Scuba Steve

Hey folks, those of you who cut your own foam probably have had this same question... I'm working on a new circular fan-in-wing design and i want to cut the body out of foam (preferable in 1 piece, but might have to fit two halves together). The problem is that i'm not cutting a straight piece, and the wire won't be straight either... Is there a way (and special type of wire used) that I can bend the wire into the shape of the cross-section (see attached pic) and then anchor the arm of the hotwire to the center of a big piece of foam, and then rotate the hotwire around the radius to cut a single piece circular body? of course, i'd have to CUT the hotwire to get it off the body, but thats no big deal. if any of you have dealt with this before, please advise me on the hows, dos, and donts, and what wire you used, etc.. ESPECIALLY how you held the wire...

:drowning:
scuba

Oh yeah, the left side of the image is the INNER part of the circular body.

Cactus.

My Feedback: (1)

Last i heard for doing this was an adaption of the trigger type quick heat soldering irons, the wire tip is replaced with a flat wire bent to the shape you want. ( make sure the wire = the resistance of the old tip )
you would need two tips and a special jig. that way you can cut the centre as you rotate the foam with the soldering iron rock soild, then move the iron, change the tip and start rotating again..
i wouldnt want to do it.
from the two posts i've seen of what your doing i would build it with the shape you have as ply ribs, then bend a ply strip around a bucket and slowely build it all up like a wing

cncfoam-RCU

Steve,

I have a cnc foam cutter. Could you clarify what you are trying to do with that shape.

Im not really following what your trying to do. maybe give another explaination maybe I could figure something out.

Eric

Cactus.

My Feedback: (1)

take a look at his Avatar
its foam cutting Jim, but not as we know it

Cactus.

My Feedback: (1)

hang on, i've seen weird stuff done with blue foam in the past, he made bowls and stuff, arghhhh if only i could remember where that was. might have been Ezone

Scuba Steve

yeah i know SOMEONE has done it... just a matter of how. it shouldnt require more than just the right type of wire. i'd probably have to do multiple passes, each time with a different segment of the cross-section.

Flypaper 2

It could be done on a lazy suzan type table with a copper wire in the soldering gun trick. I imagine it could be done with the hot wire transformer and a copper wire in a jig. rotate the table against the shaped wire. Inside, cut a hole in the foam feed the wire down through to cut the inside. Anyone want to add to or constructive criticize?

Scuba Steve

that seems exactly how to do it, but what type of wire can i use that will maintain a specific bent shape even when heated? and its gonna have to be pretty stiff... also since i've never used a hot wire cutter i have no idea what temp to use.

:drowning:

Cactus.

My Feedback: (1)

did my post above about the trigger soldering iron not get posted? the trigger type have a large almost piano type wire, not a strand, you'll need a flat version of this at the same resistance.

cncfoam-RCU

Steve,
It took me awhile, duh. I can see by your little picture what your trying to do. I used .032 music wire from the hobby shop, it is stiff enough, but yet it is thin enough to heat , the heat of the wire will melt the foam before it pushes the wire back. I use a 10 amp variac to heat the wire.

I have tried other size wires, if it is too small it bends, if it is too big it pops the fuse on the variac.


A new thought would be to push a threaded rod through your foam at the center point. use nuts and fender washers to sandwich your foam. and put the rod into a drill, mount the drill on a table so that you get a spindle, like a lathe. then make another jig like a 4 jaw chuck to put in your drill to bore out the inside with another jig. you will have to leave a lip on the piece so that your chuck can grab it.

just trying to help
EZ

fprintf

Link from rcgroups...

http://www.foamfly.com/

the guys at foamfly have done a number of things with blue fan fold foam including molding them in a home oven into weird shapes. I can't get the direct link because of frame, but if you check out their gallery, then check out "the secret lab" you will find pictures of bowls and all sorts of flying circle shape things.

p.s. For the soldering iron thing, I just stuck a peice of 14 gauge solid copper wire into the end. It was not nearly as accurate as you will need for this process as it tended to be on or off for temp and burned the foam more than cut it.

balsaman

I would use a lathe and some files and sandpaper.

Eric