OT - Tactics For Connecting Shafts

Hello All;

WARNING - THIS IS OFF TOPIC. To those with a bug about that, keep reading, because this may actually provide some benefit for those doing something similar. I am using my old machines to make the pieces, so there's your hook, if you insist on one.

I am posting this here because machinists in general are great problem solvers. Those working on old machines are more-so. If you happen to be an OLD MACHINIST, then you are DEFINITELY a good problem solver, and just who I need to hear from.

I am looking for ideas on how to splice two shafts together to create an intermediate shaft for an automotive project. I have some concern about utilizing a method that will be as foolproof as the normal shafts are on these cars, which means I've never seen one fail even working with many hundreds more HP than they came with originally.

In the accompanying photo, you see the two shafts in question. The shaft section at the rear was harvested from a junk transmission fitting the CAR in question. The OD is as original, and it will be linked to the main driveshaft behind it via an OE coupling sleeve. The shaft in front was also harvested from a transmission, in this case that fits the ENGINE in question, or more precisely it's clutch disc, and will be turned down to the same OD. I have already made the pilot bearing pin you see pressed into its spline end. It had a nice machined ID, albeit for another purpose, and that application did not use a pilot bearing in the crankshaft. The pilot bearing pin was a hole other interesting and exciting adventure in and of itself, but I digress.

After a lot of wrangling about how to achieve this union, I've landed here, hoping to bring them together via a turned sleeve that they will press and weld into. The fit will be tight enough and the sleeve long enough that I am assuming a nice square and even registration of the two sections of shaft by default. The problem now is that I want to assure that I am as close as possible to approximating the spread of load throughout the entire assembly, as though it was one solid bar as per original.

My notions of a sleeve started at about 2.5" in length, about 1.5 thou less in ID than the shaft OD, at least .125" in wall thickness, and turned from a nice length of W1 tool steel I have. My first thought was to simply TIG weld each end, but as the concern over load transmission creeped in, I began thinking of ways to further integrate the pieces of shaft together over more of their length. Concern over concentrating too much load right at the welds brought me to the notion of only partially welding the ends, say at 12 and 6 o'clock, and then staggering a couple of plug welds in the body of the sleeve, at 3 and 9 o'clock, halfway toward where the ends of the shafts meet. Then I thought of making the sleeve much longer and doing more plug welds along its length. I've even wondered about some way to key the assembly together internally. I'm far removed from the ability to grind my own spline, or machine and broach the bits square.

Problem is, I've got ideas, but no real experience at this. The main goal is one and done; never having to build a second one. I'd much rather be accused of over engineering than ignorance, so any and all ideas are most welcome, and appreciated.

Holes bored cross-wise through the sleeve, and welds into the body of the shaft? That would be my first
guess at reducing the stress at the ends of the sleeve at the circumferential welds.

You might consider what the heat affected zone would be for the parent material, as well as the sleeve
material. Also consider that the yield strength of 1018 and W1 are about the same.

Another joint technique you might consider, if you want to spread the force out along the entire
sleeve length, would be silver soldering. Properly done this eliminates any need for post-weld annealing
(if HAZ is an issue) and will approach the strength of a welded joint.

BAM;

Exactly what I was hoping for.

jim rozen said:

Holes bored cross-wise through the sleeve, and welds into the body of the shaft? That would be my first guess at reducing the stress at the ends of the sleeve at the circumferential welds.

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Exactly my thinking. End welding the sleeve would place all of the stress at those weld roots, which does not necessarily appeal to me. I've seen areas such as this partially welded before, I assumed to send some stress past that localized point.

You might consider what the heat affected zone would be for the parent material, as well as the sleeve material. Also consider that the yield strength of 1018 and W1 are about the same.

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I might, and likely should, but that goes a little beyond my pay grade. I would have no way of knowing exactly how each material would be affected. All I know is the sleeve would be W1, and the shafts are good German steel. I'm not even sure if they are hardened, partially or wholly. The thought of some sort of post-weld annealing or normalizing did occur to me, but I confess that I know little of that process either.

