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u/CrazyPlato Aug 24 '26
Weird geometry thing. You measured the circumference of the core rod. But the foam is thicker than the measuring tape. If it’s 1/2” thick, then you’d need to account for that extra bit of diameter in the math.
Better to overshoot the length you think it is by an inch or two. Once you’ve glued the foam down around the core, and reached the other side of the foam, find the point where the ends should meet and cut the excess away with a knife. Finish gluing it all together then.
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u/No-Compote-8920 Aug 24 '26
You are not accounting for the thickness of the foam and your measure tape is slanted or at least looks slanted. Are those things not supposed to have a metal tip?
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u/zigithor Aug 24 '26
lol yes they normally do. It was a bit hard for the video but all measurements measured in better condition are 5-1/8”
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u/joeshmo101 Aug 24 '26
The measurement is 5-1/8" for the inner radius of the foam, but since the foam is pretty thick it ends up with a different inner and outer radius. However, the foam doesn't stretch very well, so when you bend it around the staff it compresses the inner side instead of expanding the outer side. This would be negligible with paper but craft foam is much thicker. Also, this measurement assumes you can get the foam to perfectly contact the staff, which is likely not the case, at least without adhesive.
What I would recommend is wrapping the foam around the staff before you cut it, starting from one edge of the foam. Mark the top and bottom (of the staff) on the top layer (of foam) where it starts to overlap the bottom layer, and cut using that line instead of trying to measure it out
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u/Clothes_Chair_Ghost Aug 24 '26
You are not taking the thickness of the foam into consideration.
Here is a tip. From the foam cut a strip of every thickness you get. Use that as your measuring guide. Can use a marker to make incremental marks on the foam if it helps
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u/jokerswildecosplay Aug 25 '26
As others mentioned, need to add the thickness. One thing some people do is make rulers of each foam thickness so you can measure it correctly..... I often forget that too lol
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u/zigithor Aug 24 '26
My fellow scholars,
I want to thank y’all for all the comments and help! As some have mentioned, the real answer is probably to just wrap the foam, mark it, cut it, and forgo any math. This my recommendation as well after some testing…
However…
I’m now curious about how you would math this out. As some have suggested I found my diameter, added 2x the thickness of the foam, and used that new diameter to get a new circumference. Theoretically this is the new circumference after the wrap.
I cut it to this length and it was a bit big actually. So I wrapped and marked the ideal spot to perfectly wrap. What I found was that it was about 1/4 the difference between the original circumference and the new circumference less than the new circumference. Might be hard to follow so I’ll post my quick math as well.
145mm was what ended up working in the end.
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u/PykeAtBanquet Aug 25 '26
I would treat it like this:
It links only if the outer layer does. Therefore I would measure the circumference of the foam for two radius points: one at the inner part and the other one at the outer part with delta being the thickness. After that I believe it is enough to cut off so much foam that it is outer circumference wide because in that case it will wrap no matter what.
In other words, we need to calculate the circumference of the outer layer that incorporates the added radius due to thickness, and this is how much we should cut, as it is going to be larger than the inner circumference.
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u/natuprunk Sep 09 '26
Some useful tips I have learned: 1. You should make a ruler out of foam for various thicknesses. It will allow you to see how long the piece actually needs to be, because you can see how much longer the outer surface is on a curved surface.
Bevel the edges you need to glue, like so \. The sharper the angle you can cut it at, the more surface area you have for the glue, and the less tension the surface experiences.
To get a really neat glue seam, even on a straight edge cut, after gluing wrap the whole thing in tape, making sure the tape is taught and pulling the edges together. Allow to dry properly. Bonus effect: it helps pull off any excess glue on the surface!
This is especially useful on really small circumferences, like when you're wrapping a staff, because the pull of the foam is so strong.
For larger, short cylinders a long piece of tape horizontally across the seam could work, but for best results I just wrap the whole thing to have a steady pressure pushing the edges together
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u/Timely-Morning-3839 Aug 24 '26
You aren’t accounting for the thickness of the foam.