Spur gears

Discuss the prototype and how to model it.
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Mike Garwood
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Re: Spur gears

Postby Mike Garwood » Sat Aug 15, 2020 9:07 pm

CDG

Did I miss something? How is the motor held within the chassis at the required angle? That motor combo cannot be as deafening as the DJH motor and gearbox I have in one of my 56xx's. It's so bad I have a new gear box on it's way to replace it. I have a feeling that the worm gear on the motor has cracked (these are some sort of plastic material)...hence the noise.

regards

Mike

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grovenor-2685
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Re: Spur gears

Postby grovenor-2685 » Sat Aug 15, 2020 9:42 pm

Quote from one of the Mike Edge links I gave,
This is more of an innovation now, an n20 motor and gearbox driving the trailing axle through bevel gears - paint on the motor shows that I forgot to mask it before spraying primer but it doesn't seem to have affected it. The gearbox frame is simply soldered into the frames. Bags of power from this and I can fill the huge hole in the firebox where the K's motor went with lead,

but i think he was talking about 00 frames so you would probably need to make up a little cradle for PF, and certainly would if powering on a sprung or compensated axle.
Regards
Keith
Grovenor Sidings

Alan Turner
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Joined: Sun Jul 20, 2008 4:24 pm

Re: Spur gears

Postby Alan Turner » Mon Aug 17, 2020 9:23 am

Phoenix Paints do a selection of bevel gears: https://www.phoenix-paints.co.uk/products/bevel-gears

I've just bought a pair of 1:1 from them.

regards

Alan

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CDGFife
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Re: Spur gears

Postby CDGFife » Mon Aug 17, 2020 2:41 pm

Mike
I made up a mount plate with the two bolt holes and slot for the shaft to solder in as a frame spacer. Thus I can un-bolt and slide out the whole motor to remove it. You can just see the spacer, top of the slot and the two mount bolt-heads in my pic.

The hole diameters and positions are part of the N20 standard and as such the chassis has the facility to interchange different rpm motors to see how they go.

Hope that helps

Dave - thanks for this info - very interesting. I suspect as you say the course-ness of these gears is working in my favour!

CDG

Stephan.wintner
Posts: 28
Joined: Sun Mar 15, 2020 11:04 pm

Re: Spur gears

Postby Stephan.wintner » Fri Aug 28, 2020 11:59 pm

Just a source of small gears I've not seen mentioned :

http://kkpmo.istore.pl/en_US/index?currency=EUR

I don't have any experience with them, but they had some interesting sizes.

Stephan

nigelcliffe
Posts: 605
Joined: Mon Jul 21, 2008 8:31 am

Re: Spur gears

Postby nigelcliffe » Sat Aug 29, 2020 7:38 am

Stephan.wintner wrote:Just a source of small gears I've not seen mentioned :

http://kkpmo.istore.pl/en_US/index?currency=EUR



Mentioned in the fourth post in this thread....

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steamraiser
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Joined: Thu Dec 31, 2009 4:49 pm

Re: Spur gears

Postby steamraiser » Sat Aug 29, 2020 8:30 am

Chaps, I see gears as being quoted as for example Mod 0.2 or Mod 0.5.
What does this relate to please?

Many thanks

Gordon A

nigelcliffe
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Re: Spur gears

Postby nigelcliffe » Sat Aug 29, 2020 8:45 am

steamraiser wrote:Chaps, I see gears as being quoted as for example Mod 0.2 or Mod 0.5.
What does this relate to please?


Module number. A measure of the tooth size and spacing. The metric equivalent of DP numbers. Smaller Module numbers are smaller teeth.

Very roughly, Mod 0.4 is similar to 64DP (and will often engage with each other).

There's also stuff around gear tooth shape which matters for low friction and good transfer of power - even straight cut gears are not simple triangular teeth !

- Nigel

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steamraiser
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Joined: Thu Dec 31, 2009 4:49 pm

Re: Spur gears

Postby steamraiser » Fri Sep 04, 2020 9:03 am

Thank you for your reply Nigel.
Does the Mod number equate to an actual dimension on one gear tooth.

Gordon A

davebradwell
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Joined: Fri Jan 18, 2019 3:48 pm

Re: Spur gears

Postby davebradwell » Fri Sep 04, 2020 9:18 am

Module is diameter of gear (measured half-way up teeth will do for now) divided by number of teeth so a 25mm diameter gear with 50 teeth is Mod 0.5. In imperial units we use DP (diametrical pitch) which is essentially the number of teeth on a 1" diameter gear so DP gets bigger as teeth get smaller. Only a straight rack has straight teeth and this brings us to pressure angle which is now pretty standard at 20 deg but gears stripped out of old equipment may be 14.5 deg and when mixed they make a fair racket.

You should get all tooth dimensions from these numbers using appropriate formulae - see Wikipedia. It gets quite involved, especially with small numbers of teeth.

DaveB

nigelcliffe
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Re: Spur gears

Postby nigelcliffe » Fri Sep 04, 2020 9:24 am

steamraiser wrote:Thank you for your reply Nigel.
Does the Mod number equate to an actual dimension on one gear tooth.

Gordon A


Yes-ish. For an Rack (straight line of teeth), Module * PI = pitch of the teeth in mm.

More useful is the pitch circle - the value used to calculate where two gearwheels mesh.
Pitch Circle Diameter (mm) = Module * Number of Teeth
Outside diameter (mm) = Module * (Number of Teeth + 2 ).

The distance (centres) between two gear wheels (mm) = Module * (ToothCountGear1 + ToothCountGear2) / 2


If needing to convert to DP, DP = 25.4 / Module


Small tooth count gear wheels are sometimes "corrected" so they may have a diameter which isn't what the calculations suggest they should be. That can get messy, though if someone just tells you a 13T is dimensionally a 14T, you use the 14T for centre calculations and 13T for gear ratios.


( All written up 25 years ago in the 2mm Magazine - I have a habit of recruiting S4 modellers to 2mm :-) ).


- Nigel

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steamraiser
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Joined: Thu Dec 31, 2009 4:49 pm

Re: Spur gears

Postby steamraiser » Fri Sep 04, 2020 10:22 am

Thank you Dave and Nigel for your replies.

Yes Nigel I have been known to make an appearance at 2mm shows and have an enjoyable day.
Having seen what you boys and girls achieve in 2mm, I go away thinking I should be able to do something similar in 4mm.
Quite inspirational.

If I have the skills - that is another matter altogether.

Gordon A

Alan Turner
Posts: 576
Joined: Sun Jul 20, 2008 4:24 pm

Re: Spur gears

Postby Alan Turner » Fri Sep 11, 2020 7:28 am

You may wish to view this page from Ultrascale: https://www.ultrascale.uk/node/15

regards

Alan


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