Shaking my tin cup....

[trbig]

As some of you know, I just went back in to my motor for another gear fix. I have noticed that as I grind on the gears to bevel them, the first few thousandths of metal on the surface is extremely hard. After this initial hardness is gone, the metal underneath is fairly soft. This resulted in some really terrible looking gears that somehow were still functioning.. but I fear not for long.

So here's the deal... I have been approached for an experiment that may help anyone who ever needs to do the gear fix. I have just about exhausted my supply of gears between the sets I have done for me and the sets for others that I donated. The few I have left are the worst of the bunch and doubtfull they are even fixable. So I sit here on the street corner, rattling my cup, hoping not to get laughed at and spit on.. lol. I am hoping someone can dig into their stash of parts and find a decent set of gears they'd be willing to give me.. I would pay for the shipping. 3rd gear rarely goes bad, so I would only need 1st, 2nd, 4th, & 5th.

The experiment has to do with re-tempering the gears after being ground and making them hard again. This process unfortunately will temper the whole gear.. not just the surface.. so my fear is that the gears may be too brittle for use. The difference with this process is that it doesn't involve heat tempering that makes things very hard but brittle.. it's done cryogenically. It is completely different on a molecular scale. They use this process to harden tooling tools (Which are extremely hard anyway) and it makes them last 5 times longer than they normally would. That is a metal on metal application, which makes me hope this would work for the gears on our bikes.

It would mean going back into my motor and replacing the gears I just put in AGAIN.. along with a minimum of going back in to examine them again in the fall. (If they last that long) I was kind of "Nominated" as guinea pig to do the trial since I have been known to abuse the transmissions a bit more than most.

XSChop is the one I am working with on this. IF this works, he would be able to get this process done to a complete set of gears (All 5 gears) at a so far estimated price of $100 plus shipping. That's cheaper than you can buy just one new gear for.

I'm not much of a salesman and don't like to ask for parts (And REALLY not looking forward to tearing apart the motor again) but I would like to see if this works. Anyone out there willing to part with a set of gears to help with this?

Thanks.

Tod

[madmax-im]

I have a set

Tod...last year I offered you a set as I did not do the dremel thing but just replaced all the gearsets 1/4 and 2/5.So now I can dig them out...Pm me with your addy and I pack 'em up...I'll let you know how much the shipping is...as this is for the greater good of our XSive community I am willing to donate them. I would be very interested in what your findings and conclusions will be.

[trbig]

Wow.. that didn't take long. Now how about some beer money while I'm beggin'?

I'll PM you my address. Thank you very much.

I think we have sort of decided to change these gears out with the motor in at the Meeting of the Minds in June at John and Wildkat's house. Harry (Bigfoot) has done this a couple times recently and plans on helping me do it there. If it doesn't work.. we'll be in a good spot to go ahead and tear the motor out really quick. It just doesn't really seem to be a true MOTM without me having a motor scattered all over the place anyway.. lol.


Tod

[dbeardslee]

Tod - What a great idea. I know cryogenic hardening has been used for some time on knife blades with excellent results. I also know of one watch manufacturer that treats their cases with a cryogenic process to increase their strength. Unlike heat treating it doesn't create a thin layer of hard material - it goes all the way through. Can't remember exactly how it works - has something to do with packing the molecules very closely together and locking the carbon atoms into a more even distribution. Fascinating process. Good luck with it.

[madmax-im]

Just curious about this process would you dremel the gears before or after hardening them?

[trbig]

Unlike heat treating it doesn't create a thin layer of hard material - it goes all the way through.

See.. and that's what scares me about it. I have always watched these knife/sword making shows and they say you need a softer metal for the backbone of the knife so it's flexible, with the knife's edge being harder/tempered. That's the problem with ceramic knife blades.. almost as hard as a diamond, but fairly brittle.

I think when you heat temper the gears, they are TRYING to only get the surface hard with the softer metal underneath for flexibility. You could certainly harden the entire gear full depth if it was desired..

Anyway... thanks to BNE.. we shall see!

Just curious about this process would you dremel the gears before or after hardening them?

Yup. You'd get them beveled correctly and get them ready first.. then have them treated.


Tod

[oseaghdha]

Not sure if cryo will do any good on an aged part.
I believe it is generally done on fresh meat as it were.

What you are seeing is the case hardening being broken through with grinding.
Gears could be re-cased, but they would have to be annealed first.

[tarzan]

Why not just case harden them again?

[dbeardslee]

Here's a link to a website with lots of info on cryogenic hardening. http://www.nitrofreeze.com/racing.html There's a price list at the bottom of the page. I say go for it.

