Next up: A hot wire foam cutter

[john vanhoozer]

Hey, Guys

I'm working on a hot wire foam cutter for a buddy who does CosPlay - actually he's a costumer for a living, too.

These things are pretty simple and you may have seen them about.  A piece of NiChrome wire, a powersupply, some wires and VIOLA (yes, it looks like a big violin :)  )

I've found a lot of information in the web about how best to do this.  One of the most helpful has been Jacobs Online where they even have a calculator to help determine the size of the power supply.

So, what's my question?  Well, I'm a bit confused about one thing:  the Dimmer/Potentiometer.

The simplified diagram they have would look something like this

wall socket -> positive     -> fuse ->  Dimmer switch -> Step down Transformer -> Nichrome wire

                 -> negative    -------------> 

That's the basic layout.  There are other things they recommend and, of course, it's all grounded.  My design will use a Switched powersupply instead of a step down transformer and it outputs 5v at 5 amps.

It seems to me that instead of the Dimmer Switch with the Transformer, that I'd be better off with a pot controlling the voltage to the wire.  And that a nice little LED to show that the thing is on would be handy.  It would be really nice if there was a temperature display, but that's for the long run.   

What do y'all think?

[Randy Ohman]

Excellent idea.

 

On Friday, September 16, 2016 at 2:03:55 PM UTC-5, john vanhoozer wrote

[john vanhoozer]

Yup...

Gonna have to be a potentiometer after the powersupply.  

It seems the powersupply, converting from 110v AC to 5v DC is sort of an all or nothing deal.  SO... now a pot that will handle the current/voltage

And I have no idea how to buy one of these :)  (that is what resistance,etc, I need)  got to figure that out.  

Or maybe see if I can find some junk lying around with a Pot in it and see if it works ;)

[john vanhoozer]

Ha!

I've been making it hard on myself.  It turns out that this 5v DC power supply has a little potentiometer built in to the board and can adjust the votage +/- 10%.  That's more than enough.  

According to the Jacobs wire calculator, with my 22 gauge NiCr wire, I'll need to go back to 12 inches (the original design) to keep the temp between 740 and 860 degrees which is plenty for the purposes my friend needs. 

And I think I have the "arm" for the cutter figured out.  I'll have to work a few things, but this might get done tomorrow night!

[john vanhoozer]

Well, It's done.

I have some tweaks to do, like re-locating the powersupply, and I'd like to come up with a better mounting system for the wire. But it's cutting and my buddy is happy with the result.

I've shrunk the wire to 10 inch because for cutting EVA foam (like what is used for those mats that relieve back strain when you are in a shop) just took too much pressure on the wire.  

If you remember, I was working on a motor to raise and lower the solar screen/curtain outside my windows (still in progress) and that it uses a hand crank.  Well, I took that aluminum pole/crank and carefully bent it over my knee to create the arm for the cutter.  Then ran the write through it, mounted the powersupply underneath, added an on/off switch, and used click butt connectors at the ends of my leads to connect to the NiCr wire.  Flick the switch, and it heats up nicely in about 10 seconds and cuts well.  

The click connectors are OK, but I need something better.  Too much tension and they will pop off.  I've left it on though for 30+ minutes and the connectors never show signs of over heating or melting (whew).

The powersupply has a small LED on it to show power.  I think I'll see about figuring a way to mount that so it's visible.

And last but not least, I need to clean up the table top.  I used some slick strip on the surface of the plywood.  Not sure if that was a good idea or not, but to accommodate the center hole, I worked from the outsides in (not the best idea) and left a strip up the center that I need to fill in.  That I'll do tomorrow.

If I can, I'll bring it by on Saturday since I can't seem to upload the video - too damn big.

[Don Smeller]

Pictures. Your faithful fickle audience demands pictures.

Don S

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[john vanhoozer]

Thanks to everyone for the encouragement and ideas in this project.

We discussed some changes that I suggested for version 2, which are more to the table configuration than anything else.  Next version will allow for the arm to be tilted side/side for angle cutting....

But I did find a new power supply option that I'll be investigating in the future, too.

I delivered what I had on Sunday - he is working on building a costume that needed to cut some  6" x 2'x2' foam to make shoes for his "Travelocity Gnome" costume right away followed by "Mojo JoJo" costume.  For those that don't know, Mojo JoJo is the bad guy in a kids cartoon called "The Powerpuff girls".

Here's a pic

On Friday, September 30, 2016 at 4:34:44 AM UTC-5, Don Smeller wrote:

Pictures. Your faithful fickle audience demands pictures.

Don S