Machining A Vise Square

[lpeedin]

I purchased a new milling machine a few weeks to step up from my mini-mill that has served me faithfully. When I did, I went ahead and got a larger vise to suit the new mill. The vise was relatively inexpensive so I didn't expect it to have Kurt quality. However, I found that when milling a pice of stock approx. 6" long, I was getting approx. .004 - .005" of variation along the X axis, which is a little more than I would accept. I was getting approx. .002" of variance along the Y axis over 4", so that wasn't too bad in my opinion.

I figured that now with my bigger mill, I could mill the vise flat. I proceeded to flip the vise over on its ways, clamp it down lightly, just enough to hold it, and milled the bottom. Then I stoned the bottom. What I found is that when I flipped the vise back over, I had the slightest amount of rock in the base. I could still fit a feeler gauge approx. .0015" thick under one corner.

So, I lightly clamped the vise down and milled the ways. Then flipped it over and checked. Same thing, there is a slight rock. I then checked my mill table, and double and triple checked the vise. It appears that the vise is flexing ever so slightly when I clamp it down and this is transferring into the cut.

So, with the vise clamped lightly. I actually hand scraped everything and stoned the ways again. Now I am within .0005" in both axis'. But, when I unclamp it, the vise springs back and then there is .002" or more deflection.

I was thinking of using a feeler gauge to check where the base doesnt meet the table, then install shims as needed to insure the base is held flat when I clamp it down lightly. Then mill the ways. Then flip it over and repeat. Anybody have any other suggestions?

Thanks,

 

[Vladymere]

Have your trammed your mill to the table and then the vise to the head?

Vlad

 

[Andre]

The vise sounds like it's springing because the vise bottom isn't flat. When clamping it you deform it flat, mill everything parallel, then when it springs back everything goes wonky.

1. Don't clamp anything, scrape the bottom flat.
2. Make sure there is no rock anywhere on the mill table
3. Clamp the vise down lightly and dust the surface of the ways
4. Un-clamp the vise, bring it over to the surface plate and see if everything is flat and parallel.

If there is no rock after your good to go, stone the milled surfaces and tram your vise in.

 

[kd4gij]

That is a good job for a surface grinder. That is how I did mine. But most don't have one.
The problem on a mill is unless you have a fly cutter large enough for 1 pass cut. The mill would have to be trammed dead nuts and that is almost impossible

 

[lpeedin]

Mill is trammed. Head to column, column to table. Not sure hot that would have any effect on the vise being square? The only issue an out of tram mill would ha e is that it would leave ridges with each pass of the end mill.

Scraping the whole bottom is beyond my capabilities. I wish I had access to a surface grinder, then this would be a non issue. Anybody in central North Carolina have a surface grinder I can use?

 

[Andre]

That is a good job for a surface grinder. That is how I did mine. But most don't have one.
The problem on a mill is unless you have a fly cutter large enough for 1 pass cut. The mill would have to be trammed dead nuts and that is almost impossible

You might leave slight ridges between cuts but the entire area will still be flat. A flycutter is just a larger endmill, whatever problems you have with an endmill your going to double, triple, or quadruple the error using a flycutter.

 

[Andre]

Scraping the whole bottom is beyond my capabilities. I wish I had access to a surface grinder, then this would be a non issue. Anybody in central North Carolina have a surface grinder I can use?

You don't /have/ to scrape it flat. You can mill it, but be very methodical in how you hold it on the mill table and make sure it doesn't flex in any direction.

 

[chips&more]

You might leave slight ridges between cuts but the entire area will still be flat. A flycutter is just a larger endmill, whatever problems you have with an endmill your going to double, triple, or quadruple the error using a flycutter.

Very true Andre! You are much better off taking narrow passes with an end mill. Both the end mill and fly cutter will leave there own undesirable finish. But when using an end mill the project should have a flatter overall in plane result. A surface grinder or Blanchard grinder would be nice to have right about now…Dave

 

[mattthemuppet2]

could you also be relieving stresses when you remove metal? That might result in a warp too? It seems like one of those tricky problems where you need one surface to act as a reference to get another surface right, but you can't get that original surface flat.

as a general question - is there any way to blue the bottom and then carefully shim and clamp so that you have the base in its "natural" state on the mill table? I.e. if you know that the center is 0.005 high and both sides are the same, could you clamp it so that you use a DTI in the quill to make sure when clamped down the center is still 0.005 high and both sides are the same? Then if you take that off 0.005 off and reblue, the base should be mostly flat. Is that feasible?

 

[lpeedin]

mattthemuppet and Andre, both of you are thinking along the lines of what I was thinking. I figured that the ways have the least amount of surface and they will sit very well length wise on my mill table. So I was going to flip the vise over on the ways and then use a feeler gauge to identify gaps that could use a small amount of shimming so that when the vise is lightly clamped, I wouldn't torque anything. But I like your idea about bluing the bottom.