Adjustable Hotwire Foam Cutter with Fence

Initially starting with Creativeman’s Mighty Goliath I decided to create a foam cutter that was adjustable for various angles, had a fence to facilitate straight cuts, made removal and installation of the hotwire easy, and folded for taking less space when stored. Additionally, I wanted the table to be an element unto itself – the idea was to use a battery charger as my transformer, along with a separate control box and foot pedal (that are used in other projects) so that I would not have to have a single power source and controller for the three tools I use them with.

Step 1 The Table

1.     As pictures explain quite a bit I won’t go into to details of the construction but I will point out a few of my reasons for building it the way I did. For those not familiar with hotwire cutters there are several other folks with instructables that explain the theory and even include electrical diagrams. I am no electrician (although I have been known to provide them with employment if not entertainment) but a basic knowledge of wiring is all I needed for this project.  For the table (please excuse the Jackson Pollack design – I reused my children’s design table which I painted this way to hide their messes - if you can’t beat ‘em join ‘em) I decided that a round shape would give me more space and made it easier to place my fence at any location in regards to the wire. The elongated slot gives enough room for the wire when the arm is rotated and is probably wider than it needs to be. Four legs form the base and the arm is made from three separate wood pieces, two horizontal and one vertical. At the pivoting section of the arm, provided by a 6 inch bolt, there is enough friction between the two wood pieces to hold the arm tightly without shifting. The fence is just a smooth piece of rectangular aluminum and has a small bolt at one end with a round wood washer to clamp or pinch the table to hold it tight. At the other end I use a cheap plastic spring clamp since it is easy to place at any point on the length of the fence.

Comments

[johnketta]

Nice project!
Do you have an electric wire diagramm?

Thanks in advance
John

[jafo]

So, let me see if this is right. You are using the complete #10 guitar string length, and 12 volts DC for cutting. Do you know what the string resistance is? While the foot pedal is a good idea, is it necessary to use the pedal on and off to keep the wire at cutting temperature, or is that just a safe way to insure that it is not left in the on position? BTW, I like the fact that you can pour complex parts with the foam variation of the "lost wax" method of making jewelery. Very clever! How small (diameter) must you maintain to get a guaranteed good pour? I too, am pleased with the nice workmanship of this project.. One last question. Other than sand, what material would you use to make smaller aluminum castings if you had to make a small part?

[oompa]

I do not know what the resistance of the string is - I bought several sizes, #10, #12, #14, etc. but so far have only used the #10. I have burnt through it (snapped the string) once so far, with (really rough estimate here) about 20 hours of cut time. All of this is variable - I can increase the voltage (amperage) of the charger which results in a slighty higher temp on the string; this allows you to push the foam faster or cut 2 to 3 layers of foam at the same speed. Or, if you push the foam slow, you will cut a wider kerf in the foam. I found the pedal to be handy because I found many times that in the middle of a cut (like doing inside cutting instead of an outside form) I needed to turn off the charger so I could reposition the piece. However, it never fails that keeping the foam still with one hand AND turning off the charger with the other results in melting something I didn't want melted such as an otherwise smooth clean edge. The pedal keeps both hands on the foam at all times and the wire cools immediately - I can actually touch it after one second. Most of my pours have had a sprue of at least an inch in diameter. In my pours I am trying to feed the aluminum in the mold ASAP before it starts cooling. Most of my parts are not very small, i.e. not jewelry sized so I have not needed a small sprue. It always ets cut off of my forms anyway. In any case, the process is the same for large or small parts. While there are other methods to use for casting aluminum, I certainly do not have the expertise to talk about them. I read somewhere that certain types of production casting may use steel forms but that kind of work is well beyond home casting. I know that some home casters have created molding sand from regular beach sand and kitty litter as the "binder". In my case I just found a local aluminum foundry and they let me buy a couple of 40-pound bags of Petro-bond. This is a reddish colored oil-bonded sand and well worth the slight expense if you decide to persue metal casting as a hobby. My initail forays into casting were from reading Dave Gingery's series of books "Build Your Own Metal Working Shop from Scratch". Thanks for the comment!

[Lectric Wizard]

Nice instructable !! It is good to see someone who takes pride in his work, EVERYTHING is so neat  well constructed ... Love the wine box idea !!

[oompa]

Thank you - I got the idea for the wine box (I work in a bar so I have a few of these) from another instructable about a "mad scientist's light".  I can't say I take the time to do all my projects nicely, but this one turned out very well and I like to use it - that makes a HUGE difference in my opinion.

[tcase]

May I ask, what do you exactly use this for? I know cutting foam, but, what are you making the foam into? Do you have any pictures of things you made?

[oompa]

Hi Tcase,

I built this foam cutter to supplement my metal-melting hobby.  Basic pattern making for aluminum casting generally involves making a pattern out of wood then putting this pattern in a 2-part sand mold, packing the sand around the pattern, then opening the mold and removing the pattern.  Then you pour molten aluminum in that empty space and once it cools you have a copy in aluminum of your original pattern.  The big benefit of foam however, is that you do not have to remove the form from the sand - you just pour the molten aluminum on top of it and it vaporizes instantly (molten alum being around 700 degrees), filling that space with the metal.  It makes it MUCH easier to create complex shapes (I also use a hot glue gun to attach foam-to-foam pieces, the glue melts/vaporizes also) that might prove very difficult to remove from the sand without ruining the sand mold.
I included a picture of a couple of things I have made in aluminum, they are exact replicas of what the foam pattern looked like.  Regarding the metal gear blank - I used adhesive spray to glue a white paper gear blank to a foam circle and followed that outline with the hotwire cutter.  The gear was a missing piece in a set of compound gears on my metal lathe.  I wanted to cut a particular thread on my lathe and of course Murphy decided I needed that one missing gear to cut that particular thread.  While generally one would machine-cut the teeth on a blank metal circle, I didn't have that setup.  It wasn't perfect (I made three patterns, used the best one, and still did a bit of hand-filing to get that good one to run smooth), but in the end it worked.  Yes, I could have bought one and saved myself quite a bit of time but what fun would that be?  The main reason is that, though - to create patterns for metal casting.  An added benefit is that this cutter keeps my 6 year-old son occupied cutting three scrap pieces of foam into 30000 totally useless little pieces while I work on other projects in my shop :)  It is pretty easy for my kids to manipulate too!

[oompa]

[plasticisfantastic]

 Thanks for your posting. Is it possible the pdf is broken? can not download

[oompa]

I just downloaded it myself without problems - are you right-clicking and choosing to "save as . . . " to your computer?

[prova]

La cara vecchia spina SIP 

[oompa]

Eh si, ce ne son ancora una ventina!!  Sono forte, devo trovare un uso per loro . . .  (translation - I still have 20 or so more!!  They are cool, I need to find a use for them . . .)

[Creativeman]

Thanks for the nod, oompa. Excellent 'ible, and your design looks well thought out.  A little more complicated than mine, I think, but we work with what we have so I understand.  They are a lot of fun to have and to work with for sure. Good job. Cman

[rimar2000]

Good work, and good instructable!!

[oompa]

Thank you - I am a bit surprised after so many views to not have any questions.  I didn't explain as much as I thought I should, but I know I usually don't have questions if enough pictures are provided of the process.