Buying small spur gears off-the-shelf.

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Owen_N

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I am looking for standard timing gears that are good for higher temperatures, and capable of being run in mesh at 6-7000 rpm.
I think cast iron gears may work, Unfortunately no-one sells them retail.
Non-ground steel gears cannot be run this fast.

They also need to be machinable, so that I can bore them and add keyways.

About 6 to 8mm width, pcd diameter in the range of 18 to 50 mm.
Acetal gears may be too temperature limited.

KHK gears seem to have quite a range, but they tend to be expensive, and charge freight rates of $90 nz plus ($64 us)
For even small quantities.
This is substantially over the usual of $43 US for about a kilogram.

If I want ground and hardened steel, then I can't machine them.
Any ideas?
I posted this separately from my design thread, as it is more of a general topic.

<edit>
example of KHK steel-nylon gears.
- very expensive!
I can get plain acetal ex Australia for a 10th of the price, buy possibly not suitable for cutting large bores out of.
My temperature range may be a bit high, too.
I will check.
<edit>
Acetal is good for 120 degrees C. Nylon will do more.
Nylon gears are generally stronger.
 

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Owen_N

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Continuation:
Working out the torque loading, we get 10 N-m , peak, which is quite a lot.

this would generate a tooth shear loading of 250 MPa in a module 1 gear of 40mm in diameter,
and 5 N-m at the crankshaft.(this is divided by 2 as the initial load is at half crank speed).


Average engine torque output at 5hp, 6000 rpm = 3800 W (P), rad/s = 628 (w) , and T = P/w = 6.05 N-m average.

consider the combustion event only covers 1/4 of 2 revs, that is 48N-m net average over the combustion cycle, plus
another 20% for the compression cycle overall.

The sliding exhaust seal is consuming up to 5% of the total power output of the engine.

- It is best compared over the 1/4 rev, as that is when the power is generated, and seal load will average out in much the same way as the
torque output.

However, I am comparing average engine torque with peak seal drag, when maximum torque will be a lot higher than the average value.
the average seal torque is probably less than half of the peak.

Anyhow, the loading is looking like higher tensile hardened , ground steel should be used for the gear, maybe module 1.5 instead of 1,
8mm width is OK, but it will need a full 5mm wide key to transfer the torque at the centre bore.

These requirements may make a home build rather expensive, if gears have to be specially made.

Some design elements would have to be changed for this kind of loading.
 

lohring

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Look at RC car gears. They may be hard to find, but try Search Results There are smaller matching pinions available other places.

Lohring Miller
 

Owen_N

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Look at RC car gears. They may be hard to find, but try Search Results There are smaller matching pinions available other places.

Lohring Miller
RC car gears tend to be in the wrong size range and module.

I had a look through the KHK catalog, and I can get some in 10mm face width.
20T carburised chrome steel, $76.52 (US)
40t carbon steel, induction hardened teeth, hub- $64.06, 30T hubless carbon steel, induction hardened teeth, $50.31.
the carbon steel ones could be machined.
the carburised chrome steel one could be ground down a bit.
Narrowing the teeth section should probably be done by grinding.
diameter 40x10x works out at around 100g.
2x30, 1x40, 2x30 would do.
basic price 76.52 + 64.06 + 100.62 = $177 US or $248 nz approx. (plus freight)
 

animal12

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I know its a long shot for you , but you may look at Boston Gear .
animal
 

Drawfiler

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You ask for ground steel gears but I don’t understand how grinding would make them hard, I think what you mean is that any in heat treated gear won’t do.
if you want this type of performance no plastic gear will do, they will break down at the higher tempreatures and certainly any metal gear will outperform them.
i would consider these solutions
A make the gear in a suitable steel and then case harden it, in these sizes it will work
B use pre toughened steel like EN 24t
C use helical tooth gears to give smooth running and reduce individual tooth loading.
I would experiment with B first.
if you can’t source what you want, I can hob you a set of any of the above.
 
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The site edited my message which gave the email address, you'll find Gears and Sprockets in the UK but I guess the hyperlink in the original reply will work.
Graham
 

Owen_N

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You ask for ground steel gears but I don’t understand how grinding would make them hard, I think what you mean is that any in heat treated gear won’t do.
if you want this type of performance no plastic gear will do, they will break down at the higher tempreatures and certainly any metal gear will outperform them.
i would consider these solutions
A make the gear in a suitable steel and then case harden it, in these sizes it will work
B use pre toughened steel like EN 24t
C use helical tooth gears to give smooth running and reduce individual tooth loading.
I would experiment with B first.
if you can’t source what you want, I can hob you a set of any of the above.
The gears would be induction hardened then ground.

I am now re-designing the engine as a two-stroke, which will meet my weight target and be a lot easier to make.
Adding four fairly hefty gears is not good for weight saving, and there are less potential ways to have failures with a two-stroke.
I used to quite like the old two-stroke triple motorbikes!

See my thread on the wobble-plate engine. - now changed to swashplate/cam-plate , for simplification.
 

ajoeiam

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I am looking for standard timing gears that are good for higher temperatures, and capable of being run in mesh at 6-7000 rpm.
I think cast iron gears may work, Unfortunately no-one sells them retail.
Non-ground steel gears cannot be run this fast.

They also need to be machinable, so that I can bore them and add keyways.

About 6 to 8mm width, pcd diameter in the range of 18 to 50 mm.
Acetal gears may be too temperature limited.

KHK gears seem to have quite a range, but they tend to be expensive, and charge freight rates of $90 nz plus ($64 us)
For even small quantities.
This is substantially over the usual of $43 US for about a kilogram.

If I want ground and hardened steel, then I can't machine them.
Any ideas?
I posted this separately from my design thread, as it is more of a general topic.

<edit>
example of KHK steel-nylon gears.
- very expensive!
I can get plain acetal ex Australia for a 10th of the price, buy possibly not suitable for cutting large bores out of.
My temperature range may be a bit high, too.
I will check.
<edit>
Acetal is good for 120 degrees C. Nylon will do more.
Nylon gears are generally stronger.

Dunno if they have something exactly like what you're looking for but small size gearing is this companies wheelhouse - - -


(Haven't even been a customer - - - only know of them and NO idea as to pricing!)
 

Rocket Man

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Try Boston Gear or Browning, when I worked as design engineer I use to buy gears all the time. They come in, any size, any tooth, any width, any diameter, any material, any bore, you can make changes, drill hole to make them lighter weight.
 

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