Monday, September 17, 2012

Spherical Lathe Work 2

Another shot of the roughing process. If you ever have to estimate a job with a large amount of material removal be sure to do the math. Its easy to under estimate the time required to get down to the finish shape. The Okuma had plenty of power to remove the material it turned out to be a tool life problem. The concave side needed an insert with a more pointed geometry to clear the bottom so it wasn't as durable as we would have liked.
On the Okuma it has a programmable cycle that automatically generates a roughing and finishing cycle based on a few input parameters. Given the starting position, depth of cut and the final finish path the machine control figures out the rest. Pretty sophisticated for a 1986 machine. I bought the machine through a sealed bid government auction. As it turns out the very people that this spherical job was for. I did get a chuckle out of that.
Before we removed the convex side the mill features were added so we could easily fixture the soon to be sphere. The small hole you can see in the bottom was the only connection to the outside world.There is a small lip near the ID that is hard to see. This hemisphere was slightly more that a half to allow it to index into a counter-bore in the other half.
One of the trickier operations was getting an accurate start for the counterbored holes. The angle of approach was so steep making it difficult to get a flat spot to start the drill. Originally the drawing called out #6 machine screws to hold the two parts together. We asked it we could increase the size to make it a little easier. I'm really glad they let us increase the size because it was hard enough even when we went to #8.
The finished job.
Cory wrapping the pair of sphere's for shipping. I almost said balls but that would have been a low blow. These have a wall thickness around three quarters of an inch so they were very heavy. Nobody wanted to be the bozo that dropped one.
Another interesting sphere of sorts. But I'll save this one for another time. It got the shop nickname of the Death Star.


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