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Help! How to cut Foamboard properly?

#1
Does anyone know how to cut foamboard properly? Whenever I cut it, it either goes off-center, the blade chips, the foam breaks, the foam pulls, and generally doesn't cut right. I have made 4 foamies before and all of them have crashed or been very draggy because of this problem. Does anyone know how to fix this?

Thanks in advance
 

Corsair714

Well-known member
#3
Samh is right, a sharp blade is important for a clean cut. Another tip for a clean cut is go over where you are cutting several times. Don't cut through the foamboard in one pass. First cut through the paper on top then half of the foam then the other half of the foam then the paper on the bottom this will give you the cleanest cut possible. So a lot of passes on the same spot.
 

Flyingshark

Master member
#5
Does anyone know how to cut foamboard properly? Whenever I cut it, it either goes off-center, the blade chips, the foam breaks, the foam pulls, and generally doesn't cut right. I have made 4 foamies before and all of them have crashed or been very draggy because of this problem. Does anyone know how to fix this?

Thanks in advance
It sounds like you need a sharper razor blade, as everyone else has said.
 

Merv

Legendary member
#6
+ 1 on the sharp blade.
I prefer the utility blades, I buy them by the 100, $10-12 for a pack. I prefer using them with a handle, it gives me more control over the blade. You will get a smother cut by holding the blade at an angle. When they start to drag flip the blade over or replace it. If I cut foam directly on my workbench the blades dull quickly. My blades last longer if I put something plastic under the foam. I use a scrap of coroplast anything plastic will work.
1609964603464.png 1609964665123.png
 

Merv

Legendary member
#7
On bevel cuts, I make a good cut, that is, get close with a blade. Then a few strokes with with a sanding block will turn a good bevel into a prefect bevel. To make a sanding block, glue a bit of sandpaper to a bit of scrap wood.
 
#8
Well that would be an issue of blade sharpness. You want to use brand new sharp blades every plane or you get this issue. I don't think you can crash planes because of bad foam cuts. That seems like a issue on behalf of the pilot but idk
It sounds like you need a sharper razor blade, as everyone else has said.
I tried using a brand new blade
@Samh is right. For straight cuts you can use a ruler to guide the razor blade. Make sure to go through 3 or more times since if you try to cut through on the first pass it’ll make a bad cut.
Samh is right, a sharp blade is important for a clean cut. Another tip for a clean cut is go over where you are cutting several times. Don't cut through the foamboard in one pass. First cut through the paper on top then half of the foam then the other half of the foam then the paper on the bottom this will give you the cleanest cut possible. So a lot of passes on the same spot.
I already do 10-15 passes and it still does that, and I do use a ruler
+ 1 on the sharp blade.
I prefer the utility blades, I buy them by the 100, $10-12 for a pack. I prefer using them with a handle, it gives me more control over the blade. You will get a smother cut by holding the blade at an angle. When they start to drag flip the blade over or replace it. If I cut foam directly on my workbench the blades dull quickly. My blades last longer if I put something plastic under the foam. I use a scrap of coroplast anything plastic will work.
View attachment 188156 View attachment 188157
Plastic may help I guess. I use a similar blade as you. My blade (I think) doesn't flip over to use the other side. Thanks \\\\\\\\\\\\anyways! it may be the blade I am using- it says that its for heavy duty.
https://www.amazon.com/dp/B01MSWKPKF/?tag=lstir-20
Will using a dedicated craft knife like this help?
Thanks!
 

JasonK

Master member
#10
I tried using a brand new blade


I already do 10-15 passes and it still does that, and I do use a ruler

Plastic may help I guess. I use a similar blade as you. My blade (I think) doesn't flip over to use the other side. Thanks \\\\\\\\\\\\anyways! it may be the blade I am using- it says that its for heavy duty.
https://www.amazon.com/dp/B01MSWKPKF/?tag=lstir-20
Will using a dedicated craft knife like this help?
Thanks!
that first one you linked should work find with fresh good blades.
 

PsyBorg

Wake up! Time to fly!
#12
I bought a plastic case holder with fifty box cutter replacement blades and use them. When they start tearing the foam or paper I hit it with the whet stone for a fast refresh and cut more. I only toss the blades when they start rusting from hand sweat and or start leaving color marks on the paper or foam. I think I went thru MAYBE four or five blades in the course of projects that used 22 out of 25 foamboards.
 

Intashu

Well-known member
#14
SHALLOW angles helps the blade slice, the more perpendicular the blade is to the foam, the worse it will cut.

it shouldn't take 10-15 cuts, it should take 3, maybe 4. I always cut the top paper on the first pass, the foam on the second, and the third and fourth are to clear the paper on the back side.

I use the break-away blade utility knives and a single plane typically I've used up the whole blade. a fresh clean edge cuts great and the second it starts to lose it I clip it, they're not expensive enough to worry about using it too much.

I also cut mine parts out on a spare piece of dollar tree foam-board, it's a good cheap sacrificial piece that saves the blades and my wood table from being damaged!

