Chuck Jaw Terminology Question

markba633csi

markba633csi

Mark Silva
H-M Supporter Gold Member
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sharsjawscorrect1.jpg I'm currently going back and forth with Shars concerning a poorly made set of jaws. It seems they use inverted terms than I do- what do you call this type of jaw (picture)? They call these "internal jaws" for reasons I don't understand. Aren't these used for grasping the outside of cylindrical workpieces? Therefore "external" jaws? Who is correct here, and what is the other standard or "jamming" set called?
Mark S.
 
They look external to me. Like to grab/clamp the workpiece externally.

Not sure what you mean by "jamming". It seems the industry standard is for the longest step of the jaw to be towards the center of the chuck, with two steps each smaller in progression to the outside. In this configuration, a person can place a cylindrical workpiece over the outside of the 3 jaws and then "open" them/scroll them outwards to grasp the workpiece from the inside.
 
What was the first language of the person who wrote the Shars text? I could understand an argument that these jaws clamp on their interior surface....

Also I'd say poorly described, they look well made to me.
 
The jaws pictured are external jaws.
The other style is called "internal" jaws, not sure what you mean by "jamming."

Don't get bogged down with definitions when making a dispute. Send them a link to your image, and simply state this is what you call an external jaw. It also happens to be what the rest of the world also defines as an external jaw.
 
These are the jaws I'm having an issue with- see the problem? The first picture was what I was expecting to get but didn't. Anyhow, I've gotten my credit card company involved, so either I'll get a jaw set that makes sense, or I'll get a partial refund and regrind them, or I'll send the whole mess back and go buy from someone else. It's a shame cause I got the backing plate turned perfectly and the chuck runout with the standard jaws is only 0.0018 so I'm almost there..
Mark Sjawmeas108.jpg
 
What Planeflyer21 describes is what Shars apparently calls jamming- opening up the jaws to hold a hollow workpiece (like a piece of pipe) instead of closing down the jaws so the tips do the holding.
MS
 
Mark,

What you have there is an optical illusion there. The runout of the chamfer on the inside corner is not complete, resulting with that shown in your picture. If you look at the upper bite, you can see the radius of curvature of the bite being the same from front to back. The radius of curvature are not different, it just the way they were chamfered.

Ken
 
I see what you mean, but if the radius of curvature of the workpiece exceeds that of the bite only those inner two corners will make contact. Think about gripping hex stock with those jaws.
 
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