Wednesday, September 12, 2012

Martins 15mm thru axle ti fork...

To compliment Martin's Ti frame, he requested a rigid ti fork, as the harsh desert climate he lives in eats away the stantion tubes of suspension forks.  The goal was a compliant fork to take the sting out of the trail, but with lateral rigidity so that it tracks well.  We decided on a 15mm thru axle design that would allow compatibility with a Fox suspension fork if he decided later he wished for more squish  :).

To get started, I designed the frame and fork around some medium numbers that would allow some diversity in fork choices in the future...one of the nice benefits of a 650b.  If fore thought is applied, it can fit a 26" 100mm suspension fork, a 650b specific fork, and a 80mm 29er fork with very little change in axle to crown length and resultant handling. ,allowing for a frame that has long term viability regardless of parts availability.

I began by bending up the unicrown blades...


Once I had the desired shape and angle, into the horizontal mill they go for mitering...


The finished cut fits the desired steerer tube, the miter positioned to allow for offset and lateral position to place the dropouts at the proper spacing...


Checking the fit...


Work next began on the steerer tube crown race by boring out a piece of 3/2.5 Ti tube to a tight slip fit ID


The tubing was then turned on the lathe to create a press fit lip for the headset race and then parted off so it can be welded to the steerer tube...


The finished crown race for the Ti fork...


The next project was to tackle the machining for the 15mm dropouts.  I started with some heavy wall Ti tubing, some solid Ti bar, and an indexed insert from Fox.  The tubing was turned in the lathe to open up the ID to accept the .875 bar stock which will be machined for the thru axle and the insert.  Below you can see the four finished pieces; the tubing has been machined for a press fit with the internal axle pieces and a hooded relief created to allow maximum surface area contact with the fork leg.  The two axle pieces were designed to allow precision fit of the 15mm thru axle with an inset cup for the indexed aluminum piece...

Placed together, this is the final configuration of the dropout.  The piece was welded and then face machined to insure that all the surfaces set parallel to each other.


Once all the fiddly bits were done, it was all loaded up into the fixture, purged, and welded together...


The last bit to complete were the post mounts for the disc brake and the index point for the axle position.  The index tooth was machined and welded to the rear of the dropout, allowing for the female index insert to be lifted out and rotated to fine tune the position of the quick release...


A 3mm tapped hole on the face of the index tooth allows a retaining plate to be mounted once all adjustments are made...


So that's it, a nice ti fork with 15m t/a , post mount disc brakes, and silky smooth ride.

Tomorrow, final pics of the bike and a blog post from Martin's perspective on the process and his visit.

cheers,

rody

4 comments:

Joel said...

Can we see the fork disc mount?

Jamenstall said...

That is slick.

Larry

Rody said...

Joel,

I'm afraid I don't have any shots of the fork post mount and the bike is shipped away...sorry. Basically .500" 6/4 rod that was drilled and tapped, then scallop cut to match the inside of the fork leg tapering to a radius to match the curve of the leg. The latest post has a shot of the rear post mount, fwiw.

dicky said...

Am I the only one who can't even imagine how much this bike is going to cost? Sooooooo much labor. Gonna be unreal when it's done.

Incredible work, Rody.