Possible to weld cogs together?
 

What is the composition of freewheel gear cogs and can they be welded together without significant loss in strength?
I want weld only the inner ring of one cog (ground down enough to use as a spacer between gears) to an intact cog. This is to try for extra gear on the middle step of a freewheel body?
I have the Shimano MF-7400 Freewheel Body in mind. Obviously all spacers on this freewheel will be ground down to a 9 speed gap. (4.34mm)

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...see if you can get someone to move this to C+V or Mechanics.
I don't think any of these guys use freewheels any more in road. :)

There are different cogs, made of different stuff. I've never tried welding them.
Most of them can be welded using proper material and technique, but I'm not sure about warping with the heat and cooling.


I honestly cannot picture what you're proposing to do, and cannot imagine it would not be easier to just get a freewheel with an extra gear.
I think they make them all the way up to 8 cogs now, but most of mine are 7 or less.

Epoch 9 Speed Freewheel Nickel Plated in Tree Fort Bikes Multi-Speed Freewheels

(Says it's threaded.)

You can probably weld them. My guess is it is some type of chromoly alloy, perhaps varying a bit by brand. I'd do some rudimentary heat treating and tempering of the teeth afterwards.

As njkayaker mentioned, there are a couple of brands that make 7, 8, 9, and 10s freewheels. DNP Epoch is one that provides 11T. But, unfortunately, they don't do tight gearing throughout the sprockets. It is also a relatively large freehub body, and thus not practical for building tight gearing cassettes.

Firstly, we are posting about freewheels. Secondly, I do not follow why it is not practical?

If there won't be much stress on the weld, since it's just a spacer, then it should be fine with a few tack welds. That will minimize heat and possible warping.

If it is just a spacer, why does it need to be attached to a cog ?

If it increases the freewheel width, you may need a longer axle, and a bit of "oomph" to spread the dropouts when installing the wheel.

A spacer that is supporting the third cog which is only partially on the freewheel body. If it is just a spacer then a normal spacer would be used.