Bed-of-nails closeupIf you're considering building a bed-of-nails for your pressure demonstration don't waste your time trying to drill 400 or more holes in a sheet of plywood. Go pick up some pegboard at your local home improvement center. The key is finding the "correct" kind of pegboard. I've found that there two kinds of "peg-board" that you will find at a Home Depot or Lowe's home improvement kind of store. I call them Big-hole and little-hole. You want the little-hole version. The little holes appear to measure 3/16th of an inch and are set on a 1inch spacing. This hole size works great for a 16-penny galvanized steel nail. The fit is just tight enough that a layer of 4 sheets of the peg-board will securely hold the nails in place. If you happen to know what this kind of peg-board is called add a comment to this post!
The Big-hole pegboard has holes about 1/4 inch diameter and I was never able to find a nail big enough at a typical home supply store to fit it. You may have to dig to find this board since I don't think it is the stuff you put up on your garage wall with those little silver tool hangers. Lowe's had it in Toledo, but Home Depot did not.
About the nails, don't worry about the points unless they are obviously goobered-up. Some people seem to think you need nails that are all exactly the same size or rounded over. Your back is not perfectly flat, so the nails don't need to be perfect either. Use common sense, from each box of nails you'll end up tossing away maybe 5 nails that are obviously too long/short/goobered-up. Cut the peg board to be about 2ft wide and about the length from the bottom of your neck to where your lower back is. If you make the bed longer, 1) it gets really to heavy to move around easily, 2) you end up hurting your butt or head on the nails.
Carefully placing the cinder block on top of the teacher. Notice the two small blocks under the block.
For pounding the nails in, I line up the boards on top of two work benches that are next to each other with about a 3-4 inch gap. As you pound in more nails you can spread the benches apart. This way you are always pounding near the edge of a table with support so you don't crack the boards. I'd leave a few inch border with no nails so you can grab the thing. In the ideal world (of the four of these I've made this has never happened) you would build a nice frame around the pegboard that has handles for easy transport. It would also stop the board from getting worn looking over time. I've just ended up spray painting the top board (the one on the pointy side) with black paint. This seems to make the silver nails stand out more and it just looks cleaner.
Once you've built the bed-of-nails there are a few things to keep in mind before running off to do a demo. First off, when getting on and off the BON be sure to be careful. It sounds obvious, but worth saying. Be careful not to crush the first row of nails by sitting on them. The proper placement of your body on the BON will make a huge difference in your comfort. Try to situate your lower back at the bottom of the BON. You don't want your butt on the Bed. It's your lower back and upwards that works well. As far as you head goes, I think it not only looks funky, as well as a bit uncomfortable to just have your head sort of hanging off the BOD. Grab a pillow, or something to rest your head on.
A not-so-small Kid sitting on on top of the bed-of-nails.Not everyone is comfortable with the "breaking the cinder block" thing, so an alternative is to have a really small child sit on top of the top bed. It's a good idea to have another person plant the child on top rather than having the kid climb up on their own. Of course breaking a cinder-block on top of you is the really big show. If you do use a cinder-block, make sure you place two spacer blocks of wood under the block. These are about 1.5 x 1.5 x 8 inches and will make a huge difference in the comfort of the person pinned. If you have someone break the brick just sitting on top of the bed, it will break, but you are going to feel a pretty good impact. I've found that the little spacer blocks seem to lessen the impact a bit.
Make sure the person swinging the sledge has a good feel for how hard to hit the block. Most people the first time will not really hit it hard enough. This is especially the case for TV news reporters! Another plus of the little spacer blocks is that if the sledgehammer comes down a little soft, the block will still collapse a bit in the middle.
One last safety tip is to protect your face! Of course you have that nice face shield on, but I always suggest putting both of your hands facing palm up over the top of the mask to deflect any huge chunks of block that come your way. Once you've had a hunk of brick bounce off your face you'll remember to put your hands in place before they smash the block. Leather work gloves are a nice touch as well. Showing the audience that you are taking some safety precautions is always a good thing.
Below is a super quick TV spot we did at COSI Toledo in 2006.
