Depending on the type of glue you're using, this can take anywhere from 2 hours to a day or so.
Now, let's get Mathematical!
Step 1: Prepare Thyself!
Sharpie or other marker
liquid nails or other strong glue (depending on the type of foam you're using)
large-ish work table
For materials, you will need:
1 roll of blue camping foam (Walmart, about $6) or any other medium density foam rubber. I found this black one for $3 at goodwill
1-2 sections of fiberglass tent rod (recycled from a broken tent is best, but you can get replacement ones also for about $6)
2 pennies or washers
4-6" section of 3/4" pvc
a couple good handfulls of sand
2-3" block of open-cell cushion foam
Step 2: Measure Twice, Cut Once!
Bigger isn't better, necessarily- if you're 4 feet tall, you probably don't want to be swinging around a 6 foot sword. (Tempting, though, isn't it? That would look totally Algebraic! That would be pretty tough to carry around when you weren't using it, though, and longer swords tend to wobble like noodle-y arms in techno music) A good rule is to measure your leg, hip to heel, that's about as long as you want your overall sword to be.
Once you decide on the overall length, you'll want to make your fiberglass core about 4" less than that, for the extra padding at the tip. The person I'm making this for has a leg that's about 34" long, so the core I want will be an even 30". That means I'll be using just over 1 section of the tent pole, and gluing them together. Use the hack saw to cut it, and don't push down too hard to prevent splintering. The ends should fit pretty snugly in the metal joint, but if the 2 parts wiggle at all, add a pinch of sand around the part you're inserting.
Step 3: Get a Grip!
Next you've got to give your sword a proper hilt. Unless you've got really tiny hands, that fiberglass stick isn't going to fit very comfortably. You also want to make sure the ends don't go poking through all the foam and duck tape you're about to add on. Best way to do that is to add more surface area, by which I mean increasing the overall diameter of the terminal edge of the cylinder by a factor of pi, enhancing the... er, I mean, just tape a penny to one end.
Rip a piece of duck tape about 6" long, and then rip that in half the long way to get 2 narrow strips. Cross them over the penny, and wrap them around the end of the rod to make a cap. Then slide the piece of PVC pipe over the other end, and snug it up against the penny and tape the whole thing together. Now you have a place to hold your sword! DON'T HIT ANYBODY YET!
Step 4: Weight a Minute...
After making dozens of swords like this, I was getting frustrated that all the weight was on the blade end. This made it tough to swing repeatedly, and tougher to gauge the force I was using. Then I figured out to fill the handle with sand! This added stability to the core inside the hilt, AND evened out the weight distribution to make a better balanced blade!
Well, *I* thought it was clever, anyway.
So, if you want to do the same, stand your fiberglass core in the bowl of sand, with the open end of the pvc facing up. Try to fill it evenly from all sides, so that the fiberglass core stays centered. If you've got a small funnel, that might make the filling go faster, but I was able to get it packed after only a few minutes using just my hands. Once it's full, put some glue around the top to seal it in, and then wrap that tightly with Duct tape. Doesn't that feel better? easier to wield? more like an extension of your arm? DON'T HIT ANYBODY YET!
Step 5: It's What Inside That Counts
Step 6: I See a Little Silhouetto of a Sword
Once you've got the basic shape drawn out, you can add whatever details you want- saw teeth, spikes, curves... the more complex shapes will be tougher to cover securely in tape later on, but the nice thing about foam and duck tape is you can cut stuff off and fix it with more duck tape whenever you need to! If it doesn't come out the way you wanted, don't worry, "sucking at something is the first step to becoming sorta good at something!"
Once you've decided on your shape, use the scissors to cut it out of the foam. Try to cut on the outseide of the line- you can always cut more off later on, but trying to add more won't be as strong or look as good! When the main shape is free, use it as a template to trace and cut 2 more pieces just like it.
Step 7: Swords Are Like Onions...
Actually, a good boffer sword is more like a sandwich.
First, you want to cut a slit up the center of your middle layer, the one you traced the core on.
Then, squeeze the core into that slit, and tape in place on both sides- that's your meat!.
Next, apply a generous helping of glue over the entire face of the blade, like mayonnaise.
Layer on the bread... I mean, one of the other foam pieces, and slide it around a little before the glue takes hold- that helps it spread more evenly without getting your fingers sticky!
Flip those two over together and do the same mayo-and-bread combo on the back, and you've got a delicious sword sandwich that tastes like victory!
DON'T HIT ANYBODY YET! In fact, step away from the table. You're drooling all over the place, and the glue needs time to dry. Go practice your newly honed sammich making skills on an actual sammich. In the meantime, you can help make a strong bond by laying a scrap of wood over the length of the sword, and piling a few heavy things on top of it. Try to keep the weight evenly distributed, and use just enough to make sure the foam keeps contact all along the blade.
Also, wash your hands before touching your food!
Step 8: Shape of Things to Come
Some LARPs have very specific rules about how thick a striking surface can be, and whether you need to specify if your sword has one sharpened edge or several. If you're making this for a specific kind of game, check with your gaming admins before you finalize your design.
Step 9: Getting to the Point
Step 10: Horsing Around With the Pommel
For mine, I cut a couple 2" squares from the foam I had left over, stacked them together and cut the corners to round them off. Then I taped that to cap off the end of the handle, just like when we put the pennies on the core.
Looking pretty good now, isn't it? You can see all the parts coming together! DON'T HIT ANYBODY YET!
Step 11: Lay It on Me!
Step 12: Finishing Touches
Smack yourself in the leg. I'll wait.
If you're going to use this sword in any kind of mock combat, you'll want to know that you can take a hit, and you'll also want to get an idea of how much wallop this thing packs so you know how hard you can swing it safely. There you go! Twirl it around, get a feel for the balance of it! Actually wait, you should probably do that outsi... Uh oh. Was that your mom's vase? You killed a vase with your sword on your first day?!? THAT'S AWESOME! IT WORKS!
That vase was probably harboring an evil spirit anyway. Now, go forth and fight for Truth, Justice, and the forces of Good!