Best steel to make gears?

Laverda · Oct 9, 2014

Hello all,

What is the best steel choice for making gears? I am thinking 8620 but now have told by a few people that 3310 or 9310 may be a better choice????

I need to make five gears in total. Three will be driving the camshafts off the crank and the other two gears will be in a transmission. The original gears were made in 1929 and I am guessing the steels I am considering using did not even exist back then.

Thanks,
Bruce

Krovvax · Oct 9, 2014

I would go with 8620 im not a gear professional but most of them are made from 8620 (correct me if im wrong always here to learn) so it would be my choice too.

atex57 · Oct 9, 2014

8620 will be as good or probably better than what was used. It is the modern goto steel for this app.

Ed.

johnoder · Oct 9, 2014

All the steels mentioned (up to now) are intended to be carburized and hardened

Here are photos of the rig Lehmann Lathe used in lapping their head stock gears after carburize/harden

http://img.photobucket.com/albums/v337/johnoder/Lehmann Lathe/ToolingForGearLapper.jpg

http://img.photobucket.com/albums/v337/johnoder/Lehmann Lathe/OlderGearLapper.jpg

http://img.photobucket.com/albums/v337/johnoder/Lehmann Lathe/NewerGearLapper.jpg

The master disc tooling stopped the process when pitch circle (possibly with a little built in backlash) was reached

Rickyb · Oct 9, 2014

Laverda said:
Hello all,

What is the best steel choice for making gears? I am thinking 8620 but now have told by a few people that 3310 or 9310 may be a better choice????

I need to make five gears in total. Three will be driving the camshafts off the crank and the other two gears will be in a transmission. The original gears were made in 1929 and I am guessing the steels I am considering using did not even exist back then.

Thanks,
Bruce

8620 is used extensively in heavy duty gears. Case carburizing to a depth of .05"-.06 is the norm. Gears are normally lapped after heat treat to get the surfaces to mate properly.

Too shallow of a case and it will crack under high loads. Carburizing makes the surface file hard. The infusion of carbon into the steel takes about 14 hours in a special ammonia atmosphere furnace and makes the surface 86100 which responds wonderfully to heat treat. The core stays soft 8620 because the carbon can't travel that deep. Yes the carbon actually migrates into the solid steel surface at 1600 degrees F. Super duty gears are made from carburized 4320 where the core will respond somewhat to heat treat and reinforce the case under extreme loads.

An alternate to lapping is hard grinding of the tooth profile after heat treat. One or the other process is normally necessary because the tooth profile changes during heat treat. The carburized area will increase in volume during heat treat and some tooth profile compensation is required to allow for it.

It seems to me that this technology is beyond the capability of most shops. It is necessary for reliability and longevity. It also allows for a very small gear. All of this technology can be compensated for with size. So If size is not an issue make the gear big and out of cast iron and you don't need heat treat.

rollmaker · Oct 9, 2014

1141 and 1144 are often used also.

reedeprintice · Oct 9, 2014

8620 and carborize it .

Mcgyver · Oct 9, 2014

johnoder said:
All the steels mentioned are intended to be carburized and hardened

John, would they have been ground or lapped subsequently? ie how big an issue would warping be from the heat treating?

just read your post Ricky, so many were done with no corrective work on the geometry to fix warping (lapped not ground?) Or was the lapping somehow controlled - ie was it with a lap or just some abrasive thrown in as they ran against other gears?

billmac · Oct 10, 2014

Mcgyver said:
John, would they have been ground or lapped subsequently? ie how big an issue would warping be from the heat treating?

just read your post Ricky, so many were done with no corrective work on the geometry to fix warping (lapped not ground?) Or was the lapping somehow controlled - ie was it with a lap or just some abrasive thrown in as they ran against other gears?

I spent some time working on rear axle gears, specifically hypoid crown and pinions, but this was over 40 years ago so things may have changed since then. Crown wheels were carbo-nitrided, and then press quenched. This meant taking them out of the oven (hot) and then manually putting them into a press with specially shaped dies containing channels. These closed and then quench oil was pumped through. The significant pressure and the shape of the dies reduces the tendency of the gear to warp. They were then lapped under carefully controlled conditions (definitely not 'some abrasive thrown in' :crazy:

). the whole gear set and the entire production process was designed so that the end result was quiet, accurate long lasting gears. The process we used was Gleason, and the amount of investment in research (by Gleason), in capital equipment, in skills and knowledge is enormous, way beyond the capability of most outside of a very specialised area.

timvercoe · Oct 10, 2014

Lots of great advise here. I watched a you tube video where a guy made a tooth for a cast iron gear and brazed it in place. The reason I bring this up, is you haven't mentioned the application where these gears are going to be used. So........maybe 8620 and heat treating are unnecessary.......I have a real fascination with gearing and absolutely no experience with making gears. Would enjoy a more indepth discussion, about applications...

