Cutting Depron

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Ian
Posts: 170
Joined: Mon Nov 11, 2013 1:44 pm

Cutting Depron

Post by Ian »

Most of you know that I'm currently into Depron models. It's nice and easy to work with, but the process can be tedious: the plan on the computer is printed on to a number (usually 9 or 12) of A3 sheets which are then lined up and taped together. The parts are then roughly cut out, stuck to the Depron with spray adhesive, and cut round.

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.
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Ian.
Alan
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Joined: Tue Nov 12, 2013 10:54 pm

Re: Cutting Depron

Post by Alan »

Ian, I take my hat off to your ingenuity, fantastic !!!
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Alan Meaney
Andy
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Joined: Sun Feb 09, 2014 12:50 pm

Re: Cutting Depron

Post by Andy »

Impressive stuff Ian, well done!
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Mike P
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Joined: Sat Nov 16, 2013 7:26 am

Re: Cutting Depron

Post by Mike P »

Great idea and yet a bit more work for the 3d printer me thinks.
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Ian
Posts: 170
Joined: Mon Nov 11, 2013 1:44 pm

Re: Cutting Depron

Post by Ian »

…so as I was saying… (almost a year ago) the next step is to make a bigger CNC machine. And finally after much fiddling and several re-designs, here it is. Today it flawlessly cut out parts from two and a half sheets of Depron for my next project, the Buccaneer, for which I’ll do a separate thread shortly. The accuracy is excellent, parts are exactly the right size and fit perfectly, and after all this effort it’s great to just sit there and watch several dozen parts just appear.
Here's a bit of video showing it in action:
https://youtu.be/DC5id8_G6OY

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/
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Ian.
jason
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Joined: Wed Sep 21, 2016 8:18 pm

Re: Cutting Depron

Post by jason »

Wow thats amazing Ian - be interested in seeing this progress!
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Ian
Posts: 170
Joined: Mon Nov 11, 2013 1:44 pm

Re: Cutting Depron

Post by Ian »

The Needle cutter has been in use for almost 3 years now, although obviously it only gets deployed when cutting out parts for a new Depron model. Although generally reliable, I have had problems in overheating of the nozzle, even with cooling fins fitted. The needle is 0.55mm running at 6000rpm in a 0.6mm tube, which gives very precise and accurate cuts, but gives rise to a lot of friction heating, causing melting of the foam, leading to jammed or broken needles.

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!
Needle cutter at work on a 1000mm x 700mm sheet
3mm copper coil wound and soldered around brass nozzle
PVC pipes to cooling head
Pump and hi-tech reservoir!
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Ian.
Andy
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Joined: Sun Feb 09, 2014 12:50 pm

Re: Cutting Depron

Post by Andy »

That's very clever Ian.
I think you're going to have to add coolant engineer to your list of skills!
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