I am providing an update for those following. I received the foam samples from the Foam Factory (canada.foambymail.com) and completed a quick machinability test. I uploaded the video to my YouTube channel TMDesign - here is a direct link to the video:
I asked them to send 5 foam types that I thought might work, and they are referenced in the video, with their details available on their website. Note that my discussions with Datron confirmed that their foam cutting endmills work best on 2lb+ foams, and at very high RPMs (31K for my 5 mm tool). My RPM and feed rates were lower than ideal, but the cutter performed very well.
Three foams machined with good results, and I will share below the summarized results of a few calculations I made to determine the least costly option:
The poly foam gave the best result, and happily was the least expensive.
I based my calculations on a foam package that has two sides machined with the profile of the bird. These are from a large 1 1/2" thick sheet, and each package half is 6"x10".
The price per bird shipped for the poly is roughly $2.30CA, which includes Canadian taxes and shipping. It would ship from the USA (they ship to Canada once per week).
The other cost effective option is from a local GTA supplier, and it is the plank foam I used in my previous video. The cost per bird shipped for this foam is roughly $2.75CA. I save shipping as they will allow pickup from their distribution centre.
As discussed above there are other ways of packaging the sculptures, with the ‘3 layer’ method getting support. After viewing many videos, and some machining experience now as well, the answer is not as clear. I believe the toolpaths have the greatest impact.
For example, although I like the idea of a 3 layer solution, the middle layer can not be cut out of the 2" foam with a simple, single contour toolpath. It would need to be done in small adaptive clearing moves which (not yet tested) I believe will end up taking longer than cutting the shape of the bird in two halves of 1 1/2" foam.
I will put this project on hold now until I know what the demand will be for my birds with friends and family, and if I will later decide to sell them to the public. At least I have my toolpaths, and a few proven options for the foam type and purchasing source.