rehardening gears?

[John Orchard]

If I grind (undercut) engaging dogs on gears, do I need to get them re-hardened?  Where do you send them for that?

[brucey]

Hmmmm it depends on the depth of case at the start

Usually i would take a stock gear and do a Rockwell test in a corner / face not used and then take off 0.25 mm and retest if no hardness change another et etc until you find the depth and work around that

This is for the older honda gears i have done (all Black) but anything modern where it has been copper plated and has the teeth only hardened is another matter

I use my local heat treaters to anneal all my parts its to hard to do at home, and then to recase it when I'm done (i like to get my bits nitride cased to about .020)

In Melbourne we have Alpha H/T and Oppy H/T who are more then capable of annealing and re casing

Good Luck with it

Bruce 

[Slakewell]

Heat treatment in Brisbane ( if its still called that ) did mine.

[Lozza]

If I grind (undercut) engaging dogs on gears, do I need to get them re-hardened?  Where do you send them for that?

Go see Col from Coljen in Heidleburg West which think is still with Stackers??? Col's undercut several gearboxes for me haven't been annealed/hardened (good idea though). My understanding is that the dogs/slots should be indexed as accurately as possible and that avoids 'point loading' (one dog or slot engaging first and taking all the load and shock of the gear change) which is the cause of the wear on dogs and slots 

[sleepy]

Most of the wear on the drive dogs is on the corners which will stay hard even with quite a lot ground off as the hardening is atleast 1mm deep all over.
Caution should be taken if heat treatment is considered as the base metal is of an unknown grade and after the procees the gear will go out of shape slightly or even become so hard they are brittle resulting in tooth failure.
When a gear is made the metal is of a known grade and also they are made dimensionaly knowing they will grow in size after case harding. A set of gears I made for a speedway GS1000 shrunk the bore by .003" after hardening requiring honing to fit.

[John Orchard]

Thanks Guy's  :-)

I remember as a 14yo I use to undercut the dogs on my TM125, only because I couldn't afford to buy new gears once the dogs got a little rounded, it seamed to work ok, I never got them re-hardened then.  I use to slide them on the shafts and use bearing-blue to confirm that all were contacting so that one dog would not have to take all the load.

I remember having to get the inlet valves hardened on my race Honda RC30 (VFR750RJ) back in the early 90's, after losing a couple of valve-heads I was advised to get them tuftrided instead of niterided as it is less brittle.  The problem turned-out to be, not enough valve-spring preload cause the valve to 'float', the piston was knocking the head off (lol). I had cut the seats to get a better flow but forgot re-check the valve spring pressure.  Ahh the mistakes you make as a kid  ;-)

[JohnnyO]

I had the gears on my CR250M hardened at Heat Treatment in Brisbane after getting them backcut.
Not only had the gears shrunk or distorted slightly and needed to be honed to fit back on the shafts but the hardening made them very brittle and they chipped off in chunks after a couple of rides and had to be replaced.. I'd never go down that road again.

[sa63]

there is a place in Bris that will remake /manufacture gears, but cant remember the name. In Archerfield I think.
Couldn't hurt to talk to Simon Healy in Mel. as he is a gearbox specialist.

[paul]

Coljen Gear Cutting And Machining
Gears-W'salers & Mfrs - Heidelberg West, VIC

Factory 3/45 Kolora Rd, Heidelberg West VIC 3081

EXelent workmanship and a good guy to boot,col can make anything

[Momus]

I had the gears on my CR250M hardened at Heat Treatment in Brisbane after getting them backcut.
Not only had the gears shrunk or distorted slightly and needed to be honed to fit back on the shafts but the hardening made them very brittle and they chipped off in chunks after a couple of rides and had to be replaced.. I'd never go down that road again.

That is bad workmanship; probably too deep a case and perhaps not tempered back enough to give core toughness.

Gears can move around quite a lot when they are quenched.  Often with jobbing work the material is unknown and the heat treater takes them to too high a temperature and they move with a shrunk bore being the most obvious result

I make a few gears for car applications and always give the heat treater the material spec. and a tight fitting mandrel to keep the bores sized.

[Paul552]

Case hardening and full hardening are totally different processes.

[Lozza]

Gears should be as soft as butter under the hardening.