Stock is the original piece of material that is being milled. Stock can refer to a big sheet of aluminum, a VersaTube, just whatever you need to mill. Almost everything we mill is either sheet or a tube.
Flat piece of aluminum-6061 or polycarbonate that get screwed down onto the wasteboard. The sheets we stock come in sizes like 16x30”, 18x24”, or some combination of numbers around that range. Because of the range of travel of the CNC, the max size we can mill 24x30”.
24” in the x direction is because of the wasteboard, you can slightly push the 30” if you zero aggressively on the left, but 30” is a comfortable limit.
Thicknesses for aluminum are 0.09”, 0.125”, 0.1875”, and 0.25”. For polycarb, usually anything between 0.0625”, 0.125”, and 0.25”. Specifics on thickness aren’t too relevant, just know that thicker stocks are harder to cut through.
For sheets, you need to drill holes and screw them down onto the wasteboard, or they will move around during the op. Any stock will vibrate when it’s in contact with a bit. If your stock isn’t rigid and it vibrates a lot, it generates a lot more energy that transfers into the bit (physically knocking it, cutting more than intended, heat, etc.) that will break it. It’s also important to keep it as flat as possible, to minimize curve in part / make as accurate as possible.
Sidenote, this is also why the wasteboard needs to be as flat as possible. You could use a skim cut (more skim surfacing) to flatten it. (I’ve never done it, but we should lol)
The easiest way to accomplish this is to just add as many screws as you can easily. One screw in each corner is a given. Try to screw closer to the area being milled, as screws far away won’t do as much.
If you can confidently figure out where the bit won’t go, then throw a screw on open areas that won’t interfere with the op. If the bit hits a screw however, it’ll break, so be careful.
The best (and fastest) practice is to drill a pilot hole first (in just the stock, not wasteboard) and then screw in. Even with sheet-metal screws, they’ll wear out after several uses.
It’s likely that when you screw in, the sheet will lift up a bit as you screw in, making it not flat. The trick here is to just take the screw out, hold it down with your hand or something heavy, and screw it back in. Try to hold it down the first time so you don’t have to go out and back in and widen the hole.
After the pocket and before the final contour, you need to screw down the parts. Otherwise, as they get more separated from the rest of the sheet, they’ll move everywhere, get cut inaccurately, and go flying randomly when it’s done.
If there’s existing hole pattern, screw down at least 2 of the holes per part. The more the better, but 2 or 3 does perfectly fine.
If there’s no hole pattern, it’s helpful to add some in the CAM beforehand. You can also just freehand choose 2 holes before running the contour.
Once everything is milled, undo all the screws and put them back in the box to reuse for the next op. Throw out any ones that are completely stripped or ruined.
We use the WCP CNC Tube Fixture, which is on the back (-X side) of the mill. Just like sheet, it needs to be fastened down securely before any milling is done.
The tube fixture works with these hex nuts that clamp down the tube. They can be moved to different holes in 0.25” increments, from 0.75” to 2.25”. The edges are precisely milled (by WCP) to be straight.
Before putting in the tube, use the air compressor hose and/or vacuum to make sure it’s clear of any shavings or debris. Slightly untighten the nuts, slide the tube in, push it up against the walls of the fixture, and tighten down the nuts down.