Ok first a bit of the back story for this question. I am working on makeing a mascot head for a friends school. Normally I would just free form this out of foam but I wanted to play with modeling the head out of clay then pulling a pattern off of that using tape.  Here are a couple shots of the clay head and then the foam prototype. The prototype is the pattern I pulled increase by 150% and then made with 1/4 inch foam.  The prototype is perhaps about half the size it needs to be in the end product.



We are planing on using a bicycle helmet on the inside of the final head. the helmet needs to fit inside the head so the performer can look out the mouth of the mascot.  Here is my question or what I am trying to figure out. I can measure the outer circumference of helmet and then the outer circumference of the prototype where I figure the bottom of the helmet should be in order to try and figure out how much more I need to increase the pattern but I am not sure how to take into consideration the 1/4 thickness of the foam.  Are you following me yet?  I really need the inner circumference of the prototype but can't really get inside there to measure accurately.  I am pretty sure that I can't just subtract a 1/4 inch from my measurement or do I? I was always so bad at math.

Perhaps if I state the problem in a different way. If I have an hollow ball that has a 1/4 inch wall and measure the outer circumference how can I find the inner circumference?

BTW: Once I finish this project I want to do another one which I'll detail and do a tutorial on the process of making a clay model you can pattern off of.  There are a couple things about this model that would not really work as a hand puppet but the increase of 150% from my original to prototype is just about right for a hand puppet. Figured it would be a great way to get some shapes and patterns for things that folks are always asking about.

Another quick note. The images in the above are hosted on Dropbox.  It is another one of those services like Flicker. The cool thing about it is that I can take pictures with my camera and then with their app I can send them right to Dropbox.  There is also an app for your computer that lets you access the files and share them.  It is a pretty sweet set up and basic service is free. http://db.tt/8HJP5Dye

Shawn,
   What is the circumference of the helmet?  Foam head? I think I might know, but I want to check the figures.

Julie

You would ask a question I don't have the answer to yet.   Have not gotten the helmet yet... was just trying to be prepared. Hope to get the helmet this next week. I am kind of tag teaming this project with another person and they where going to pick up the helmet.

I do have the measurement on the prototype of course. I guess it really is not a full circumference because I am measuring from the back of the mouth around the back of the head to the back of the mouth on the other side. That is 22 1/2 inches.  I am going to have to kind of eyeball the measurement I think on the helmet most likely because I want the front of the helmet to come to just about the back of the mouth or set back just a bit maybe.

So, do you think you want the brim/edge of the helmet to fit at the bottom edge of the head or would it sit deeper into the head?

Julie

I am thinking that the brim or bottom edge would fit right along the line you see through the cheek. Does that make sense? The front front or brim of the helmet would fall right behind the back part of the mouth. the mouth itself is going to have screen in it. Still playing things a bit by ear. I think the farther forward I can get the face in mascot head the more visibility the puppeteer will have.

The scale is kind of off on this but maybe this gives you an idea of where I am going.

You know the more I look at my mock up I am wondering if I am going to end up with the performers head further back in the puppet head. hmmm... I may end up having to cut the mouth a bit further back to open it up some. BTW this is the image of the mascot I am working from that they have on the wall of their gym.  I am going to have to add on top of my base structure to really get the angry look of their mascot but that does not really worry me to much.

I'm going to chime in, but not with math...since I am not that hot in that department.

I just wanted to say that

A) The foam looks great so far. I am super jealous of your talent and

B) Once you get the helmet, I would also double check the height (i.e. how far down is it going to go to meet the fabric for the rest of the costume, covers the chin, etc.) once you figure out the size you need to fit the helmet, just to keep it in mind when you are doing your build. I did a cosplay build for someone once, and I was off by one inch on the height, and had to go back and start again. (I didn't get all the way through, since I had the forethought to have them try it on first.)

Anyway, please post pics when you are done. Can't wait to see how it turns out!