Another joint technique you might consider, if you want to spread the force out along the entire sleeve length, would be silver soldering. Properly done this eliminates any need for post-weld annealing (if HAZ is an issue) and will approach the strength of a welded joint.

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I must say that I had not thought of it, and that this idea appeals to me greatly. I know that a solder joint is much stronger than most people would believe. Whether it is strong enough here, I would have no way of knowing. My sense is it might be, and the length of the sleeve could certainly be tuned to suit, but it again would take someone with a far higher degree of knowledge/experience than I to pass judgement. The notion of proper and thorough penetration also would concern me. I'm not sure how one would tell if the entire joint were properly wetted out? Perhaps a small side fill hole(s) such as an electrical butt connector has?

I've only silvered once, on very thin .035" CroMo tubing to repair minor surface anomalies, and found the process much more difficult than I imagined. It took far more heat than I was anticipating, and the melt point of the filler was far more volatile and unstable than I envisioned. Closer to TIGing aluminum than brazing. The "properly done" notion brings still more questions. I might envision that requiring stuffing the hot assembly into a bucket of sand to cool slowly and evenly, or something similar.

Making my own bellhousing from scratch was quite a challenge. I expected this driveline coupling to offer at least an equal challenge, and as of now I've not been disappointed. Please do expand on the questions your kind submission raises, if you will. I'm all ears!!

I would agree that properly done, silver solder might be a good choice here. But I'd caution that concentricity of the two shafts is important for the functional life of all the associated parts, not just the shaft itself. As such, unless it's prohibitively expensive I'd rather have a custom shaft made from a single piece with the geometries needed.

A search for custom transmission parts may find companies equipped to do the work.

If you go with a sleeve and silver solder, I'd be inclined to use 4340 rather than W1 for the sleeve.

RedlineMan said:

If you happen to be an OLD MACHINIST, then you are DEFINITELY a good problem solver, and just who I need to hear from.

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What you need IMNSHO, and from a lot more years in day to day automotive, may need no machining at all. Unless this has been done before, and often, there may be no info out there in internet land, so a physical, not online, search through parts-bins where they have massive stocks AND your are trusted to wander without constantly having to clap your hands.



Long and short of it is that flywheels, pilot bearings, throwout bearings, their positioning fork, the input shafts of transmissions, their splines, nose and shield diameters, the splines on clutch driven disks, the flex plates for torque converters, yadda yadda, HAVE, by age and era, existed in GREAT variety but that variety still falls far short of "infinite".

Mix and match will nearly always find goods that want only a change in spacing, not machine work and certainly can avoid welding or pins on the hardest working parts of all.

If this were my task - and it assuredly HAS been, plus those of numerous other engine swappers - I would expect - yet,again - to end up with several era's by age of parts, and a different race or tribe of donor of goods that ultimately were 100% "stock" parts, even if no longer common. Most of all they would FUNCTION if they had all been selected by designers doing not all THAT different a "package" themselves as they tried to use stock parts for best economy and least risk of production line bottlenecks for the automaker as paid them.

WHEN mods are needed? They are to the opening in a fork. The anchor pivot. The actuator, A custom pilot bearing. Even an alternative splined clutch center is but a box-tick from those who make or rebuild driven disks.

To be avoided is having to pin or weld or couple a critical power-transferring shaft.

Change, instead, as much as must be changed all AROUND it so as not put the most highly stressed component into position as also the weakest, most likely to fail, AND MOST HEAVILY ALTERED position.

Keep any part that need alteration work one of the cheap and easy ones. Fab spares right up front. Do not modify ANY part that will be expensive, time-consuming, exotically modified as to leave the vehicle stranded, even if it is a speciality-use one, not a "daily driver".

2CW and "stranded' but the one time. before I did that parts-bin walk to discovered a stock Dodge throwout bearing could mate GMC motor to AMC's variant of Aisen AX5, unaltered when a machined alteration had failed and seized. A throwout fork was found, GMC parts-bin. It needed 60 thou ground wider. Chopsaw blade in table saw. Done in minutes, by hand, spare as well, then put by.

