Wednesday, 23 October 2013

The Halloween Machine ...

Recently we've been showing the kids how things work, and how things are made and I was trying to explain to the kids what cams are, and how they are used in engines and in other types of machinery, I wasn't convinced I was explaining in a way that they would understand.

I've worked with machinery/engines of various sorts since I was 15 and because of that I sometimes forget that I might need to simplify things a little, so we built The Halloween Machine, which uses cams to animate a Halloween type scene.

It's made of wood, and although it's not very precise I have taken some care with it, other wise it wouldn't work properly, there's a video of it in action at the end of this, it shows it working in the dark and in the light so you can see how the cams work.

Here's what it looks like in the dark and back lit -


It has to be said I got a little carried away with it, but it turned out well, and it's a good demonstration of how cams can be used to turn rotary motion into liner motion, this is basically how the valves in a car engine work, they are operated by cams, these open and close the exhaust and air inlet valves.

The first thing I did was to make a cam template, to do this I marked out the centre of a piece of wood and then using a hole saw I marked out a slight circle on the wood, next I marked lines either side of the circle and then marked lines from each edge of the circle, then I cut out the shape on my scroll saw.

Here's a few pictures to show you what I did -

Centre line marked out.

Circle and hole made with hole saw.

Lines marked either side of circle.

Basic cam shape sorted.

Once the template was done all I needed to do to make the other cams was to drill a hole big enough for the dowel I used as a cam shaft (I used 9mm dowel) and with the template on the dowel I just pushed it into the hole and drew round it.

Here's how - 

Off cuts come in handy.

Just need to draw round it.

I originally wanted 3 cams, but ended up with 6 small cams for the bats and a larger one for the witch (see what I mean about getting carried away?) so once I'd got enough cams for the bats I needed to make them all the same size, so I put all 6 cams on a piece of dowel and then sanded them until they were all the same.

Like so - 

Cams ready for sanding.

Seems I wasn't very careful when I cut them out.

All sanded and virtually identical.

Next I drilled a small hole in each cam, the reason for this is because once I had the cams where I wanted them on the shaft I didn't want the moving about, so once they were right I used the holes I'd already drilled as a guide and drilled into the shaft, then used a small peg to lock them in place.

Locking holes drilled - 

Cams done.

On to the box to hold the cam shaft, this is basically 4 bits of wood with a hole drilled in each end for the cam shaft to fit through.

Making the box - 

The 4 parts ready cut.

Centre of each end marked.

Fixing holes and cam shaft holes drilled.

Box finished.

The box that holds the cam shaft and the bat and witch figures is really simple to make, once I had it fixed together I marked out and drilled 7 holes along one of the longer sides, these holes are where the posts that hold the witch and bats will sit, I made the holes 10mm and the posts that hold the bats and the witch are made from 9mm dowel.

Post holes marked and drilled - 

post holes marked out.

Post holes drilled.

Next I cut out the bat shapes, these I printed out and stuck to the wood I used, I did the same for the witch, but forgot to take pictures of that.

Bat shapes ready to be cut out -

Simple bat shapes.

The kids painted the bats using a water based black enamel paint, and the witch and the scene were also painted in the same paint, the graveyard and village scene are cut out from a thin piece of pine.

Painting - 

They did an excellent job.

And here's the finished article - 

Ready for action.

Here's a close up of the cams - 

The cam on the left is the one that drives the witch.

You can see that I've added a little wooden plate to the end of each post, this stops the whole thing jamming up, and you can also just about make out that the cam on the left has 2 metal parts either side of it, I had to add these to stop the post the witch sits on from turning round, she had a tendency to face the wrong way, the cam that drives the witch is also a different shape as we wanted her to have a different movement from the bats, which it has to be said are slightly erratic in their movements.

Here's a close up of those metal pegs, which are just bits of wire - 

A simple solution.

I also made a handle so that the cam shaft can be easily turned, I made this from a circle of wood I cut out with a large hole saw, then I drilled another hole in it and added a piece of dowel, and then I made a collar for the dowel.

The handle - 

Circle of wood.

Finished handle.

I haven't included all of the steps involved in building this, but I plan to make another one, all be it a little less complicated to show how to make one, I think the kids get the concept of cams and how they work, and if not, well it's a fun thing to mess about with.

Here's the video of it in action, the first video is a little dark, we had some back lighting issues (mainly the lack of it) hopefully this should give you an idea of how it works.

The Halloween Machine - 

Thanks for reading.

Homemade Thursday


  1. Oh, this is just wonderful and a great project to do with the kids. I am inspired now to go and have a go.

    1. Thanks for reading, it is pretty simple to make, anyone who can put up shelves will be able to make it, and kids always love things like this, I did mean to make one for Christmas, but time got the better of me as usual.