How do you cut foamboard?

sprzout

Knower of useless information
Mentor
So, here's some tools I use for my builds:

Box cutter/folding knife for long straight cuts - https://www.dewalt.com/products/hand-tools/knives-and-blades/folding-fixed-blade-knife/dwht10916

It's a Dewalt folding box cutter, and I love this thing. One of the reasons I like it is because it's not the standard grey, but that bright "construction yellow" color, which makes it really easy to see on my build table and self-healing cutting mat - I tend to "misplace" items on my build table easily, and having them be a bright, obvious color makes it easier to spot. Also, this particular knife has a quick release for changing the blades, which is kind of nice - it means I don't have to use a screwdriver to disassemble the cutter and turn or swap the blade like I would with many other box cutters. Is it necessary? No, but it is nice to not need another tool cluttering up my build table. :)

Blades for folding knife - https://www.homedepot.com/p/Husky-Heavy-Duty-Utility-Blades-Dispenser-100-Pack-HKHT19057/205037418

I bought the 100 pack of these blades at my local Home Depot. I had originally bought a set of 50 blades at the local Harbor Freight, a box of no-name brand blades, because they were like, $3 for 50 of them, I think? Turns out the blades were junk. I could get only a few passes with them before they were dulling and I was having to go through the hassle of sharpening them, flipping them around, or swapping them after a couple of long cuts. Spending a little more for the "heavy duty" blades, they last a lot longer and are well worth it, in my opinion, especially if your box cutter requires you to disassemble and reassemble it with a screwdriver.

Cutting Mat - https://www.amazon.com/dp/B0006SDOFO/?tag=lstir-20

I use a cutting mat like the one above to make all of my cuts. There's a couple of reasons for that - it doesn't dull the blade as quickly as cutting into something harder, and since I'm usually doing this in the living room on a coffee table, it saves my coffee table from getting all of the nicks of the blade (and prevents my hide from being tanned by the wife if it were to leave a mark in the table!)

Cork backed metal ruler - https://www.amazon.com/dp/B00094A48A/?tag=lstir-20

I use a cork backed metal ruler for cutting for a couple of reasons - I can lay it down on my pattern and give myself a nice, straight edge; the cork prevents it from sliding too much when I'm cutting, and I end up getting a nice, straight edge. I only have a 12 inch ruler, as shown above, but they come in 18" lengths for not much more. Also, the metal ruler is nice when I do something like glue poster board down for shaping - the metal prevents my fingers from getting burned and transfers heat more evenly if I press it against the poster board and the foam. See the MiG-3 build video for an example - it really does help save yourself from glue burns and it allows for a smoother edge.

Exacto knife with #11 blades - https://www.amazon.com/dp/B0000DD1N4/?tag=lstir-20

I use something like this to cut my curves and smaller cuts with, such as the rectangular inner holes that a wing spar might fit into. Many times, the box cutter/folding knife blade is too big to get in and cut effectively; the Exacto knife is much more precise and easier to wield. Also, you can buy a box of 40 blades for around $10 for this knife and they'll last you through many builds.

I should mention that I've seen some people say that they use T-squares for their long cuts; I tried to do that and failed miserably, because the straight line cuts never seem to be at right angles to the foamboard - it's always at various angles, and so I could never really get the t-square to sit properly on the foamboard. That's where the cork backed ruler worked much better, at least for me.

Hopefully this info helps with your builds!
 

checkerboardflyer

Well-known member
On straight cuts a small hobby table saw comes in handy. I use one to cut bevels in control surfaces. If you are using a foam board without paper covering, such as Depron or MPF, then a hotwire comes in handy. It gives a clean cut. Hobby saw post on my blog HERE. Hot wire post HERE. Tips for foam board R/C modelers on my blog HERE.

table-saw-bevel-fbf.jpg


hotwire-rib.jpeg
 
Nothing too radical for me. I use the adjustable, disposable blades for my main straight cuts, roughing out pieces, and even gentle curves.

https://www.amazon.com/gp/product/B07NRLHJ2T/?tag=lstir-20

A fine tipped X-Acto for the tight curves and fine work. Just go along very lightly on the passes until you're through.

https://www.amazon.com/gp/product/B07CR7QBRB/?tag=lstir-20

Fiskars 24"x36" cutting mat.

https://www.amazon.com/gp/product/B000YZASYO/?tag=lstir-20

A pair of 12" and 24" steel rulers.

https://www.amazon.com/gp/product/B01884OU6Y/?tag=lstir-20

I really like the Logan Foam Works tool for making the partial cuts and bevel cuts. Not a fan of the proprietary blade design, but the blades don't get much use beyond those two cuts, so they last quite a while. I'm sure there are some decent 3D printed version of this concept that would work pretty well also.

https://www.amazon.com/gp/product/B001JSQX3K/?tag=lstir-20
 

checkerboardflyer

Well-known member
This is the Stanley FatMax Utility Knife model 10-481. Up until now I have been using the inexpensive, throw away, plastic knives. The ones I have use 2 buttons; one to lock the blade in position, the other to slide the blade in and out. FatMax has just one button and a wheel or knob near the front to lock the blade. And it has some weight to it. It feels substantial. Spare blades are stored inside. It just seems all around more comfortable to use. More tips & resources HERE.

stanley-fat-max-2.jpeg
 
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Thorondor

Active member
This is the Stanley FatMax Utility Knife model 10-481. Up until now I have been using the inexpensive, throw away, plastic knives. The ones I have use 2 buttons; one to lock the blade in position, the other to slide the blade in and out. FatMax has just one button that does both functions. And it has some weight to it. It feels substantial. Spare blades are stored inside. It just seems all around more comfortable to use. More tips & resources HERE.

