- Joined
- Jan 20, 2018
- Messages
- 5,557
I bought an old McKissic Mighty Mac chipper shredder off CL for $200 the other day. The motor on it was a well-worn 6.5 hp Greyhound (Lifan) from HF. It had some minor issues but started and ran well. While using it I noticed that gas leaked from the filler cap due to vibration. I tried replacing the poorly improvised gasket, with something better, but the leak continued. I then realized that the cap was cracked. After an hour or two searching online, I realized that I was going to have to make one.
About a year ago I assembled an 80/63 transposing gear set, but had never gone any further with it. This was the obvious opportunity. The filler measured 55.6 mm, so obviously a 56 and the threads were a 2.5. I set about trying to figure out what other gears I might need, but was getting more confused as I went. Then I read that the transposing gears effectively converted the 8 tpi leadscrew into a 2.5mm, and the light went on. I mounted the transposing gear on the banjo, leaving the stock stud and screw gears. Then I set the QCGB to 8 tpi and made a test pass on the piece of gray PVC I had selected. Voila, 2.5 mm!
I set about making the blank, then started threading. I made a few false starts trying to thread from inside out, including cutting left hand threads. I finally settled for the slowest back-geared speed, threading in the conventional direction and stopping the lathe before I hit bottom. All I had to go by where the major diameter of the filler neck and the minor diameter of the old cap, and none of it really made any sense. I ended up having to remove the part from the chuck twice to go out and test it, then put it back and pick up the thread again. The threads are less than perfect but more than adequate.
It's little things like this that made me want to learn machine work in the beginning. It's only taken me 40+ years to get here.
I realized that an added advantage to the 80/63 transposing gear is that you can leave it mounted, simply reversing the screw gear and re-positioning the transposing gear on the banjo makes the transition from imperial to metric.
About a year ago I assembled an 80/63 transposing gear set, but had never gone any further with it. This was the obvious opportunity. The filler measured 55.6 mm, so obviously a 56 and the threads were a 2.5. I set about trying to figure out what other gears I might need, but was getting more confused as I went. Then I read that the transposing gears effectively converted the 8 tpi leadscrew into a 2.5mm, and the light went on. I mounted the transposing gear on the banjo, leaving the stock stud and screw gears. Then I set the QCGB to 8 tpi and made a test pass on the piece of gray PVC I had selected. Voila, 2.5 mm!
I set about making the blank, then started threading. I made a few false starts trying to thread from inside out, including cutting left hand threads. I finally settled for the slowest back-geared speed, threading in the conventional direction and stopping the lathe before I hit bottom. All I had to go by where the major diameter of the filler neck and the minor diameter of the old cap, and none of it really made any sense. I ended up having to remove the part from the chuck twice to go out and test it, then put it back and pick up the thread again. The threads are less than perfect but more than adequate.
It's little things like this that made me want to learn machine work in the beginning. It's only taken me 40+ years to get here.
I realized that an added advantage to the 80/63 transposing gear is that you can leave it mounted, simply reversing the screw gear and re-positioning the transposing gear on the banjo makes the transition from imperial to metric.