Flattening Cones

Update:  I just updated this frustum calculator with javascript versions that will run from the browser.  One will calculate the flattened frustum from the radii, the other uses the circumferences of the frustum shape.

Have you ever wanted to lay out the frustum of a cone on a flat surface?”
“A what?”
“A frustum, the part of a cone that is left when you lop off the top.”
Oh, yeah. If I had a nickel… sadly, I’m still poor.

It can be a little intimidating if you’re not familiar with the concept of how to go about it. Our draper came to me wondering how she could accurately lay out a dress based on an actor’s measurements. (Apparently the traditional layout method wastes fabric.) So I came up with this simple excel sheet that does the calculations based on the following measurements: waist (small circumference), hem (large circumference) & inseam (height of the frustum.) It gives back the details needed to lay the cone frustum out on a flat surface. The diagram below gives the general gist of what’s what. There is a larger version of the image in the excel document.

Frustum.xls
From fabric to sheet goods, I hope this calculator finds some use.

frustum-model
Update: There is a great description of how to flatten a frustum in AutoCAD over at Woodweb.

Paste & Punch Templates

While in grad school I became a fan of what I like to call Past & Punch Templates. When you need to fabricate a part that is particularly funky or needs to be exceedingly precise, you print a full sized drawing from CAD and past it onto the material that needs to be machined. Fairly simple right?
For years I’ve used spray 77 to adhere the template to the part, but then you have to deal with removing the adhesive from the part when it is going to be painted or moves against another part. A step I feel too lazy to take at times.

Last week I got to thinking how ideal Post-it glue would be for this kind of work. Post-its don’t mar other surfaces, and it is a hell of a lot less hazardous than spray 77. If only they sold the glue without the Post-It. Well they do (kinda, see here). You can find the adhesive at Amazon. It comes as a glue-stick that couldn’t be easier to apply (added bonus: it brings back memories of kindergarden.)

Perhaps this could be used to afix routing templates as well. I haven’t tried it yet, but it sounds good in theory. I’m ordering a stick this weekend and I’ll let you know how it goes. So as to not sound like a 3M shill, you can also Google “repositionable adhesive” to look for similar products.

Fun links:
Electron microscope image of Post-It glue.
Wiki link on Post-it notes.
Re-stickable Glue Stick MSDS