Mill vise problem

[kmanuele]

I was machining a piece of big box mystery metal square using parallel bars. I noticed that when I tightened the vise the parallel bar on the fixed jaw would become loose, and I couldn't tap it down onto the parallel. I finished the job anyway and noted that there were lines where the end mill overlapped. Barely sensible but there.

Putting the work piece back in the vise, I found that as I tightened the vise the edge of the work piece against the fixed jaw would rise up off the parallel. Loosening the vise, I could feel and hear the piece drop back down onto the parallel. It didn't matter which way I flipped the work, or if using a soft rod on the moving jaw.

Everything on the vise seems to check out, except that the fixed jaw base is tilted forward toward the work piece.

I can easily shim the jaw make it square but I wonder if this is intentional, or a mistake?

 

[mmcmdl]

The problem is most likely not with the vise . Are the sides that are in the vise square or do you have a basically a parallel -agram situation ? Try clamping with a piece of round stock on the jaw . These are all basic squaring up procedures .

 

[markba633csi]

Usually with cheap vises the movable jaw will be the one that rises when tightening. As mentioned, there is a procedure to follow when squaring stock to get the best result. Your fixed jaw might be a bit out of square or the bolts are loose
Often you can use "buffer" pieces of wood between the work and jaw to add some crush and reduce clamping error

 

[Papa Charlie]

Not suppose to be like that. Check all of the vices surfaces (jaws and bed) the surface with a dial indicator in the spindle on both X, Y and Z axis. This will help you identify if there is a problem between the vice and the mill.

It appears though that the problem is in the tolerances of the vice itself. It appears that the fixed jaw is removable. If so remove it and check the jaw for squareness and the base that it sits on. It may be just a poorly assembled (dirt or something else throwing it off) or poorly machined part. If it is poorly machined you can either have it ground if it is actually hardened (questionable with Chinese product) or machine it if it isn't too hard. Last resort and not the most desirable would be to shim the jaw, but this will create a weak point that could and will most likely cause you problems down the road.

 

[Mitch Alsup]

I have a similar vise.
I had to completely disassemble the vise, wash every single part in WD-40 in order to get all the machining/grinding crud out.
After reassembly it has worked well ever since.

 

[benmychree]

Another proposition is to use vise hold downs (available from Starrett or other providers) They sit on parallels, either ones supporting the part or another set, and engage the vise jaw and the part on both jaws, they are angled so that they force the part down tightly. HAving said that, it is obvious that the vise needs TLC.

 

[kmanuele]

I used a soft copper wire as a buffer when initially milling, and during these tests.

I flipped the piece over and around in all permutations and it still lifted on the fixed jaw, never on the moving jaw (which is square to the vise base).

As a sanity check, a 1-2-3 block in the vise in all three dimensions gives the same effect.

The rise off the parallel is a little over 0.001".

 

[kmanuele]

I have a similar vise.
I had to completely disassemble the vise, wash every single part in WD-40 in order to get all the machining/grinding crud out.
After reassembly it has worked well ever since.

Understood. This one, a clone like others, is from a more reputable vendor, and is pretty clean. No crud, no voids in castings after machining, etc.

 

[JimDawson]

Some years ago I has a similar problem with a good quality import vice. Mine was a 6 inch. The fixed jaw would tend to lift. I also checked that the top and bottom of the vice was parallel.

So to fix it I drilled and tapped through the fixed jaw and replaced the original 1/2 screws with longer 5/8 grade 8 bolts and torqued them to about 300 ft/lb. This required opening up the pockets for the bolt heads on the bottom for socket clearance. Then I cut a chamfer on the bottom of the fixed jaw to allow end mill clearance for the next operation. Once this was done I carefully trammed in my mill and took a cut on the fixed jaw to insure that it was square to the table. All of this pretty much ended the problems.

Later I bought a couple of Kurt vices and have not seen this problem with them.

Also I don't use hard jaws, I make mild steel or aluminum soft jaws as needed. This allows you to take a cut on them any time it is needed to square them up.

 

[kmanuele]

Solution:

I put a narrow strip of 0.002" shim stock behind the bottom edge of the movable jaw. It is now (or nearly) square with the vise base.

No more lifting, and the work piece stays down onto both parallels when tightening the vise.

Thanks for all the input.

Some years ago I has a similar problem with a good quality import vice. Mine was a 6 inch. The fixed jaw would tend to lift. I also checked that the top and bottom of the vice was parallel.

So to fix it I drilled and tapped through the fixed jaw and replaced the original 1/2 screws with longer 5/8 grade 8 bolts and torqued them to about 300 ft/lb. This required opening up the pockets for the bolt heads on the bottom for socket clearance. Then I cut a chamfer on the bottom of the fixed jaw to allow end mill clearance for the next operation. Once this was done I carefully trammed in my mill and took a cut on the fixed jaw to insure that it was square to the table. All of this pretty much ended the problems.

Later I bought a couple of Kurt vices and have not seen this problem with them.

Also I don't use hard jaws, I make mild steel or aluminum soft jaws as needed. This allows you to take a cut on them any time it is needed to square them up.

re: hard jaws. good tip. Maybe a next newbie project.