[Ironchef]

I made a mistake and got the wrong size sprocket for an electric bike I'm making. The sprocket is a double D but I need a single D. It is also a slightly larger bore. I was thinking I could fill the bore with TIG then bore it to the correct size and then fill it again with TIG and file down to fit the shaft.
What TIG settings would make sense? I'm not sure what kind of metal the sprocket is made of.

[noddybrian]

Hi - I'm not familiar with the terminology of your sprocket - but all chains & sprockets will be hardened - each component slightly different from it's mating part to maintain a good wear life - ( alot like undercarriage components on track layers ) if you weld on it this it will likely not last long - is it possible just to turn up a bush on the lathe & press fit it or loctite / peg it to the sprocket to make it fit ?

[WerkSpace]

It seems like a lot of work, why not purchase the proper sprocket and sell the one that you have?

I made a mistake and got the wrong size sprocket for an electric bike I'm making. The sprocket is a double D but I need a single D. It is also a slightly larger bore. I was thinking I could fill the bore with TIG then bore it to the correct size and then fill it again with TIG and file down to fit the shaft. What TIG settings would make sense? I'm not sure what kind of metal the sprocket is made of.

I'm working on a similar project with a Volkwagen turbodiesel AAZ engine crank gear.
They are notorious for failing (when mechanics don't replace the crankshaft stretch bolt.)
Eventually, the crank gear becomes just loose enough to destroy the key way cast within the gear.

The popular solution to the problem is to replace the crank gear with a Volkswagen TDI D-type gear.
Some machining of the AAZ engine crankshaft nose is necessary to accommodate the new gear type.
http://www.youtube.com/watch?v=uAl_8GwCLXw

[blaz]

Easier to bore and bush (says the machinist with access to a lathe). Not all sprockets have hardened teeth but you can soften the ones that are hard by over heating them. If you throw up some pictures we may be able to help more.

[noddybrian]

@blaz

Bushing seemed the logical approach in my opinion - it will not heat damage / warp the original part & it should still run true & maintain original heat treatment - build up & re-machine as the OP queried I would say was second choice - sometimes you have to do this but it's not usually 1st choice.

So is owning a lathe a crime where you come from ? - some people that weld have other skills as well !

[blaz]

@ noddybrian

I have met lots of people with lots of skills. The comment was meant to be funny because not everyone has a lathe in their shop, and we all do what we can with the tools at our disposal. No disrespect is ever built in to my comments. Safety concerns will be stern though.

@ Ironchef

I remembered what twin D bores were and have to say they are a PITA. I have used 2 set screws simply because of ease of manufacturing them. If there are no hubs on the sprockets then I think you will be able to weld and file the sprocket to the desired shape. Minimal heat input will limit distortion and tempering. Good luck.

[Ironchef]

Thanks for your suggestions. I've decided to try to find the correct sprocket.

As for the jokes, my id "ironchef" is a combination of a welding and a culinary degree.
I'm also known as ironchef de biciclet to include my cycling hobby.

[zetasj55]

Not all sprockets have hardened teeth but you can soften the ones that are hard by over heating them. If you throw up some pictures we may be able to help more.