# Hot wire cutting.

### Help Support HomeBuiltAirplanes.com:

##### Well-Known Member
I always had trouble using plywood templates. Couldn't get the edge smooth enough where the thin hot wire wouldn't dig in a little and get caught and make a rough place on the surface of the foam. Went with thin aluminum and polished the edges.
The templates for my 25% scale model were CNC cut from 1/8" plywood by Bob Holman Plans from .dxf files I sent him. He did a great job, amd the templates were delivered less than a week after I sent him the files and payment.

Before...

During...

After...

But I have learned that thin plywood templates are good for about 4 hotwire passes before the edges get thrashed by the wire. So, for the sake of absolute accuracy on the full size plug, the templates will be done with SS (vendor TBD), while the wing jigs will be done by Eureka CNC.

#### stanislavz

##### Well-Known Member
HBA Supporter
Couldn't get the edge smooth enough where the thin hot wire wouldn't dig in a little and get caught and make a rough place on the surface of the foam.
I did uses rollers to solve it in my childhood. make drawing a little harder, but it was worth it. But still gone cnc way as soon as possible.

#### Geraldc

##### Well-Known Member
Just found this foam cutter.
And with this foot it looks like it can take flat strips of stainless that you can form to your required shape for leading edge molds etc.
The length seems to be only restricted by the length of material.

#### Vigilant1

##### Well-Known Member
Just found this foam cutter.
And with this foot it looks like it can take flat strips of stainless that you can form to your required shape for leading edge molds etc.
The length seems to be only restricted by the length of material.
View attachment 105758
The ad says it is appropriate for cutting polyurethane foam. Sure, it will cut it, but the person using the hot knife should be breathing outside air under positive pressure at the time to avoid some very dangerous gasses that result.

Last edited:

#### wanttobuild

##### Well-Known Member
That is what I use, and it works well. Found the box at Hobby Lobby, and sourced the internals at Lowes:

View attachment 102957
View attachment 102958
View attachment 102959

As enjoyable as it was, I am not looking forward to doing this again for the full size plug (the finishing part at least)! Will not use plywood templates, though...we will have the full scale ones cut from stainless steel.

#### Geraldc

##### Well-Known Member
A regular soldering gun with a custom-bent wire attached with the normal screw terminals on those guns would be considerably cheaper.
As long as it is bigger than the 100 watt one I tried that would not heat up a long stainless strip.

#### Topaz

##### Super Moderator
Staff member
Log Member
I'm another whose always used regular stainless safety wire for hot-wire cutting. Adjusting the proper temperature is key, as is actually practicing a number of times before you try cutting actual parts. I've always cut with a partner, rather than machine or pantograph. A little practice and a team of two can turn out wonderful cores with almost no wastage.

It's just not that hard.

#### Geraldc

Very cheap. A scrap piece of #12 copper house wiring works great. Started using it in 1970. I paid $4 for my soldering gun in 1954 and still use it. We don't use #12 copper here but I found a bit of 1/16 copper wire and tried that in my Weller soldering bolt I got for$15 a while ago(the $4 ones were sold out) and fitted it up. Worked well .Thanks Pops What I am trying to do is make female molds with compound curves that you can't possibly do with a straight wire and I want to avoid the dust from a router. #### sigrana ##### Well-Known Member We don't use #12 copper here but I found a bit of 1/16 copper wire and tried that in my Weller soldering bolt I got for$15 a while ago(the \$4 ones were sold out) and fitted it up.
Worked well .Thanks Pops
What I am trying to do is make female molds with compound curves that you can't possibly do with a straight wire and I want to avoid the dust from a router.

I built my two hot wire cutters in the '80s (last century of course) and they are working excellently well after thousands of wings and fuselages cut with them. A simple C shaped wooden or mild square steel tube structure, with one isolated end and an adequate spring (or bungee) on the opposite side, which take care of the obvious wire elongation with temperature changes. I use 0.8mm stailess steel wire, powered by my fully adjustable 0-30V, 0-30A AC/DC power supply, built on a Variac. The varfiable settings are very usefull when cutting different foams and thicknesses.

#### Attachments

• 40.2 KB Views: 19

#### Protech Racing

##### Well-Known Member
Some one asked about the foam guides for cutting ribs. I found a roll of Veneer birchwood that should work fine with a hot wire. Just dont stop..
Lowes .