Repairing cast iron gears with involute gear cutters

The thread about gear cutters finally prodded me into action to have a go at the pair of gears that connect the horizontal and vertical feed on my royal
shaper. The lack of any interlocks has allowed a previous owner/operator to engage both the vertical and horizontal feed in such a direction that teeth have been stripped off the gears, at least twice!
Since the gears are 30 tooth 16DP gears and since our friends at RDG have some 16DP cutters, albeit 14 1/2 PA, I sent them some money. I had originally been intending to do the job with a indexing head, a drum and wire and a single point tool on the shaper, but I thought I would be more likely to actually do the job with an involute cutter.
The significant part of the problem is this... I can build up the broken bits on the gears either with nickel rod or with mild steel. I have both and either would give adequate strength. The gears are also small enough that I can fully stress relieve and anneal the parts before doing any machining. Cast iron gears are good and mild steel ones are passable but I am less sure about nickel gears.
Any suggestions as to which way I should go?
Mark Rand RTFM
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On Fri, 14 Jan 2005 01:52:25 +0000, Mark Rand

Are you sure you'll be able to get rid of the hardening which is almost inevitable in the interface between the nickel & the CI? I'm no metallurgist, is it just a simple annealing matter? Can't comment on nickel vs mild steel. What about building them up with bronze? If the gears are small & you have the right cutter, why not just make new ones?
Cheers Tim
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I'm not sure about the nickel iron alloy bit. I hadn't even thought of a layer of super-alloy at the weld. I know that if you weld to cast iron with mild steel electrodes that you get a layer of quenched high carbon steel that is harder than HSS because I've done it in the past. The quenched carbon steel layers are amenable to annealing and stress relief would probably be vital to avoid the new teeth falling off. The reason I was thinking about nickel rods is that I've got some in the cupboard waiting to be used. The only bronze I've got is bearing stock, not brazing rod.
The main reason for not making new gears is that they are 17/30 segments of gear with the mounting for the ratchet pawl integral to one side of them. an easy casting job, but over complicated to fabricate.
Mark Rand RTFM
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Be very careful building up cast iron parts with mild steel. Because the two materials have different contraction rates you can get cracking as the part cools. Pre and post weld heating can help, but is not guaranteed to avoid the problem. Using cast iron rods would probably be best (but they are horribly expensive).
Regards
Kevin
On Fri, 14 Jan 2005 01:52:25 +0000, Mark Rand

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Try the Mehanite continuously extruded cast iron, sold by one of the Collegey named suppliers.
(Why have two common suppliers both got "College" and "Metal" in their company name? Very confusing!)

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