Hi Moonlight Machine:
I can't claim to be an expert on either process but I have both in my shop and I use them both a lot.
I would be very hesitant to try this...if you are making just one gear set, you have no margin for error, no margin for testing, and you're planning a joining process you cannot fully evaluate except by destructive testing or a failure.
The wire cutting is no great problem...you have to find a way to fixture them accurately enough to get the runout within acceptable limits (it's harder than it sounds on a wire), but beyond that, chopping out the core of the gear is straightforward for any competent wire shop.
However, planning to re-use those hubs is a total non starter...you need a start hole, and you need to make skim passes to get the new bore in the gear properly cylindrical.
Also, you can't just use fine wire to cut something like this...the finest commercially available wire EDM machines use 0.02mm wire (0.0008") and there are severe thickness restrictions on what you can cut with a wire that skinny. (think more like 0.1" rather than 1")
Realistically you're looking at standard 0.01" wire which leaves a kerf of 0.0135" when you rough with it, so your slop in the set when you reassemble them is 0.027" best case with 0.010" wire
Moving on to the welding...yes electron beam welding can make a full penetration butt weld in surprisingly thick material, (several inches) but it's not an easy or inexpensive task to make this happen, and to have assurance it actually DID happen on your final weld.
In addition, many metals can be welded, but not all make strong welds, and the alloying elements that promote good hardening tend to make for crappier welding as a general rule, so if the gears are made from an alloy that falls into this category, you do not know how tough the weld is until you destructively test it but you can presume it's probably not very good.
Laser welding something like this is a non-starter...if you put enough energy into it to get decent penetration, you will have ruined enough of the heat treat in the weld zone to have broad areas of HAZ, so you'll have two rings of relatively weak weld and HAZ that have to take all that torque in shear.
newtonsapple offers a theoretically good workaround in post #5 where he advocates ovalizing the bore and new hub, in the hope it will be able to transmit higher torque without failure, but the risk is this will simply burst the gear if the welds fail by camming the lobed hub inside the lobed bore when the welds let go.
If that were the approach then I would prefer to see a splined connection.
If a failure occurs during racing with one of these gears, my suspicion is that a lot will be wrecked, not just the outcome of the race.
So after all the cost and effort to make a bodge like this would you really trust putting 500 odd ponies through it at a gazillion RPM and having it sitting in the transmission tunnel right next to your leg?
That's the million dollar question.
Cheers
Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining
Edit: I misread newtonsapple's post a bit.
He actually DID advocate a splined connection but lobed rather than sharp cornered, which makes sense from a stress riser point of view.
I stand corrected, but I'd still be afraid of splitting the gear if the welds fail unless the spline lobes are large enough to transmit the full torque by themselves without the welds