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Foam cutting tips?

I've been practicing and even built an FT3D that looks ok, but I struggle with my cuts. It seems that even with a straight edge, my cut lines occasionally aren't truly straight. What I mean is, no matter what blade I have, I struggle to keep it vertical the entire time, so many of my lines look beveled. I tried screwing a blade to a block of wood, but tightening it down too much bends the blade a little and doesn't seem to work well. Too loose and the blade doesn't stay put. Are there any tools out there or examples of tricks you guys use.


Senior Member
I use a metal yard ruler to make my cuts, but they aren't all straight either... My suggestion I'd to make all the non straight cuts face in so you don't see them...hehe
What are you using as a cutting mat? Is your knife tip perhaps getting caught in it, throwing off your cuts?

Are the cuts that you are making clean? You don't mention this as a problem, but if it is, you need a sharper blade. Cutting foam board with anything but the sharpest of blades is guaranteed to cause you no end of suffering.

Unless I am very careful, my cuts are always off by a few degrees, but this never a problem.

Otherwise, I can't really think of anything other than more practice.

Perhaps maybe you could post a picture of your cuts, or better yet a video of you cutting?
It's definitely not the knife. It's the person holding it. I use a cutting mat and the blades are plenty sharp. The foam or paper doesn't tear, i just seem to have trouble keeping the blade perpendicular to the foam. I always at some point end up holding it on an angle like a pencil which results in unnecessary beveled edges.


Posted a thousand or more times
Do you mind posting a picture of how you are holding the blade? I use a utility knife to do my large, straight and curved cuts. I use an X-Acto style knife to do my small cuts that require precision. I have learned to hold the utility knife in a way that gives me decent results. I hold the X-Acto knife like a pencil. I'm am still refining my cutting technique, and at times my cuts are not great, but I'm getting better, and I now do just about all my cuts free-hand (it's my gluing technique that need help!). What may help, is doing each cut with a series of passes, instead of trying to cut all the way through with one pass. It will allow you to put less pressure on the knife, which will essentially give you more control.
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Have you tried a larger box-cutter? The larger, non-circular handle may give you better blade control.

Personally, I prefer the old-standard #11 x-acto blade for most cutting work, but I have found that most handles just suck. The #1 handle is just far too small and light for my tastes, and I can easily see why that would lead to poor blade control. I have amassed quite a collection of oversize handles over the years, and while some are better the balance was just wrong on all of them. Eventually I just gave up and made my own handle with the proper size, weight, and balance.


Junior Member
I use sailorJohn's method that is outlined in his article Tools for easier and faster foamboad building. However, I use the blocks for all my cuts, not just hinges and straight cuts, but also rounded cuts. I find that I can put better pressure on the foamboard and keep the blade perfectly perpendicular. I highly recommend viewing his video as it has made my scratch building experience much better. Plus, once you get the blades set up right, it will just go through the foamboard (or half way or beveled) so I think it makes cutting through the foamboard easier, as all you have to do is get the block flat, press down and slide through without much worry as to whether it is going all the way through because it is. Therefore you can just concentrate on following the pattern.


edited to fix link


Amateur Extra Class K5TWM
I had that issue when I began with the Xacto # 11 bladed knives. I only use them now for fine radius cuts or other fine cuts prefering for general cutting a Stanley Utility Knife with its much bigger blade. It tends to travel much straighter in my cutting since a tiny change in my cutting doesn't have such a large effect as when a small blade is moved slightly askew.
For me the utility knife blades are easier to use and sharpen and have 2 cutting ends for extended use.

I use #11 blades for everything. I keep them razor sharp, if they start to drag I replace them with a new or re-sharpened blade. My suggestion Fbords would be to obtain a straight edge that is at least a 1/4" thick and metal. When you start your cut lay the blade against the straight edge, angled towards the handle (yourself) and keep as much of the blade as you can in contact with the straight edge. With a little practise you will find that you are putting less down pressure and more side pressure on the blade and your cuts will be perpendicular to your cutting surface. As for your grip, try putting your index finger on top of the blade (control downward pressure) and pinch the handle between your thumb and second finger (control side pressure). I hope these couple of hints will improve your cuts, happy building! WJ.


I'm a care bear...Really?
I had that issue in the beginning but then I changed how I cut the foam. Keep the blade vertical and cut that line two or three times. Works for me.


CrossThread Industries
Try breaking off the tip of the #11 blade, too. That is what a lot of balsa guys do. The very fine point on the stock blade is wobbly and bends as you cut, especially if you are using tons of down pressure.


Junior Member
you could use a thin metal ruler with a slot to guide the blade, tacked with hot glue and on both edges of the foam to keep your blade 90 degrees upright. When you are done you could heat above the points that you tacked the ruler in place with and remove the glue hope this helps.


Senior Member
Reading through this thread made me realize that I am not on par with many of the builders here lol. I never care too much if my cuts are exactly 90 degrees. It doesn't seem to affect fit all that much in my opinion. However, I can see if you were building a really detailed plane for show where it would be an issue.