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Okuma LS 50T Phenolic Gear

JDToumanian

Plastic
Joined
Sep 6, 2009
Location
Phelan, CA
Hey Group,

My 18" Okuma LS lathe's 50T phenolic gear is cracked... I have a piece of 3.5" phenolic rod and was getting ready to make a new one but I have a few questions. I know other Okuma owners have replaced this gear, and a lot of others here have much experience machining gears, so maybe someone could help.

The steel splined center hub looks like a pain in the butt to machine a gear to mate with. Should I make a gear from 100% phenolic, omitting the steel hub? My gut tells me it might not last long. Maybe machine a new non-splined hub and attach the gear with Loc-Tite or epoxy? Skip the phenolic altogether and make a new gear/hub from solid brass? Or something else?

My other question is what gear cutter to buy. I have a mill and rotary table, as well as a gear cutting book, and no doubt could study, measure, and figure it out, but if someone knows offhand what cutter I need to buy I'd love to get right to making chips. Thanks!

Regards,
Jon
 

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I think starting with a disc cut from phenolic sheet would last longer .. better configuration of the lay of the reinforcing fibres.

Thanks for the suggestion! I admit, I'm having a hard time wrapping my brain around how this stuff would handle forces in various planes trying to split it apart. When I researched this phenolic material, I chose Garolite CE because it said "easy to machine into mechanical parts, such as pulleys, gears, bushings, and washers" ... but maybe a sheet of the proper thickness would have been better than a rod?

So far there are only two things I don't like about this lathe, and using a sacrificial gear as a safety is one of them. A soft key or shear pin would have been much better! I've never owned a lathe with a crash safety like this, and I've never crashed a lathe (knock on wood)... So using brass (or cast iron) is tempting. The other annoying thing is all the JIS fasteners... M5x0.9 for example, instead of the more common M5x0.8. Hard to find and expensive when they're buggered up.

Jon
 

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The steel splined center hub looks like a pain in the butt to machine a gear to mate with. Should I make a gear from 100% phenolic, omitting the steel hub? My gut tells me it might not last long.
That's what my gut says too .... but

310173d1610233691-okuma-ls-50t-phenolic-gear-img_5024.jpg


for a onesy, you could make the bore normally, then cut four keyseats into the phenolic gear and bang in square stock, rather than trying to make the damn things as a circle with four stickouts ... if you get what I mean.
 
I doubt your 'mechanical fuse' hypothesis. IME phenolic gears are usually used for noise reduction. Besides I suppose it depends where you live but down here a suitable piece of phenolic would likely cost more than similar in cast iron. From memory cam drive gears in the Index 25 autos were phenolic with face width at least 4 inch.. made from sheet, or should I say 'plate'.
 
Make the gear from plate, no bushing. The shear area of the key to phenolic plate is likely large enough that the force to damage the gear bore will be higher than what will damage a tooth.

I would also agree that tooth strength will higher with the plate fiber orientation over a "rolled" rod.
 
Thank you all for the help, I really appreciate it!

Can`t you buy a stock plastic gear Works as well

Peter

I believe I did find stock gears... I think I've identified the gear as module 1.5, but I haven't measured the pressure angle, either 14.5 or 20 degrees. I found steel and nylon stock gears but they're only 15mm thick. I don't have the gear in front of me at the moment but I think it's quite a bit thicker than that. Also I think the phenolic material (harder, and reinforced with either cotton cloth or fiberglass) would be quite a bit stronger than just nylon.

I doubt your 'mechanical fuse' hypothesis. IME phenolic gears are usually used for noise reduction.

It's only this one gear... All the others are steel (or maybe it's cast iron). If it's only for noise reduction, I would definitely prefer to use cast iron, brass, or steel.

Jon
 
Thank you all for the help, I really appreciate it!



I believe I did find stock gears... I think I've identified the gear as module 1.5, but I haven't measured the pressure angle, either 14.5 or 20 degrees. I found steel and nylon stock gears but they're only 15mm thick. I don't have the gear in front of me at the moment but I think it's quite a bit thicker than that. Also I think the phenolic material (harder, and reinforced with either cotton cloth or fiberglass) would be quite a bit stronger than just nylon.
Jon

you can bolt 2 of them together and/or mount 2 of them on the same hub to get a thicker gear
I would make a hub with a flange between the 2 gears and bolt the gears on the flange
This one is more than likely 20°PA concidering its age
Nylon is strong enough and easy to replace

Peter
 
If you go with plastic gears, buy an extra set (they're likely not hugely expensive), and prep both sets for the application. That way you're ready if the first set fails.

OTOH, you'll lose the second set, so you have to plan for that! ;)
 
Regardless, do not use phenolic rod- the lay of the fabric will not support the bending load on the gear teeth.
You really want to saw a blank out of plate material. My guess is a keyway cut in the phenolic will last for a considerable period of time.
 








 
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