Fabricated Steel Triple Clamps

Being a big suspension geek, I bought an R1 front end to install on the ZRX. Of course, the R1 forks are 24mm shorter than the stock ZRX forks. When I bought them, I asked for a measurement from the axle to the top of the fork tube. What I failed to do was completely extend my own ZRX forks when I measured them. I had thought they were less than 1/2" different, and that I could simply press in a new steering stem.

As a result of this, as well as the desire to maintain the stock instrumentation and ignition lock, I decided to fabricate my own triple clamps. I participate on a forum, the Motorcycle Chassis Design List, hosted by Michael Moore. There was a pretty lively discussion of various techniques for making one's own triple clamps, and one list member, whom I have worked with before, volunteered the use of his new CNC mill to whittle the clamps out of aluminum. I was somewhat skeptical that between my inexperience with CNC and my inexperience with designing triples, that I could get a useable product the first try.

So, I decided to build a set of fabricated steel triple clamps. The plan is to use my recently-refurbished lathe to turn precise collars, add pinch bolt lugs, and weld up the whole mess using tube steel. Great idea on paper. It allows me to droop the top clamp to regain the missing inch, the material is cheap, if an error is made the parts are easily duplicated and cheaply scrapped, errors in one part don't threaten the whole project, and I can accomplish the entire job using my own tools. While it is entirely possible to produce aluminum triples from solid using a manual machine, I wasn't comfortable with the process. One distinct downside is weight: I have been pretty generous with the wall-thickness in the design.

I ordered the steel and got busy on the lathe. First were the pinch bolt lugs. They have a flange on the end for the nut/bolt head, and where the red dashed shows, they were flycut to match the OD of the collars. This was the first project with some new carbide insert tooling, and I made all the lugs before discovering that the carbide insert was quite high, well above the center line of the lathe. Unfortunately, the finish wasn't as nice as possible. I had to mill my tool holder to get the carbide on center.

In a fit of "almost genius" behavior, I ordered 2.5" OD tubing with 3/8" wall thickness. Stout stuff. The reason it was almost a stroke of genius is that I can cut out the 54mm lower clamp collars AND the 50mm upper clamp collars out of the same stock. What I hadn't accounted for was the HUGE amount of material that had to be wasted with the boring bar. Fortunately, the revamped lathe runs the boring bar quite nicely without chatter. This is a major improvement, and well worth the effort. Now, I just wish it had more power.

Since the upper and lower clamps have to align perfectly, a jig is in order. I welded up a steel box out of quarter-inch material, and added clamping feet to hold it on the milling table. I used a flycutter to make the top and bottom parallel, and the sides perpendicular. Next, the aluminum slugs were turned on the lathe to a sliding fit with the collars. The have a 3/8" hole, which is filled by a 3/8" bolt that hold them to the jig. The plan is that I'll make the larger clamp first, then turn down the slug to fit the smaller clamp. Hopefully, that will result in perfectly aligned clamps.



Of course, I got lazy and didn't measure the location of the vertical webs on the jig before I welded them up. One of the holes for the bolts is cocked because the tap was pushed out of alignment by the web. I drilled and tapped new holes shifted by 3/4" to one side to miss the webs. It's unfortunate, but at least now I can slot the clamps without cutting my jig. Small consolation.

More to come.