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Hotwire Foam Cutting Table

I have plans to make a modular gaming table and to do that I needed someway to make the 2' X 2' sections.  What I really needed was a way to cut foam that worked like a table saw did for wood.  I looked for some to purchase but they didn't look like they would cut the size foam I needed and they cost a fortune.  This walkthrough will show you how to build your own hot wire foam cutting table.  The finished table can cut foam up to two and a half feet wide and be adjustable to cut any smaller size as well.  This entire table should be able to be built for under $100.  I'm not putting any prices I paid on this page because that seems to be dependant on what's available in your local area.  You'll have to go wander around your local home improvement store and see what's available.  This project also requires a basic understanding of carpentry and electrical wiring.  All construction and wiring used here are very basic and not terribly complex but I'm not going to go into great detail of how to attach boards together with screws.

It should be noted that you can change the way this table is constructed in many ways and all are perfectly valid.  One example of this is that I used screws to hold it all together because screws are much more sturdy than nails.  You could build this table with nails and it would probably work out just fine.  The important thing is that it works for what you use it for.

Total Construction Time: about 3 hours.  It might be a bit less if you really are good with carpentry and electrical stuff.  A bit longer if you're new to either (or both).  I'm not particularly great at either one but I have some experience in both.

Sections
Materials
Construction
Electrical (in part 2)
Using the table (in part 2)
 

Goals

Materials
 

Quantity

 Description Use
1 24" X 48" X 1" board Table surface
4 2" X 2" X 26" boards Feet to raise the table off the floor, the cutting arm, bracing for the arm
2 1" X 3" X 24" boards Adjustable rail for foam measurement.  Edge piece to divide the cutting surface from the power supply
~4" NiCrome wire.  I bought 33 feet of wire from eBay which should last me forever.  I bought way more than I needed because I didn't want to mess with buying more. The wire that gets hot and cuts the foam
8' Electrical wire.  I got two rolls so I could have different colors because it is easier to wire that way. Wiring
1 Power Supply.  I got one from Radio Shack. To provide power so I don't spend a fortune on batteries
2 small metal straps with holes to use for attaching the NiChrome wire to
1 1/4" eye bolt top side the wire attaches to
3 1/4" nuts attaching the electrical wire to the eye bolt
1 1/4" wing nut adjusting the tension of the cutting wire
  2" long screws (I got #8 but as long as it's 2" long it should work) construction
6 3/4" long screws (again I got #8) construction
1 small hinge To allow the cutting arm to rotate up [Optional]
1 a straight edge drawing straight lines
1 a tape measure for measuring stuff of course
1 a pencil for drawing lines where we're going to drill and cut stuff
1 a drill for drilling all the holes for the screws
1 a saw (I used a circular saw I had but a hand saw would work just as well) for cutting
1 nail, any size marking where to drill holes
2 spring loaded clamps holding down the cutting guide

Constructing the cutting table

The first step is to cut one of the 2" X 2" X 36" boards into 2 pieces 4" long and 1 piece 3" long.  These are going to be the vertical post the cutting arm is attached to and the two side braces to prevent the cutting arm from moving side to side.  You can make the cutting arm sit higher than 3" off the table if you want to.  One advantage of making it higher is you have more room to adjust the tension on your cutting wire which has been an issue a time or two for me but overall 3" works well.  If you do increase the height make sure to increase the height of the braces the same amount so they reach the cutting arm.  I used a circular saw to do this, but a handsaw would work (but it'd be much more effort).

 Now we're going to start on building the table itself.  The first thing we're going to do is attach the base edge.  This is a 1" X 3" X 24" long board.  You have to go to some trouble to make sure it's perpendicular to the length of the board so that if we decide to cut a piece of foam to our maximum size it will come out straight.  I picked up a cheap pressed wood board that was 24" X 48" long at Home Depot to use as the table surface.  There are probably better boards you can use out there but this one will be fine for what I'm planning on doing and it's price appealed to my cheapness.  First measure your 1" X 3" X 24" board and see how thick it really is.  I know the description says it's 1" wide but it's not really (I just use 'em, I don't explain 'em).  Once you have this distance you have to subtract it from 6" to get the midpoint of where our board is going to go (NOTE: You could just draw a line 6" from the edge of the table surface and use that as the center point of your board but then your available cutting area would be slightly less than 2' 6".  If this is fine with you then by all means do it the easy way.  I'm just a perfectionist).  Once you have this distance measure it out and draw a line across the table and make sure there are marks on the sides of the table.  Next measure to the mid point of the board across it's short side (the supposedly 1" side that isn't 1") and mark each end of the board where the midpoint is.  We're going to use these marks to line up the base board. 


Next take your pencil and mark 4 spots along the line you drew.  This is where you're going to put the screws that hold the base board to the table.  Take your drill and drill the holds as marked.  Once your holes are drilled in the table line up your base board using the marks on the side of the table and the sides of the base board.  Once that is done poke the nail through the holes you drilled so that it just slightly pushes into the base board.  Once you remove the base board there will be nice little indentions in the wood that show you where to drill the holes in the baseboard.  Once  you have the holes drilled in the base board attach it with your screws.  I used a screwdriver attachment to my drill for this mostly because I'm lazy and didn't want to do it by hand.