New oner has been driving it for over 2 years. The above approach meant AX5 to AX15 trans upgrade was a drop-in. He had needed new brakes all around, new exhast pipes, new tires and a new Fuel pump. Zero exotic parts.

28 years after the initial conversion.

Set your goal to enjoy use instead of F-Withing.

Milland said:

I would agree that properly done, silver solder might be a good choice here. But I'd caution that concentricity of the two shafts is important for the functional life of all the associated parts, not just the shaft itself.

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Good points, to be sure. It is assumed that the shaft piece in the background is concentric, having been machined its entire length at the factory. The only non concentric portion of this at the moment is the "free" end of the shaft in the foreground, having been cut/ground down from a transmission input shaft. I am assuming that chucking it by the bearing land near the spline end would allow me to turn it to the proper concentric OD for the mating ritual.

As such, unless it's prohibitively expensive I'd rather have a custom shaft made from a single piece with the geometries needed. A search for custom transmission parts may find companies equipped to do the work.

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A point whose wisdom cannot be argued, if such a place could be found. Having said that, I would have to think that having a custom shaft ground with different splines and diameters on either end, plus a pilot pin, would fall under prohibitive for a one off part.

If you go with a sleeve and silver solder, I'd be inclined to use 4340 rather than W1 for the sleeve.

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Would this be a strength -vs toughness issue? Amongst all the zillions of things I am not, add to that a metalurgist!

Thanks for playing. I do appreciate it. It's not an easy problem to solve, but as my friend keeps telling me, if it were easy..... To date, no one ever has.

thermite said:

What you need IMNSHO, ...................................

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I cannot argue with a word of that. If it were possible, even feasible, I'd do the parts bin shuffle in a NY minute. I already have been to a very great degree. Conversely, with this specific issue, I'm not getting any younger.

"I know that a solder joint is much stronger than most people would believe. Whether it is strong enough here, I would have no way of knowing. My sense is it might be, and the length of the sleeve could certainly be tuned to suit, but it again would take someone with a far higher degree of knowledge/experience than I to pass judgement. The notion of proper and thorough penetration also would concern me. I'm not sure how one would tell if the entire joint were properly wetted out? "

You make the sleeve with about one thou of diametral clearance. Flux it, and flow the silver solder from one end. If the
joint is done correctly there will be a ring of sliver solder at the other end of the joint when you are done.

If you cannot tell how to make a weld joint strong enough, then not knowing how to make a sliver solder joint strong enough
seems like not much different to me.

The issue of a heat affected zone for a weld joint like that can be a real issue. The shafts are probably high carbon steel and
possibly heat treated to finish at some very particular hardness. Can you mark them with a file or do you have access to a
hardness tester?

The overall goal here is to not have the parts fail because the weldment winds up extremely hard and brittle. Your pay
grade just got elevated so you need to understand what you have in hand and how best to joint them.

RedlineMan said:

Would this be a strength -vs toughness issue? Amongst all the zillions of things I am not, add to that a metalurgist!

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Toughness. This is a gut choice, but I don't associate W-1 as being a high fatigue life steel. Lots of shafts are made from 4340, for the combination of strength and life. Silver solder, done right, should give you some more tolerance against cracking failure than all but an expertly done weld and stress relief.

One other thing you can do to improve fatigue life is to taper the ends of the coupling so you have a better torsional stiffness match with the original shafting. perhaps start with a wall of .1", increase to .2" over an inch or so at both ends. Again, just a seat of the pants take on this.

Milland said:

Toughness. This is a gut choice, but I don't associate W-1 as being a high fatigue life steel. Lots of shafts are made from 4340, for the combination of strength and life. Silver solder, done right, should give you some more tolerance against cracking failure than all but an expertly done weld and stress relief.

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Shafts for high loading are of alloy well-know to the major makers and the bad-boy performance builders who have to offer better-yet after busting OEM parts. Do as they do, etc. Might be a skosh more Vanadium, Manganese..?? Not my current TV but not deep secrets, either.

If no parts bin?

