Squaring a Vise on a Mill - Machine Like a Pro

Squaring a vise is an important step to complete before you start machining.  If you work in a shared work space, it is always a good idea to check before starting your project.  It's not that hard and after doing it a few times it will only take you a couple minutes.  

Dial Test Indicator (DTI)
R8 collet to hold the dial test indicator (typically 3/8")
Dead blow hammer
7/8" wrench

Ensure both the mill table and bottom of vise are clean and free of debris.

Using the channels (t-slots) on the mill table, align the back jaw (fixed) with the t-slots by eye.  

Our bolts are too long, so we need a spacer below the bolt to make it work.  Install on both sides.

We need to create a pivot point on the vise for fine tuning.  Tighten one bolt approximately "monkey tight" and leave the other bolt a little loose.  Where is our pivot point on the vise above?  Answer at bottom right.

Put the mill in low gear.  This prevents the spindle and our dial test indicator from rotating.

Use a lot of care with dial test indicators; they are very precise instruments and typically cost more than $100.  If you drop the indicator or expose it to an excessive amount of shock, it won't be as accurate.  A machinist is only as good as his measuring tools.

To square the vise, we position the dial test indicator on the fixed jaw and note the value on both sides.  When both values are the same, BAM!, the vise is now square.  You can continue being awesome.

It's easiest to lower the quill to position the dial test indicator on the fixed jaw.  You could also raise the knee of the mill to bring the vise/table to the top (this would be a more rigid position and is recommended during milling operations), but this takes quite a few turns and isn't necessary.

Quiz: Is the quill locked or unlocked?  

Is the quill locked or unlocked?

Move y-axis (bring the vise towards you) so indicator touches the fixed jaw.  You only want to deflect the needle on the indicator a few thousandths.  

We are starting on the left side of the vise.  You only want to deflect the needle on the indicator a few thousandths (a few big tick marks).

Big tick mark to big tick mark are thousandths (.001").  

Small tick mark to big tick mark are half-thousandths (.0005").  

This dial is reading, in machinist lingo, "a little more than ten and a half thousandths (.0105)."  Remember that value.

Now that you're here, hit the back button and look at the needle on the dial.  Where is it?  Press forward and come back here.

Move the indicator to the right side of the vise.

The indicator is now on the right side of the vise and the needle shows about 9 thousandths.  The difference between the left and right side is one and a half thousandths.  

We need to adjust the vise so both values are the same.  

Using the numbers here:

Right Side = .009"
Left Side = .0105"

Left Side (minus) Right Side = .0015"

.0015" is the maximum amount we want to move the right side (towards us).  

Lightly tap the vise with a rubber mallet (dead blow hammer) to rotate the vise towards you.  Rotating it towards you increases the value on the indicator.

After lightly tapping with the dead blow hammer, here's the new value (.0105").  Let's check the other side!

Here on the other side (left) the indicator now shows 11.5 thousandths, it was 10.5 thousandths.  Let's go back to the right side and slightly adjust.  

Now I'm on the right side.  Tap, tap, moving the vise towards me makes the value increase from 10.5 thousands to 11.4 thousandths. 

I like to adjust the vise while reading the indicator only on one side.  In this case we are measuring on the right side.

Let's go back to the left.

BAM POW.  11.5 on left 11.4 thousandths on right.  


Since this indicator is accurate to .0005" (half thousandth) as stamped on the dial, I'm calling it good.  

It's time to tighten down the bolts and secure the vise to the table.   

Monkey tight, not gorilla tight my friend.  There's no need to go freakishly tight on machine tools...especially when you have a long wrench that gives you a lot of torque.  

It might be hard not to rotate the vise as you do this, so try to do it carefully.   

Run the indicator across the vise as a final check.  If it moved slightly while tightening and it's something you want to correct, you can give it a little tap while it's fully secured.  This last ditch alignment is ok and will only move .0005".  If it's still way off the mark, repeat the steps and get it aligned.  Tightening a bolt to be a snug pivot point takes a little practice.  

Unlock the quill, retract the it, and remove the dial test indicator and collet.  

You are awesome.  Now go make something great!