pic: Macbooks aren't the only Unibody Construction

[artdutra04]

Originally Posted by Cory

What was the run time for one of those?

Sadly, no where near as fast as I originally wanted. I had to run these on a TM-1, as the VM-3 and VF-4 were both already being used. It ended up being a little over an hour for each one on the TM-1, mainly limited by me manually slowing down the program to 4000rpm and 40ipm to avoid throwing chips and coolant everywhere (which it still did). Also, if I was going to do this again I'd optimize the CAM toolpaths, as my software added some dumb things in there that just wasted about 15 minutes doing nearly nothing. I would have loved to do this on the VF-4 at well into a triple digit ipm feed rate, with much faster rapids, and nearly instantaneous tool changes.

Edit: Also, if I make these again I won't be as lazy. The only two three end mills I used were a 1/2" flat carbide, 1/2" ball carbide, and 3/8" chamfer. It would have been nice to also add in there a 1" carbide flat end mill to hog out the pockets faster, but that a: would have been pretty scary at full force in a TM-1, and b: I would have had to walk across campus to the other machine shop to borrow another tool holder. ;-)

Originally Posted by AdamHeard

Just curious.

What's the weight difference to an optimized design with standoffs?

I imagine at this point it doesn't matter, and the reduced number of parts outweighs it as you were already underweight (iirc).

The unibody transmission bodies shown here weigh 5.44 ounces. Before I designed this, I did a plate and standoff design using 1/8" plate and 3/8" aluminum hex standoffs, which actually ended up being 1.6 ounces lighter. However, when I added 1/16" polycarbonate side shields to it along with a few #4/40 screws to hold it in place, the difference was essentially nothing.

The side shields were somewhat necessary in that this transmission is mounted right near one of the handles added onto to the robot to act as a safe lifting point, and also only a few inches away from the cRIO. Adding an ounce or two of shields is way easier than filling out the mountains of paperwork for that one impatient person to stick their arm into the robot reaching for who knows what only to have their fingers meet up close and personal with a gearbox.