For the manner in which men live is so different from the way in which they ought to live, that he who leaves the common course for that which he ought to follow will find that it leads him to ruin rather than safety.

Please visit my new blog:

Saturday, December 6, 2014

Racin' Parts: Swingarm pivot

A good friend of mine road races a 500cc Triumph. He's getting his bike ready for next season and asked me to help by making a new swingarm pivot.
It's an interesting project and not the easiest thing I've ever made. I got about half way through it today:

Here's the original pivot. It consists of a shaft, washer, nut, and adjuster quadrants. The shaft is hollow, with a .800"- 20 thread. That thread is far from standard. The quadrant on the left side is welded to the shaft.
I decided to start with the quadrants. I used the free quadrant as a template, transfer punched the holes, and scribed the outline. Just one teeny little problem...

Transferring the .800" hole isn't as easy as it looks. Anyone have a .800" transfer punch? Didn't think so. I turned a piece of aluminum to fit the hole and ran a .250" hole through it. Now I can use a .250" transfer punch...

...and it goes something like that.

All holes have been piloted, two were enlarged to .250" so I could fasten the two quadrants together for shaping. Here, the shape is just roughed out. Final shaping will be finished later...time for the shaft.

Here is a step I believe I failed to show the last time I ran a long shaft. This pivot is a hair over 10 inches long. When turning a shaft that long, always check the alignment of the machine. At each end of the shaft, take a cut at the same depth. Measure the diameter at the location of each cut. If the cut to the right is larger, then the tailstock needs to be adjusted towards you. If the cut is smaller, the tailstock needs to be adjusted away. It only takes a few minutes, and you can have the shaft true to within .001"-.002". Once you are sure that the machine is aligned, you can turn to final diameter. In this case, .801"-.803".

The threaded end is approx. .500" long. A wide tip sharpie and a scribe line makes it easy to see.

I cut the threads to be a snug fit to the old nut.
This is why I love indexable tooling. I chipped my cutter. Back in the day, using HSS cutters, I would have had to remove the cutter, regrind it, check alignment, and blah blah blah. Now, I can just rotate to the next sharp point and move on.

That's a really long drill. Really, really, really long. The center of the shaft is being bored to .4375" (7/16).

Today's progress.

No comments:

Post a Comment