CNC Hotwire 4 axis foam cutter

**Skipsoaring** · 04-06-2015

Hi there!
I will be building a 4 axis CNC hotwire maching for cutting cores for Radio Controlled gliders.
I am just starting the serious research (when I am not being seconded into the real world) and so far I'm thinking that due to my current space constraints I will make it so that it holds the foam vertically against the garage wall.
The machine size is still up in the air and will depend on the size of the blocks I can source. The largest wing panel I can see myself making is 1500mm, although being CNC made (accurately compared to wire dragged over templates/fences) I could make the panels in 2 parts as the majority of the wing panels would be 750mm.

I have a LOT to learn as I am trying to teach myself CAD (Onshape and Sketchup), am yet to learn anything about CAM and have always been petrified by Electrickery!!

I have chosen to build a CNC hotwire as it should be relatively simple and I want to build a CNC router next, having learned some lessons along the way.

The basic idea of the CNC Hotwire machine is to enable me to cut eliptical wing panels which requires independent movement of each end of the wire along the x axis and z axis (hopefully got them right from a gantry machine perspective)

The x axis travel shouldn't need to be more than 500mm and the z axis travel should be similar. I do need to figure out if I would need more though. If, for example, I was to cut a 750mm panel with an elliptical shape and the posts were 1500mm apart, the x axis travel would need to be much greater than if the posts were 800mm apart. Perhaps I need to look at designing my machine to have relocatable rails for the x axis?

I understand that from a construction point of view, my two machines will be worlds apart, the lessons I'm hoping to take to the next build will hopefully be software, electrical and generic.
Anyway, gotta go do the school run.

Cheers
Clayt

**Skipsoaring** · 04-06-2015

Just re read above and it read like i was planning to have the foam on the wall. I meant the machine BASE against (or leaning onto) the wall.

**Skipsoaring** · 11-06-2015

After some computer issues, I can get going on the learning side of things again.
I found Autodesk Fusion 360 (thanks again to the info here) which integrates CAD and CAM so have started using it. I'm brand new to Macs so am still learning the in's and out's of screen shots etc.
I won't be having the foam cutter anything other than flat as it wouldn't be possible to keep the foam block and the cut part in the correct position at the end of the cuts and would cause damage to the parts. With the block flat, I can use double-sided tape and gravity.

Better keep drawing, hopefully have some info and pics for you soon.
Clayt

**Boyan Silyavski** · 12-06-2015

Show us what exactly will be the final part. If its a 3d shape you will need a router, not wire cutter.

**njhussey** · 12-06-2015

Originally Posted by silyavski

Show us what exactly will be the final part. If its a 3d shape you will need a router, not wire cutter.

Boyan, if it's for cutting RC plane foam wing cores then a hot wire cutter (4 axis) is the thing to go for. I'll be making one at some stage (10 years time at my current build rate! !!) For exactly the same use.

**Skipsoaring** · 12-06-2015

Originally Posted by silyavski

Show us what exactly will be the final part. If its a 3d shape you will need a router, not wire cutter.

Normally cutting wing cores from foam requires passing a hot wire over 2 fences shaped with the aerofoil at either end of the foam block. CNC will provide the same service and remove timing errors and snags (getting stuck) giving a much more accurate wing core.

**mitchejc** · 15-06-2015

Sorry can't help you with any info on the 4 axis hot wire but Silyavski may have a point depending on what you want to do. If you need to cut a lot of wing profiles rapidly the hot wire is obviously the way to go but if time is on your side then simple 3 axis milling is not such a bad idea as it gives you a lot of options that hot wire can't do. A relatively flimsy but fast 3 axis router dedicated to foam cutting should be easy to build.

Had to dig around to find the model but several years back I did cut a few gliders for a friend on my router. He asked me to cut two wing profiles and I suggested we cut the whole aircraft in one go. The entire model including the fuselage was cut from one big piece of foam with a two sided strategy excluding the wing tips which were glued on afterwards. The screenshots below shows the model I drew using his wing profile. I know sh%t about aerodynamics so I just went with a sort of a teardrop shaped thing for the fuselage so he's got somewhere to put the battery and receiver:-) The white round bits you see on the wings are just supports used when I turned it over to cut the bottom profile. The piece of foam was bigger than the model so it was supported at the wingtips as well.

Don't think I have any pics of the actual cut models but apparently they flew very nicely :-)

**rckeith** · 21-07-2015

I've built a 4 axis hot wire machine you can see my build and plans at http://www.rckeith.co.uk and have used it to produce wings and fuselages. I don't really have a limit to the size of wing as the two towers can just be moved further apart. I usually secure them to a board to prevent them moving. I've found the best result are obtained with really thin wire( I think the size is on my website). If your wire is long then you may need to experiment with feeds and current as it may vibrate a little and give poorer results. The biggest challenge I've found is the software. Not much around for 4 axis hot wire so tends to be more expensive. I've spent more on software than hardware. I use Profili2 Pro and Dev Fus Foam but its a bit of a learning curve. Straight wings are fairly easy but tapered are bit more challenging. If you don't have positioned correctly in the machine according to the distance specified in the software the wing comes out larger or smaller. My first flying wing came out a bit smaller than I expected but it was a bonus because if flies absolutely fantastic. Hope that helps

Keith

Originally Posted by Skipsoaring

Hi there!
I will be building a 4 axis CNC hotwire maching for cutting cores for Radio Controlled gliders.
I am just starting the serious research (when I am not being seconded into the real world) and so far I'm thinking that due to my current space constraints I will make it so that it holds the foam vertically against the garage wall.
The machine size is still up in the air and will depend on the size of the blocks I can source. The largest wing panel I can see myself making is 1500mm, although being CNC made (accurately compared to wire dragged over templates/fences) I could make the panels in 2 parts as the majority of the wing panels would be 750mm.

I have a LOT to learn as I am trying to teach myself CAD (Onshape and Sketchup), am yet to learn anything about CAM and have always been petrified by Electrickery!!

I have chosen to build a CNC hotwire as it should be relatively simple and I want to build a CNC router next, having learned some lessons along the way.

The basic idea of the CNC Hotwire machine is to enable me to cut eliptical wing panels which requires independent movement of each end of the wire along the x axis and z axis (hopefully got them right from a gantry machine perspective)

The x axis travel shouldn't need to be more than 500mm and the z axis travel should be similar. I do need to figure out if I would need more though. If, for example, I was to cut a 750mm panel with an elliptical shape and the posts were 1500mm apart, the x axis travel would need to be much greater than if the posts were 800mm apart. Perhaps I need to look at designing my machine to have relocatable rails for the x axis?

I understand that from a construction point of view, my two machines will be worlds apart, the lessons I'm hoping to take to the next build will hopefully be software, electrical and generic.
Anyway, gotta go do the school run.

Cheers
Clayt

**Skipsoaring** · 22-07-2015

Thanks Keith. Things are a bit stop-start at the moment, with more stopping than starting.
This affects my focus and I find myself drifting off-target and 'considering' getting a cnc converted Mill (or converting one). Imaginations hey? Where would we be without one!