Monday, October 16, 2017

 Starting the little big bike: mid fat, 148mm rear. Size Extra Medium
I chose the stainless dropouts this time as the last (1018 steel) thru axle drops that I used seemed to have too tight of tolerances for any kind of coating. 

A 20mm QR axle that I had in my old parts box measured 148mm and the slots of the dropouts are 20mm. All I needed were a few Gyro tabs and a new slot for the slightly smaller diameter dummy axle.
I forgot to order barrel nuts for the brake mount so I had to make a few out of stainless. The ones Paragon sells are AL or brass, so these might actually be better than what they sell.

Saturday, October 14, 2017

Trials 24"

 Finally got the 24" close to coating. Tensioners and a brake brace are next
 The first set of stays below had the bosses too narrow. At 83mm, the brake arms had to aim too far outward, even with the convex washer removed. The good ones here are sitting at 91mm apart. This wouldn't have been a big deal had I not had to make the removable V brake mounts each time (my usual sources are out of them).

Friday, October 6, 2017

The trials frame is awaiting some details on sprocket size
I was thinking about trying to sell my 8.3"s but they might just go on my road/commuter bike. My back has been hurting after riding long distances with the bars that sit even with the seat height. My dad asked for taller bars on his road ride and I think I'll do the same (2-3" above seat height)
Brent's 17 backsweep bars are ready to go


Thursday, September 28, 2017

31.8s


 
Rob's 22 frame is ready to go. Most of the past few week's work has been outsourcing

 One hard peg chink and the aluminum 20mm axle that I made stripped out. I lathed down a hollow steel one, but I'm not sure a shitty old thru axle hub can take peg abuse like a BMX hub. If this fails I'll just make a thru axle rigid fork.

 Apparently, the unintended micro knurl grips better than expected (after coating) Best of these three actually:



Tuesday, September 19, 2017

knarly knurling the sequel

I figured out some things:

I could/should have bought a scissor/clamp knurling tool that would not require side pressure on the rotating tube. This side pressure can deflect the tube and the result is a messy, unintentionally repeating groove (micro knurling). This might have been okay except that powdercoat is pretty thick and requires larger, deeper grooves... Otherwise the knurls just get smoothed over and don't bite into the stem like they should.

The live center that should have prevented the deflection appeared to creep away from the rotating tube. The force of cutting the grooves was enough to wiggle the tube into the lathe chuck and away from the live center. I could probably have reversed cutting feed direction but I had thought of a better solution:

The solution was to use bearings instead of a live center:

With a chuck in the tail stock, I ran a bolt through a few 7/8" diameter bearings and clamped a tube block on the rotating tube and the bearings. This made it so that the tail stock didn't need to apply any force towards the chuck and could move with the rotating tube without consequence. With minimized deflection, the tube was rigid enough to have clean, intentional grooves... at least some of the time. It turns out that this takes some trial and error. The amount of force applied to the rotating tube (when first contact is made) affects the radius at which the knurl wheels sit and this can determine whether the initial cut is in phase or slightly out.