Following my recent failures at actual milling I’ve got to add some guards to the machine.
Aside from reducing the likelihood of personal injury these are necessary to keep swarf (and eventually cutting fluid) confined to the tray. The shields need to be made of polycarbonate to resist fracture on impact. They also need to be secure but readily demountable to allow full access to the bed.
I’ve drawn up an aluminium frame from extruded angles that should provide plenty of support for the 6 mm thick polycarbonate The frame bolts to the tray and polycarbonate. If necessary I will alloy-braze the frame to improve the strength.
Note that while thinner polycarbonate sheet will probably withstand the impact or an errant part it isn’t very rigid and will be difficult to support over the required spans. Even the 6 mm sheet is fractionally more flexible that I would have liked, but if necessary this can be reinforced with adhered polycarbonate or bolted aluminium profile. The front of the shield simply slides upward for ready access to the bed and spindle.
Figure 1. Safety Shield Design Concept
The shield is 400 mm high which extends over the full Z axis traverse. Unfortunately I need to move the machine on the tray to ensure that the X axis can fully traverse between the hard stops without hitting the guards. Ideally the tray would have been say 100 mm longer and wider. I will seal the errant holes with aluminium and epoxy or silicone - not ideal but functional.
I had to purchase an entire sheet of 10 mm thick polycarbonate which was three times more material than required and rather expensive (~$400). The excess will probably find a use in cover for my 3D printer.
The machine guards were fitted today. They are robust and secure. The front is locked in place by two 6 mm diameter steel pins. Remove these and the front sides up and free, allowing unfettered access to the bed. Each side guard can be removed by undoing four M4 bolts. The whole guard assembly is fixed in position by forty-five M4-0.7 bolts.
Figure 2. CNC Mill Guards Fitted
In the event of a part becoming airborne the sides are all retained by a 50 mm wide aluminium profile on the lower and vertical edges. I expect that the guards will deflect a way but they cannot reasonably come loose.
The fit is a fraction bit tight, with just 5 mm between the X axis and the guards and full traverse, but this is adequate. The machine wont be crashing into the guards.
I expect that over time the guards will become abraded through swarf impact (even though polycarbonate is very tough). Time will tell on this aspect of the build.
Click here to link to cutting fluid Mist Spray