I'd want to skip all the messing about with any sort of joint and start with getting the blanks ready to go to a gear cutting guru. "N+1" parts.

Seen a lot of these parts. Never yet run across one that was raised from seed nor hatched from an egg, so "produced' they were and can still be.

Some several somebodies out there are already doing this as a line of business, for-sure.

Just not for free, nor even cheap.

Also the ends of sleeve could be fish mouthed so that weld was not going around circumferance.

I'm fairly good at mechanical and automotive type things, but i'm having slight trouble trying to figure out your end result. Im curious for more details.

Is this a manual or automatic? Rear wheel drive ?

Is this a bastard trans that you need to adapt to both ends, or one end only ? Like driveshaft to trans ? Or clutch or converter to flywheel of engine ?

If flywheel side, and assuming starter location is not moveable, then i might try keeping clutch/converter original to trans your using, and if clutch/converter distance is about right to flywheel, drill new holes. If distance is too far, make an adapter ring between clutch/converter and flywheel. If too close, adapter between flywheel housing, and trans bell housing.

If driveshaft end, get correct output shaft, with u joint, or entire driveshafts. Every city has a driveshaft maker. Cut opposing ends of driveshafts and have them welded together if ujoints are not compatible, assuming rear wheel drive.

I dont like that sort of custom work to hard and solid shafts. Too easy to be out of whack, leaks, vibrations, breaks and such. I'd prefer adapter plates, and aligning original parts.

" As such, unless it's prohibitively expensive I'd rather have a custom shaft made from a single piece with the geometries needed. "

This is the correct answer. No way I'd try this kind of joinery in a high power application. Needs to be made as one piece.

[If you go with a sleeve type coupling, I offer the following:

1. Use a steel with a carbon content below about 0.4% for weldability. W-1 has about 0.90% carbon and requires special filler metal and pre and post heat to weld successfully. There are all manner of "miracle tool steel weld-anything electrodes" out there on the market, and while they may well work, I do not recommend using them or a high carbon steel in this application.

2. I would make the coupling sleeve out of 4130 steel, which is weldable with anything from an ER 70 series filler rod on up, or you can use a 4130 filler rod but will likely need to preheat and postheat the welds and heat affected zones.

3. I would bore and turn the mating parts for shrink fits. This insures good and complete bearing contact between the coupling sleeve bore and the shafts.

4. When machining the shafts for the fits into the coupling bore, use a four jaw chuck and indicate the shaft to be turned for the fit so it is running absolutely
concentric with the splined end. If need be, put a center in the plain end of the shaft and support it on the tailstock center. The idea when putting together three
separate parts to make one single unit is to try for 0.000" total indicated runout on each shaft relative to its splined section. Hopefully, the plain sections of
each of the shafts are of the same diameter so there are no transitions in diameter with resulting stress concentrations.

5. If you do have to change diameters on the shaft from the spline section to the section to fit into the coupling, grind a form tool to cut a radius'd fillet
rather than a square corner at the shoulder where the diameter changes. Radius the outer corner of the shaft on the larger diameter as well. No sharp corners,
no tool marks or gouges as these are stress risers.

6. I'd try to design things so the coupling sleeve is one continuous bore with the shafts each having the same plain end diameter for the fits into the coupling sleeve.

7. Pinning is not something I would suggest without running calculations as to peak torque with an allowance or factor for shock or impact loading. A cross pin in double shear can transmit a surprising amount of torgue, but without running the numbers, I would not go with it instead of welded connections.

8. By running the weld as a multi-pass fillet and laying it on so there was enough meat for finish machining, a generous fillet can be formed. This will go a long ways to reducing stress concentrations at the transition from the outer diameter of the sleeve coupling to the smaller diameter of the shafting. Again, grinding a radius'd form tool will go a long ways here. Trying to approximate a radius by "profiling" ( cranking the cross slide or compound while feeding the carriage) with a round-nose toolbit might work, but the potential for creating ridges or grooving is great. This is where the form tool is the preferred way to go, in my opinion.

