Two keys on same connection?

NRDock · Mar 2, 2020

We have this ~60 year old design which currently has a 9" long cast iron hub keyed to a 7.5" diameter shaft. Various updating has gradually been done, and we've gotten to a point where we really need to shorten the hub and end of shaft by about 2". A known, but not very common, failure mode is through the existing keyway. Everyone agrees the hub has to be changed to steel.

At this point, we have two camps:
One camp wants to replace the keyed connection with a Ringfeder type locking assembly. Claims two keys can't share the load equally.
One camp wants to put two keys in the shaft/hub connection. Claims the locking assemblies are too hard to remove.

SO, can you highly skilled machinists put two keyways in both a hub and shaft accurately enough to share the load?

A guy on You Tube says the locking assemblies are easy to remove IF the correct (non-intuitive) procedures are followed, while extreme measures (maybe destruction) are required if the correct procedures are not followed. Hey, they are so simple, who would take the time to read the instructions, right?

I'm most interested in any input and experience from PM.

jrmach · Mar 2, 2020

Yes,2 keyways done all the time in performance engines
of course you got to know what your doing,,,Precision wise

DDoug · Mar 2, 2020

What is the machine ?
a punch press ?

winger · Mar 2, 2020

With a ring fedder, the hub has to be thick enough for the expansion stress. Steel would probably be better than cast.
We had a 4.5 shaft with a 1.25 keyway. even with proper radii in the bottom they still broke and the crack started at the end of the keyway and went into the solid area which was 5"

The shafts were turned to 4.25 and no longer broke. Just found the next weaker point of course.

The flywheel was about 3800 pounds with no outboard support.

Dave

NRDock · Mar 2, 2020

digger doug said:
What is the machine ?
a punch press ?

Not a punch press. Mostly moderate steady loads with occasional heavy impact loads or just plain excessive heavy short term loading. BTW, 30-45 of these shaft connections per machine. Rather not define the machine.

NRDock · Mar 2, 2020

jrmach said:
Yes,2 keyways done all the time in performance engines
of course you got to know what your doing,,,Precision wise

Yes, well the two key camp knows a thing or two about performance engines. The Ringfeder is less than $500, and needs comfortably toleranced bore and shaft. Hard to believe I can get two precision keys, four precision keyways, four 3/4" tapped holes and a retainer plate for the price of the Ringfeder. Price is only the tiebreaker. Best solution comes first.

EmGo · Mar 2, 2020

You're not going to like this, but a spline would work well.

ratbldr427 · Mar 2, 2020

The ring fedders are pretty impressive.I haven't used any as large as that.Taper locks are a mix of both and have only had a few failures.Keys only are dependant on a good shaft fit.Vibrations and a loose fit will kill a key only application(or maybe the vibrations cause the loose fit).On smaller shafts Woodruff keys seem to last longer than square keys.
Hardly anything has the dynamic loads of an auto crankshaft (in its size) and a press fit/Woodruff key is pretty fool proof.

Since you already have a history of time to failure if it was me I would try the Ringfedder and improved steel hub.I'm convinced that the shaft fit is what determines how long the keys last.Heat shrink on that size shaft would be a bitch to remove.So the Ringfedder would be my pick,I'm pretty sure I'v seen some other types similar to the Ringfedder.

I like the Ringfedders because of the lack of stress risers in the joint.

EmGo · Mar 2, 2020

ratbldr427 said:
Heat shrink on that size shaft would be a bitch to remove.

Oh ! Since you brought it up ... don't know if this would work for you but they put lobes on large engine camshafts this way, and I once did a gear with a very large bore that worked like this --

Make it a shrink fit, but you put a groove in the center of the bore all the way around. Then you drill into that groove from the face. To install, the shaft has to have an area that is slightly undersize, the length of your bore. You slide onto this area, then pump in hydraulic fluid at a few thousand psi. The part then expands a touch so you can slide it the rest of the way onto the shaft where you want it. Remove the oil pressure and viola, a shrink fit that's easy to remove.

Phil in Montana · Mar 2, 2020

You want free engineering but you " Rather not define the machine" I hope this train wreck works out for you...Phil

ratbldr427 · Mar 2, 2020

That's how a lot of large bearings are installed/removed and basically a hydraulic version of the Ringfedder.

Mud · Mar 2, 2020

ratbldr427 said:
That's how a lot of large bearings are installed/removed and basically a hydraulic version of the Ringfedder.

SKF's take on that - SKF
A keyway might complicate that.

Gordon Heaton · Mar 2, 2020

Phil in Montana said:
You want free engineering but you " Rather not define the machine" I hope this train wreck works out for you...Phil

What are you getting at, Phil? There are a lot of reasons he might not want to ID the machine. Are you just miffed that your curiosity isn't satisfied? Seems to me he's given the relevant info for the help requested.

