Making gears

Making gears on the lasercutter/scrollsaw.

 

First Gear train

First Gear train

This is the first proper gear train I’ve made. Both this and the initial tester are made from scrap fibreboard in the box next to the lasercutter.

The tester (below) is for testing the use of the software and the first proper sample (above) was to check if the principle worked, which it does

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Software used

Firstly, to design the actual gear train I used Gear Generator, a handy online tool that can generate gear trains, including the diametric pitch and so on of the gears, also allows axle connections which was vital for this work. I used this as my engineering maths is not up to speed enough to figure out the gear ratios on my own. It also displays the ration next to every gear in the system, which is immensely handy as you can muck about with the number of teeth in each gear to get as close as possible to the desired ratio. I also used it to make sure that gears weren’t meshing where they weren’t supposed to and it works up to a point but in practice two gears were very nearly clashing when they weren’t meant to, so should be more careful with this in future.

 

Secondly, to generate plotting date for the gears I used Matthias Wandel’s  Gear Generator Program, which is very nice indeed and nicely makes sure that the gears don’t clash, which is very handy. The program automatically makes the gear mesh perfectly, but in practice you want a wee bit of slop, which as the man himself explains is naturally afforded by the kerf on any given cutting tool, whether that be a saw or a lasercutter type device.

In order to generate files for use with the lasercutter software (lasercut 5.3) I had to use HPGL, an old plotter format as this was the only one that would output the files at exactly the correct size so they wouldn’t need any finickity post processing. In order to use this correctly, you have to input the amount of plotter units per distance unit. In this case I was using inches so the amount of plotter units is 1016. There’s probably a handy chart somewhere.

 

Anyhoo, the gears came out very nicely, so that’s good.

The holes the cutter made for the axles weren’t quite big enough so I drilled them out on the bench drill and attached them to the 2×4 with teeny wee nails. This works alright, though I think in future I may want to put washer between the gears and the board in order to reduce friction.

Also, in order to make the axle connections on the second gear train I glued the rough sides of the gears (fibreboard, innit) together with a glue gun. This does alright, but it tend to break open very easily. One issue is that I cut the smaller gears with spokes cos i thought they looked lovely (and they do) but it didn’t allow for a great deal of surface area to make the bond. Another is that hot glue really doesn’t turn out to be the best for joining this material. I should’ve used wood glue and would have if I’d remembered to bring some from home.

Another issue is that the bottom and top gears from adjacent sets were rubbing on each other so I clearly need something to seperate gears in a stack in order to avoid this problem. I’ll probably have to make inserts or something. Or rig up some kind of double layer system or something.

 

All in all it works fairly well for a first attempt. Next time I’m going to try making them from birch, etching the pattern on the lasercutter then cutting with the scrollsaw and see how that works. Bond with woodglue and big heavy clamps, use washers to avoid friction and also make seperators to avoid friction between adjacent non-meshing gears.