Laser cut large Campagnolo pattern sprockets - Update

[fausto99]

One recent rides I was very annoyed to find that the chain was jumping teeth on my custom laser cut 32T Campy pattern sprocket (viewtopic.php?f=5&t=130536) .

Of course it worked perfectly on the stand but anything steeper than ~8% on the road was very iffy.
I was surprised to see the original thread is dated June 2019, so I guess the sprocket is now on its third year. However, I only ride that bike in what I call intermediate weather, so I doubt I have got even close to a few hundred miles on that cog. I have a full on winter bike and I ride my "road" bike in the good weather. So much for being told that the laser would harden the steel where it had cut.

I could not see any wear on the teeth, nor could I measure any wear on the chain. So I finally got around to taking the cassette off and looking at the 32 cog... and this is what I saw. Pictures below.



I don't know for sure that all the little burrs are to blame but it's a fair bet. So, the next step is to file them off and try some case hardening. However, I can't find any local firm to do it for me. Has anyone tried this at home? I haven't done it since leaving school in the um, er, 1960s.
Any tips gratefully received.

[cycle tramp]

If you type 'blacksmith case hardening' into the search engine of your choice you should get about three or five 'how to videos' appear as well as a few book titles. I'd be interested to hear how the project goes

[531colin]

In the dim and distant past I had some expert help on this type of topic from forum members.
I'm sure it depends on the type of steel you start with......for example, I seem to remember that you can't harden ordinary mild steel, it has to be "high carbon" steel in the first place.....goodness knows about stainless
I was wanting to make a spoke punch to my own design....I could easily grind up something like a wheel spindle to the right shape, but I couldn't get it properly hard, so the end "mushroomed" in short order.
I could easily buy joiner's nail punches, but I couldn't easily work them.....they are hard!
If memory serves, in the end I heated up a nail punch to cherry red, and cooled it in air, this "softens" it so I could work it.
Having worked it, I heated it up cherry red again, and quenched it in (engine) oil.
This is a "near enough" method of hardening high carbon steel, and 100% easier than the "proper" way, which involves heating to cherry red and quenching in water, making it "glass hard"....(wear resistant, but can crack )....then taking the glass hard steel and heating it to a defined temperature (thats the difficult bit) and cooling in air ......this is "tempering" I think. The defined temperature bit goes by the colour of the oxide....as you are heating it in a gas flame....its meant to be "straw-coloured" I believe....good luck with that!
Somebody with good searching skills could find this stuff?
Theres case hardening, too....

Found some! viewtopic.php?f=5&t=59955&p=507653&hili ... ng#p507653

[fastpedaller]

Are the burrs the cause of the problem? Could it be that if you remove the burrs, the sprockets will be fine without case hardenning?
When I had a part laser cut it had burrs which could only be seen on close examination, so are the burrs just left from the laser-cutting process?

[fausto99]

No. All the unused sprockets are burr free.

[fastpedaller]

No. All the unused sprockets are burr free.

Fair enough. From my school days, the compound for case hardening was cassenite (sp?) or if there is no supply to use sugar!
IIRC heat up red and plunge into the cassenite. One issue could be that the sprocket may warp, the other (very unlikely) is if the whole thing becomes hard and snaps. I had a Sun Tour freewheel once that snapped 3 teeth of a sprocket when I put my (not considerable) power down - teeth must have been over-hardened!

[Jdsk]

From my school days, the compound for case hardening was cassenite (sp?) or if there is no supply to use sugar!

Kasenit?

https://tttg.org.au/Content/Docs/Articl ... dening.pdf

Jonathan

[alexnharvey]

Might it be cheaper/better to get suitably hard steel waterjet cut than messing about trying to case harden the mild steel.

[fausto99]

Fair enough. From my school days, the compound for case hardening was cassenite (sp?) or if there is no supply to use sugar!
IIRC heat up red and plunge into the cassenite. One issue could be that the sprocket may warp, the other (very unlikely) is if the whole thing becomes hard and snaps. I had a Sun Tour freewheel once that snapped 3 teeth of a sprocket when I put my (not considerable) power down - teeth must have been over-hardened!

