Got maybe half way through making the crank pieces, need to figure out a good way to attach the sprocket next, since it will be welded inside the crankshaft sides.
Rough cut the flat bar and rod pieces on horizontal bandsaw
For the rod pieces, I then faced off both ends in the lathe, then used height gauge to scribe a witness mark and measure total length. Then when putting piece in the chuck I set it up against the bit and set a dial indicator to 0 and knew exactly how much to take off, got them all within a thousandths (which is very unnecessary)
Showing how the pieces of the crank will go together, the non zinc plated rod will be welded to the sides with the ball bearings already on the shaft. Will probably 3d print a jig to hold the sides when welding to be sure they are as parallel as possible
Made a large quality control mistake, I didnât measure the dimensions of the center supports of the linkages before gluing half of them together. When I was cleaning up the edges of the pieces after CNC router I used the horizontal belt sander and just my hands to square hold them square to the belt which was much too aggressive. Ended up sanding off 20 thousandths (~1/64 of an inch) off the ends of some of the pieces, these pieces are the only thing that set the distance between and parallelness of the sides of the linkages. So now the distance varies slightly between the ends of the linkages. The options are either remake these pieces or just sand down the mating piece to add in more clearance.
I should have designed in more clearance (~1/16") to each of the joints. Can see the height difference here, the linkage is one that is glued together already
Crankshaft and a jig to hold the offset sides during welding, will be interesting to see if 3d printed jig immediately melts to the metal during welding
Using jig (2 holes drilled 17.168" apart) to glue to together strut K, which is the longest bottom strut that needs to have a slightly offset shape to avoid colliding with the rest of the leg. Also cut out another square piece to glue to the bottom that could reinforce the two arms, but it seems fairly strong as is.
Not sure if this is a standard size, but Iâm impressed that the spoke holes are the same diameter as the sprocket holes, will just have to figure out how to mount axle housing in bridgeport, does DMS have the tool needed to remove bicycle gears from axle housing?
I used 3d printed jig and got one piece welded when I realized that welding each piece individually(6 joints that would all need to be perfectly 90 degrees) and then hoping that they end up lining up enough to rotate without binding was a really bad idea.
So I cut apart that one piece back apart, and instead I will weld together the frame first (out of 3/4" square tubing 1/16" wall), then weld the crank bearing pillow blocks onto the frame with a solid rod aligning all of the bearings, that will guarantee that they are all lined up, then I can weld the individual crank arms onto smaller rod pieces inside the frame (using same 3d printed jigs for 120 degree offset)
Instead of using the pieces I sanded out of shape for the final 3 struts, I made some precision thickness wood using the bridgeport
You could make a mold of the jig and then cast plaster (dental plaster is harder, Plaster of Paris is cheaper) into the mold - itâd likely hold up better than the original plastic part would.
The one piece I did weld I didnât notice any melting, of course I didnât do a full bead. But ended up cutting this one apart since I decided to weld together the frame before the crank. The flat bar is 3/16" thick, so it has a decent amount of mass to soak up the heat
Plan for the frame, could also make it out of plywood (would require both horizontal and vertical portions to get the needed strength), but since will be welding the crank anyway going with square metal tube seems easier to get attached to the bike. (Plus the metal from home depot is the same price as another 2âx4â piece of plywood)
There will be two struts going straight down to attach to the bolts on the rear wheel axle, and another strut going forward to attach to the bike around where the rear brake typically is.
Pipe hangers / tube straps will secure the main axle to the frame with bolts, which means will be able to remove the plywood legs from the frame easily by removing 14 bolts, the main crank pieces and bearings will be welded in place on the frame and wont be removable
Pro tip, before taking apart rear bicycle wheel know the difference between a cassettee and freewheel type rear gears and if you have freewheel type do not remove the wheel from the sprokes before taking the gears off, now I need to loosen the gears and donât have a good way to hold the hubâŚ
Helps to have someone holding the shop vac directly adjacent to the cutting tool capturing the overwhelming majority of the chip stream before it has a chance to land. At least thatâs how we did it last time for the trebuchet.
Yeah I was holding the vacuum next to it while cutting and it was very effective at collecting all the sawdust, in hindsight I should have grabbed a vacuum out of woodshop instead of using the metalshop one, as the sawdust would clog the filter much faster than typical metalshop use, Iâll empty / check the metalshop vacuum filter the next time Iâm at DMS.
I suspect woodshop probably wouldnât appreciate any small quantities of incidental oil sucked up either. Does workshop have a vac that might be more of a middle ground compromise? Might already have some oil contamination, but still dry enough to easily clean the wood chips out of?
Catching the chip stream as itâs being generated isnât going to suck up any meaningful quantity of oil. Cleaning off the bycatch from the machine itself and particularly the ways will be different.
I had no idea what the proper order of operations were to disassemble a bicycle wheel, here is where I got before realizing I had done things out of order and had to spend an hour re attaching the spokes to the wheel
Unwelded first attempt at welding and mounting the crankshaft sprocket, I initially tried to do it in multiple operations where I welded on one plate, used inner bore to find center in bridgeport and drilled that plate, then welded other plate, then used that hole to relocate center on bridgeport, but that ended up with too much play as I didnât relocate the center perfectly
On attempt two I welded the plate on both sides of the sprocket first, then used edge finder in the valleys of the sprocket to find the center of where the chain will rotate, drilling through the center of both plates in a single operation (32 teeth is nicely divisible by 4)
Iâm assuming that the outside edge of the hub is perfectly concentric with the bearing race pressed inside the hub as thats what I indicated on, the existing spoke holes were about 20 thousandths off on one side
Instead of being able to bolt on a split block to hold the main axle on, I decided to just run the main axle through the frame tube itself, reducing number of machines operations and parts needed at the cost of making it a bit harder to assemble
Getting annular cutter to match the bearing holder diameter for the 4 stands was well worth it, using a parallel as a stop was able to very quickly make 4 stands / risers that are exactly the same height
After letting it cool I removed the jigs and realized that the welds on only one side of the relatively thin wall tube caused a curve, bringing the ends of each tube together by about 1/8". I was able to run beads on the back side of the tube to pull the curve out to a satisfactory degree
Next steps are just mocking it up on the bicycle so I can get measurements for the support struts, and then welding the crank pieces together, and it will be ready for a test drive
Youâre going to need one of these if youâre converting a geared bicycle to a single speed.
There is no way to take out the slack otherwise on the chain, unless you happen to have sized your rear gear to allow for minimal slack on the chain(possible but youâre not always left with the gearing you desire).
P.S.
No longer relevant to you now but to remove gears(sprockets) from the rear hub you would need these.
The chain tool to hold the sprockets, and socket/cassette tool to remove the lock ring on the sprockets.
