Sunday, August 5, 2012

CNC Machining the body

Ok, here is where the CNC fun starts. I made sure to design the body with the fact that I would be contouring the body on my CNC machine with a 0.250" ball end mill. Also, the design of the car required that I be able to machine the car at least from the left right and the bottom. I ended up building a fixture out of some scraps I had in my scrap bin.

At the left side There is an expanding mandrel I made from a piece of 1" hex stock steel and a rubber expansion nut. The middle school car is placed loosely on the end of the mandrel. The real stock wood fits all the way up to the steel shoulder. The expanding rubber section holds the wood on the steel shoulder and prevents the block from rotating. The hex shape allows me to rotate the part around the longitudinal axis as 60 degree increments. The hex mandrel is located against the two dowels in the fixture. You can see the block fixtured in the background of the second picture.

I used HeeksCNC to generate the tool paths to cut out the part. Here you can see the part positioned in the 6 orientations it will be cut in. With the six positions every spot on the car should get a good change to have the tool cut the surface at a close to normal direction to prevent needed to use extremely close contouring lines. 
And here is a screen shot of one of the finishing profiles.
And finally at video of one of the programs.
Note that I will manually cut the front of the car with a band saw and create a good looking tip to the car.

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