Cutting aluminum sheet on the Shopbot
Aluminum sheet can be cut on the Shopbot, but there are no good guides available for doing so. These are notes about the author's experiments in doing so.
Material: 2024-T3 aluminum sheet, .020" and .025" thick. Bit used: Yosoo 1/8" 4 flute bit with 1/4" shank - 5 of them for $12 on Amazon. These bits are for cutting wood/aluminum/plastic.
Experimental method: Find setting that does not break bits, then try to increase speed.
Method 1: Stacking multiple pieces of aluminum sheet under a 1/8" thick plywood, screw down to surface, cut slowly at depth increments down to 0.020".
Result of Method 1: Stacking 10, 4, or 2 sheets all has similar problems - on the lower sheets, the bit would load up with aluminum and smear, rather than cut, the bottom sheets. On the thicker stacks, this would eventually break the bit.
Method 2 (aka "the method that actually works"): Single sheet thickness, cut slowly. Set the Z-axis to the surface of the Shopbot table. Either mark the edge of the piece(s) you want to cut onto the table or use one of the deeper existing lined cut into the table as an edge.
If there are any sections that will be cut free (e.g. hole centers), cut one pass of your design at a depth of .020" into the table. Use a square to mark the center points of the sections to be cut free and the distance from the edge line onto the table.
Place an aluminum sheet onto the table lined up with the edge line.
Mark the corners for screwing the sheet down and the center points of sections to be cut free with a sharpie, remove from table surface. Do not put screws in the cutting path, it will ruin your bit. If cutting multiple sheets, place the marked sheet on top of the stack. Drill the screw holes in all locations.
Take ONE aluminum sheet and screw down the sheet and any sections that will be cut free to the board. Set up the cut as follows in V-carve:
Cutting depth: 0.020"
Cutting depth per pass : 0.020"
Cutting speed: 6 inches per minute (0.1 inches per second)
Plunge speed: 6 inches per minute (0.1 inches per second)
The Z-axis zero point should be the surface of the table, not the top of the aluminum sheet. This will mean that the edge of the milling bit will be doing the cutting, not the tip. This reduces the chance of aluminum chips loading up the bit.
Cutting faster will load up the bit with aluminum and prevent it from cutting cleanly, and will eventually snap the bit.
Methods may be different with a bit with fewer flutes or larger bits. As of this writing, this is the only known success of cutting sheet aluminum on the Shopbot at LVL1. Experiment at your own risk. The author broke 7 bits while experimenting.