9. I'd run the welds using GTAW (aka "TIG") to tie the shafts to the coupling sleeve in small stitches, quartering each pass and using a "backstep" technigue. I would also use an air needle scaler and lightly peen each pass to give some stress relief. Once the shafts and coupling sleeve were fully welded, I would set it up between centers on the lathe and indicate it to see if it were still straight. If it had picked up a bow or dogleg, I would use a small brazing tip and a wet rag or compressed air jet and try to flame straighten the shaft. I've had good success with flame straightening on jobs where welding has caused things to pull or cock. It is less brutal than using a press. A little bit at a time with the flame straightening.

When making a built up rotating assembly like this shafting part, I try to start as true in terms of runout as I can. Using shrink fits to set the shafting into the coupling sleeve eliminates any clearance in those fits with resulting runout from that clearance. I would machine the coupling sleeve from a piece of 4130, and once the shafts were welded in and any flame straightening done, I'd take a cleanup cut on the outer diameter of the coupling sleeve with the shaft assembly supported between centers on the lathe. This assures the outer diameter of the coupling sleeve will be dead true to the bore and shaft centerline. Lastly, I would make sure all sharp corners were rounded off and blended, then polish in the lathe with emery cloth and oil. No tool marks or discontinuities such as undercut in the weld, weld ripples or low spots in the weld should be visible when you are done. Every little bit helps.

RedlineMan said:

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See first-generation Pontiac Tempest. Speedometer cable on steroids? Neighbour had one. I never had it apart, just read about it. And NO relationship to the GTO driveline!

Then see Alfa-Romeo "75" AKA "Milano". Managed to not tear those apart, either, when renting them in Europe, but given how much fun I was having in Rome's traffic? Pure luck!.

Point is, that one carried more serious power, AND at high RPM.

One of the best-behaved cars for road manners, especially on verglas and in freezing rain on 2-lane - or a bit LESS -blacktop up around Republicca di San Marino that I have ever been blessed to drive. Classical motor forward, drive wheels rear, De Dion controllability, tires kept square to the road surface, not all swinging and skidding about with camber changes, and balanced so very well.

Thermite had an idea which appeals to me. Look at the driven plate with an eye toward a modified center section with the desired spline. A close fitting trapezoidal thread has a real potential. The engine is only going to turn in one direction unless it is a very large marine application. Unscrewing in engine braking would be easily handled with a TIG pass. The trapezoidal thread is used in deep drilling, one of the most severe torsion applications that there is. Make a spare or two while you are at it.

Well your making something ! Not sure what, haha, but you got something going on. I'm guessing its not a vehicle with the fixxed shaft or outer tube to the other housing.

Vehicles, and even most stationary industrial stuff would need u joints combined with a slip joint to deal with flex, expansion and twist, be it motor mounts, rear diff or whatever moving around a bit.

Most boats i see have a pretty rigid driveline for main propulsion. With solid engine and gear mounts, plus prop shaft bolted directly to gear with no flexible coupling. But serious alignments are done with tolerances for heat expansion factored in. In some cases there is a heavy rubber coupling between engine flywheel and gear input shaft.

What is the driven equipment, or load going to be ? And what type of internal driveshaft inside tube/pipe ?

texasgunsmith said:

Well your making something ! Not sure what, haha, but you got something going on. I'm guessing its not a vehicle with the fixxed shaft or outer tube to the other housing.

Vehicles, and even most stationary industrial stuff would need u joints combined with a slip joint to deal with flex, expansion and twist, be it motor mounts, rear diff or whatever moving around a bit.

Most boats i see have a pretty rigid driveline for main propulsion. With solid engine and gear mounts, plus prop shaft bolted directly to gear with no flexible coupling. But serious alignments are done with tolerances for heat expansion factored in. In some cases there is a heavy rubber coupling between engine flywheel and gear input shaft.

What is the driven equipment, or load going to be ? And what type of internal driveshaft inside tube/pipe ?

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You've shown your age, or lack of it. That arrangement was used in various autos for about 50 years and apparently is not dead. It can have advantages and I'm not ruling out that the OP might be onto something. Then again he could be barking up the wrong tree , but he is entitled to learn that the hard way.