it is dead center.  Woot!  We chopped the handle bars, and lengthened the stem extension about 4".  We temporarily took an old thumb shifter and hooked up the derailleur to see how it shifted, so no we had to take it for another test ride.

     It handles MUCH better than it did, now that the front wheel is where it's supposed to be.  The shifting was smooth as silk, due in part to the fact that the front shifter cable is so short and realtively straight.   The bike wants to pull slightly to the left when you pedal, especially pedalling hard, but that's likely because the chain is to the right of the pivot point, and when you apply pressure to the chain, it can either roll the front wheel forward or pivot the front wheel to the left.  By applying steady pedal pressure and relaxing your hands and arms, this is all but eliminated.  Riding a bent with tiller is also something to get used to because it is so easy for even the slightest arm movement to translate to steering input.  I learned this with the high racer.  Some of the interesting little quirks of a twist chain FWD, but minor issues, IMO.  One thing we did decide was to slot the down tube and give the bike some more head tube angle, to make the steering a little heavier and give it more trail.  After the angle/trail increase, it handled better still.  I'd like to tweak it back a little again, just one more time, because it's at about 1" of trail and 70 degree HTA.  I'd like to get into the 60s and get to about 1½" of trail.  Aside from that, I'm very happy with it and so is Marcel.

     It was raining when we were doing the testing and the tires are pretty slick so while it corners really hard, it doesn't do that very well on wet roads :)  During one of his test rides, "Marcel the Cat" pushed a little too hard on a fast 180 and the front end washed out, he went down, and snapped off the wing on the right side of the seat base.  It's too bad because I think it was an awesome looking seat.  He says he'll take the other side off too, sand it off smooth and use it for a negative mold for fiberglass later.

     Marcel took the bike to his place to do some weld clean-up and seat repair, and then we'll deal with rim brake and fender installation.  9½ hours to date.

2 June 2006

     Front V-brake posts were welded on and brakes were set up.  It stops really well now, and it just needs to have hte posts mounted on the rear end, possibly give it more head tube angle, reinforce the front, bottm joint, a little bead clean-up, and shee's good to go for paint.  The rust is from us being a little too eager to test ride it in the rain.

     Close to 10 other people have tried the nitro clone so far, and all of them could ride it and none of them disliked it.  Time to make a jig :)

10½ hours so far.

18 July 2006

     About 4 days after the last update, even before the Nitro was finished, a guy bought it.  He uses it as a commuter and has done a few more mods to it.  Hopefully I'll have some pictures of it's final form.  In the mean time, to the right are a few finished pictures, and some of the details.

     The top picture is a detail of the phenolic chain pulley I made.  Details will be under the Tips/Help section soon.  The return side pulley is a small commercially available pulley for chain management on DH bikes, I think.  Below that is a picture of the 58T Vuelta chainring, bolted onto a custom 145mm 110mm BCD crank set.  It was an old crankset that a friend had kicking around, that had fat enough crank arms to take the shortening procedure.  Details here.   Lastly, the final picture of our Nitro clone before it rolled out the door to its new owner.

     I think the plan might be to swap out the 58T ring and replace it with a 60T ring for a little more top end.  The owner says he has no problem with up-hills so the loss of a few gear inches shouldn't be a problem.

22 Mar 2008

     The original seat had seen some better days and was starting to crack due to the weight of the rider.  He asked me to make a new seat for it, so I made a tube and mesh seat.  As the seat had a totally different design to it, the frame had to be lengthened too.  When a bent is built with a fairly minimal cockpit, it's tough to make a single change without having to make a bunch of additional changes.