Strange Gears

[Neil WyattModerator @neilwyatt]

[Neil WyattModerator @neilwyatt]

I've been making some gear cutters in some gauge plate offcuts (thanks Graham)/. they are 1 Mod gears, and I'm using the Tubal Cain method*, rather than the Ivan law approach I usually take.

The curiosity is that i want to make 40 and 20 tooth gears (or 19 and 41, but I'm using 20 and 40 tooth gears as templates). Now these gears should require quite different cutter profiles,. Yet, as far as I can tell, the tooth-spaces appear to be almost identical, even to the extent that looking at the 40-tooth gears the tips of the teeth are noticeably thinner as a result. This is across six gears of metal and nylon construction and from at least five different sources.

Cutters made to fit both the 20 and 40 tooth gears appear to virtually fit the other one equally well – I can hardly tell which is which!

There ought to be two other cutters between the two I've lovingly crafted.

An eight tooth gear and 45 (and up) tooth gears are all noticeably different.

I'm wondering if some corners are cut regarding the profiles of commercial gears in this range?

Neil

*basically you file the cutter to fit a tooth space in an existing gear – it works, especially if you use a grinder or linisher to rough out the shape first, then 'hollow' it with a fine file!

[BazyleParticipant @bazyle]

mmm My 18DP No 4 commercial cutter 'looks' like it fits a 34 tooth as well as it fits the one hundred tooth. At least at the bottom of the gap but there is more freedom towards the tips of the teeth.

Perhaps our CAD experts can come up with supersized drawings that illustrate the difference. Now where's my Odontograph when I need it?

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