Tim

Zahnrad Kopf · Oct 10, 2014

This is worth exactly what you have paid me for it -

I make gears _almost_ every day of the week. I make gears for everything from hand tools, to machinery, to surgical tools, to off-road vehicles, to race cars, to motorcycles, to electric vehicles. Your material needs will be dictated by much much more than just a cursory knowledge of a crank, a cam, and a tranny. HP, torque, environment, and other design parameters have as much to do with it as anything else. You'll need to give a lot more information than that for a meaningful recommendation, but suffice to say that 4140, 4340, 8620, and a number of others will most likely suffice your needs. Grinding, lapping, or skiving are not always necessary, either. Again, it depends on your needs.

claya · Feb 23, 2021

We need to replace a gear on two different tractors. Reverse engineering is the only option, as they are not available anymore. One is a simple spur gear with an internal spline, the other is a more complex helical tooth transmission transfer shaft.

The spur gear is for a 19HP compact tractor. The original gears fail easily, with chipped teeth, or sheared teeth. I would like to make some more robust gears if possible. It is a 4WD shift gear, so gets some shock load, as the front wheels turn at a much different rate than the back wheels.

We can have the spur gear wire edm locally, but we do not have a local heat treater.

The complex helical gear will need some reverse engineering/design assistance. It is from a Caterpillar hay loader transmission. They no longer are available from Cat.

I have drawings of both gears.

Suggestions on the above?

EmGo · Feb 24, 2021

claya said:
Suggestions on the above?

If you want max life and strength, then it's 9310. If you need to go crazy, have a few pancake forgings made, forged has better grain direction and density than barstock.

Forget about making them yourself, it won't work, you don't have the stuff. Talk to Dan from Oakland here, or zahnrad, or Borg Gear in Redwood City. Talk to an actual gear guy, that kind of part is not suitable for part-timers.

(p.s., your wire-edm'ed through-hardened gear will last about two hours if there's any load on it. Sorry.)

claya · Feb 24, 2021

EmanuelGoldstein said:
If you want max life and strength, then it's 9310. If you need to go crazy, have a few pancake forgings made, forged has better grain direction and density than barstock.

Forget about making them yourself, it won't work, you don't have the stuff. Talk to Dan from Oakland here, or zahnrad, or Borg Gear in Redwood City. Talk to an actual gear guy, that kind of part is not suitable for part-timers.

(p.s., your wire-edm'ed through-hardened gear will last about two hours if there's any load on it. Sorry.)

Yes. I would prefer to not wire-EDM these, if I can find a real gear maker shop that will do a small 2-3 piece batch.

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Illinoyance · Feb 24, 2021

Recently I purchased a couple gears to replace missing change gears. One came from China, the other from Netherlands. Both were made from C45 steel. Both had induction hardened teeth. Based on that I would choose 1045 or 1144 for gear blanks and have the teeth hardened. If you wan to case harden then use 8620.

claya · Feb 24, 2021

The teeth sheared clean off the hub this time. I would prefer to never have to replace this gear again. Which hardening process/material will handle shock loads better?

It is a poor gear/transmission design. We beefed up the transmission design flaw, so now the small shift gear is taking the brunt of the load.

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10 fingers · Feb 25, 2021

Some things never change.

rcoope · Feb 25, 2021

EmanuelGoldstein said:
(p.s., your wire-edm'ed through-hardened gear will last about two hours if there's any load on it. Sorry.)

Could you elaborate on why this is vs induction hardened teeth which seems to be the way it's usually done?

gbent · Feb 25, 2021

claya said:
The teeth sheared clean off the hub this time. I would prefer to never have to replace this gear again. Which hardening process/material will handle shock loads better?

It is a poor gear/transmission design. We beefed up the transmission design flaw, so now the small shift gear is taking the brunt of the load.

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If its a poor design, you will find yourself chasing the next weakest part. Forever. Think of Sisyphus, rolling his rock uphill.

claya · Feb 25, 2021

Understood.

The rest of the geartrain is pretty equally matched. The shift gear and it's shaft mount were the weak link. Now it is just the gear we need to get stronger.

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Best steel to make gears?

Cast Iron

Hot Rolled

Stainless

Diamond

Cast Iron

rollmaker

Guest

Stainless

Diamond

Stainless

Hot Rolled

Diamond

Cast Iron

Diamond

Cast Iron

Stainless

Cast Iron

Hot Rolled

Stainless

Diamond

Cast Iron

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