Opening of machinist vises

josef

josef

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I have a basic question about the jaw opening specification of machinist vises. I ask this because I bought a 5" machinist vise from Precision Matthews several years ago when I bought my PM932 mill drill. I somehow thought that it would open 5" as well as have jaws 5" wide. But, it only opens to 2.1875" if I want to use the full jaw depth. If I want to hold something bigger I have to move the jaws around and I then don't have the full depth or the open area between the jaws.
So, are all machinist vises made this way? If the vise spec says "jaw opening 5.9" does that mean deep as in opening up with the crank or is is a marketing spec that means it will accept a piece 5.9" because the jaws are 6" wide? Is there a machinist vise made that say can hold a piece 5"x5"x2" between the jaws without moving the jaws around? I'm trying to come up with a way to ask the question to be sure it asks the correct question.
My question seems odd to me but it occurs to me that I never see a picture in an advertisement showing the vise with the jaws open to their deepest extent.
The vise I have is good. I've done a lot of good work with it. But I'd like to have something that opens farther.
 
So far as I know all mill vises are built the same way.
Other ore experienced folks may know of one that open as you describe.
 
I have 3 mill vises, and none are built that way.

8" Palmgren
The jaws are 8 5/16 wide, they open to 8 1/4", and are 1/2" thick.

6" Bridgeport
Jaws are 6" wide, they open to 6 1/4", and are 1/2" thick. I also have a set of 3/4" thick jaw faces that will only allow the vise to open 5 3/4".

4" Vevor
Jaws are 4" wide; they open to 4 3/4" and are 1/2" thick.
 
As far as I know when they state a vise size ie 3”,4”,5”,6”,8” that is telling you the jaw width. Not the open size which they usually call out in the spec sheet.
 
The typical machine vises like a Kurt or Bridgeport tend to have a jaw opening greater than the jaw width. My Kurt D688 is a 6" wide jaw model that opens over 8"...that's pretty typical. A 4" model opens over 6" in the same style.

Is it possible you have more of a drill press vise? Those often have less opening than width. Can you post a picture or a link to the one you have?
 
A picture of the vise would help. If it's a Kurt style vise then there's almost certainly something wrong with it, as they all open at least the same as the jaw width
 
I have to agree with @mattthemuppet2, my 4" Glacern vise opens to 4.5" on the inside jaws.
 
I only have 3 vises in the 80# and up category. I made sure before buying that all opened at least as wide as the jaw width (plus room for custom jaws). I like knowing that any vise in my shop will open and close on a part equal to the jaw width. It's not "a" rule of thumb so much as "my" rule of thumb. I absolve myself from any offense by declaring I'm "just saying" here.
 
I have a middling PM 4" vise, it opens up to 4.25". Also have a Kurt DX4 and it opens up at least that much. Are you sure there isn't something jammed in there preventing it from opening further?
 
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