Scratch Building for Scale

by FOAMBIRDS RC | May 3, 2022 | (5) Posted in Tips


What's up everybody? 

So scratch building is a big part of foam board RC. For starters, any design without a speed build kit needs to be cut out somehow, and for us poor souls without laser cutters, scratch building is the only way we can get a design from our head to the foam board. The other, and in my mind more important, factor is price. Speed build kits are expensive- you have to pay for the cutting, packaging, and shipping as well as the foam board. On the other hand, in a scratch build you only pay for the price of the foam, not anything else. However, with these positives come some negatives. Scratch building takes time, effort, and most of all, practice! But once you get the hang of it, scratch building becomes second nature. 


So once you decide to scratch build, there are two techniques that I know of that you can use. I will go over both of them here, but if you want more detail, and some visual references, be sure to check out the video above. 


The first technique is quick and simple, but does have some downsides. The idea is that you use some spray adhesive (3M Super 77 or similar), to spray the sheets of paper to the foam board. This works great, and is very simple. You have a ready made template literally glued to the foam board, and all that's left to do is to cut it out. But, there is a problem with this technique, and that problem has to do with weight. Adding around 40-50 sheets of paper to your airplane is not a great way to conserve weight. Since foam board airplanes are light anyway, it is not a huge problem for sport builds, as you can sneak a little bit extra weight on and get by. But for any build that adds on weight in other places: painting, scale detailing, etc., the added weight of the paper becomes a big problem.


So, introducing my technique! My dad and I developed this method when we were just starting to scratch build, and since then, I have used it almost exclusively for a few years, slowly getting it to a place where I feel that it is ready to share! Before we start, I just want to say that if you are interested in implementing this technique, please refer to the video above, because I talk more about some minor details that I will only briefly go into in this article. 


This technique starts with cutting out the blank borders of the sheets of paper, and then taping them together so that the parts perfectly line up. After that, you tape or pin the plan to the foam board. 


Once the paper is firmly on the foam board, the next step is to "connect the dots." Use any sharp poking tool, like an awl or even a push pin, to make holes at the beginning and end of every straight line in the part. For curves, put a hole every quarter inch or so, so that you can easily freehand the curve just by connecting each dot. 


Once all of the holes are poked into the foam board, you can remove the paper. Now that you have all of the dots, its time to connect them! Use a Sharpie marker or a pen to draw the part using the holes that you just made. For long straight lines, use a ruler to connect the dots representing the beginning and the end of the line, and draw a straight line using the ruler as a guide rail. Be sure to leave a little bit of space between the edge of the ruler and the dot, so that the tip of the Sharpie is running flush with the beginning and end hole, instead of being slightly offset. The reason that this happens is that the edge of the Sharpie is what is running against the ruler, but there is a slight gap between the edge and the center of the Sharpie, where the actual line is being drawn. Moving the ruler out about an eighth of an inch will keep that from happening. For the curves and smaller straight lines, it is easier just to freehand them, instead of using a ruler.


Once all of the lines are drawn onto the foam board, it should exactly resemble the part on the paper. Check it against the paper template just to make sure. It is much easier to add little details that you forgot right now instead of waiting for later!


Now that the part is drawn onto the foam board, it is time to start cutting! Be sure to have a fresh blade on your knife, as fresh blades cut through the foam a lot easier and smoother than dull blades, and you end up getting a much better looking and working part. For curves, I like to bring my knife almost vertical to prevent accidently beveling the foam.


Once the piece is cut out, you have a finished part! This process is very simple, and once you do it a few times, you will definitely get the hang of it, and will be able to cut some really beautiful parts!


Well, I hope you guys enjoyed this little tutorial, and hopefully it will inspire some of you to get into the art of scratch building! Thanks so much for reading, and until next time, I'll see you guys at the field!


FOAMBIRDS RC

COMMENTS

JDSnavely24 on May 10, 2022
Great! Thanks for sharing. Here is what my son and I do that you might find helpful. 1. We first print the plans. Then tape the plans together and make sure the joined paper is taped on every part, trying to avoid any places that will be cut. 2. cut out all the pieces to within 1/8". 3. Arrange all the pieces on foamboard to determine how much foamboard can be saved but do not attach to the foamboard. Then one-by-one cut out the pieces. The trick is to use blue painters tape to hold the pattern on the foam. Use real small fragments of painters tape about 1/4 inch wide. Cut red areas first and use painters tape to retain the shape of the pattern. Cut out internal cuts (all the way through) and cut dots in the pattern for the green placement marks for reference. Also for the blue bend lines. Then simply just cut along the lines as a final cut and you have a completed piece almost as good as a lazar cut piece. The key is to tape the red cuts as you are doing them as you cut completely through even though not completely through the foam. I also fully complete the part as I cut them out as I have the pattern right there. Remove the foam and sometime even cut the bevel. The build then goes real quick!
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JDSnavely24 on May 10, 2022
I meant to say. You cut completely through the paper pattern when cutting the red lines but not completely through the foam. Therefore it is helpful to use painters tape as you are cutting the red lines, that is cut 1/3 or 1/2 and then tape and cut the rest. This makes things go fast and you don't lose the pattern's placement.
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FOAMBIRDS RC on May 16, 2022
Thanks! I'll definitely have to try this!
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Spacemonkeykj on June 15, 2022
nice! My friend and I tried almost that exact technique for a sea otter build to make it go quicker (it worked great). previously I would cut out all the templates and tape them together which takes up to a couple of days for the larger builds like a Guinea pig. thanks for sharing this helpful method!
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FOAMBIRDS RC on June 15, 2022
Thanks for sharing! Glad you found this technique helpful!
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LordVader on June 15, 2022
Would love to see FliteTest make it possible to get the plans for their speed build kits by giving them out for free or a small fee to get them. Other sites do this and have been for years. You are correct in the price for the speed build kits are high when most of us have been doing this ourselves for years. Just need the plans. I would gladly pay for the plans instead of the entire speed build kit.
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FOAMBIRDS RC on June 15, 2022
Hi LordVader!
A lot of FliteTest designs are available in plan format for free. Just go to the flitetest.com home page, and scroll down until you find the plans. Some other plans are available through an FTCA (FliteTest Community Association) membership, which is not very expensive.
Hope this helps!
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LordVader on June 15, 2022
Hi FOAMBIRDS RC,
Thanks for the tip. I have been following FT since they got started and have most of their plans already. Have built several over the years. I was speaking of their latest planes like the Zero, Spitfire, F18 and others from John Overstreet. They sell build kits but I would like to just have/purchase the plans.
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FOAMBIRDS RC on June 16, 2022
Hi LordVader!
Thanks for responding! They actually do have plans for the spitfire, as well as the mustang and the P-47. The plans are on the Flitetest Forums. Just search "flitetest master series spitfire plans" and they should pop up!
Foambirds RC
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Jim Ross on June 17, 2022
The connect the dots, pin method is what I've used since the start. Works great.
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Scratch Building for Scale