The rear part is a salvaged tubular steel swingarm that will be rigidly mounted to two ¼" Al side plates.  The side plates are welded to the center section of the frame which is also slavaged from the MTB.  The top of the side plates sticks up higher than the seat, but they will be trimmed once the final seat position and angle is decided upon.  The downtube is a piece of 2"OD x .049" 6061 Al tubing, as is the boom.  The head tube, and the BB shell/front derailler tube were also salvaged.  The seat frame is made from EMT and a .040" piece of sheet Al.

     Top and rear view of the modelled frame.  The front forks will be made using the fork jig and the preliminary specs are to have a 73º head tube angle.

11 Aug 2007

     Today, most of the Al parts were cleaned up so the forks were addressed.  The forks are made fomr a MTB tube with the legs cut off at a 45º angle, right by the fork crown.  The legs were cut off an old 10 speed fork and left extra long to be trimmed later.  The top picture is the steer tube/crown mounted in the jig and the legs have been mounted up after be trimmed ot the proper length.  The nice thing about cutting the MTB legs at a 45º angle is that the road bike forks fit very nicely into them once trimmed to proper length.  This also allows the top of the fork/crown to be narrower than the two other forks I did.  The bottom is the fork after welding.  With a little "cosmetic" weld bead refinishing, the forks should look pretty sweet.  We did this set of forks offset by ½" to the left, just like the ones for the '44, but these are much nicer :)  I think this is the way to do dual leg forks.  The end product is much nicer than chopping and splicing the legs - narrower too.

13 Aug 2007

     Today I welded up some of the pieces of the frame.  I did some practice beads first, but Al welding has never been my forte and not welding any of it for 9 years just makes things worse.  However, I gave it a shot and aside from some touch-downs, there were no major holes blown and the major frame parts are done.  The top picture shows the down tube welded to the main frame section, and the rear end/swing arm brackets welded to the back end, on the left side of the picture.  The bottom picture shows the 2" tube welded to teh BB shell and the steel swingarm is below that.  The next job is to cut the appropriate angles on the boom and downtube ends, and notch them so they meet around the Al headtube. Then, mount the forks and the seat, see what is needed for chain routing and take a look at what we've got so far.

18 Aug 2007

     All the frame sections are all tacked together now and the frame jig did a great job of properly aligning the round tube sections.  As I don't have enough time on the TIG with aluminum yet, I persuaded my friend to let me take the tacked frame down to a local welder and have them finish the beads.  For $60, it was well worth it and the beads are nice and smooth, and sufficiently full to spread the loading out.  Because one of the loaded joints on the Raptor 74 just failed while riding hard, I am definitely getting a creepy feeling about the durability of the aluminum frame without proper heat treatment.  I guess we'll see.  I'm thinking a gusset will need to be added where the down tube meets the main frame at the bottom.  To the right is the frame mocked up into a rolling chassis just before going to the welder.  I think it's a nice looking little bent, although with a 48" wheelbase, it ain't 'zackly little.

      The bottom picture shows the rear disc brake caliper mounted to the top section of the steel swing arm.  The swing arm mounts at the rear were the perfect width and a few small mods to a piece of 1/8" steel were all that was needed to get it mounted straight and true.  My friend only wants a single brake, so that's what he's got.  With radial lacing, the rear wheel has some fore/aft oscillation when the brakes are applied so I'm thinking he might need to add a few more spokes to stiffen that up.  Next on the block is to trim the aluminum brackets off, shorten the steerer tube by an inch, and make an adapter to neck down the 1 3/8" head tube to fit the smaller bearing cups.  We're also making a set of 58/48/38 triple oval rings for the 4 bolt 140mm cranks.

25 Aug 2007

     As my friend was getting ready to move soon, we decided to make a last push and get all the welding and fabrication done, if possible, so paint and assembly would be the final things to do after the move. We took the frame in to a local welding shop to have some good, fat beads welded around the downtube/headtube/boom joints becaue I didn't want to attempt them and screw things up at the last minute.  We also got the seat frame welded up out of 3/4" EMT and got 4 small tabs welded on to mount the seat to the frame.  After the tall aluminum flanges were cut down, and the desired seat angle was set, the rear seat tabs were added and bolted in place.  Then a .040" piece of scrap 2024 Al was pop rivetted to the seat frame.  Slowly, it's starting to look like something.  The 2nd picture is a closer shot of the seat frame and how it mounts to the rear of the bike.  The seat is set at roughly a 30º angle.  A headrest will need to be added likely, and that will be done later on.

     Once the seat was on, we could start fabricating the handlebars.  He originally intended to have bullhorns, but decided to go with a praying hamster tiller setup like on the '74 instead.  The bottom pictureis the process of taking an old stem, cutting it in half and welding in apiece of 1" bike frame tubing to push the bars back towards the rider.  About 9½" were added.  Straight handlebars were added and cut off to about 6" on either side of the stem.  We also took an old, small steel brake lever housing, cut the flanges off it (like with the '74) and welded it directly to the bottom of the tiller to be used as a thumb brake.  He's only using a single rear disc, so only one brake was mounted.  At this point, the batteries died and I don't have any more shots.

     In the mean time, two ¼" pieces of AL flatstock were welded to the bottom joint where the down tube meets the backbone for some extra gussetting.  The handlebars and tiller had the beads cleaned up and painted flat black.  We made a couple pulley options of an AL one like the '74 and a roller blade wheel that is mounted right below the front seat mount.  Once my friend gets situated a little at his new place he's going to send me some more pictures.