This is how I made this scary jack-o-lantern with big snapping teeth.
Check out the video to see it in action!
Step 1: Build the Drive Mechanism
First I cut a circular piece of wood from a piece of scrap using a 4 inch holesaw. Make sure you use clamps here or the wood can fly off. Next widen the centre hole using a wood bit, it needs to be the same size as the bolt you are using, I used M6 bolts but you can use whatever you have lying around. Then drill another hole in the wheel near the rim and fit another bolt and lock it in with a nut on the other side.
Then make a push rod by taking a piece of wood about 12 inches long and drill a hole at either end. Your holes need to be big enough to let the bolts at either end rotate freely but not so big as to allow too much play. To keep the push rod in position on the bolt thread use a technique that will be familiar to anyone who has ever adjusted caliper brakes on a bicycle - thread two nuts onto the thread to just beyond where you want the push rod to sit and tighten them into each other using two pairs of pliers. This will prevent the nuts from moving up and down the thread in operation. Fit the pushrod and use another pair of nuts on the other side to hold it in place. Again the fit around the push rod should be snug but not so snug as to prevent it rotating freely.
Finally you need to fit a bolt in the other end of the pushrod, again locked in place with a pair of nuts. The free end of this bolt will operate the jaw mechanism.
Step 2: Build the Jaw Mechanism
The jaw mechanism is simply two pieces of MDF (or any reasonably study sheet material) hinged together, the upper of which is fastened to a small piece of wood with a hole to receive the bolt at the end of the push rod.
Draw around the base of your pumpkin on your MDF for a cutting guide. You will have to eyeball this a bit but you are aiming for two pieces roughly 2/3 the size of the middle of your pumpkin with one flat edge for the hinge. Obviously use the first one you cut as a template for the second. Cut them out with a jigsaw then drill a hole in the middle of each. You then need to go back through this drilled hole with the jigsaw on each piece to cut a large section out of the middle to allow the pushrod though. Once this is done screw a small piece of wood onto the top of one piece and drill a sideways hole in it to receive the bolt at the end of the pushrod. At this point you should attach the pieces together with the hinge. NB you will see from my pictures that I did the hinge first however in hindsight the other steps would have been easier if I left the hinge until the end.
Step 3: Build the Stand
You will need a large piece of sheet material around 12 x 24 inches and you need to elevate one half of this by an inch or so for the drill to sit on, using other pieces of sheet material. Exactly how high will be determined by how fat your drill is but you want to get your drill lying on its side with the drive mechanism in the chuck and the wheel not to touch the ground. Then you need to build an elevated platform for the pumpkin to sit on, again the actual height will be determined by the size of your pumpkin, the length of your push rod, and how your jaw mechanism sits inside the pumpkin so eyeball it for now and don't fix anything permanently until then end. Remember you will need a hole in the top of the stand to allow the push rod to go into the pumpkin, if you are clever you will use the piece of wood you cut the wheel out of earlier. There also needs to be space at the side of the stand for the drive mechanism to pass through.
Step 4: Carve the Pumpkin
First cut a 4 inch hole in the bottom of the pumpkin and scoop out the innards. Next you need to cut the pumpkin in half around its middle, remembering to put some nice big spiky teeth on the front half. Once this is done you can start fitting the jaw mechanism inside the bottom half of the pumpkin. Try sitting the frame in first and score around this with a knife to give you a guide to remove flesh so the frame sits snugly, however this step is more trial and error. Make a cut, try and fit the frame, then repeat until it sits snugly and flush with centre line of the pumpkin. Take your time here and once you are happy do the same again with the top of the frame and the top half of pumpkin. What you are aiming for is both halves to close neatly around your frame. Once this is done, fasten the bottom of the frame to the stand with a pair of long screws straight through the pumpkin, and attach the top of pumpkin to the top frame by knocking some nails through the pumpkin into the front and back of the top frame.
Finally cut out some eye holes in the top half.
Step 5: Put It All Together and Test
Because this project uses a pumpkin and all pumpkins vary, I cannot give exact measurements for building so instead you need to bodge it a bit. Once all the earlier steps are done you can assemble everything and see if it works. If not you will need to make adjustments and the most likely parameters to adjust will be the height of the pumpkin stand and the locating nuts on the push rod. Once its all working smoothly you can fix everything down permanently and move onto decoration.
Step 6: Decoration
Obviously you can't put a candle in a pumpkin like this so battery powered fairly lights are a good option. I covered mine in a green stage lighting gel and taped it up for a ghoulish green glow. I also sprayed the teeth white and outlined them in Sharpie to give some definition.
Step 7: The Things I Used
M6 nuts and bolts
Green LX Gel
Step 8: Turn Out the Lights
Turn out the lights, put the pumpkin in the front window and scare the pants off your neighbours!
Thats it, I hope you enjoyed reading this Instructable and please let me know if you try and build this yourself. Check out my other projects and also my Youtube channel where I try and upload new content at least once a week. If you want to support me then head on over to my Patreon page where you can help me create bigger and better projects with a small donation.