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Identify these shop mysteries?

Dave A

Titanium
Joined
Jan 4, 2005
Location
Roseville, CA
I picked up these small pieces of steel amongst an assortment of old machinist tooling. I do not have a clue what they are, so am posting a photo so the experts on the arcane and seldom used can identify them. I first thought they were some sort of chuck jaw, but there are no matching sets.

Some information in addition to the photo.

1. They vary in size and dimensions.

2. They can be filed, but are hard, about like the shank of a HSS end mill.

3. They are tapered on one face at about .027 per inch.

4. One of them has been hammered on the large end.
 

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Patrick Black

Aluminum
Joined
Dec 11, 2007
Location
Middle Tennessee
Called "gib keys" or "gib-head keys". They're often used to hold flywheels and sheaves on old stationary engines. They fit in a keyway like a regular square key, but the taper allows them to lock the hub to the shaft without using any other mechanical fasteners such as a shaft nut or set screw or clamp. They can be a pain to remove :angry:. I took one out of a sheave a couple weeks ago by welding a piece of all-thread to the end of a key to use as a slide hammer after wedging under the head failed.

Pat Black
 

Dave A

Titanium
Joined
Jan 4, 2005
Location
Roseville, CA
Looks like another mystery (to me) solved.

If anyone can use these keys, I would be happy to send them to you, as I doubt that I will ever have a use for them.
 

Joe Michaels

Diamond
Joined
Apr 3, 2004
Location
Shandaken, NY, USA
You have what are sometimes called "gibbed keys", or tapered keys. They are used to lock a hub on a shaft. I believe the standard taper to them was 1/4" to the foot.

We had to put a flyhweel on a shaft of the horizontal steam engine at Hanford Mills. The engine had last run in a quarry in Vermont in the 1930's, and had been run into the ground. The flywheel was supposed to be held by a tapered key to lock it onto the cranksahft, No key was used, and the clamping power of the setscrews was evidently enough ! This on a 3 1/2" diameter shaft, sloppy fit in the flywheel hub.

I took measurements not knowing what I had to work with in the way of a taper. The crankshaft had the straight keyway, flywheel had the taper. I think the key was about 9" long, and it was a stepped key as well as having the taper (someone probably put a flywheel from something else onto that engine). When I ran my numbers for the taper, based on my field measurements, I had 1/4" to the foot, which corresponded with my Machinery's Handbook data for this type key.

I did make the gibbed or trussed head, as there is no way otherwise to get the key pulled out, should it be necessart (no way to get at the small end of the key to drive it back).

I could see the wisdom in the use of the tapered key. It would prevent the flywheel from "walking off the shaft". If used with a belt that might run slightly off, or just from eccentricity or shaft whip, any of these could walk a flyhweel or pulley off a shaft. The tapered key wedges fast and there is no moving the hub on the shaft. I think I would have to jack the hub away from the key to get the key broken loose on the Hanford Mills Engine. I do not think there is any way that putting a pinch bar under that gibbed head would loosen that key. We are all quite happy eith the result of using the tapered key as wre know the flywheel is on the crankshaft to stay. With the public coming into the engine room and standing near the running engine, we do not need a flywheel walking off the shaft.

Mike Korol, the Skinner Engine erector told me of a tale of a flywheel walking off a shaft on a smaller engine. This was a Troy vertical steam engine driving an induced draft fan in a NYC Hospital (Harlem Hospital, possibly). The ID fan engine sat up on a platform, and ran pretty much "out of sight out of mind". One day, the engine launched it's flywheel. It just worked off the shaft, and took a good trajectory. The flywheel made it out of the boiler room via an opened door, and rolled accross the street and slammed into a masonry building wall, doing some damage. At the powerplant where I work, we had a Kellog air compressor in the plant garage. A mechanic had just overhauled the compressor and put the flyhweel back on. He claims to have "reefed the snot" out of the pinch bolt in the hub of the flyhweel. He fired up the compressor and before it made it to full operating speed, and despite a multiple vee belt drive, it launched the flyhweel. The flywheel came off the compressor crankshaft, hit a concrete block wall a short distance away, and made a nice hole in the masonry.

Point of both stories: a tapered key would have prevented both incidents. The compressor had a straight key and pinch bolt. I tend to believe the mechanic who worked on the compressor was one of those OCD types who also thinks he knows more than he really does and it does not translate into his hands. His idea of reefing the snot out of a pinch bolt, and the next guy's were likely vastly different. A tapered key would have probably saved the situation.

I think with the advent of "taperlock" bushings, the need for tapered or gibbed keys as shown in this thread kind of dried up. The tapered key requires a tapered keyway, not so easy to cut as a straight keyway. Taperlock bushings make a better job in terms of holding power and concentricity, and are easier to get off (or at least are supposed to be), so the tapered keys fell out of disuse.

Main use is on heavy flyhweels on things like old engines and rock crushers or other heavy, slow speed machinery. Stuff like some of the hit-n-miss engines or other old engines would be likely places this type key would turn up (pardon the pun).

Joe Michaels
 

Dave A

Titanium
Joined
Jan 4, 2005
Location
Roseville, CA
The knowledge on this board just amazes me at times.

A member via PM has expressed a desire for these small treasures and as soon as I get an address, they are off to a new home. :D
 

tgw

Aluminum
Joined
Dec 21, 2005
Location
Central Texas
Taper keys

Taper keys are really useful for some applications. We used them a lot in oil field machinery. They allow you to position a sheave or pulley with a slip fit and then lock it with the key. Getting it loose is another story. There were different kinds of pullers for this but I don't think they would work good on a key that was rusted in place. We had a puller that had a pair of serrated jaws that worked in a taper slot and screws that pushed against the hub. I never used it because most of the keys we ran into had the heads broken off. Our method was that mentioned above. We had a 6 foot or so piece of sucker rod with a slide hammer that weighed about 50 pounds with handles welded to it. We would weld it to the key and let it completely cool and most times it would come out pretty easily. The trick was to let it cool and that could take some time for a big key.

The antique engine folks probably have a lot of experience with these. I think Mr. Michaels is right, the taper lock bushings made them obsolete. I suppose they are still available and you can find the standards for making them in Machinery's Handbook.

Thanks for showing them. I haven't seen any in a while and it brought back memories.

Terry
 

gmach10

Hot Rolled
Joined
Dec 27, 2008
Location
N.E. Illinois
I've fit quiet a few of these in my career. We used them on moveable bridges, all the gears on the machinery are held in place by these. The trick is to fit them right in the first place, fit file fit file etc. If they were fit right removal wasn't to evil. Of course a 3" wide key that's been installed in a bridge for 60 plus years will give you a run for your money. There is a formula for how far the head is to stick out in relation to the width of the key. Some of the oldtimers had a "Goss Bar". Seems they used these on the newspaper printing presses made by Goss, and the bars were a piece of about 1/2" thick plate about 3 1/2" wide with a small hook on one end and a large hook on the other. They were designed by the Goss engineers to remove Gib keys, if you were lucky enough one got willed to you!
 

k3vyl

Stainless
Joined
Feb 13, 2008
Location
newark DE USA
gib keys

A non tapered version is used on vertical shaft water pumps as part of what they call the coupling.The motor shaft is hollow and the pump shaft comes up through it.The "coupling" is at the top and has a nut that lifts the pump shaft to establish clearance at the bottom of the pump which can be 100 ft down.Again the gib key is used so it can be removed from that end.
 








 
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