# Choosing A Gear's MOD

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Hi,
How do I go about picking a suitable MOD?
Cheers,
Michael
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Try wearing a short skirt and sixties shades ?
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Or spot the Lambretta or Vespa crowd
AWEM
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(I see I'm going to have to play the age card here :-) )
You would have thought being one of the rare few young'uns (16) these days that is interested in engineering I would have a better response....
Now gentlemen you were saying? :-)
Michael
(Who only knows what you are talking about thanks to Wikipedia)
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"Michael"
these days
response....
Wots Wikipedia then
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Andrew, look it up on this site:
Always found it to explain most things (Except choosing gear MOD of course).... :-)
Michael
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I was thinking it was more long the lines of a formula/equation......
2HP motor, turning 5000 down 3:1
Cheers,
Michael
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Right, given the specific information above the formula is 1/2 past cheese divided by the glasshouse pump.
.
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As much as that? Strewth, I would never have thought it. I must defer to the resident gear expert, though.
Cheers Tim Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
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If it's for a new pair of gears then:-
decide on the ratio you want for the pair, say 'r:1' and the shaft centre distance, say 'd'. say the gear has 'A' teeth and the pinion has 'B' teeth
we have:- r = A/B so:- A = r.B
we also have:- module.(A+B) = 2d so:- A+B = 2.d/module substituting for A gives:- r.B+B = B.(r+1) = 2d/module and so:- B = 2.d/(module.(r+1)) A can be got by substituting in the top equations.
Eliminate all modules where Module/d isn't an integer for a start.
then try one of the remaining choices to see if B comes out at an integer number of teeth. If it does A should as well (I think), do a check anyway.
Once you've done that you can quickly substitute other modules by comparison. e.g. twice the module means half the teeth.
12 teeth is the minimum practical size for a commercial pinion. If the load is going to be significant, then consult the gear manufacturer abour load ratings for different modules. HPC have these in their catalogue as HP for a given gear size and speed and Daval have a formula in theirs that you can plug into a calculator or spreadsheet.
Note that this advice is worth what you paid for it!
Mark Rand RTFM
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Thanks Mark,
Michael
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First, pay no attention to those who, on the face of it, are older and wiser but overexcited by the proximity of Christmas. They will calm down as the credit card bills accumulate and the prospect of another 3 months or more of crap weather sinks in.
While waiting, you could have a look here
to see if there is anything useful.
Some random thoughts (probably not all relevant or even correct)
A 1mod gear with 24 teeth will have a pitch circle diameter (the circle where the teeth mesh) of 24mm. A 0.5 module gear with 24 teeth will have a PCD of 12mm. So, a larger module size means bigger gears. If two gears are to mesh, they will have to have the same module. Chunkier gears (large module) will generally be needed to carry a larger load. More reduction stages means more losses but a more compact gearbox. Gears close to the motor in a gearbox will turn faster and be subject to lower torques so you may use smaller module gears there. Broad gears will better carry a heavy load. Small diameter gears will have less inertia. Multi-stage gearboxes will inevitably have more backlash. Ready-made gears are not cheap. Ready-made gearboxes might be. Making a mulistage gearbox might be too much effort - they need to be well made to work well. Stripping a few gears is an expensive but potentially effective way to learn a lot about gearboxes.
(To be fair though, you could have given a more detailed description of your application)
Pete Harrison
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LOL!
Nick
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Maybe you should ask your question different: Do you have a given load, distance between axles, ratio, RPM, limited space, ...
Nick
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Thanks Pete,
Michael
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A gear, singular, is not particular, any MOD will do, however if it needs to engage with another that is a different matter. Matters of centres, ratio and hp transmitted need to be addressed. Perhaps as a young 'un you need to address the paucity of information you supplied, then you may tend to receive more pertinent responses. Text messaging has a lot to answer for.
Tom
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Nick,
Although I do need to work out a suitable gear MOD it was also a question of general interest.....As I said in a previous post, I was thinking there would be some super duper formula or equation that gives you it.....
I've now worked out I'm looking at somewhere in the 2 -2.5 range thanks to the HPC catalogue (had one under my bed - as you can imagine I'm not your average 16 year old :-) )
Michael
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That's unhealthy, you need to get a life
Mark Rand RTFM
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Could go on to drugs and loud music if you like :-)
(Probably be cheaper lol)
Michael

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