It’s not every day I find myself taking a lathe to an expensive pair of carbon suspension forks (honest!) but that’s exactly the situation I found myself in at the Cytech workshop last week.
Why commit such a wanton act of destruction Jules? Have you gone mad? Well… no, thankfully and in answer to your first question I had been asked by the guys at Madison (official UK importer for DT Swiss) to prepare a cutaway of one of their top end suspension forks, the quite lovely and very light XMC 100.
Our first job was to disassemble the fork to remove the lowers and internals to allow us to machine away the stanchions and lowers to reveal the internals. A point worthy of note here is that the DT Swiss lowers were different to remove than the ‘footnut – crush washer’ assembly of the Rockshox units, the bolts are reverse threaded into the bottom of the lowers and to remove the lowers you need to screw the bolts INTO the fork legs freeing the lowers using a 4mm hex key.
The forks were air sprung, so not much to see on the spring side save for a few elastomer bottom out bumpers. The interesting part was the Damper leg, which, when we removed the cartridge, bore more than a passing resemblance to a Fox FIT unit. Further investigation of the ‘Twin Tube’ unit revealed separate damping circuits for compression and rebound with some neat, if tiny, shim stacks. We were impressed with the unit and a lot of thought seems to have gone into it. Shame we’d never get to ride it!!
I was a little concerned about cutting through the Carbon Fibre, I needed to leave a good clean edge and Carbon is not the nicest of materials for your health when being cut, so the correct safety measures had to be followed.
My concerns were ill founded as the Carbon was dead easy to cut through (with the correct tool of course!) if not a little bit scary given the cost of the stuff!!
With the lowers prepped, we moved on to machining the stanchions which I had foolishly believed to be the easy part of the job… It wasn’t. The Stanchions are hard anodized and getting the machine tool to bite through them proved challenging (the good news is I wouldn’t be concerned about rock damage to them on the trail after having done this!!) We had to jig up a special tool to hold the Stanchions whilst they were being machined and then prepare the edges to allow them to slide back into the lowers correctly.
Once we had trial fitted the lowers and were happy with the fit, we re-installed the damper and air spring cartridges and gave the unit a good ‘show’ polish ready for it to be displayed on the DT Swiss stand at the recent Ice Bike show. Did you see them? Now you know how they were done!!
If you fancy learning more about the specifics of suspension then get yourself booked onto a Cytech Level 3 Suspension course here at ATG-Training pronto!!