Yes I remember Kasenite from my school days, but it doesn't seem to be available any more. I didn't know about sugar though.

Anyhow I've bought some "Beta 1 Case Hardening powder" from eBay and we'll see how it goes. In light of your teeth snapping comment I won't do more than one pass in the powder. Alternatively I could harden then temper, rather than just harden.

What concerns me the most atm is how to get red hot sprockets into a tray of powder quickly and safely. There's not much thermal mass in a sprocket so I'm wondering how long it will stay red hot once I remove the flame. Will I need to sacrifice some pliers by letting them get to red hot at the tips in order to be able to hold and transfer the sprocket from bricks to powder without them cooling down?

I suspect my Campy 8 speed setup is not going to last much longer. In the long run, I may swap the whole lot out for some Claris 8 speed shifters and levers; then I'll have my pick of large Shimano sprockets.

[531colin]

Hold the sprocket with a couple of bits of wire? Doesn't matter what happens to the wire.

[cycleruk]

Be very very careful with case hardening powder !
The stuff we had at work was kept under lock & key.
Very poisonous but I presume probably not the same stuff if it can be bought over the counter.

If deciding to switch from Campag' to Shimano remember that the cassette pitch is slightly different and Shimano cassettes won't normally fit Campag' freehubs..
Plus Shimano STI don't have the brake cable release as per Campag'.
Can be a pain when removing a wheel so would really need Shimano brake callipers as well.

[fausto99]

Hold the sprocket with a couple of bits of wire? Doesn't matter what happens to the wire.

Isn’t red hot wire likely to break?

[Tompsk]

One recent rides I was very annoyed to find that the chain was jumping teeth on my custom laser cut 32T Campy pattern sprocket (viewtopic.php?f=5&t=130536) .

Of course it worked perfectly on the stand but anything steeper than ~8% on the road was very iffy.
I was surprised to see the original thread is dated June 2019, so I guess the sprocket is now on its third year. However, I only ride that bike in what I call intermediate weather, so I doubt I have got even close to a few hundred miles on that cog. I have a full on winter bike and I ride my "road" bike in the good weather. So much for being told that the laser would harden the steel where it had cut.

I could not see any wear on the teeth, nor could I measure any wear on the chain. So I finally got around to taking the cassette off and looking at the 32 cog... and this is what I saw. Pictures below.



I don't know for sure that all the little burrs are to blame but it's a fair bet. So, the next step is to file them off and try some case hardening. However, I can't find any local firm to do it for me. Has anyone tried this at home? I haven't done it since leaving school in the um, er, 1960s.
Any tips gratefully received.

From the pictures the edges of the teeth seem to be non chamfered, the laser seems to give a sharp edge. Perhaps when the chain is at an angle the burrs build up and then the chain climbs the burr and it jumps? Rather than case hardening perhaps the teeth need shaping so when at running at an angle it no longer rubs the sides of the teeth?

[fausto99]

From the pictures the edges of the teeth seem to be non chamfered, the laser seems to give a sharp edge. Perhaps when the chain is at an angle the burrs build up and then the chain climbs the burr and it jumps? Rather than case hardening perhaps the teeth need shaping so when at running at an angle it no longer rubs the sides of the teeth?

Yes, my thoughts exactly so I've filed off the burrs and will take off all other sharp edges before attempting to harden. The laser cut sprocket worked very well when new so I don't think it necessary to do anything else. I know Shimano used to do a twisted tooth cassette which worked quite well, but I won't be attempting that.

[fausto99]

Powder arrived in the post today but I don't have a small metal tray sorted out yet so won't be attempting the hardening just yet. Does any one know if case hardening will result in any significant change of dimensions? Should I be filing and polishing for a slightly looser fit before the event?