Taper-Lock vs tapered shaft

I've long wondered how well a "taper-lock" pulley secures to a shaft, relative to a traditional tapered shaft and bore.

The idea would be to use a taper-lock flange on a straight shaft engine to drive a flange-driven load like a single bearing generator. No immediate project in hand, just curious.

Thanks for reading,

bob prohaska

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My sawmill has a 6.5HP gas engine connected to a 3/4" extension shaft through a Lovejoy coupler, and a taper-lock hub pulley on the far end of the shaft. When the engine lugged starting the saw, because the new belt and pulley wouldn't slip, the black rubber spider in the coupler was torn up. I had used the L095 that had worked fine on the previous 5.5HP engine borrowed from the splitter. I looked up the data and found that I should have upgraded to an L100 to handle the engine's peak torque which for a 4-stroke is several times the average, as calculated from the horsepower and speed.

The 3/4" extension, same as the engine's, and 1" shaft in the speed reducer were calculated for a rotational torque of 1/2 the UTS of mild steel, with a margin, at 10HP.

Other than that it has held up well. The hardest part was aligning the engine and extension shaft to within Lovejoy's angular and offset specs. The mount for both is a weldment that shifted from shrinkage.

Price the taper lock pulleys and hubs. They, the pillow blocks and shafts cost as much as the engine.

I personally wouldn't rely on the engine shaft to drive a rigidly attached load unless it was located by precision surfaces on the engine block.

Understood. Some sort of centering bosses on the engine and load are mandatory, with matching features on the adapter, whatever that turns out to be.

I'm mostly wondering about how well taper-lock style couplings resist vibration over time. A traditional tapered shaft in a tapered flywheel or coupling flange is more-or-less an eternal union provided it's assembled correctly. Is a properly-assembled taper lock comparably permanent? The static torque rating on a 19 mm (~3/4") shaft appears to be around 40 ft-lbs, which is adequate for a 5 hp engine provided it stays tight under engine vibration.

Thanks for writing,

bob prohaska

I'm mostly wondering about how well taper-lock style couplings resist vibration over time. A traditional tapered shaft in a tapered flywheel or coupling flange is more-or-less an eternal union provided it's assembled correctly. Is a properly-assembled taper lock comparably permanent? The static torque rating on a 19 mm (~3/4") shaft appears to be around 40 ft-lbs, which is adequate for a 5 hp engine provided it stays tight under engine vibration.

Thanks for writing,

bob prohaska

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"Slip will tend to occur at the bush/shaft interface, at the prescribed torque, unless a key is fitted. With a key, the slip tendency transfers to the bush/hub interface at a greater torque value related to the ratio of bush outer dia. to bore dia."

You might try downloading the Audel Millwrights and Mechanics Guide. I have a hard copy and need to limit my monthly cellular data use so I didn't try any of the links.

A common pulley which might help with your question is a two piece pulley that joins a hub with a ring by a taper. All I have seen use bolts to pull the two tapers together. Some also use a split or semi split hub to clamp onto the shaft, but others use a key.

The first noticed point of failure I have seen a couple times is that the bolts holding the two piece together break off. Whether they broke, from being over torqued, from vibrations, or because the pulled do something I do not know.

I suspect for most tapered motor shafts a tapered pulley is pulled onto the shaft with a bolt in the end of the shaft.

A washer between the bolt and the pulley/shaft could be another pulley I suppose, but centering could be an issue.

You know... I don't know if any of that is useful, but I'm going to hit send anyway.

The first noticed point of failure I have seen a couple times is that the bolts holding the two piece together break off. Whether they broke, from being over torqued, from vibrations, or because the pulled do something I do not know.

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That fits with farrelbearings' statement that the tapered bushing may slip in the pulley hub if a key prevents it from slipping on the shaft.

prohibition on lubricating the taper in any way, with a warning that it might cause splitting of the bushing or bore. That would seem to fairly large clamping force on the shaft.

Couldn't find any no-cost downloads, a physical copy is 60-80$, so I'll wait till it's actually needed.

Thanks very much for writing!

bob prohaska

Couldn't find any no-cost downloads, a physical copy is 60-80$, so I'll wait till it's actually needed.

Thanks very much for writing!

bob prohaska

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Among other ways the book shows identical hubs on the driving and driven shaft, the same diameter and faced flat and square, like the two sections of an edge finder. The Lovejoy coupler mounted backwards worked for me. You adjust until they meet exactly.

<snip>

Maybe🤷

Leon Fisk

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Thanks, that is quite a collection.

+1

bob prohaska