[KC8QVO]

John, could you explain what arborite is? I dont think I have ever heard of it.

Ken, what size and type wire are you cutting with? I am going to construct a large bow today so I can cut my giant trainer cores. The cores will be about 43" (each wing half) so I will need quie a bit of tension to keep the wire straight.

Steve

[Vulcan1]

Arborite is the stuff that you cover kitchen counter tops. All sorts of colours and mostly stocked in 8 x 4 but if you are like me you have a friend or know of a place that does finishing work in houses. Great supply of cut-offs.
Ken may have a different way but on my long bow(5ft) I use the 1/4" piano wire and can put a lot of tension on the wire. I don't think you will get sagging but you will have the drag and get the curves in the surface if too fast or not enough heat. To me hot wire cutting makes it harder when the longer you go the more heat is required to get a nice cut. Practice on a couple of pieces of scrap foam that is the same length to get your temp. before cutting the core. My dimmer switch is marked for different lengths of cable so I do not have to play much with it. Just turn to the mark and turn it on.
Hope this helps.
John

[igor_throw_the_switch]

This thread covers the whole shebang as far as making your own foam cutters.
http://www.rcgroups.com/forums/showthread.php?t=287621

Steve: Fine "angel hairs" means you have the heat about right.

Brad

[KC8QVO]

1/4" thick for the cutting wire or 1/4" thick for the supports????? that seems a bit thick for cutting

Steve

[Ken Currell]

Hi Steve

I use .0031 inch nichrome wire. (31 thou) This is strong wire and can handle a fair bit of tension. It also retains its heat quite well. Just don't go too fast when cutting. Take your time and draw lightly on the bow. Try to maintain an even speed on the cut. If you pull too hard on the bow it will make the wire bow and ruin your core regardless of the amount of tension on the wire.

I don't like to use piano wire as springs as they are live conductors when connected to the charged wire. Even though it is low voltage it is safer to use wood.

I will be modifying my bow shortly. I will make it so one end is able to swivel. One the end opposite the nichrome wire I will make 2 hooks out of coat hanger wire and use screen door closer type springs on that side of the bow. If I need more tension I will add more springs.

It will look like the one in the thread that Brad posted.

Tx for the link Brad

Cheers

[igor_throw_the_switch]

No probs, Ken. My long bow is an "H" frame as well. The uprights are about 24". and the crosspiece is 54". I just drilled a hole in the top of each crosspiece and threaded in some of that yellow polypropylene rope with a big turnbuckle in the middle for tension. I use SIG control line wire (.018 SS) to cut with, and I have it *very* tight - about the same key as a D string on a guitar. I have no wire lag.....

Brad

[Vulcan1]

I get a lot of tension using the music wire for the ends and use the same line as Brad although mine is stranded. As for being hot(live) they are. But when you are by yourself and cutting for years you don't handle it by the wire. I keep my ends fairly short around 8"which makes it easier to use the centre piece and keep it as lite as possible. One of the reasons I want to make a cnc one which is after this model. I have all the parts.
John