It's a good idea to regularly tram the mill head with an indicator to make sure it's maintaining a proper alignment with the table. It's more convenient if this operation can be accomplished with the milling vise installed. Having two preset positions and utilizing a Starrett 196, this indicator holder can sweep the mill table with the vise installed to check head tilt and can also sweep a circle in the center of the mill table to check head nod as well.
For the past few years I've been checking the head tram when the vise was off using a Starrett 196 and some of the hardware included with the indicator kit. Years ago I made a setup to check the head tram with the vise installed using a dial indicator and a couple of 1-2-3 blocks, but I found I prefer using the 196 with a large tip as it can easily sweep the table directly. Now I have a spare 196 with a snug that I wish to dedicate to an indicator fixture just for sweeping the mill table so it's time to get building.
The beginning of the project. At the upper left is the old dial indicator setup. The only thing that was purchased specifically for the current fixture project was the 1/2" dowel pin.
A scrap piece of 1" square tubing will provide the body of the indicator fixture. It's always a good idea to build this type of fixture as strong as possible for measurement repeatability. It's surprising how much flex you can induce while using these fixtures.
The hole for the 1/2" dowel pin has already been drilled and reamed and the dowel pin was pressed into the tubing. Here the holes for the rod holding the indicator are being reamed for a precision fit.
The indicator rod will be held in place with a knurled knob. A brass rod is installed into the end of the knob to avoid marring the face of the indicator rod.
The indicator rod was recycled from the old 196 fixture. Here I'm rounding off the end of the rod with the boring head ball turner.
The completed body of the indicator fixture with two plastic end pieces installed. Two holes in the side of the fixture body were tapped for the knurled knob that holds the indicator rod. The indicator rod had the end turned down to fit the snug.
The completed indicator holder with a Starrett 196. A hole was drilled into the plastic cap so the indicator rod can be stowed inside the fixture body.
Here the indicator is sweeping the table using the inner hole. In this way the entire table can be swept to check both head nod and tilt. Since this mill doesn't have an adjustable head nod (it's bolted-down to the column with shims) the nod shouldn't change but it doesn't hurt to check once in awhile. Of course the head tilt can be checked at the same time. Ideally the number shown on the indicator shouldn't change while sweeping a circle on the table.
Using the outer hole of the fixture, the indicator is sweeping the table around the milling vise checking the head tilt. This is great for a quick check while using the mill in case you do something stupid and fear you changed the head tram. Compared to the earlier indicator sweep using the inner hole, the larger amount of distance from the spindle to the indicator makes this check more accurate.
A video detailing the exciting head tramming action.
For repetitive jobs like head tramming, it pays to expend the effort and make a dedicated fixture that will save you time and frustration. The easier head tramming is to do, the more you will actually do it which may lead to more accurate work. It also removes some of the reluctance to use the mill's head tilting feature.