3 Effective Methods for Tramming a Milling Machine
Tramming is a fundamental process in any machine shop equipped with manual milling machines. The process consists of checking and adjusting the squareness of the mill to the top of the machine table, AKA the tram.
The goal of tramming is to make sure that the cutting tool is perpendicular to the table surface in both the X and the Y directions to avoid the formation of a saw tooth pattern on the milled surface and to ensure that the milled surfaces are mutually perpendicular.
A mill head’s tram should be checked fairly often, particularly if the machine features a swivel head that is designed to cut at angles other than square. At the very least, the tram should be checked at the beginning of every new project, although most machinists check the tram when they come in every morning since they share machines with other machinists.
There are several different methods and tools that can help you get your machine in tram. Let’s look at the most common and most reliable ones.
Tramming with a DTI
One of the most common methods for testing the tram of your machine is using a dial test indicator (DTI). The process is fairly simple, it’s accurate and doesn’t require a big investment since most of the tools required should already be in your toolbox. The method involves attaching the DTI to the spindle of the machine and test that the readings of the indicator are the same along two points of the X-axis and two points of the Y-axis.
- DTIs (see our recommendations here)
- Indicator holder (either with clamp mount or shank mount)
- 1-2-3 blocks or parallels
1 .Remove any vises and clean the tabletop thoroughly. It never hurts to use a brown India stone to remove any nicks and burrs that could give a false reading.
2. Attach the DTI holder to the spindle or insert it in the collet chuck.
3. If you are using 1-2-3 blocks or parallels, place them at an equal distance from the spindle along the X- or Y-axis, depending on which axis you are measuring first. The distance from the spindle, or radius, can vary. For accurate measurements, it’s generally recommended to set the radius at 6” or more.
4. Adjust the DTI holder to match the radius you selected.
5. Lower your quill until the tip of the DTI touches the parallel/table and zero it.
6. Swing the spindle 180 degrees and check the reading on the opposite side of the axis.
7. If the readings are the same, your machine is in tram. If the readings are different, adjust the head of the mill until the readings match.
8. Repeat the process on the other axis.
Tramming using a machinist square
The machinist square method is the simplest and quickest way to check the tram on your mill, although not the most accurate. All you need to do is position the machinist square on the mill tabletop, lower your machine’s quill and place the perpendicular side of the square against the quill. If the surface of the quill is in full contact with the square, your mill is in tram. If not, you’ll need to adjust the head. Just as with the previous method, you’ll need to check the tram of your head on both the X- and Y-axes.
A similar but more accurate alternative tool to the machinist square is the cylinder square. Although checking the tram is similar, the magnetic base that characterizes these tools makes them stable and guarantees perfect squareness to the table, making the process more precise.
Tramming using a spindle square
Spindle squares make the tramming process more accurate and faster. These T-shaped tools are designed to fit into the collet chuck and feature two dial indicators at the opposite ends of a bar that is perpendicular to the spindle. To tram your machine using a spindle square, follow these simple steps:
1. Insert the spindle square in the collet
2. Lower the quill until the two indicators are touching the tabletop
3. Check that the readings on both indicators are the same
4. Adjust the head orientation
5. Rotate the spindle 90 degrees and check the tram on the other axis
Before getting started with this method, it is important to calibrate and zero both indicators. In one of the many great videos featured on his YouTube channel, Keith Rucker provides a great explanation on how to do that. Here’s the video.
If tramming using a spindle square, here are some of the tools we recommend:
Which is the best method?
Although all the methods listed above are simple and accurate, we’d recommend the spindle square method. It’s simple, quick and accurate enough. The only downside is that you have to invest in a specific tool, but given the importance and the frequency of this process, it’s an investment that it’s worth making.
Do you know any other effective methods for tramming your mill? Let us know in the comments below.
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