The material on the site seems to suggest that you want to do your grinding and polishing after the cryo treatment.

[red bandit]

Why not just case harden them again?

You could but you would have to know the specific material the gears are made of and the hardness you want.

trbig, have you thought about checking the hardness on the factory(undremeled) area before and after. Just so you know what is was and what is is afterwards. Don't know if they can control things like they can in heat treating.

[xschop]

cryo

I just recently did this to a low mile ring and pinion, haven't installed it yet, but the 4x4 guys are doing this and are not snapping their R&P's under extreme load. The case hardening is accomplished by introducing more carbon into the upper layers of metal when it is quenched. My friend who is a master machinist says that Cyanide was used when he did alot of this work, but old burnt motor oil is just as good (and less toxic!) as the substrate for the carbon. The cryo teating should be done after the carbon intro (hardening/wear resistance) so that it lays the molecules uniformly throughout the piece, making it super strong. I will be doing a whole set after Trbig Gineas a set.....

[BigDick]

Now for my two cents! ! !----DUCK!

Back in high school I did case hardening in machine shop, we would pack our parts in cast iron chips/flakes in a shoebox sized steel box then heat the whole shebang up to whatever. The basic process is your part would leech the carbon out of the cast iron in to the top layer of your part. This would give ~.020" of hardened steel, which is quite a bit considering how hard this makes it. Also worked in a factory where we made gears, then shipped them out to be hardened. They were induction hardened, they heated the teeth of the gear but not the center then cooled them rapidly. Either of these methods could be done in a decently equipped workshop.

[trbig]

So the process so far that we are considering for this...

1. Re-temper the areas that have been dremmeled by heating just the dogs and just the area of the slots that have been ground on and quench in a high carbon bath (1/2 used motor oil and 1/2 kerosine) This will introduce a good amount of carbon into the metal.

2. After return to room temperature, the part will be placed in CO2 freezer to reduce the temp slowly to @ -118 degrees F

3. Then the gear will be placed in a liquid nitrogen bath to reduce it further to @ -300 degrees F for 24 hours.

4. After the part returns to air temp, it then gets re-heated in an oven to @ 300 degrees to help reduce the brittleness. I'm thinking the parts could be shipped back and let the owner do this in their own oven. I've read that a triple round of this is best. (heat to 300 degrees, let cool to air temps and repeat for a total of three times.)

Any thoughts?

Tod

[BigDick]

4. After the part returns to air temp, it then gets re-heated in an oven to @ 300 degrees to help reduce the brittleness. I'm thinking the parts could be shipped back and let the owner do this in their own oven. I've read that a triple round of this is best. (heat to 300 degrees, let cool to air temps and repeat for a total of three times.)

Any thoughts?

Tod

Just a couple thoughts, this heating to ~300 degrees is normalizing (if I remember the term correctly) it reduces the internal stress between the molecules in the metal. I think the correct "formula" is 1 hour for each inch thickness, ie. if the thickest section of the part is 1 inch, 1 hour at 300 degrees is sufficient. I believe this "formula" is also used to determine how long it takes to get the parts up to temperature all the way through. Therefore the full time in a oven at 300 degrees would be 2 hours for a part that is 1 inch thick. (This just occurred to me, put the part in the oven while you bring the oven up to temp, then maintaint the temp for however long, then we would just shut off the oven and leave it sealed overnight or however long to let the part come back down to room temp.) I do think we went to 400 degrees though.

Also good case hardening info here.

[oseaghdha]

So the process so far that we are considering for this...

1. Re-temper the areas that have been dremmeled by heating just the dogs and just the area of the slots that have been ground on and quench in a high carbon bath (1/2 used motor oil and 1/2 kerosine) This will introduce a good amount of carbon into the metal.

2. After return to room temperature, the part will be placed in CO2 freezer to reduce the temp slowly to @ -118 degrees F

3. Then the gear will be placed in a liquid nitrogen bath to reduce it further to @ -300 degrees F for 24 hours.

4. After the part returns to air temp, it then gets re-heated in an oven to @ 300 degrees to help reduce the brittleness. I'm thinking the parts could be shipped back and let the owner do this in their own oven. I've read that a triple round of this is best. (heat to 300 degrees, let cool to air temps and repeat for a total of three times.)

Any thoughts?

Tod

You may want to inspect the gears for runout after all that drama.
If you just heat parts of it, I would be concerned with distortion.

I don't believe the 300 degree cycling will accomplish anything useful. That's well within the operating range for that material (4340 or similar).