machining gearbox dogs

bushmechanic · Dec 22, 2008

Taffy did a post on this a while back im in a hurry, big fire needs attention nearby

ok so there are 2 ways to feshen up the dogs on the 5th/6th slider and idlers on the input shaft

as I see it I can stick em in the lathe and regrind the face of the dogs so the rounded corners are sharpened up but then the height of the dogs is reduced.

or I can spend hours grinding back the leading edge of each dog and matching that to the also ground idler gear ..........

has anyone done either ?

Taffy · Dec 23, 2008

no but when you come up with an idea let me know! i have a CR box here i need to freshe up!

regards

Taffy

Krisbrumm · Dec 23, 2008

I'm afraid it's not reliable repair.The gears are heat treated , but just on some depth inside the material, ussually 0.5-0.8mm.That gives hard surface, resist to friction, and soft core, resist for impacts and cracking.That's the nature of gear work.The teets when comes between the gaps, "bang"on the teeth.That why the gear has to be impact resistant!!! If you grind them, you'll remove hard surface, and that which will be exp[osed, is soft and will gone blunt very very quickly! I've done that before, It's not worth do that.that repair gives you just one-two days of riding, and fault comes back again!It the edges are blunt, YOU MUST REPLACE THE GEARS!!! trust me, dont waist the time by double-stripping the casings with same fault.And if the gears starts jumping out, try to imagine, how the barrel and forks are suffer...

jockular · Dec 23, 2008

i have to concur with Krisbrumm on this, i tried to grind the dogs on a CR250 once. even removing the bare minimum and not putting to much heat in to the gear is mearly a temporary fix, it only lasted a ride before it started jumping out again. i had to split it again and go and buy new gears. its the only fix i would say unless you can reliably case harden, but do you really want the hassle of stripping it again when it all goes wrong?
Ho Ho Ho

bushmechanic · Dec 23, 2008

can do case hardening with some nasty powder, mostly wondering which bit you guys ground off, the face - ie the easy way or the stronger harder way involving either an indexing table and a grinder in a mill or a lot of trial and error

thanks for the tip , Im impressed someones given it a go :thumb:

jockular · Dec 23, 2008

i ground off the actual contact area and did not reduce the overall width of the gear. Grinding table and milling machine you say? if by that you mean a vice and a 4" grinder then we are talking about the same thing! some trial, but mainly lots of error.

bushmechanic · Dec 23, 2008

a vice and a 4" grinder then we are talking about the same thing! some trial, but mainly lots of error.

ho ho ho yes

i was looking for a way to cheat

if the angle grinder and the vice are used I think its nearly impossible to be certain that all the dogs are trying to engage simultaneously so first one (or even one part of the dog that sticks out a bit) cops all the whacks then when its eventually rounded, the next one cops it and so on till they're all stuffed ?

its common practice in drag bikes to both undercut the dogs and back cut the dogs on the other side to let them engage quicker under power it also means they jump out if you back off. not everyone case hardens them but if I can be bothered to machine the gears at all Ill test the edge hardness and tickle em up a bit if they're soft.

Krisbrumm · Dec 23, 2008

Hi guys.I cant belive it!!! You talk like blokes from some backstreet garage into UHE!!! Do you know about a structure of dogs? First of all: the angles.The dogs aren't built with 90deg.angles.It's not so simple like in castle tower top! In dogs, you got "gaps" between the dogs.As deeper you are going in the gap, as wider gap gets.These paralell surfaces in gap, they aren't paralell as they look!!! there are slightly diagonal!!!.It's usually 2-3degree per each surface.Can you do that with angle grinder and vice???
Second: You've got i.e.6 dogs.That means if the dog is on with own other part, all the pressures at all over the dogs needs to be the same!!!I'm trying to say that they are machined with high accuracy machine.The dog wheel is fitted to machine called ROTARY TABLE WITH DIVIDING PLATES,and looks like that :
http://www.rafela.com.pl/upload/_1181052681_0.jpg
which gives you very accurate dividing of 360deg circle to as many parts as you want!!!That tool does dividing the circle to exactly the same parts!That gives you the same loads onto dogs when it gets engage with other dogwheel.
third:who can tell me, what is the HRC( hardeness factor) of top surface and deep inside.what the steel is that(symbol and features)?Can it be rehardened or not?Or, at the end of the day: what are the conditions of heat treating?
Too many questions, too less answers.It's not worth to try.The new one is always right!!!
By the way: I used to build gearboxes fo race and rally cars.Usually not-synchromesh ( conversions to g/box with dog cluthes), with limited slip diff.All machined from zer

nly the casings left from oryginal ones.I know what I'm saying!!!

bushmechanic · Dec 23, 2008

You've got i.e.6 dogs.That means if the dog is on with own other part, all the pressures at all over the dogs needs to be the same!!!I'm trying to say that they are machined with high accuracy machine.The dog wheel is fitted to machine called circle divider, which gives you very accurate dividing of 360deg circle to as many parts as you want!!!That circle divider does dividing the circle to exactly the same parts!That gives you the same loads onto dogs when it gets engage with other dogwheel.

[quote:1bfp7ni3]
Hi guys.I cant belive it!!! You talk like blokes from some backstreet garage into UHE!!! Do you know about a structure of dogs? First of all: the angles.The dogs aren't built with 90deg.angles.It's not so simple like in castle tower top! In dogs, you got "gaps" between the dogs.As deeper you are going in the gap, as wider gap gets.These paralell surfaces in gap, they aren't paralell as they look!!! there are slightly diagonal!!!.It's usually 2-3degree per each surface.Can you do that with angle grinder and vice???

[/quote:1bfp7ni3]

krissbrumm

this is exactly what i am saying too.. I both 100% agree and appreciate your advice on the topic.

I know plenty about gears BTW thats why Im asking this question: to find out if anyonehas actual practical experience acurately machining the dogs in a Hberg gearbox and testing/rectifying the hardening. a symbol is worthless usually.

It appears they have not.

I have to say if the oem gears were "correct" they would not loose their hardening on the tooth faces or break dogs as often as they do.

merry christmas
Bushie

jockular · Dec 23, 2008

cogbox

Hi Krisbrum, i hope you realize that you have, by divulging your level of expertise in this field left yourself open to a barrage of gearbox related problem solving!
how ever getting back to the question in hand, i was mearly trying to convey my own experience of the question Bushie was asking. I know what i was attepmting at the time was sheer unadulterated bodgery of the first degree, but have you never heard of budget racing? and as my circle divider was away getting fixed that week i did the best i could with the tooling available to me at the time. i had to try the bodge, if it had worked it would mean more beer tokens in my pocket, it did not work though, and i had to strip the b@stard again and fix it with shiny bits. my point being, you got to try these things to learn, and yes, i did own a back street garage for a while, and proud of it!
Merry Christmas, hope santi is guid tae ye.
Jockular.

bushmechanic · Dec 23, 2008

RE: cogbox

i was mearly trying to convey my own experience of the question Bushie was asking. I know what i was attepmting at the time was sheer unadulterated bodgery of the first degree,

thanks for posting Jock

thats exactly the kind of experience I wanted to learn about.

machining gearbox dogs

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