Now that we've got our base board attached we're going to attach the cutting arm.  We want the arm to be centered on the table.  First step is to measure and draw a line from the edge to the base board down the center of the table.   

Then measure and mark the center of the cutting arm post (the 3" long one).  Then place it with the center of the post lined up with the mark you made on the table. 

Hold it in position and gently draw around the base of the post with a pencil.  This will give you a guide on where to drill the holes for your mounting screws.

Here is a good example of why you need to pay attention to what you're doing.  I forgot that I was going to hinge the cutting arm and drilled it and the post for screws to fix them together.  Oh, well.  A couple extra holes doesn't hurt anything. 

You can see where the holes are drilled in the table for the post mounting screws.  I used the nail method to mark the post where I needed to drill the holes then drilled them separately.  You can use the outline you drew earlier as a guide when holding the post up to mark it with the nail.

Next we have to attach the cutting arm and the braces for it.  I'm putting a hinge on my cutting arm so I can do circular cuts later on but you can screw down the cutting arm and lock it in place instead.  Permanently attaching the cutting arm would probably make the whole thing less likely to move side to side.  As it stands any sideways movement is insignificant and doesn't affect the cutting operation.

Here you can see where I marked the supports for the cutting arm.  These pieces are there to prevent side to side motion of the cutting arm and still allow it to swing up to accept an attachment that allows the rotating cuts.  If you're going to permanently attach the cutting arm so it won't rotate up then it would be a good idea to attach these braces to the cutting arm as well.

To the left is a good shot of the hinge attachment.  You can use the extra hole at the top to run the wiring for the cutting wire.

We also need to drill a hole in the table for the cutting wire to pass through.  We attached the cutting arm first so we could get a good idea where to drill the cutting wire hole.  With the cutting arm down in the cutting position (if you used the hinge, if you attached it directly then it's already where it needs to be) mark a hole roughly in the center of the cutting arm but a little bit past the end.  It doesn't have to be far from the end just so there's enough room for our attachment to hang over the edge of the cutting arm and for the eye bolt to pass through.  I put my hole about 1/2" from the end of the cutting arm. 

Now that we've got our hole for the cutting wire we need to attach the bracket that will hold our eye bolt.  This is just a flat plate I found on the door hardware isle of Home Depot.  I imagine it's some sort of bracing plate but I'm not sure.  It works fine for my purposes.  It came in a pack with two of them plus screws to mount it which was perfect for me since I needed one on top and one on bottom for the wire. 

To attach the plate we need to make sure it lines up fairly well (it doesn't have to be perfect) with our cutting wire hole.  To make sure it lines up I used a screwdriver that I put through the plate and down to the hole.  Once I got it where the screwdriver was straight up and down I marked the holes in the plate on the cutting arm with a pencil and drilled the holes for the attachment screws. 

Now for the cutting wire bracket on the underside of the table.  We need to keep the wire off the underside of the table so we have room to attach it to our bracket.  I used a small piece of scrap plywood I had lying around my garage.  You can use any small piece of wood that's smaller than our 2" X 2" boards we're going to use as feet for our table.  A small piece of 1" X 3" board (if you have some scrap) would also be perfect for this role.

Here's the bracket for the bottom of the cutting wire.  I just lined the holes up by eye and drew a circle where the mounting screws went.  The cutting wire will go in the far left hole and the electrical wire will be attached to the second hole on the bracket.

For the table feet it is not nearly as important for everything to be straight.  All I did was to measure the same distance (it doesn't matter what that distance is) from each side of the table and then attached two 2" X 2" X 36" boards for the feet.  You can make 4 separate legs at the corners but that was too much trouble for me.  This way I didn't have to do any extra cuts.  The main purpose of the feet are to keep the table up off whatever surface you're using it on so the wiring doesn't get damaged.  As long as that happens the feet/legs can be whatever you want them to be.

You can also see where I took a scrap piece of plywood I had lying around and attached it near where I drilled the hole for the cutting wire to go through.  This is so we have room to attach the cutting wire to our attachment under the table

 

Here is how we're attaching the eye bolt for the cutting wire.  It just goes through the hole at the end of the bracket on the cutting arm.  The two nuts at the bottom are where we'll attach the electrical wire for the current and we'll just wrap the NiChrome wire around the end of the eye bolt.  There's a second nut right under the bracket so we can lock the eye bolt in place.  If you leave off this nut then the eye bolt can rotate and mess up your straight cuts.  To adjust the tension on the cutting wire all you have to do is loosen the nut under the bracket and tighten the wing nut on the top.  Then you can run the bolt under the bracket back up so it's snug.  You can also take the wing nut completely off and remove the eye bolt without changing the cutting wire to allow the cutting arm to rotate up and then you just have to tighten the wing nut back up and everything should be just as you left it.

This completes the construction phase of this guide.  Next we'll tackle the electrical side.  Below are some photos of the table after construction is finished and before the electrical wiring is done.

 

Part 2: Electrical wiring