Coupler Ingredients
This weekend I spent some time in the machine shop making a shaft coupler for the car.
The two main ingredients in my design are a Mitsubishi clutch plate and a sprocket I bought from surpluscenter.com for $12.
Since I had already given away my Fiat clutch disc I ended up getting a Mitsubishi clutch disc instead, I found one for dirt cheap on eBay. I can recommend clutchnet.com if you ever need to figure out what clutch discs fit a particular transmission shaft.
My intention is to keep the clutch spring mechanism, to protect the transmission from high transient loads while shifting, by bolting the hub of the clutch disc to the sprocket. I chose to use a sprocket since it already has the appropriate size bore, keyway and set screws.
In Progress
First task was to turn the sprocket and remove the teeth. I then drilled out the rivets that hold the clutch disc together. After measuring the location of the holes I drilled and tapped four holes in the sprocket for 1/4-20 bolts. I also had to make some custom spacers on the lathe to keep the plates at the right distance.
After bolting it together with grade 8 hardware and plenty of thread locker I stuck it back in the lathe and turned the clutch disc down to the same diameter as the sprocket hub.
Finished Coupler
The whole thing is quite heavy, currently 5 lbs. I considered removing some more material from the sprocket to lighten it up but I didn't have time for it this weekend and I'm not sure it's worth the effort.
Lucy sniffed it briefly and gave me a yawn of approval.
Lucy Approved
When I bought my sprocket from Surplus Center they sent me one with hardened teeth. I didn't realize at first so I dulled a few lathe bits trying to cut it. I learned that the discolored teeth are a sign of induction hardening of the metal. I couldn't scratch the metal with a file, which means it's too hard for normal machining. But, all was not lost. I was able to anneal the sprocket so that it was workable. Here's what I did. I heated the sprocket up with a oxy-acetylene rosebud tip. It was nice and hot. I then placed it into a shoebox of vermiculite for slow overnight cooling. The next morning, I was able to file and machine it normally. When I ordered, there was no way for me to know that the sprocket was hardened.
I learned a bit of metallurgy and got a nice looking sprocket in the meantime. Not too bad.
Looks like the coupler came out great. That little tidbit about how to work around the hardened teeth is great info, I'm positive it will come in handy at some point. Keep it up :)
Do you think it would be easier to get a piece of aluminum machined to fit the motor's shaft? If you're already machining an adapter plate, you could use the scrap for the coupler.
