Best method to cut foam? - RC Groups
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Apr 17, 2012, 01:10 PM
Redacted per NSA "suggestion"
dedStik's Avatar

Best method to cut foam?

What's the easiest way to cut foam without a CNC or hot wire cutter?

I ask because I'm working on a foamie now, and I bought a wire cutter but I do not like what it does to the foam (hardens up the edges, makes sanding a PIA). So I ask how do you cut foam by hand?
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Apr 17, 2012, 02:21 PM
An itch?. Scratch build.
eflightray's Avatar
Very sharp knives are useful, I use those with the snap off blade sections to always keep the tip keen.

But if your hot wire cutter is too hot then it can cause melt back, you could try a lower temperature cut, depending on what type of cutter and controller.
Apr 17, 2012, 03:29 PM
Snipe the Skies!
snipeworm's Avatar
Depending on the foam you have hotwire can be much easier. I had great luck on dollar tree board using sharp hobby and exacto knives. On this 2" foam I picked up at Home Depot I get awful cuts with a blade. I too have noticed the rigid edge produced by the hot wire cutter but if your cut is on the mark then it actually adds a lot of rigidity to your foam. If your are using this thicker stuff try making your cuts as close to your finish mark as possible and use lightweight spackle to fill in the areas needed then sand.... works pretty good for me.
Apr 17, 2012, 03:32 PM
Registered User
The Hotwire cut, if done right, will harden the edge it cuts, which will help make the foam more rigid... requiring less support. True it makes it a little more work on sanding, otherwise... lots of new razor blades.
Apr 19, 2012, 12:48 AM
Foam Av8r
RogueTitan's Avatar
the trick to making good cuts with a hot wire router is:
1. probably the most important not to have the wire too hot.

2. make sure the edge of your templates are smooth and free
of any places that can catch the wire

3. keep the same travel speed with no stops and starts.

4. don't put pressure against the wire with the template
this will cause the underside of the cut to have a miter

5. sand the edges of the cut part before removing the
template with a Emory board
Apr 19, 2012, 09:17 AM
SG Talon... Super Genius.

I have built more planes than anyone on RCG would believe. Every single one of them was cut with a single edge razor blade and a straight edge. I just bought another pack of 100 at Home Depot for $6. Got them from the paint department.

They look like this -

As soon as they start dragging instead of slicing through easily i swap it out for a new one.

When i have to do tighter radiuses I bust out the Exacto Knife. But i ONLY use it for small tight cuts.

Of course the really best way is to get them CNC cut from a friend with a machine I really hate cutting out kits.
Apr 19, 2012, 01:18 PM
Redacted per NSA "suggestion"
dedStik's Avatar
Yeah the cutting was the worst and some of my seams and cuts could have been straighter. For my first build up from plans I think my results are outstanding. Next build I have much I learned to bring to the table. I had gotten a metal ruler 56" for measuring long and making straight long cuts. Next build will remember when cutting to actually use clamps so my ruler doesn't walk on me.

I did find that using a utility cutter was a pretty good solution, though it takes forever.

Also a mistake I made I didn't realize until my brother pointed it out. I mounted the servos under the wing. In doing this I've exposed the control rods to possible damage on landings. I suppose it's a learning process, I originally built it to aileron train me before I fly my trainer .40 electric conversion, I guess since I learned so much putting it together it's already paid off.
May 10, 2012, 01:22 PM
Registered User
sixfins's Avatar
I like my Hobbico Hot Knife with a straight edge. It's bascally just a 25w soldering iron with an exacto blade attachment. It cuts smooth and quick, don't stop or you will get the hard edges and possible burnout of the foam. I tried the razor blade method on my first build and very much prefer the hot knife as it is much quicker/easier.
May 10, 2012, 03:35 PM
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dedStik's Avatar
My cuts have since improved. I moved from using a utility knife to using an xacto. I'll swipe the blade across a sharpener a few times before making my cut, I try not to cut more than 12 inches at a time. I also picked up a tip from Freddie B for cutting out smooth circles. I'm using 1/2 inch copper tubing that has been sharpened on the insides.

Since learning these methods and practicing a few times, I'm really getting quite good at cutting.

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