How Does Weld Yoke Work?

Stellrammer​

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• 53 minutes ago
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I’ve had to replace the centering yoke attaching to a cardan joint. The previous runout on this and the corresponding counter weights was considerable. I have the replacement part in place and running within .002”( phased to within half a degree)
I’m not competent enough to weld it, should I tack it and send it out ? Is it better to weld it between centers to avoid shifting , is tacking it before sending it out going to cause problems ?

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If you do decide to weld, What ever you do, Do not ground you lathe, Ground your shaft or as close to your weld as possible. Logic being is you might arc your ball bearings or cylindrical roller / taper roller bearings in the headstock.

You will get different approaches from the members on this forum, In the end do what makes you feel comfortable.

Gluck!

What would make me comfortable would be the mating parts not shifting out of alignment from heat, maybe I’m being unnecessarily cautious about it moving.

Do not ground you lathe, Ground your shaft or as close to your weld as possible. Logic being is you might arc your ball bearings or cylindrical roller / taper roller bearings in the headstock.

@Stellrammer - I'd also turn off and unplug your lathe so there are no ground paths.

I'd do a set of tiny tacks if I were you. But if you are worried about it moving, I might epoxy it in place in four locations for now and let the weld shop remove the epoxy after tacking it between the 4 epoxied spots. I have shortened several driveshafts, never on a lathe, just zip cut and a wrap around, no vibration issues, but you can always send it out to get balanced after the fact

4 solid tacks, and weld, I've always welded them in 4 quadrants (before lathe, no positioner) weld one quadrant then the opposite quadrant and don't take a break in between

You are lucky that is a pretty short shaft, the shorter the less inclined they are to vibrate

If you are doing it on the lathe, like everyone has stated, do not ground the lathe

It's not as scary as you may think, even if you can do a half way good MIG bead you'll be fine...driveshaft guys aren't exactly pro's (I bought a shaft once....what a waste of money) I’ll be the odd man out, I don’t mind. I would recommend sending it out to a driveshaft shop, it’s what they do day in day out they should do a good job

If it’s double cardan it’s likely a front axle driveshaft- the old rule of thumb was front axle was 4x4 only, not likely for high speeds or constant use, so home shop welding was fine, as it didn’t see highway use

So I would say weigh how much it will get used, at what speeds, and how much you need to trust it I'm happy enough sticking a PTO shaft for a tractor implement together, but those don't turn all that fast ( RPM max, 540, for most of my stuff).

You are gonna have to send it out to a driveline shop to get it balanced anyways, yeah? So tell them what you need it at, as far as dimensions, and get on with fixing something else!

“Most” driveshafts don’t need to be balanced. Is it a good idea? Sure, but it’s extra money, too

Like you said in your post earlier, usage is going to be a factor.

If the OP is not confident in welding it straight, as stated, then it's a no-brainer for me, to say it goes to the shop. If it merits the balancing, and the OP states, if I understood him correctly, that it was pretty loaded up with weight to get it balanced before the works commenced, then it probably would not be a bad idea. Fewer guys around with a balance rig, but if anyone doe have it, the driveline place would be it. My skills as a welder are not up to this task, it is definitely going out to be welded.
It is pressed in pretty tight and needed a BFH to persuade the replaced centering yoke to clock true. My only concern is that alignment being influenced by heat or some undue knocking about. Welding and its effects on steel is not in my wheel house.
Judging by the welds from the factory on the frame, and the haphazard assembly of the drives shafts I’m beginning to think the Ford Truck Assembly plant in Wayne Michigan suffered the same issue. If you tack weld it in three places and then put it back in the lathe and check the run-out.
If its changed you can adjust it by peening the tack welds. Once your happy that it is close
enough weld it. If it vibrates it might need to come back out and be balanced.
I had a 87 mustang that had a slight vibration that started at 90 Kmh and stopped at 105 Kmh.
By putting a hose clamp on the drive shaft and moving it around and from one end to the other
between test drives I was able to eliminate the vibration.

So I suggest you unplug the lathe and pull any fuses it might have.

That was my advice earlier too. But it got lost in the length of the thread.

It isn't enough to put the welder ground close to the work. Anyone who has ever looked at what a welder does to the supply line voltages would quickly realize that it isn't just the weld current that is a problem. So are all those spikes on the supply lines. Best to totally remove all possible ground and supply line noise by Disconnecting the machine. Removing the fuses is a good idea too. It's not really that damage is inevitable. But why take silly chances.

It's funny. With all my automotive design experience you would think I would have dealt with drive shafts before. But I haven't. I've only ever had to specify what I wanted and then deal with poor quality suppliers. Finding problems after the fact is always a lot easier than making sure they don't happen in the first place.

I think @Stellrammer is right to just let someone else handle it. Especially since his welding skills are probably a lot like mine. Then he doesn't need to worry about damaging his lathe. I’d still put on one of those driveshaft loops on it just to make sure, when I needed a different driveshaft I’d go to the wreckers with a tape measure. My 58 Chevy use to eat the stock 3 speed tranny’s and one time at the wreckers they wanted way to much for them so I told them I’d go down the street later that night I went back and carried out two one in each hand.

There's a very big difference between an AlMg alloy (that contains a few percent mag) and a Mg alloy that's around 90% mag with a little aluminium, zinc and other ingredients but my money's on an silicon based alloy- either AlSiMg or AlSiCu

Magnesium isn't banned for automotive use, far from it in fact. As well as wheels (for those with deep pockets) it's being used more and more in the search for better fuel economy- excellent strength to weight ratio and castability. VAG have used it for ever for various castings, these days more and more manfacturers are using it for components like steering wheel cores, seat frames, various drivetrain castings, the inner frames of some panels as well as varoius brackets- there's a good 10-15kg of mag in many modern cars

While mag swarf, ribbon etc are very flammable (as is custard powder) a chunk of the stuff is actually very hard to ignite. Welding mag isn't really any more dangerous than welding anything else (just make sure all swarf is cleaned up!)- there's a mag foundry near me (primarily aerospace components) that have a full time welder on site whose main job is repairing castings that failed QC. No problems regarding penetration if the repair is prepped properly That's an odd area to crack. It wouldn't be instant death if it failed - the bottom yoke still holds the forks, and the steering stem is under the yoke. What that's doing is attaching the handlebars to bike. If it cracked all the way through at the bottom point, you've still got the forks clamped through the holes, so the bars will stay on - no death, still rideable but not advisable.

Did someone overtighten the nut that goes through that part?

what bike is it from? I'm reckoing it's from something old and Japanese, given the fork size. Prolly hard to get these days?