Milling Vise Squareness

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kl7sg
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Re: Milling Vise Squareness

Post by kl7sg »

Maybe I am over simplifying this.

But, it seems an easy test, without machining anything would be to place shims under the vise to see if the will correct the Y axis tilt and jaw tilt.
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Mike
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Harold_V
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Re: Milling Vise Squareness

Post by Harold_V »

I'm not quite sure I understand your comments in regards to the Y axis. If the vise is set up with the vise ways parallel to the table of the machine on which the base would be altered (to correct the existing problem), the vise and its ways, after machining, would be parallel to the table on which it would be used. There would be no need to do anything with parallels aside from using a set that is already straight and of identical height. The only other correction I can imagine is if the alteration of the fixed jaw then created a parallelism error with the face of the moveable jaw.

Beyond that, if the assembled vise, before correction, had been ground parallel. In that case, the height and squareness of the jaws would have been altered by the correction. The tops of the jaws would no longer be parallel with the base. Having corrected the fixed jaw (for perpendicularity), the face of the moveable jaw would then no longer be parallel with the fixed jaw and may require correction. Am I missing something?

H
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kl7sg
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Re: Milling Vise Squareness

Post by kl7sg »

Now I understand your earlier post.

what I was thinking is the fact the ways are not parallel to the y axis is one problem.
And, the fixed jaw misalignment might be caused by the y axis misalignment. Thusly causing the appearance of two problems.

Placing shims under the vise to correct the y axis tilt might be a simple test to confirm this.
Anyway, I am just thinking out loud.
Have a nice day,

Mike
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Harold_V
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Re: Milling Vise Squareness

Post by Harold_V »

kl7sg wrote: Fri Jun 18, 2021 3:55 pm Now I understand your earlier post.

what I was thinking is the fact the ways are not parallel to the y axis is one problem.
I'm not sure that condition was of concern, but if it isn't parallel, then, yeah, it is of concern. A vise should replicate the degree of precision provided by the machine tool on which it is used. If it doesn't, it simply won't serve as it should.
And, the fixed jaw misalignment might be caused by the y axis misalignment. Thusly causing the appearance of two problems.
Of that there is no doubt, but that problem could be rectified my proper machining of the fixed jaw. At that point, the moveable jaw would need to be addressed, too.
Placing shims under the vise to correct the y axis tilt might be a simple test to confirm this.
I believe shimming is what brought this to our attention. Unless for a specific purpose, one normally doesn't have to shim, so if he/she does, there's something amiss with the vice, or the setup.
Anyway, I am just thinking out loud.
Yeah, that's what I'm doing, too. It's much easier to have the item in one's hands, where discoveries can be seen. It wouldn't take much to correct the errors, assuming a decent surface grinder and related accessories. That's assuming I understand the true condition of the vise. It's getting all too easy for me to get confused these days. Getting old!

H
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kl7sg
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Re: Milling Vise Squareness

Post by kl7sg »

Having hands on the equipment makes it pretty easy to evaluate problems.
Anyway, it will be interesting to see how this is resolved.

Cheers
Have a nice day,

Mike
Mr Ron
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Re: Milling Vise Squareness

Post by Mr Ron »

The way I would fix a vise would be to 1st disassemble the vise; turn the vise upside down and resting on parallels, surface grind the base. Then flip the vise right side up and surface grind the vise jaw tops. This would establish the relationship between the vise and the milling machine table. Parallelism between the table and the vise sliding surface would be addressed with shims. Just thinking off the top of my head.
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Harold_V
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Re: Milling Vise Squareness

Post by Harold_V »

Mr Ron wrote: Sat Jun 19, 2021 3:43 pm Parallelism between the table and the vise sliding surface would be addressed with shims.
If a vise is re-machined (ground or fly cut) as you suggested (that's precisely how it would be done if it was my project) there would be no need for shims. For that matter, I can't think of anywhere you'd put them.

