Jeroen is on the build list but is a ways down, however, we are doing what we can to get him into a Groovy build asap. You see, has is quickly losing a key physical attribute for mountain biking that we take for granted...his sight. Hindered with a degenerative eye disease, he has continued to ride the last few years using the periphery of his vision as the central focus is gone. He has ridden amazingly well, navigating his way through Colorado and Moab trails better than I, but unfortunately, life is changing for him so it is my hope this build will give him hope and inspire others.
Here's the rundown...this bike is to be a steel 29+, which is a wheel size that is about a half inch bigger in diameter than a standard 29er and has a width of 3.00", giving it a nickname as a "mid-fat" wheel size. The goal of this build was to create a bombproof chassis with a wheel that can roll and float over obstacles that Jeroen may not be able to navigate with the same precision as others but still have that cross country handling and feel.
The materials selected include a mix of True Temper OX Plat tubes, curved and shaped on the main triangle and straight gauge 4120 for the rear end.
I usually start with the seat tube. In this case, I wanted to create shorter stays with a little extra clearance, so I choose to roll and shape this hardened tube. Curving/rolling OX Plat tubing is not easy, as if you get too aggressive, it can fracture at the stress points. For success in creating the oval shape without fracturing, I filled the tube with cerobend, rolled it in a die one size up (1.375 for this 1.25 tube), and got a nice round to oval shape for the tire clearance. I also put in all the braze ons before welding up the tube, so that no introduced heat stress will mess with the alignment of the frame once out of the fixuture.
Once all the tubes were mitered/coped up, I began working on the dropouts for this build. Jeroen is a child of the 80's and I wanted to create a dropout that was similar to some used in that period that would be incredibly strong. As I am also looking to use this dropout in the future for a single speed and a Rohloff build, it had to meet the criteria of having enough horizontal motion for tensioning as well. I drew up the design and then the fabrication plan and got to work.
The dropouts were machined on the mill out of 4130 plate...
and the hoods were created out of 4130 tubing, bored to the correct inner diameter and then cut and shaped to fit the profile of the plates. I will likely leave the derailleur tab on the other builds just to give the possibility of using it with a derailleur as the mount is fairly low profile and unobtrusive...
Welded up and ready for action...
I'll be using a Yoke on the rear to help achieve room for the tire and a large chainring for the 1x10 setup with a standard 73mm bottom bracket.
What's tough is about to come, creating chainstay profiles that are a fixed length, come straight off the fitment on the yoke and fit precisely to the hood on the dropout. To accomplish this, it took bending the .875" diameter tubing in three planes; one bend to move it out laterally even with the 135mm axle, a second opposite bend to bring it back straight in line with the droput, and a third bend to bring the end of the tube up to the hood to compensate for the bottom bracket vs axle height, otherwise know as bb drop.
Once bent, I created a sub assembly for the rear end and welded it up using the fixture I created earlier, noted in the blog.
With the sub assembly done, I meticulously cleaned all the tubing, fit it into the fixture and welded it all up. Lots of folks always want to know machine settings..."what do use for max amperage, pulse settings, slope up and down?" Here's the skinny, this was all welded with the amperage set on 80 and running hot and fast, allowing the dipping of my filler metal to create weld bead pattern. No fancy settings, no fancy machine, just plane welding, controlling the puddle with the angle of my torch, rate of filler, and overall heat input with the remote pedal. Practice is what you need to know, not how to manipulate machine settings.
The final aspect was creating the seatstays and then post fab finishing, which consists of reaming the seat tube, facing/reaming the head tube to fit the headset, and tapping the bottom bracket and derailleur.
The final fab'd frame, ready for the paint booth to come.
rody
