I’ve got total gear ratio of 3.428 but it’s a double step up gearbox. So I have to sq root it get the ratio of the pairs which is 1.851. For the small cog I have to use a min of 18 teeth. So teeth x g = 33.326. How can I get a real gear ratio? I’m not sure on if I round the 33 down or up to 34. As I don’t have 33 on my Lewis form factor. For the assignment I have 30 and 34 on form factor. I’m not sure what to use. Thanks for any help.
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So use a whole number of teeth ie integer. Then work out the numbers given a starting point like the 34 you suggest. – Solar Mike Dec 04 '22 at 13:43
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Hi Mike, even if I use for example 20 teeth it works out as 20 x 1.851 = 37.02. Which is the same problem with 18 teeth it doesn’t give me the Y value for it on my table as I have values for (30,34,38etc). So I can’t use it for the calculations. – Efan Dec 04 '22 at 14:52
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Well, had a differential with a ratio of 4.78:1 and there were an integer number of teeth. Swapped that for a differential of 3.54:1 and that also had an integer number of teeth. In fact having stripped, repaired and built many gearboxes I have never seen a fractional tooth on any gear - except broken ones... – Solar Mike Dec 04 '22 at 14:57
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I’m not questioning the amount of teeth on a real life application can’t be fractional or decimal. I’m just confused when my nearest integer is 33 and I don’t have any values for that? – Efan Dec 04 '22 at 15:20
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if its for an assignment then, you shouldn't worry too much. One solution is to use the 34 (which has a Lewis factor)
Another is to do an interpolation between the lewis factor for 30 and 34
Yet Another is to find out other tables/equation that allow you calculate the factor for 33. E.g. there is an online calculator at engineersedge
NMech
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