Machine vise how flat should the jaws be.

Bill D · Jul 3, 2018

I bought a old vise for a milling machine. It is in decent shape but the jaws are dished in the middle. The fixed jaw is dished in like 10 thousanths fairly symmetrical with the maximum in the middle. I have yet to measure the movable jaw.
I just have no idea if these jaws bend at all to remove some of that gap. Or should I consider them to be ridgid. This is a 5" vice if that matters. Not a more modern angle lock either. For now I have learned light cuts only. I think I will try a piece of index card between the jaws and the work.
I found numbers for how parallel they should be but not how flat. I suppose it needs to have the removeable jaws removed and ground flat. Any idea how much that will cost?
Bill D.

M.B. Naegle · Jul 3, 2018

What kind of vise?

I don't think they should bend at all. I surface grind hard jaws that are too out of line to grip. If you are holding small parts, .010 can be a big deal. If they were tightening it down enough to bend the jaw, it either was cheaply made, or they didn't know how to get the chips out between parts.

EPAIII · Jul 3, 2018

I have found several vises that I have used on milling machines to have jaws that were not flat. Instead of removing them for corrective machining or grinding, I usually just mount the vise on the mill table and use a long milling cutter to refinish the fixed jaw in the mounted vise. The table X slide should be adjusted fairly tight for this operation and the Y slide locked down. And tram the head square to the table first. If the vise has one or both sides machined or ground, you may want to take care to mill the fixed jaw square to that side(s).

As for the movable jaw, if it is off by a large amount, that can be more problematic. I do not recommend trying to machine them in place like the fixed jaw. Many movable jaws have some amount of looseness that will allow them to self align to the fixed jaw and, with care, you can remove them and machine or grind them flat. But the more expensive milling vises will have little looseness and you will need to be more careful about keeping/making the movable jaw aligned to the fixed jaw. This may require some careful measurements and testing. As a first attempt, I would certainly try a lapping session and check the results. You could also lap the fixed jaw after roughing it as I described above but I never have.

Whysosharp · Jul 3, 2018

If you have a surface grinder they will sit on a magnetic chuck without issue. After a few operator crashes we’ve taken jaws off and taken a thou or two off to fix them up

JRIowa · Jul 3, 2018

I bought a Kurt clone years ago. After a day on the surface grinder, it wasn't a bad vise. I'm guessing my Kurt is flat, square, parallel within 0.001"
JR

plastikdreams · Jul 3, 2018

Once I see any deviation over .0005 they come off and get ground....I have no tolerance for nicks and scratches on my jaws lol.

Bill D · Jul 3, 2018

Thanks, I really did not think they could bend enough to eliminate the problem. I will have to figure how to check to make sure how flat and at 90 degrees thy are to the rest of the vise and the table it sits on.
Bill D.

Whysosharp · Jul 3, 2018

Remove the jaw and run an indicator down the jaw block to see make sure the vise is square first. If it is then grinding the front and back faces of the jaw making it flat should resolve any issues. the jaw doesn’t need to be a perfect rectangle as long as the front and back are parallel to each other. I’m sure some would agonize over making the jaw dead nuts on 4 sides and even the ends but that is not critical to clamping a workpiece

DMF_TomB · Jul 4, 2018

Bill D said:
I bought a old vise for a milling machine. It is in decent shape but the jaws are dished in the middle. The fixed jaw is dished in like 10 thousanths fairly symmetrical with the maximum in the middle. I have yet to measure the movable jaw.
I just have no idea if these jaws bend at all to remove some of that gap. Or should I consider them to be ridgid. This is a 5" vice if that matters. Not a more modern angle lock either. For now I have learned light cuts only. I think I will try a piece of index card between the jaws and the work.
I found numbers for how parallel they should be but not how flat. I suppose it needs to have the removeable jaws removed and ground flat. Any idea how much that will cost?
Bill D.

.
remove back vise jaw and indicate surface back vise jaw mounts on is flat. both vise jaw mounting surface and the vise jaws can be milled. hardened steel i just use a 1" carbide end mill and only take .001" at a time
.
obviously if back vise jaw mounting surface is flat but at a angle you need to adjust vise and retighten bolts
.
if back vise jaw mounting surface is curved than somebody for some reason probably made it that way on purpose. not sure why

Conrad Hoffman · Jul 4, 2018

Maybe I'm just too fussy but jaws should seat solidly against the vise, or it should be corrected if they don't. The jaws themselves should be ground on the surface grinder and be true and parallel to 0.0002" or better. 0.010" might as well be a mile- that's unusable.

Larry Dickman · Jul 4, 2018

They should be flatter than my ex wife. And that's pretty fucking flat.

Danny VanVoorn · Jul 4, 2018

First thing I would check is the mounting surface, I can't imagine what it would take to dish a vise but it could happen. If the vise runs true and it's only the jaw that's warped/dished whatever then just mill it or grind if you're that picky. I would think the mounting bolts would pull some warp age out of the jaws but not if the vise itself is warped. Could also get some aluminum the appropriate size and make some soft jaws while your at it, I find them real handy for adding a parallel step or something along those lines when something special comes along.
Dan

Toms Wheels · Jul 4, 2018

After checking out the vise jaw mounting surfaces, if you can't find someone to grind them in CA, sent them to me. Just pay the postage.
Tom

plastikdreams · Jul 4, 2018

Conrad Hoffman said:
Maybe I'm just too fussy but jaws should seat solidly against the vise, or it should be corrected if they don't. The jaws themselves should be ground on the surface grinder and be true and parallel to 0.0002" or better. 0.010" might as well be a mile- that's unusable.

Precision parts call for precision tools...for the past few weeks I have been making some cmm fixtures. My height tolerance is +/-.002 from tooling ball center to tfg tip. Out of the 20 stands I've made 1 needed a shim to get in tolerance(my fault), the rest are .001 or less to nominal. All done on a Bridgeport. Moral of the story is, you can't do that with shitass jaws on a poorly cared for vise.

LKeithR · Jul 4, 2018

As others have said, check the vise body itself; if it's true then do a search for "Monster Jaws". They sell a ton of jaws at
very reasonable prices--should have something that will fit your vise...

qwhit · Jul 19, 2018

I made machine vises for 10 years and we ground a 'belly and taper' in each jaw. This was not much, about .001 to .0015 from top to bottom and edge to center. This caused the first contact point on the edge and top of the part. As pressure is applied the jaws flex to contact the middle of the part.

thermite · Jul 19, 2018

Bill D said:
I bought a old vise for a milling machine. It is in decent shape but the jaws are dished in the middle.

Then thou dish may as well be a mile, it is only 5", and it has no angl-lock or equivalent pull-down?

Don't bother even putting it on any mill with more balls than #2 Morse spindle.

Leave it as-is, relegate it to bench or drillpress, and go find a proper MILLING vise that does have pull-down.

Then you have something actually worth the effort of truing-up.

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Machine vise how flat should the jaws be.

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Bill D

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