Friday, July 15, 2011

And Back to the Mill

Just got some more time on the mill to finish out the cassette transmission plates.  The last post on these ended with the first operation complete.  The next steps are to machine a fixture plate and then run the 2nd operation which includes boring the bearing seats to final size with a +.0002/-0 tolerance.  That's pretty tight, about 10% of the thickness of a human hair.

Here's the fixture plate, a piece of MIC-6 cast aluminum ground tooling plate with dowel and mounting holes:



Here's the part after finishing the profiles and roughing the bearing bores:

Now I'm finish machining the bearing bores with the custom boring bars ordered from Microbore:

The reason I am using such a long tool for this operation is that the same bore sizes need to be machined deep inside the lower crankcase girdle casting.  By dialing in the size with these shallow parts I can use the same tool later on when line boring the block and be sure the bearings have a consistent fit.  The primary and output shaft and shift drum bearings were all single point bored to size with these long tools.

Tomorrow I'll do a test fitting of the gears, shift drum and forks, the shifter pawl assembly and try to stuff it all into the crankcase girdle casting.  Look for another post soon as the bottom end starts to take shape.


Chris

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