Monday, April 19, 2010

Making a Conoco Gas Truck, Part VII

Well, partial success. I made some mistakes, and I need to make some adjustments. But first, the results. As you can see, I now have lids for the tanks, as well as oil cans.

 P4190839_400

I’ve included a close-up of the two oil cans. These have some flash, and other issues, but the corrugation is clearly visible. Even with the naked eye you can tell that the corrugation is there, so it was definitely worth the effort.

P4190840_Cans

So what are the problems? First, the extra flash is a result of a small mistake I made creating the tool paths. The milling machine ended up making the first pass two large, which results in extra flash and obscuring the fine detail of the two “ears” on the top of the can. I figured out what I’d done wrong after making the test mold. Here is a side-by-side comparison that shows what I cut on the left, and what I should have cut on the right (these images show the simulation of what the mold will look like after a pass with a .015” diameter bull-nose cutter):

Bad ToolpathGood Toolpath

Second, the oil cans are a little bit too large. They don’t quite fit into the troughs. They go about half way down and then stick.

As to the tank lids, the hole I made for the handles is too small, so the handles don’t fit into the hole. I think I’m going to change this so you can use a standard size drill to open up the hole. Getting the holes just the right size with my milling machine is a little tricky because of backlash, which results in holes that aren’t precisely round.

I’m really glad I made a test mold. In fact, given the problems I ran into, I think I’ll make one more test mold of just the tank lids before making the production mold.

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