Wednesday, September 7, 2011

Finishing the primary drive gear

After the two lathe operations to create the primary drive gear blank I need to do one mill operation to create the clutch basket mounting holes and various weight reduction features.

Switching from machining aluminum to machining steel is like getting a 2 flat tires.  With aluminum you can spin the spindle as fast as it can go and then just push the end mill though the material with little regard for cutting forces or temperature.  Chips fly and progress is made, quickly.  With steel, especially this high strength 4340 material, the spindle needs to slow down a lot and the feed rates seem to be just above a crawl.  End mills wear quickly and if you're not careful with the cutting parameters you will be treated to the sight of a glowing end mill spitting out glowing chips.  Pretty, but not good for material integrity.

To hold the part I machined soft jaws (similar in concept to the lathe ones) in the Kurt vice, clamped the part, and indicated it for concentricity just to be sure.
After setting up a set of the same tooling used to machine the crankshaft journals we're ready to run the program.  It is not too complex a program, just some holes and pockets.  The finished part looks like this:




and after repeating a few times we have a nice group of parts:
The parts are now ready to be sent out to the gear house who will cut the gear teeth on the outer diameter of the part.  It will then go for plasma nitriding to surface harden it and after that the part is ready for use.

Tomorrow I'm going to switch back to aluminum and start machining the clutch side cover.

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