How to Cut Large Swept Back Wings and Save Foam

The Problem: running out of machine travel

If you’ve ever tried cutting a high-sweep design like a flying wing, you’ve likely hit a frustrating wall: running out of horizontal travel on your CNC foam cutter. I use a clever alignment trick in DevWing Foam (and previously Profili 2 Pro). By aligning the leading or trailing edge directly with the hot wire, you can cut wings that would otherwise be ‘too big’ for your machine.

The solutions

  • DevWing Foam 2
  • https://kruissen.nl/

These solutions are especially useful for things like flying wings, swept jets, or forward-swept designs where the root and tip chords aren’t parallel.

  • By aligning the leading edge or trailing edge of the wing blank with the hot wire, you’re essentially cutting along a fixed reference line. This keeps the wire at a consistent angle relative to the wing’s planform.
  • This helps to avoid the usual “wire lag” problem, where one end of the wire travels much further than the other, which can cause inaccurate airfoil shapes or warps.
  • On top of that, because you’re not cutting diagonally across a big chunk of foam, you reduce foam wastage — the blank can be narrower and still yield the full wing planform.

DevWing Foam 2

Aligning the leading or trailing edge to the hot wire gets over that problem, and you can cut wings with a very large sweep angle between the root and tip. Another significant advantage is that you can significantly reduce foam wastage.

path too long for hot wire
align wing trai;ing edge with hot wire
Aligning the trailing edge with the hot wire

The only issue with using this method is that you need to cut the root and tip to the correct angle either before or after the main wing cut. DevWing Foam 2 does have an option called Block Side Shaping, which can do this as well.

If you have DevWing Foam 2, then you can use the option to cut the foam block to the correct angles before or after the main cut.

The free g-code generators for wings don’t have this option, but you could, with some maths, calculate the values, or use a CAD program to draw it out and measure the angles and foam size.

Free option

A clever guy called Martijn from the Netherlands has created an excellent online utility to calculate the angles and size of the foam block https://kruissen.nl/ with a manual and pictures.

free online calculator for foam block

How to cut the root and tip-swept angle

Just enter your dimensions, and you get the size for the foam block and the angle you need to cut the root and tip.

You can then cut your foam using the hot wire. If you are using Windows GRBL HotWire Mega software there is a slice macro that can do this. I’ve shown that in one of my videos https://www.youtube.com/watch?v=-nVzzA1CwF4&t=530s

Final thoughts

Foam is now getting more expensive. Just recently, I purchased some foam from a major DIY store in the UK, and it has almost doubled in price. So, rotating the foam block option will allow you to get the most from your foam with just a little extra work to cut the root and tip angle.

I sometimes get questions asking me how big a swept wing I can cut on this machine. Well, using the methods above, you can cut a much larger sweep back than if you didn’t rotate the foam block. You can also make the wing in sections to get an even bigger sweep.

Happy foam cutting

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