12" foam NC

[David Schwantz]

Thanks, but they are masonite. Cheap, easy to cut. I am guessing cardboard would not hold up to the hot wire.

@David Schwantz So braided steel leader wire gets hot enough to cut foam?

Yup. I had picture hanging wire, but I could not get it hot enough before it got red and broke.

 

[Greg Furtman]

Yup. I had picture hanging wire, but I could not get it hot enough before it got red and broke.

I have a bunch of 4' x 4' foam in various thicknesses & some are tapered. They were tear-offs from the flat roof wing of the college I worked at when a new roof went on. They were going to be tossed away so I grabbed them.

Next summer I plan on putting a metal roof on my house with 4" of foam under the steel. In order to make my life easier I'm thinking of gluing different thicknesses together and then make a horizontal hot wire foam cutter to trim them all to 4". I have a hefty bench top variable power supply, both voltage & amperage that I will use to power the cutter. I'll probably use 20 - 24 gauge nichrome wire.

 

[David Schwantz]

I did a search on hot wire cutters. Found a site that had calculators for how much power is needed for wire size, length of cutting wire and length of supply wire. They also sold nichrome wire is various sizes.

 

[heada]

https://www.aircraftspruce.com/categories/building_materials/bm/menus/cm/hotwire.html

 

[Banzai88]

PVC pipe, 60 lb test braided steel leader, no coating on it. Went to Menards and got a door bell transformer, output is 16 volts at 30 amps. Also got a dimmer switch to control current. It has the push on/off feature so that it saves the last setting.
Got the first sanding done with 60 grit. I did not think it made to much dust. Just on the floor right in front of lathe.

I used to build a LOT of 2M gliders and .15 and .25 RC combat planes. Your rig is almost 100% exactly like the rig my club made to make wing blanks and fuselages.

 

[David Schwantz]

I've cut a couple of wing cores in my day also. I had used a train transformer before. But not enough power for this.

 

[rharshberger]

Jacobs Online is another good source for hotwire parts and nichrome for igniters.

https://jacobs-online.biz/

 

[David Schwantz]

Jacobs Online is another good source for hotwire parts and nichrome for igniters.

https://jacobs-online.biz/

Yup, looked at that one yesterday. That is what I used to size the transformer I bought.

 

[David Schwantz]

100 grit

 

[rharshberger]

Yup, looked at that one yesterday. That is what I used to size the transformer I bought.

Jacobs has great service, on the occasions I have purchased nichrome it has shipped out the very next day.

 

[David Schwantz]

1st layer of glass is on.

 

[heada]

Are you going to keep the foam core or build up the fiberglass and then dissolve the foam out?

 

[David Schwantz]

If I dissolve the foam, how many layers of cloth do you think it should have? I am leaning towards leaving the foam. I was planning on gluing the shoulder blocks to it. Also would give strength, will need weight up front anyway.

 

[heada]

I've only dissolved the foam core on small things (4" diameter, etc) and for those I built up 3 layers. Not sure what you'd need for 12" Nothing wrong with keeping the foam core unless you needed the space for recovery or electronics.

 

[David Schwantz]

Kind of think I am going to have a little room left over after all is in place. She be 12" dia and 9.2' tall.

 

[Banzai88]

My 3" and 4" nose cones that I have from Ken at Performance Hobbies that are clearly 3 layers plus gel coat.

I have a 7 1/2" Polecat Thumper that looks like the nose cone was sprayed from a chopper gun and it's .100 thick with gel coat.

 

[David Schwantz]

Thanks. Thinking I am going to do 3 layers. 2nd piece just got cut and will be on shortly.

 

[David Schwantz]

Got all 3 layers of glass on her. Now to make shoulder and attach it. Then have to make rear transition. Nice thing is I can use the same patterns.
For those that have done this and made a wooden tip, what wood did you use? Basswood? Did it have a center shaft that went into NC? Or was it just butt glued on? I was going to glass over it when done. I don't think 3 layers though.

 

[Greg Furtman]

Got all 3 layers of glass on her. Now to make shoulder and attach it. Then have to make rear transition. Nice thing is I can use the same patterns.
For those that have done this and made a wooden tip, what wood did you use? Basswood? Did it have a center shaft that went into NC? Or was it just butt glued on? I was going to glass over it when done. I don't think 3 layers though.

@David Schwantz What weight cloth are you using and what epoxy?

 

[David Schwantz]

6 oz cloth. The glue I used to glue the disc together was the same as for the cloth. Was kind a pricey , but what I had on hand. I will look for something else for gluing the discs next time as this was hard to hot wire and sand.

 

[Greg Furtman]

6 oz cloth. The glue I used to glue the disc together was the same as for the cloth. Was kind a pricey , but what I had on hand. I will look for something else for gluing the discs next time as this was hard to hot wire and sand.

@David Schwantz check out the price on WEST Systems epoxy compared to what you are using. I've been using the WEST System epoxies and additives for more than 30 years. Great stuff, especially for wetting out fiberglass cloths.

 

[David Schwantz]

I used it for the cedar canoe my Son and I built also. But the stuff I used will eat foam.

 

[tsmith1315]

For those that have done this and made a wooden tip, what wood did you use? Basswood? Did it have a center shaft that went into NC? Or was it just butt glued on?

Much smaller cone, but FWIW-
I used a standard (oak?) dowel a couple inches through the tip, with a coupler sleeve on the inside end. A dowel slid into the coupler from the bottom side for turning. Turned down the exposed dowel into a tip after the fiberglass was done and pulled out the removable aft dowel. Structural integrity was verified by ballistic recovery.

 

[David Schwantz]

So did just the tip live

 

[tsmith1315]

Survived fully intact!

Not just the tip, the complete nosecone. The rest of the rocket, too.

 

[Ez2cDave]

100 grit

That looks like a shell for a Navy battleship gun . . . Very Cool !

Dave F.

 

[David Schwantz]

I used a 1" OD PVC pipe as the center for the NC to turn on the shaft. Now I want to get it out and replace it with a tube. Will glue the foam to the tube to begin with on the next one. Tried the hot wire on scrap, not so good. Thought of a long thin metal tube to cut out the foam, but how to keep it straight??
Also, how to anchor a hard point for shock cord in the foam. Not going to trust just glue. Ply plate glued on bottom of shoulder. Bulkhead glued in to tube, that is if I ever get it cut out. Anchor in the hard wood NC, again if I get the foam cut out.
Give me your thoughts on this. Thanks.
PS, if none of this works at least I got a shell from the USS Missouri.

 

[jqavins]

One thought: perhaps just leave the pipe where it is. What harm is it doing?

• For an attachment point, make a hardwood plug that fits the bottom of the pipe and epoxy it in place. Drill a center hole in the plug and secure an eye bolt, or two holes and a U bolt, before gluing it into place.
• For the tip, make it with a shoulder that fits the pipe ID and, again, epoxy it in place.
• For kicks, place some objects inside the tube, like a time capsule.

 

[David Schwantz]

Thanks, but pipe already out. I made a 4' long parting tool and cut it out on the lathe. Already have shoulder glued on, hole bored out for a LOC 7.5" tube to be glued in that will lock everything in place. Removable nose weight system is in. The transition is on the lathe right now. Glassed and waiting final sanding to size. Made the tip out of bass wood, glued on and glassed over it.

 

[David Schwantz]

Transition fresh off the lathe. Nose cone, transition, mold for transition.