CNC Foam cutter

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Foundationer

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It finally occurred to me that I could convert the thing to cut cores/moulds of almost any size by having independent towers and a weight tensioned wire. I don't know why it took me two years to think of that but there you go. Here's a 1.8m wingtip upper mould that turned out pretty good first go!
 

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Foundationer

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That is a HUGE kerf. You must be running some major current.
Yeah probably. 36v at about 3a I suspect.

The tip is moving half the speed of the root which has a more sensible kerf but is the limiting factor. The great thing about it is you get a really nice firm surface where the foam has melted.
 

Jay Kempf

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As I remember it one of the software packages has kerf compensation. What I can't remember is if you can do different kerf compensation at each end of the wire. If I was posed with that problem I would just offset the airfoils after measuring the kerf and put the compensation in the input geometry I guess.

I have a really cheap original 4 axis CNC wire cutter. Works but really made for light model airplane applications. You did a good job of scrounging to get the cost down to 250 quid. I have an entire redundant CNC machine setup of steppers, power supplies, drivers, BOB, etc... and I was looking at making a meter cube machine and it still came out to $900 which is still good for a very rigid machine.

BTW I use .025 and .032 stainless safety wire for my rig. Works great. That way you don't have to waste good guitar strings. I keep a lot of guitar strings in stock :)
 

Vigilant1

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What is your total wire length, and what is the approx width of that kerf on the tip end (5mm?). I guess it might be possible to determine the relationship of cutting speed to kerf width and then incorporate that into your pattern allowances, if this is a critical issue.

Thanks.
 

Foundationer

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I used jedicut which took a lot of work to get right with a .dxf input as it's aimed at rc wing cutting but it does alow you to specify a kerf at each end. The real problem with this was that I only had the 'really long wire' epiphany after milling the moulds for the other tip. Each process has its own accuracy/tolerances so to get both sides identical took some tweaking. Milling makes a hell of a lot more mess.
 

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rtfm

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Hi,
I'm cutting foam ribs, not full full foam cores as you are doing. Cutting ribs, of course, is a darn side easier, and I do so on my cnc router. Like this: The nose of the middle rib hasn't QUITE cut all the way through (slight depth adjustment required) but the difference is only wafer thick.
1616361652780.png
 

Foundationer

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Hi,
I'm cutting foam ribs, not full full foam cores as you are doing. Cutting ribs, of course, is a darn side easier, and I do so on my cnc router. Like this: The nose of the middle rib hasn't QUITE cut all the way through (slight depth adjustment required) but the difference is only wafer thick.
View attachment 108825
They look great! I really like the idea of foam ribs. Are you putting glass or spruce cap strips on em?

I had a go at making a vacuum hold down for mine so I wouldn't have to keep putting all the screws in otherwise pristine parts. Be really useful for foam.
 

rtfm

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Hi,
I'm sheeting my wings with 1.5mm Gaboon ply (really light stuff), so there is no need to add ply cap strips. I find that a bit of double-sided tape works wonders. There is very little lateral pressure on the foam as the bit cuts its way through. I'm using a 3mm bit, running at 4800mm/min in a single pass. Works beautifully. Quite messy, though.

For design software, I'm using DevWing Cam (by Profili), which is great for creating complex wings (although mine are very simple).
 
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