Gear cutting - trying to get started

[Chris152]

The first thing we need to get our heads around is DP and Module. I think we're getting there, so this morning we tried to identify a couple of gears from a 1980s Yamaha YZ. One needs replacing, so it seems a good place to start.
But - my calculations leave us unclear as to what the gears are. I'm assuming Module on account of the year and source of the bike, but the numbers don't look right. Can you take a look at the pic and let us know if we've got something wrong? Neither Module nor DP seem to match the charts properly.

Thanks, C

 

[Pete.]

Automotive gearbox gears are seldom standard tooth form. Being a Japanese bike they are almost certain to be module gears but because you have several sets of ratios on a pair of shafts with set centre distances they will probably all be profile shifted to some degree or another or non-integer module sizes or both. They'll also be heat treated for toughness and on top of all that they were probably finished by grinding.

I don't mean to dishearten you but that's the reality.

 

[Brad93]

Pete is then wizard when it comes to gears.

Gears are seldom as simple as they seem.

 

[Pete.]

Another thing to remember is that module and DP are only two different ways of specifying the involute toothed gear. 1mod is 25.4 dp which are exactly the same thing as far as size and shape are concerned so if you're in a pinch and find that cutting a DP gear with a module cutter yields a closer result then that's perfectly acceptable.

For example 50dp and 0.5 mod I can only tell apart with my measuring microscope. Identifying the correct pressure angle is as important but then that changes with profile shift anyway.

 

[minimutly]

You're in for some steep learning, and ultimately you might find that the gears used are non-standard. Why? Well in a gearbox you have two shafts at fixed centres apart, then the maker wants zyz and maybe two more ratios along those shafts, with straight cut gear teeth, and the torque requirements dictate the teeth need to be a size that limits the number of them and tooth shape (pressure angle, normally 20 degrees stub tooth). So the ratio requirements dictate the number of teeth, but these can't be made to the normal shape without being too small (slack), or tight (won't fit).
The answer is to adjust the tooth design. Actually, I'm always impressed by the Japanese bike gear design - straight cut, quiet, reliable.I have a fairly wide selection of gear cutters, and a habit of "testing" to see what bike gears are made to - seldom do my cutters match up...

 

[Chris152]

Automotive gearbox gears are seldom standard tooth form. Being a Japanese bike they are almost certain to be module gears but because you have several sets of ratios on a pair of shafts with set centre distances they will probably all be profile shifted to some degree or another or non-integer module sizes or both. They'll also be heat treated for toughness and on top of all that they were probably finished by grinding.

I don't mean to dishearten you but that's the reality.

Thanks Pete. I guess the non-standard form probably draws our effort to a close - hardening is on our list of stuff to learn so could have been ok, but grind finish would also be an issue.

But - I'm interested to learn this stuff anyway, so will come up with a project to give it a go - we'll need a swager at some point, so maybe we'll have a go at gears for that.

 

[Chris152]

Pete is then wizard when it comes to gears.

Gears are seldom as simple as they seem.

And they already seemed pretty complex to me! :-)

 

[minimutly]

To ad to the above, you can make or modify a cutter of course - be prepared for more learning - a simple flycutter is easiest, and works for a small job. If you want to modify a slightly bigger cutter you will need to mimic the rake of the flanks (I made an insert with holes spaced around the circumference to use as centre points for each tooth, you will need a mounted stone to do the grinding, and a tool and cutter grinder to mount it all on. (I used a Quorn)...

 

[Chris152]

Thanks Pete. I guess the non-standard form probably draws our effort to a close - hardening is on our list of stuff to learn so could have been ok, but grind finish would also be an issue.

But - I'm interested to learn this stuff anyway, so will come up with a project to give it a go - we'll need a swager at some point, so maybe we'll have a go at gears for that.

ps - I see in Ivan Law's book on gear cutting that it's possible to make your own cutters - would it be viable/ possible for a learner to make the profile needed for these gears?

minimutly - I've just seen your reply. No Quorn here, but I'll look into the process. I have time and enjoy learning this stuff.

 

[minimutly]

Lots to learn, then you get into helical gears, which you need a universal mill and dividing head with gears, or gear hobber.
@Pete. (The jammy so and so) Has a hobber.....

 

[Chris152]

Hmm, I see Law describes creating a radius rather than a true involute, which I guess would upset the interface of the replacement gear with the existing gears?

 

[Chris152]

Before we go any further - is there a way to repair the dogs on the gear, rather than try to replace it? The rest of the gear seems fine.

 

[RichardM]

ps - I see in Ivan Law's book on gear cutting that it's possible to make your own cutters - would it be viable/ possible for a learner to make the profile needed for these gears?

minimutly - I've just seen your reply. No Quorn here, but I'll look into the process. I have time and enjoy learning this stuff.

Have a look at "clickspring" on tube, he did some vids one making gear cutters.

 

[RichardM]

APE - Transmissions

You could give Quaife a call

Quaife Engineering Ltd - Power Into Motion - Differentials, Transmissions, Gearkits...

Quaife Engineering Ltd is a British manufacturer of automotive drivetrain products, specialising in performance transmissions, gearkits & differentials.

www.quaife.co.uk

 

[Brad93]

Before we go any further - is there a way to repair the dogs on the gear, rather than try to replace it? The rest of the gear seems fine.

View attachment 486419View attachment 486420

I'd tig weld those up and file to fit

 

[fizzy]

And once the gears are all finished and on spec you then get into gear shaving

 

[Chris152]

I'd tig weld those up and file to fit

Thanks Brad.

I guess it's plan B (swager) for gear-cutting practice!

 

[not done it yet]

Don’t forget the likely ‘more than standard’ heat treatments for a highly stressed gear.

 

[bricol]

Proper, precise, shot peening makes a measurable difference too.

I learnt a few years ago during two years of design work on a 1/2 tonne hypocycloidal gearbox, that I knew bug ger all about gear design and manufacture compared to the experts!

 

[dieselsamurai]

Proper, precise, shot peening makes a measurable difference too.

I learnt a few years ago during two years of design work on a 1/2 tonne hypocycloidal gearbox, that I knew bug ger all about gear design and manufacture compared to the experts!

Ive only ever seen small applications for these, I guess at 1/2 ton that could dish out a lot of torque