By working from the existing ways of the vise, you establish parallelism with the base (assuming they are not distorted. They often are). As you suggested, grinding the tops of the jaws afterwards would create a parallel condition, but there has been nothing to address perpendicularity (there should be a 90° angle between the face of the jaws and the table), which most likely has issues if the vise isn't parallel at the outset. All depends on where the error was located. If the vise was parallel in the Y axis, but out in the X axis, it's possible that the end result would be a square jaw. Not likely, but certainly possible.

In my years of shop experience, I've often detected a lack of concern by even seasoned machinists with features that make or break a project. Those features are parallelism, perpendicularity and concentricity. That is often apparent when a machinist can't see the value of soft jaws.

H
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stephenc
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Re: Milling Vise Squareness

Post by stephenc »

Something here confuses me greatly .
So I don't get why a person should give a hoot about the top of the vise jaws except that they be reasonably close to each other to avoid tool collisions.

When I set up a vise all I care about is if the face of the fixed jaw is parallel to the axis I have it in line with and the z axis .
I want the top of vise bed that my part or parallels sit on to be level with the mill table , I could care less about the top of the jaws .
even if I use the fixed jaw as a reference point I still don't care about that top surface after all I should be using the same point for the entire job and unless you do something wrong that point isn't going to be moving .
KellyJones
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Re: Milling Vise Squareness

Post by KellyJones »

So I've been busy for a few days and am just now getting back to this. To answer some questions:

1. It's a Grizzly G7156 milling vise. Certainly not top of the line, but much better than the vise that shipped with the mill.

2. The mill is able to "nod" left and right, but not forward and aft. There is no adjustment in the fore/aft direction of either the head or the table. This is why an apparent misalignment in this direction is of concern.

3. I have not trammed the head recently, but then, I haven't moved it since I last trammed it years ago. After reading the various comments here, I think it's time to check it again. I doubt this is the problem since I run the fly cutter all the way across the work piece. I would think any tram errors would be washed out as the fly cutter cam around to cut on the back side.

4. I can tell my original post wasn't clear what the issue was. The table and vise appear to be properly aligned in both the X and Y axis. In other words, making a cut along either of those axes results in a part with nearly perfectly parallel sides. The issue is in the Z axis (parallel to the spindle rotation axis). Imagine setting a part on parallels in the vise, and then taking a single fly cut along the X axis. The resulting part has an inconsistent thickness when measured parallel to the Z axis. I forget the numbers now, but it was something like .005" as you moved along one axis and .007" as you moved along the other axis. This means the ways of the vise are not parallel to the table. I hope this clarifies matters.

Judging from the comments here, I take it this is not a common fault among vises.
Kelly Jones, PE
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pete
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Re: Milling Vise Squareness

Post by pete »

We all need to use the common accepted terms for anything or it creates confusion. Rotating the head around a point along the X axis would be called head tilt, having a milling head capable of rotating around a point in the direction of the Y axis forward or backward would be called the head nod.

IF? your mills spindle is still properly trammed and square to the table, the only way that non parallel cut in the Z axis could happen is the main reference surface we all use which is the top of the vice bed, is very seriously non parallel to the table. But if the part was sitting on parallels have you actually checked to see if they are in fact parallel and measure the same for each end to end? Some of the off shore ones are useless and there certainly not parallel. Not totally impossible, but more unlikely there's a serious issue with the way surfaces moving the vise and table either up or down in X. The table can be in a flat horizontal plane with the head trammed true to that, yet the ways could be raising or lowering the table as it's moved in either direction in X. As a start I'd open the vise jaw as much as possible, spotlessly clean everything, no chips or oil, set up a magnetic base against the rear column of the mill, zero the indicators tip on the top of the vise bed and as close to the vises fixed jaw as you can get without the indicator body touching the fixed vise jaw. Run the tables X axis so that indicator tip travels across in a side to side motion on the vise bed. Any difference from zero then write that down. Then run the table in toward the mills rear column on the Y axis and repeat the same test. Post the numbers here. Without some starting and basic numbers it's an impossible to diagnose issue. This test won't confirm if it's the vise or table ways that are out, only that there is a deviation happening and by how much. If you do see much more than .0005" - .001" change at either end of the vise bed or across it then pull the vise, strip it down to the bare vise bed and start indicating it on your surface plate I think you said you had for how parallel it is to the surface plate. Depending on the vise quality I'd still want a lot less than 1/2 a thou on a mill vise for across and along the whole vise bed though.
stephenc
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Re: Milling Vise Squareness

Post by stephenc »

I'm on the same page now .

