Engine and Transmission Tech

I was thinking of using ER70S-3 tig rods for welding the cast drive shaft ends to CDS tube.

This is for a MGB to Jag IRS conversion. thanks

If you are talking about the stub shafts going to each wheel, they are forged, not cast, and any good quality welding rod can work provided the weld is done well. 70s should definitely be strong enough.

Jim

Ah yes, forged...very helpfull thanks Jim. is it worth pre heating & slow cooling after the welding?

I seen many drive shafts welded. None were preheated or post. These are likely low-carbon steel, so not an issue. Best is to have a straight and solid press fit. REMEMBER to "index mark" before cutting apart ! Good Luck, Art.

Thanks, Ive a MIG & TIG, the TIG is the better option?, & I'm using CDS OD 44mm x 6mm tube between the yokes with about 3" press fit, same as what Jim did, would it be best to puddle fill holes in the CDS tube, or use some 10mm cross pins?.

Jim did you use a MIG or Tig when you did your jag drive shafts?



Edited 1 time(s). Last edit at 01/20/2021 06:42PM by soi6.

I narrowed a Jag rear back in the early 70's and used a similar sized tube as you are. I had a Lincoln tombstone arc welder and the welds held for 15 years until I sold the rear end. Whatever welder you use make sure you have a deep V at the weld joint so you get full penetration. You might also want to clamp the ends of the yoke where the U joints go because they can be pulled apart from the welding

Ok, thanks for that!

I stick welded them using 7018 rod. If your TIG welder can be used to stick weld you can get better penetration that way with less work. With the increased diameter of the tube there is no real need to bevel the weld area.

The big issue you run into is warpage. See the thing is that you really want to have a weld melt area into the metal of the shaft that is larger in cross section than the area of the shaft cross section (and the tube end cross section also should exceed the shaft cross section if possible although accurate engineering calculations will show that a smaller area is possible, depending on the metal composition). That is easiest to achieve with about a 1/8" stick electrode and a weave to enlarge the puddle size. A 220v MIG also works fine. If you want to use TIG you probably should do a heavy preheat and use a lot of filler rod. But with that much heat in a small area steps need to be taken to avoid warpage such as by alternating sides. The heavy preheat will also help considerably regardless of the method you use. Afterwards if you want to bury it in dry sand to cool down slowly that isn't a bad idea.

If you can mount the shaft between centers while welding you can correct for warp as you go. Otherwise you may just have to resort to other methods like going back and adding more weld to one side or using a press to straighten the finished part. That is always an option regardless of how it comes out. Any warpage will cause imbalance and can lead to driveline vibrations, however the lower speed and small diameter helps minimize those.

Jim

Jim, tats very helpfull thanks, Re; warp I note that when turning the shafts down in the lathe that the rough forging was quite uneven, so I quess its not that critical. But having siad that Ill do my best to get them true as possible.

Yeah, I'm guessing you turned them between centers, which would be the best practice. What you end up with is sort of reliant on your tube size, I used hollowbar. Seems like it might have been 2" on one and a smaller size on the other. May have been 1-1/2", maybe 1-3/4. I could measure it. With those there was no need to bevel but with a smaller tube, closer to original size you would most definitely want a heavy bevel as Jim recommended.

Many way to skin this cat. Just don't jump in with the MIG and draw a hot bead all the way around in one go. That's a pretty definite formula for max warpage. I'd probably tack it heavily in 4 places, check it, and then join the tacks.

The steel is of quite good quality, comparable to any other axle steel despite the appearance of the forging.

Jim

To add to Jim B's suggestion, check it between centers after each tack and use the next one to draw it back to straight. Same when you are connecting the tacks with final weld. Even after you have it completely welded you can use local heating and quick cooling to straighten it. It always amazes me how much you can get metal to move by heating and cooling.

Ok, I note your comments, thanks, so heat will draw & cooling will do the opposite? , Yeah Ive turned the shafts on the centers, & I'm using CDS OD 44mm x 6mm, I will weld it on an old lathe & check the run out as we go.
Ill get some pics up at some point.

Heat and immediate cooling will draw, just cooling only makes the steel cold. That is how body men shrink sheetmetal that has gotten stretched. As an experiment, get a straight bar of metal and make a weld on one side. After it cools the bar will have a bend toward the side it was welded on. If you rapidly cool the weld area, the bend will be more pronounced. If you weld and cool the opposite side the bar will straighten out. After the driveshaft is completely welded, if you have a slight warp you can heat the side you want to pull back to a cherry red and then rapidly cool it and it will tend to straighten out the warp.