You shouldn't need to apply much force and with a Shallow angle on the blade it shouldn't ever catch the foam. if it's tugging at the foam, you may be holding it too upright.

rulers too a good deal to help make cuts consistent as well.

for bevel cuts I push out a very large piece of my blade so I can angle the blade extremely shallow. using a ruler along the beveled foam so the blade can't wander into the foam, and holding my hand against the bottom so the blade doesn't drift into the paper I do NOT want to cut, and a smooth steady motion. I probably don't use the safest method as the blade is facing towards me, but I try to move the FOAM away from me instead of pulling the blade towards me when cutting.. If the bevel isn't straight, I go over it with sandpaper to get it right.

It sounds like most of us agree, you're either using a blade that's not quite sharp enough, or you're not holding the blade at a shallow enough angle to slice the foam. (Upright blade cutting is bad.) the more blade used for cutting the smoother it will glide through it.
 
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sprzout

Knower of useless information
Mentor
#18
Several things I do:

1) I've found the absolute cheapest utility blades don't hold a good edge and dull like crazy. I bought a pack of 50 from Harbor Freight and went through 2 blades cutting out a 2 sheet plane. You don't need to buy the most expensive ones, but paying a little more for better quality or heavy duty blades makes a world of difference.

2) A Cutting mat will help reduce the dulling. Cutting on a hard workbench, metal table, even a plastic folding table, will dull the blades and prevent it from cutting cleanly.

3) Having a handled blade like others have suggested, will help you make cleaner cuts. I know you mentioned that you have one already, but it bears repeating that. :) If you have one that is comfortable in your hands, you'll be able to make better cuts; some cheap utility knives don't feel comfortable or have a very thin body, and so I feel like I don't have good control - that's more of a personal preference, though, but good control will help you make smoother and better cuts.

4) Not sure if you're using them, but invest in an Exacto/craft/hobby knife with #11 blades. You can find these at just about any craft or hobby shop, or online; I would highly recommend buying one that you can replace the blades on, as you will need to change them out on a regular basis. I use these for curved cuts or small cuts - say, for example, small notches on a Mighty Mini for the control horn, or a narrow notch cut where the tip of a utility knife would end up being too wide by the time you cut through the paper. With this type of knife, you can hold it more like a pencil and get a better detail cut.

5) Be careful when you're cutting to make sure you're cutting with the blade going perpendicular to the foam board - that is, you don't want the knife to be at a 45 degree angle left or right when you're cutting, or else you'll have misshapen parts. Using a ruler will help on this, especially for the straight line cuts.

6) I didn't see anyone mention this, but if you can, get a cork backed ruler for your straight cuts. The reason for this is that the cork backed rulers don't slide like a straight metal ruler or a plastic ruler. If you're trying to do a long cut (say, for example, a long fuselage cut, or a wing cut) it helps to keep your line straight without accidentally sliding and cutting into the material you DON'T want to cut.

These are all things I do and have come up with some great scratch builds; YMMV (your mileage may vary).
 

Hoomi

Master member
#19
For straight cuts, I find that a rotary cutter, such as can be found at craft stores for use in fabric cutting, works exceptionally well. It's best to have a cutting mat beneath it, to help keep from dulling the blade any faster than normal. Use a metal straight-edge as a guide to cut along, and with a sharp blade, it cuts clean and quick. I also have a small-diameter rotary cutter that is about the perfect size for score-cuts. I'll snap a photo of my two cutters and post them. They're relatively inexpensive, and have saved me a lot of aggravation in building stuff.
 

bwarz

Elite member
#20
Several things I do:

1) I've found the absolute cheapest utility blades don't hold a good edge and dull like crazy. I bought a pack of 50 from Harbor Freight and went through 2 blades cutting out a 2 sheet plane. You don't need to buy the most expensive ones, but paying a little more for better quality or heavy duty blades makes a world of difference.

2) A Cutting mat will help reduce the dulling. Cutting on a hard workbench, metal table, even a plastic folding table, will dull the blades and prevent it from cutting cleanly.

3) Having a handled blade like others have suggested, will help you make cleaner cuts. I know you mentioned that you have one already, but it bears repeating that. :) If you have one that is comfortable in your hands, you'll be able to make better cuts; some cheap utility knives don't feel comfortable or have a very thin body, and so I feel like I don't have good control - that's more of a personal preference, though, but good control will help you make smoother and better cuts.

4) Not sure if you're using them, but invest in an Exacto/craft/hobby knife with #11 blades. You can find these at just about any craft or hobby shop, or online; I would highly recommend buying one that you can replace the blades on, as you will need to change them out on a regular basis. I use these for curved cuts or small cuts - say, for example, small notches on a Mighty Mini for the control horn, or a narrow notch cut where the tip of a utility knife would end up being too wide by the time you cut through the paper. With this type of knife, you can hold it more like a pencil and get a better detail cut.

5) Be careful when you're cutting to make sure you're cutting with the blade going perpendicular to the foam board - that is, you don't want the knife to be at a 45 degree angle left or right when you're cutting, or else you'll have misshapen parts. Using a ruler will help on this, especially for the straight line cuts.

6) I didn't see anyone mention this, but if you can, get a cork backed ruler for your straight cuts. The reason for this is that the cork backed rulers don't slide like a straight metal ruler or a plastic ruler. If you're trying to do a long cut (say, for example, a long fuselage cut, or a wing cut) it helps to keep your line straight without accidentally sliding and cutting into the material you DON'T want to cut.

These are all things I do and have come up with some great scratch builds; YMMV (your mileage may vary).
Wow - +1 on all counts - so does that make this a +6?