Welding Tips and Tricks

Im fairly new to welding and while I'm able to put down a reasonable weld im about to undertake a repair to the front prop shaft on my bmw x5 the problem i have is the Tube of the prop shaft is about 30mm diameter and the wall is 2.4 mm thick but the new spline adaptor i need to weld in is solid steel so how do i select the correct size tungsten and power required, you can look these things up on a table if all that you are welding is the same size but i have no idea how you decide with this combination just wondered if any of you experts could give me some advice, please.

The first thing you'd do is create a small bevel angle on the spline end (if viable) and probably create a gap between the tube and spline (use 0.30 MIG wire). You don't indicate the welding process (MIG or TIG?) you intend to use. If MIG, I'd preheat the spline side. I'd tack every quarter of the tube constantly checking for alignment.

Weld it hot. Focus your arc on the spline side because whatever heat is needed for proper penetration and adhesion there will be more than sufficient to burn in on the tube side.

You also need to know the nature of steel the spline side is made from and whether its suitable for welding, or requires a heat treatment post-weld. There are lots of variables to the question you ask and its not possible to accurately advise you. The above is a "general idea" on how it gets done.

****This is not a repair for a First Time Welder.**** You really, really should take this to someone competent and experienced. If that weld breaks and the tube comes free while traveling, it can get stuck into the asphalt and send your car for a tumble, or worse, kill someone. Please reconsider undertaking this repair yourself.

cj737 wrote:The first thing you'd do is create a small bevel angle on the spline end (if viable) and probably create a gap between the tube and spline (use 0.30 MIG wire). You don't indicate the welding process (MIG or TIG?) you intend to use.

He does ask about choosing the tungsten size, so it has to be TIG.

Some vehicles have a safety loop that will catch a broken driveshaft/prop shaft, but I don't know if an X5 has one. If so it's possible that the safety concerns aren't a major factor. Still, I think you're right about suggesting it be welded by someone with experience.

Tech255 wrote:Im fairly new to welding and while I'm able to put down a reasonable weld im about to undertake a repair to the front prop shaft on my bmw x5 the problem i have is the Tube of the prop shaft is about 30mm diameter and the wall is 2.4 mm thick but the new spline adaptor i need to weld in is solid steel so how do i select the correct size tungsten and power required, you can look these things up on a table if all that you are welding is the same size but i have no idea how you decide with this combination just wondered if any of you experts could give me some advice, please.

I'd also suggest caution before attempting this sort of repair yourself.

I'm not a professional welder, but pretty much everyone who has started welding has dealt with this. Ideally you'd find a piece of tubing similar to your prop shaft, then get a solid piece that mimics the adapter, and see what works. After a while an experienced welder can look at something and pick a setting that's in the ballpark pretty easily...but that only comes with experience.

Maybe someone here has done something similar and remembers the ballpark settings, the rest of us would mostly be guessing. If I was trying that I'd probably set the machine on 150A and ease into it to get the puddle started and then decide after watching the first couple of seconds whether it was in the ballpark.

Thanks to all of you who have replied, the safety aspect of me welding this is very small as it drives the front wheels the shaft is bolted at the front and welded at the back.
The spline adaptor is about 5” long with 2” of splines about an inch of no mans land and then about 2” of solid steel that need to be a tight fit into the end of the tube.
Getting someone else to weld it would be a real pain because the vehicle does not move with out this shaft it cant be welded and fitted without removing the differential and thats a big job, so if i can get a reasonable weld on it while laying under the car i can then drive it carefully to a garage and get someone to check it.

I have attached a picture of the spline unit, it is hardened but designed to be welded.

All i really need is a ball park figure for current and a tig tungsten size and filler size at the moment ive only got 1.6mm for both a best guess for both would give me a start, ive got the bit i cut off that i can practice on and tweek the current a bit.

Thanks in advance.

To weld that, I would use at least a 2.4mm tungsten, easily a 3.2mm. Filler size would be 2.4mm. Plenty of tacks. Welding underneath a car is a major PITA due to being out of position and distance.

If you can get the shaft to rotate (car securely jacked) and trans in Neutral, then rotating the shaft via the wheel will help. You might even enlist someone to spin the wheel whilst you hold a single position and lay wire, after tacking it up.

A #7-#8 cup ER70 wire. Clean inside and out of the tube well, beforehand and the spline. Wipe with acetone both pieces. The cleaner the better.

You could tack at about 160-180 amps. See how that amperage does. Maybe weld closer to 150 depending upon what you “see”. You want a fully wetter in weld on the spline end. Anything humpy or ropey, crank up the heat 10-15 amps. And wear full PPE. Welding overhead and having a molten blob of TIG fall onto your chest will leave a real, bad memory.

Tech255 wrote:Thanks to all of you who have replied, the safety aspect of me welding this is very small as it drives the front wheels the shaft is bolted at the front and welded at the back.
The spline adaptor is about 5” long with 2” of splines about an inch of no mans land and then about 2” of solid steel that need to be a tight fit into the end of the tube.
Getting someone else to weld it would be a real pain because the vehicle does not move with out this shaft it cant be welded and fitted without removing the differential and thats a big job, so if i can get a reasonable weld on it while laying under the car i can then drive it carefully to a garage and get someone to check it.

I have attached a picture of the spline unit, it is hardened but designed to be welded.

All i really need is a ball park figure for current and a tig tungsten size and filler size at the moment ive only got 1.6mm for both a best guess for both would give me a start, ive got the bit i cut off that i can practice on and tweek the current a bit.

Thanks in advance.

the safety factor is not great. if the weld breaks the driveshaft will not fall because the spline adapter is inside the shaft holding it in place. remote possibility of it sliding back back down the shaft, especially if weld was cold, broke clean and lack of front drive was unnoticed. if the shaft drops its going to make a mess of the gearbox and there is some fire risk with the cat so close.

its not just a welding issue, there is also alignment.
by the looks of it bwm only have a vibration dampener on the drive shaft (diff is mounted on the engine)
i see a kiwi crowd fit a uni to it which helps with any misalignment.

i think your better off to speak to a driveshaft specialist.
your not going to be welding it in there. its going to be a case of fit it, work out the length. either mark it or tack it.
then remove it and weld it with it aligned properly.

tweake wrote:i see a kiwi crowd fit a uni to it which helps with any misalignment.

Kiwi crowd???

Aren't you a kiwi?

Spartan wrote:

tweake wrote:i see a kiwi crowd fit a uni to it which helps with any misalignment.

Kiwi crowd???

Aren't you a kiwi?

yep, local dudes are rocking it

Cj737, thank you for the advice on consumables and power to use im going to experiment on the bit i cut off which has similar dimensions also i Will be working slightly to the side of the weld so if any drops i wont be underneath it.
Ive found a way using some big cable ties to make a sort of sling i can put my arm in to support it while im welding which should help, ive ordered the parts and it should be here next week so i will post the outcome of my first major weld when i have completed it.
With regards to the rest of you thanks for the advice and concern for my health but im 60 years old and i havent lived this long with out learning a bit of self survival and managing to complete this weld would give me a fantastic amount of self esteem and save me a small fortune so im going to have a go.