My new Hot Wire build

[belli]

Hi All,

I have wanted to do some wings, foam, glass laminate for quite some time. When I have looked at it in the past I couldn't find good software. Now that I am back at it I see that Profili (http://www.profili2.com) has come a long way it's really great. What I needed was a machine to cut some foam with!

I decided last Sunday to start with a hot wire and this is as far as I have gotten in a week, mostly evenings. The design is mostly done and so there will be few delays now except that the next three weeks is going to be really busy.

The machine will have a cutting area of 1000mm (wide), 800mm (deep) and 300mm (high), this was just the length of the materials I had at hand. I have attached some photos for all to see, I will post the drawings when I am done with it. I couldn't bring myself to use drawer runners and such but I am going with M10 threaded rod (stainless, Vesconite nuts), I can do around 1600mm/min reliably with that which should be fine for foam. I haven't decided on the control method for the wire temp, I have a few designs and will post them here closer to the time.

Enjoy!
Greg
www.cncdirect.co.za

[belli]

Hi All,

Things are moving slower that I had hoped, should have been cutting already!

I decided to make a few parts over but most parts are done now and the design is nailed down. I am using a pneumatic cylinder for the wire tensioning, I can control the tension by varying the pressure and I have 300mm stroke which is almost the corner to corner difference while four axis cutting.

I have been giving some thought to an electronic temp control for the wire, I will post details here a little later, works with an SG3525 PWM chip, I will add a shunt resistor to measure the current and as the voltage is fixed I can measure the wire resistance this way. The resistance and the wire temperature should be proportional and I hope to acheive very accurate control like that. Need some more thinking...

I've attached the latest pics.

Enjoy!
Greg

www.cncdirect.co.za

[belli]

Hi All,

I've put in a few hours lately, I've been at it for two weeks now but things are coming together. I will run it tomorrow and hopefully cut something!

I am thinking of making the table (MDF part) into a chamber with a port for the vacuum cleaner. I will put a few holes through the top and then use the vacuum to hold the foam down. Any ideas?

The electronics is ready too, I have a piece of 14R/m wire (of unknown origin) and I can drive it at 50V and 3A, hopefully enough, I'll know tomorrow. It is based on the SG3525 PWM chip and is very efficient, the mosfet is rated for 55V but if necessary I can change it to get 100V.

The wire runs through two high temp guides, I have drilled 0.6mm holes in each as it the smallest drill I have, will have to see how it works.

Enjoy!
Greg

www.cncdirect.co.za

[High Seas]

Looking good!
Will be watching/waiting to see how the pneunamatic control to tension the wire (as it heats up and sags) works out.
Man-in-the loop for control I guess. But gotta be better than using a pair of pliers!
Cheers - Jim

[belli]

Hi All,

I made the first cuts tonight, heat was in the mid range and I think it was too hot which is better than the alternative. Tensioning works great, you can watch the little block slide in and out, ran it at 1 bar, dia. 16mm cylinder which is about 2kg of tension, if I reduce the wire temp I am sure I will have to increase the pressure.

Problems I had were keeping the block stable, it bent and twisted while it was being cut, I need to think about that vacuum table seriously!

Enjoy!
Greg
www.cncdirect.co.za

[lovebugjunkie]

Hello Greg

Noticed you have not posted since June so this is a belated congratulations on making a great looking foam cutter. I like the clean, uncluttered look of it. And it looks like you kept the individual parts to a minimum.

I have been rolling the idea of a foam cutter around for the last 2-3 months and my idea is much like yours except mine uses more parts. I’m going to change mine to incorporate some of your ideas.

[belli]

Hello lovebugjunkie,

Thanks for the kind words, my shop is a real mess at the moment, I had to remove the roof while doing some building work! I will post some photos of the cutting when things return to normal (and all the mess is cleaned up!).

The PWM controller that I made works a treat, I am running at 80V and with the wire I have, 1.5 A for Polystyrene and around 2.1A for Polypropolene. The wire has a dull red glow to it when cutting EPP but I get a good finish. Cutting EPS at around 500mm/min and the EPP at around 320mm/min. When things are back to normal I have a few new designs to try.

Profili is a great package for the wings, the only one I have found that can do the interpolation correctly, they are bringing out a new package soon for doing fuselages!

I am using DeskCNC with a custom post that I wrote for all the parallel cutting.

Greg
www.cncdirect.co.za

[GARTH LEE]

Hi Greg
A really neat piece of kit 10/10 your tensioning idea is great.

[GARTH LEE]

Hi Greg
what 'Hi Temp material are you using as guides, pcb?

[belli]

Hi Garth,

I don't know what it is called, came from the Tufnol people, looks like a reddish fibreglass. Works a treat!

Cheers,
Greg

[belli]

Hi All,

Here is the wire temperature control that I am using, the files are in Eagle format which you can download from www.cadsoftusa.com/ for free. They were done in a bit of a hurry but the circuit works great and you can fit a volt meter (0-1V) to give you an indication of the current flowing. For my wire I use 2.1A for EPP and 1.5A for EPS.

Let me know if you need more info.

Cheers,

PS You will need to rename the files after downloading, delete the .txt and put the point before sch and brd (i.e. PWMController.sch etc)

[rjfurness@bigpo]

Hi Greg,
I am looking at Profili as software for my machine. Any more thoughts on how good it is, ease of learning, etc now you have presumably been playing with it for a while?

Have you used the fuselage software?

Thanks

Jason