View attachment 162249
I have something similar, but I can't seem to get the blades snapped off cleanly or without showers of metal shrapnel.
 

danskis

Master member
Since this still appears to be alive I'll throw in my 2cents. First, I only use $Tree foam and for me, the ragged edges come when you're cutting through the bottom layer. The top is usually no problem, at least on straight cuts. I use a long blade about 4" long with no handle. I've found that I get a really clean bottom cut by doing the following. Once you've cut through the foam and you're at the bottom piece of paper...pick up the board off the table (or put it on the edge of the table) and push the point of the blade through as far as it will go. Don't try to cut yet. Once there is a lot of blade on the other side pull it up towards you and along the cut. This pulls the paper into the cut where its supported by the foam instead of pushing it off the foam and pulling foam with it.
 

Thorondor

Active member
Since this still appears to be alive I'll throw in my 2cents. First, I only use $Tree foam and for me, the ragged edges come when you're cutting through the bottom layer. The top is usually no problem, at least on straight cuts. I use a long blade about 4" long with no handle. I've found that I get a really clean bottom cut by doing the following. Once you've cut through the foam and you're at the bottom piece of paper...pick up the board off the table (or put it on the edge of the table) and push the point of the blade through as far as it will go. Don't try to cut yet. Once there is a lot of blade on the other side pull it up towards you and along the cut. This pulls the paper into the cut where its supported by the foam instead of pushing it off the foam and pulling foam with it.

So poke it through and saw upwards? That sounds like it would work better than what I do.
 

danskis

Master member
So poke it through and saw upwards? That sounds like it would work better than what I do.

Exactly, you want to pull the bottom paper up towards you. That way it pulls everything together instead of pushing it apart. Its not perfect but its better. You can sand the rough parts afterwards. I use a drywall sanding block from home depot. If you aren't already definitely iron the edges. I like your paraphrase of Mr. Lincoln....but after six hours of flying all my planes are back in the shop.
 

perhapsleiana

Elite member
I actually use Lenox Gold utility knife blades, they stay sharp through a good 5 sheets of foam. When they're sharp, I can get very clean cuts by holding the blade at as shallow of an angle as the curve/line allows and cutting all the way through in one stroke. Just fast enough that it doesn't stick. Just make sure to use a proper cutting mat for this technique, and use similar yellow chromate coated blades in the shape of #11 blades (I've seen them under the X-Acto brand) for really fine work.
 

AIRFORGE

Make It Fly!
Moderator
Would it be beneficial to use a "waste" sheet of foam board beneath the sheet you're cutting? It would prevent tearing/separation, by allowing the tip of the blade to pass beyond the bottom paper layer, while holding the paper in place. I use a single waste sheet on my cnc for cutting dozens of sheets, before I need to replace it.
 

perhapsleiana

Elite member
I use a cutting mat- a 24x36 one gets pricey though. If I need something cheap I'll use plywood or hardboard/tempered MDF, but that kills blades faster.
 

danskis

Master member
Cutting mat - well I just stuck a piece of posterboard under the foam board and what a difference it makes - much cleaner cuts. I'll use a cutting mat from now on.
 
I always think I should be able to sharpen a blade. No matter what I do, I never get that laser-sharp edge again. So I like craft-style snap-off utility blades, and save the x-acto blades for tighter curves or other hairy spots. Use a light touch, a good angle and several passes over a good cutting surface. A cutting mat on a flat desk/workbench is ideal. Snap off the blade to a fresh edge and it should go through like butter. Haha all this has already been said above. :)
 

eric75

Member
This might be a little dangerous, but I really prefer plain old single sided razor blades.
https://www.acehardware.com/stanley...e-edge-razor-blade-1-1-2-in-l-10-pc/p/2197648
It is very sharp, and thin to reduce the amount of material it has to push out of the way.
It is small and light enough that I can feel how deep into the foam I'm cutting.
A fresh one makes a noticeable difference for nice foam work, but the old ones are useful for wedging, prying and opening packages.

I find I can make nice cuts down to about a 5" radius with this type. You can bend the blade a little with finger pressure. For smaller radii there are a few techniques I use:
- First cut through the top paper with the razor blade, then switch to an Exacto blade.
or:
- Break the cut into shorter segments and freehand off the corners.

I remember Josh Bixler liked to to use these in his early videos. I assume he decided to stop scaring parents with instructional videos telling kids to use an a wicked sharp blade with no handle, but in the true spirit of building with popsicle sticks, BBQ skewers and foam-board from the dollar store, this is definitely the tool you should be using.
 

USCATX

Member
I’ve tried a lot of things so far, and this NT 9mm snap off blade is just the finest little $7 tool I’ve ever owned. It’s very slim for corners and fine work.

https://www.amazon.com/gp/product/B003DXWN42/?tag=lstir-20

Blades can cut 2-3 sheets of foam with some snap offs and they’re 20 cents in 50 packs or 15 cents in 100 packs. I still keep an X-Acto #11 around for the fine work like tabs, but they don’t hold a candle to the NT Cutter for the bulk of cutting.

https://www.amazon.com/gp/product/B009F6BMQQ/?tag=lstir-20
 

Mr.Grinch

Well-known member
I don’t recall who first mentioned it, but I am really liking using a scalpel. I picked up a set of 100 blades for about $7. I still use the single edge blades for long straight cuts, but the precision of the scalpel is well worth the investment of a few extra dollars.