So please don't lump my forward thinking here as a response you'd get from a serious machinist. Many many many others will have a far different attitude and opinion then me .

I have a grizzly mill and a grizzly 4inch vise . I did my best squaring up the mill and then the vise and ceased to give it a single thought to it after that .
It is what it is and I've gotten more value then one could expect for the money .

A little nod error isn't something I'm gonna concern myself with if I can't do anything about .
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Harold_V
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Re: Milling Vise Squareness

Post by Harold_V »

KellyJones wrote: Fri Jul 02, 2021 5:39 pm I would think any tram errors would be washed out as the fly cutter cam around to cut on the back side.
If the head of a mill is dialed square with the table, there is no change when the cutter touches the back side aside from creating a crosshatch. There is also no step created when either of the slides are moved and an additional cut taken without altering depth. If no cross hatch is developed, or if the back side of the fly cutter cuts deeper, leaving only a single track mark, the head is not square with the table.
The table and vise appear to be properly aligned in both the X and Y axis. In other words, making a cut along either of those axes results in a part with nearly perfectly parallel sides.
Unless you are comparing a machined surface against the surface of the part that is not machined (like cutting a step at the top of the part, with the balance of the part not machined) the vise has nothing to do with cutting parallel sides. That's a function of the machine slides. You could mount your vice randomly and take the same cuts with the same results. The only difference, then, would be in squareness, unless you machined all four sides in the same setup, or if you compared the newly machined sides against the sides that were not machined, below. They would be square and parallel to one another, but not with the jaws of the vise, or the unmachined side, because the vise was randomly located.
The issue is in the Z axis (parallel to the spindle rotation axis). Imagine setting a part on parallels in the vise, and then taking a single fly cut along the X axis. The resulting part has an inconsistent thickness when measured parallel to the Z axis. I forget the numbers now, but it was something like .005" as you moved along one axis and .007" as you moved along the other axis. This means the ways of the vise are not parallel to the table.
Not necessarily. If you have a typical vise, which it appears you do, unless you tap the piece down tight on the parallels, which MUST be parallel, the error may be in the vise not holding the piece properly. That's one of the reasons a Kurt has been so highly recommended. While they are not exempt from that condition, they do limit how much a part can rise up when the vise is tightened.

That said, if you find the part is tight on the parallels, you can do a quick test to see if the vise bedways are parallel with the table. Simply place a DTI in a height gauge which is placed on the table of the mill, then sweep the slideways of the vise from fixed jaw to the moveable jaw with the vise fully opened. If there is an issue, it will be displayed. Both sides should be tested, with both sides revealing the same reading. If there is error in the vise, it will be displayed by this method. If you find no error, and your part is well seated on the parallels, then you must suspect the the head has a nod that it should not have. Please take note that I am referring to tilt forward/backward as nod, which is the correct term.

There is another simple test to determine if the head is square with the table. Simply take a cut with a fairly large flycutter, then, using the saddle, move the fly cutter to another location, but overlapping the first cut. Take another pass without altering depth. If you find a step in the cut, then your mill is not square with the table. It may still create a cut with a crosshatch, as it is square side to side.

One thing to consider. If you have an error front to back, when you move the knee of your machine, you lose orientation with the spindle. The amount of error you find when doing the measuring you have done thus far is transferred to the part at the same ratio when you move the knee.

Does any of this make sense?

H
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