Very good advice. Also, welds left to their own devices will often get harder while cooling which can sometimes cause brittleness as well as warpage because the surrounding metal sucks the heat out of the weld and cools it rapidly. (A good reason for preheating) There is a process called stress-relieving where the metal is heated thoroughly at an even temperature, sometimes as high as 800F and then cooled slowly over several hours. This process releases the stresses that are locked into the metal by various manufacturing processes and overall makes it more durable in general. You can use a standard household oven for this process using a relatively high bake temp and letting it heat soak for a few hours or by using the self-cleaning cycle which can reach around 700F and allowing the oven to fully cool before the part is removed. Usually an overnight process. (works on iron engine blocks also as well as degreasing them)

Then the heat/quench can be used to pull out the remaining warpage. This induces additional stresses of course but in a more controlled manner over a larger area. Frequently used to straighten driveshafts. Press straightening is also more effective after stress relieving and does little to induce additional stresses.

Bear in mind that this process is also used to "draw" brittleness out of steels during the hardening process and achieve the target Rockwell rating, and since axles often have some inherent hardness you do not want to anneal them, which is what happens if they reach a dull cherry red and begin to glow slightly. This happens around 900-1100F. Drawing is often done at temperatures as low as 400F and stress relief can occur at similar temperatures with a long heat soak period.

More than you wanted to know, right?

Here's a tip. When preheating metal that could have some heat treating try to avoid heating it beyond the point where it turns dark blue. This color indicates the most common "drawing" temperature for carbon steels and is widely used in tempering, therefore it makes a good guideline. If it goes to light blue don't be overly concerned but avoid it if you can. Yellows and browns are cooler, down in the 400-500F range.

Jim



Edited 1 time(s). Last edit at 01/22/2021 05:51AM by BlownMGB-V8.

Thanks for that, Im going to use a press to join the parts together, I'm going to heat the CDS tube before pressing it on to the jag forgings, would 4 thou cold interference fit be too much?,

It's pretty heavy. Not that it can't be done but with that much interference I'd be more inclined to do the shrink fit because of the risk of galling from heavy friction. But the tube is going to chill as soon as it hits the shaft and that'll make the last part of the assembly very tight. Personally I feel like .001-.002" would be fine, and .002 is a lot on a 1" shaft.

If the rule of thumb of .001" growth per 100F applies you'd want your sleeve to be a good 600 degrees hotter than your shaft when you started and even then move quickly and have the press set up to use quickly. And since the centering point is a pilot drill hole that makes applying heavy pressure well in a straight line something of a challenge.

Here's something else too: I understand the desire to create a solid whole but that isn't possible since you can't join the stub ends. So rather than concentrate any tube flex into the void between the stub ends it might make more sense to distribute it over the entire length of the tube between the welds. This also makes sense because if there is any movement or flex, the stubs will force the tube to maintain it's shape well beyond it's limits of flex. So I would suggest that it might actually make a stronger part if you were to use a tight slip fit.

Jim

You also have to make sure the clocking is dead on if you choose to shrink the parts together because once they cool they ain't moving. The tight slip fit allows you to adjust the clocking before you begin tacking.

Jim, I was thinking of plug welds between the shafts & the tube as well, what do you think? Im mindfull of what you said in your last post.
Talking of this axle, I was also thinkinhg about fitting stainless pistons to the calipers, Ive had jags before & never had any issues with the rear calipers sticking, what do you think?, I do need to rebuild the two units.

I'd do one or the other. The plug welds are less likely to cause warpage, no reason why that couldn't work. More likely to maintain the integrity of the stubs from the lack of a weld all the way around, less certainty they would hold up to the torque. If you do both you give up the advantages without gaining anything. They will concentrate stress in the tube more than the end welds but probably less than the press fit.

Stainless pistons are widely accepted as an improvement. I agree.

Jim

There are video's out there, showing shops welding drive shafts. I have no problem with .004" press, because tubing is relatively, thin/elastic. IF you missed your index marks, first time, tap-out the yoke and re-align. As stated, twisting for alignment, not an option.
Art.