NRDock · Mar 2, 2020

Phil in Montana said:
You want free engineering but you " Rather not define the machine" I hope this train wreck works out for you...Phil

Math I can do. Relevant experience, I ain't got.

Phil in Montana · Mar 2, 2020

How could you passably give any advise, to many unknowns, rpm, tork, hub thickness, skill of the shop, ease of removable, fit between shaft and hub, impact load, weight of parts, spent to many years trying to pry info from custs that wanted to spoon feed info. It is no big deal for a good shop to 2 key the hub and shaft, or if the hub is heavy and steel a setter will work, and what is the construction of the hub that it can be changed out to steel? If he wants good ideas, he needs to supply a lot more info and a pix...Phil

NRDock · Mar 2, 2020

The original design was shrunk on. I've seen bone yards full of examples where the customer made no effort to salvage the hub end. At the other end of the spectrum, a few customers prefer to use the hub end as a shear key, and want the hub and shaft easily separated.

If it wasn't obvious, I'm in the Ringfeder camp. I think it's the best compromise IF the things can be disassembled by following correct procedures.

NRDock · Mar 2, 2020

Phil in Montana said:
How could you passably give any advise, to many unknowns, rpm, tork, hub thickness, skill of the shop, ease of removable, fit between shaft and hub, impact load, weight of parts, spent to many years trying to pry info from custs that wanted to spoon feed info. It is no big deal for a good shop to 2 key the hub and shaft, or if the hub is heavy and steel a setter will work, and what is the construction of the hub that it can be changed out to steel? If he wants good ideas, he needs to supply a lot more info and a pix...Phil

I had Two questions:
Can Ringfedders be disassembled by following proper procedures? If yes, use Ringefeder.
Can two keys and keyways be made accurately enough to share loads equally? If no, use Ringfeder.

EmGo · Mar 2, 2020

Mud said:
A keyway might complicate that.

Don't need the key if the shrink is sufficient. The key would even be a weakness in a properly-designed shrink fit.

Being a gear guy tho, I think he should use splines

Phil in Montana · Mar 2, 2020

If the joint needs to come apart, use a ring-fitter, if the joint stays as one piece use a shrink fit and 2 keys. It is done all the time to have 2 keys share the load. The down side of a ring setter is, 1 not easy to make the hub run true with out run out, 2 can not be placed over keys that were in the old shaft,3 needs to be retorked, 4 ring setters need a real heavy wall and should be used in a high strength alloy steel.5 you need room to get the tools in to tighten the bolts . In the machinery I worked on (pulp-mill) we would use 2 ring-setter one on each side of the hub, and spent time to dial the hubs in. With a 7 inch shaft I would guess cost is not a object. If the project is life threatening if it fails, the standard has been shrink fits and keys...Phil

thermite · Mar 2, 2020

NRDock said:
We have this ~60 year old design which currently has a 9" long cast iron hub keyed to a 7.5" diameter shaft. Various updating has gradually been done, and we've gotten to a point where we really need to shorten the hub and end of shaft by about 2". A known, but not very common, failure mode is through the existing keyway. Everyone agrees the hub has to be changed to steel.

At this point, we have two camps:
One camp wants to replace the keyed connection with a Ringfeder type locking assembly. Claims two keys can't share the load equally.
One camp wants to put two keys in the shaft/hub connection. Claims the locking assemblies are too hard to remove.

SO, can you highly skilled machinists put two keyways in both a hub and shaft accurately enough to share the load?

A guy on You Tube says the locking assemblies are easy to remove IF the correct (non-intuitive) procedures are followed, while extreme measures (maybe destruction) are required if the correct procedures are not followed. Hey, they are so simple, who would take the time to read the instructions, right?

I'm most interested in any input and experience from PM.

CI is generally OK, that size. Ringfeder as an "add-on" lock well, but doesn't do squat for aiding centering unless you use the special hub with it.

As to matched "fit" in general? Those who "can do" generally do not make the attempt. It's silly.

That size, keys 3/4" or 1", mining and railway gear, yah fit a wedging key, each location if more than one. THEN they are (all) at full take-up.

Other sizes, the sheaves have to be MADE FOR the creme-de-la-creme. "QD" hubs.

Have to practically put a gun to my head to use anything ELSE, lo fifty years already.

I even scarf 'em up as NOS, strays and orphans off eBay and stash 'em to cover various sizes I might never use again in my lifetime. At bargain prices. Of course.

Second-place winner "taperlock". Takes less space, but harder to remove. Special hub bore as well. See MMC, Morse, Browning.. or whomever owns their name this year.

Either one CAN grip so tightly the keys they provide for are not even necessary.

And they tend to run true. VERY.

Something not always the case - if EVER - with keys alone.

2CW

Two keys on same connection?

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Cast Iron

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