Double sided maslow for foam cutting?

There is a community out there building campers and trailers out of foam covered by glue/paint and canvas (search for Poor Man’s Fiberglass for more info). The idea is that the new foam boards are rated to 25 psi or higher against compression, but will snap as they are bent because the outside of the curve stretches and develops a crack. but put a layer of glue/paint and canvas/window screen on it, and it’s suddenly FAR stronger. An inch or two of foam (2" 4x8 at home depot is ~$40/sheet) gives you R12 or better, which is better than most houses.

the right way to cut this sort of thing is with a hot wire, but a machine to do this on a 4x8 ft sheet is pretty difficult.

But if you took a traditional maslow, and used motors that have a through shaft so you could put a sprocket on both sides of the workpiece. you could then have the workpiece vertical with a light sled on each side to hold the hot wire and do CNC cutting of your pieces very easily.

The maslow even supports not having a motorized Z axis, so you could poke a hole through the foam and run the wire through each time it commands the Z to go down and start cutting, pulling it out when it’s done (so you don’t need to worry about making sure that the CAM program doesn’t cut through your parts on the way to the next cut)

I know that we’re all eager for the maslow 4, but this hit me as something easy to do with the old approach that’s unique to it, so I thought I’d throw out the idea and see what people come up with


Strangely I just read an article on a poor man’s teardrop foam/fiberglass trailer and thinking I should add it to the it’ll never actually happen to-do list. Routers cut foam like butter as long as the bits will reach and you can handle the tool width gap.

Back in the 80s we started building a Quickie Aircraft Company Q2 kit, hot wired boat dock styrofoam covered with fiberglass and epoxy and spent several years working on it. Like many, life (farm, children, job travel, couple moves, building an appropriate shop) intervened and it was never completed, although we still have all the parts stuffed in assorted outbuildings. Glass cloth over foam is pretty easy, as long as you don’t mind mixing, stippling, and squeegeeing. If it’s strong enough to fly around in a less weight constrained trailer shouldn’t be an issue.

PMF is far cheaper than fiberglass/epoxy, not as strong, but apparently strong enough .

routers will cut foam easily, but they make a HUGE mess and a large kerf. hot wire cutting would let you cut mating parts nested, then rotate and glue them.

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I’m currently building one of those trailers though mine is hybrid with wood panelling inside and I’m using epoxy on the outside. The kerf on a hot wire cutter is small enough I probably wouldn’t bother disconnecting and connecting for nested parts. Just glue the transit cuts back together with weldbond or the glue of your choice before coating.

However M4 appears to have pretty good dust collection which should negate the hassles of cutting XPS with a router.

Also one could use the Maslow to cut kerfs for the curved roof panels. A little calculating and a tapered bit and you could end up with essentially perfect curves without any voids.

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Our airplane parts were hot wire cut, with a shaky looking cutter made from a 2x4 drilled to hold electrical conduit (1/2 EMT?), powered with a transformer connected to a fan speed control plugged into a 120v outlet. They recommended a variac but they were rather expensive and it probably wasn’t any safer. I’m probably lucky to have survived that…

If we have a Maslow then for a few sheets of 1 1/2" extruded polystyrene the mess should be manageable, and way easier than digging out the 8’ long cutter and it’s questionable power system.

PMF? Polyester Madness Fiber?

poor mans fiberglass

starting with a foam base:

use canvas or window screen instead of glass fiber cloth
use thick latex paint or wood glue (tightbond II is commonly used, tightbond III
is listed as waterproof, but a new layer won’t stick to a dry layer, so II is
more commonly used)

David Lang

my concern would be on the alignment and potentially lots of small pieces

My thoughts exactly. I was thinking of these kind of bits cutting many parallel partial depth slots for a curved roof like a Conostoga wagon. Or for round cornered camper furniture that breaks before the human body to preserve shins and such.

Cheap enough it could be a new kind of semi permanent interior construction method for access panels. Hide your batteries, wiring, LED lights, plumbing, emergency supplies, behind a foam panel glued in place. If you ever need to get in there, simply break foam (tool free).
Cut a new panel when you get home.

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Maybe use a hot knife instead of a hot wire? With a hot knife you wouldn’t need a double sided object, just a jig to hold the hot knife. Something like this seems optimal, as it is a round “blade” so you don’t have to worry about cut direction.

my experience with those is that they are great for poking holes in things, but
as the heat comes from the handle and not from the wire itself, the area away
from the handle cools as you move through the material and soon you have a bent

David Lang

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