I figured I'd offer a step-by-step tutorial with photos for everything I did. The project cost me less than $10, and the most expensive part was the metal bracket, which was about $7 alone. I was fortunate in that I had a piece of MDF already on hand, so if you were to make one too it might cost you a little more for the wood.
This was the quick plans I sketched out on a scrap piece of note paper which I taped up outside my garage where I was working to refer to if necessary. Some of the measurements subsequently changed, but I note them below.
The table started by cutting my MDF to size. I made mine 24" wide by 36" long. While a really big table would be fun, storage is always a consideration and this should handle most projects. Some of the other versions out there use a laminate top because it is super slick and smooth for moving the foam across the table, but MDF is a very smooth surface as well.
I next made two stretchers from 2x3 board I had on hand. The stretchers run the along each long side, though not completely to the ends. I made my 24" long and centered it on the table length, that way if I chose to use a fence to help make straight cuts I'll have a place to clamp it.
I laid out three screw holes centered on the width of the boards (3/4") at 7", 18", and 29". I pre-drilled the holes and countersunk them to keep the screw heads below the table top. When using MDF it is important to pre-drill your screw holes otherwise you're likely (read: guaranteed) to split the wood.
I also glued the strechers to the table top for added strength.
I then clamped the stretcher to the top and pre-drilled it to make sure the screws went in securely (this could have been done all as one step).
I then screwed the top to the stretcher with 2-1/2" drywall screws.
Here's an end view showing the two stretchers attached.
The next step was to make the arm that holds the cutting wire. I ripped a 2x3 in half, but using a 2x2 would be a good choice, but I was trying to use up spare wood I had on hand. The riser is 22" high while the arm itself is 18" long.
They attach at a right angle with the arm on top of the rise. Once again I pre-drilled and countersunk holes to attach them with two screws. Like drilling into MDF, when drilling into end grain of wood as you are here, pre-drilling is important to prevent splitting.
The next step is to attach a shelf bracket to the arm assembly to ensure it remains rigid and there's no flex that would allow the string to go slack. I used 1" screws here.
To attach the arm assembly to the table, the riser will be screwed to one of the stretchers. An alternative method, particularly for ease of storage, would be to attach the arm assembly using two bolts run through the riser and the stretcher and held in place with either a knob or wing nuts. As I had forgotten to pick up wing nuts, I opted to screw it to the stretcher, though this can be changed at a later time.
As always, the screw holes were pre-drilled and countersunk.
Once that was done, I drilled a 1/8" hole for the wire. It is located 1/2" back from the end of the arm and centered on it. A second hole was drilled another 1/2" back, but this one did not go all the way through the arm as it will be used for an hanger bolt that can be used to keep the appropriate amount of tension on the wire.
An alternative would be to use a guitar tuning key, but my local Guitar Center told me they were sold in sets, not individually, and since I had the hanger bolts aplenty from my LED spotlights project I used them instead.
Once the arm assembly was screwed to the stretcher, it was necessary to locate the hole in the table top so the wire can pass up through the table from underneath. It should be fairly perpendicular to the table so that your cuts are straight.
Initially I was going to use a plumb bob hung from the end of the arm and then measure back 1/2" inch to align the holes. But my daughter came up with a novel, better idea: using the laser pointer on my stud finder. I turned the laser on, shined it down through the hole in the arm, and the laser dot appeared on the table top precisely in line with the hole in the arm. I marked its location and drilled through the table with the 1/8" drill bit.
I had taken a picture of the laser dot marking the spot, but unfortunately it didn't show up in the picture.
The next stage of the project was to make the PVC arch the holds the wire in place under the table. I had 2" PVC pipe on hand, but I imagine 1-1/2" pipe would work too. I cut off a ring about 1-1/2" wide and then cut it slightly more than in half to create tension when it's holding the wire. A 1/8" hole was drilled in the center of the arch.
The wire that I used was 18 gauge nickel wound guitar string. It comes with a ball at the end which is perfect for holding it in place. I got two wires for less than $2 at Guitar Center.
The wire's passed up through the arch, through the table, and through the hole in the arm. I then wrapped it around the hanger bolt to secure it. When the bolt is turned it applies tension to the wire.
At this point, the table assembly is complete.
The next step was to make the power supply, but since that didn't work out so well, I'll save that for another tutorial. My problem was I had attempted to use an old train transformer to generate the heat, but it apparently wasn't strong enough and didn't heat the wire sufficiently enough to cut through the foam. So I will build the power supply described in the Garage of Evil tutorial, but I have to order the low voltage transformer and will show the steps I used when it arrives.
Right now the table looks great and I'm disappointed the train transformers didn't work because I'm itching to give it a go.
Hopefully the steps described and the pictures provided will help you build your own foam cutting table.