Wouldn't it be nice, I wondered, if I could go straight from the computer file to cut-out parts? After all I have a CNC machine.
The problem is that a rotating cutter doesn't really work with soft materials like Depron. The cutting bit chews the Depron, lifts up the sheet, and tries to push it sideways especially when cutting thin parts. A laser seems the obvious choice, but high-power laser cutters in reasonable sizes are hugely expensive, fragile and dangerous. Low power lasers, while cheap, don't work with white Depron as the beam just gets reflected.
Recently however, I came across a fascinating thread on the Flitetest forum where an American aeromodeler had developed a way of cutting Depron based on a reciprocating needle - a piece of piano wire moved up and down like the needle of a sewing machine, punching a series of joined up tiny holes as it moves along. The concept is so simple that I had to have a go.
So here it is, made of parts I already had; a motor & speed controller, a spring from a clothes peg(!), piano wire and a bit of brass tube for the nozzle / guide. And it works! Temporarily lashed to the CNC machine and switched through a spare receiver just to prove the concept, it cut out this test piece first time. Since there is no significant force on the Depron, a couple of small lead weights were all that was needed to hold it in place. So my next project will be to build a bigger CNC machine to cut a full Depron sheet (1250mm x 800mm) in one go. Because of the tiny forces, much smaller motors and rails can be used compared with a 'normal' CNC machine. It will have to be easily dismantled as I don't have the space for a permanent machine of that size.
And while this was going on the existing CNC machine was cutting out the lite-ply parts and the 3D printer was making the other bits! For anyone really interested in the details, all this came from this thread on the FliteTest forum, but beware it’s a long thread spanning 2 years and 100 pages. I will probably post some technical details there soon.
http://forum.flitetest.com/index.php?th ... dle.24251/
So before using it this time I replaced the air cooling fins with a water cooling system. This consists of 3mm copper tube wrapped round the 5mm brass nozzle, linked by 1.2mm PVC tubing to a small aquarium pump. This is switched by the controller so it only comes on with the needle motor.
Rather to my surprise it's worked better than expected: the nozzle is almost stone cold after half an hour's cutting, whereas before it was too hot to hold. Last week I cut 5 sheets of Depron in one day for my next 2 models (of which more later), with no outages at all, 100% reliability!