3 Effective Methods for Tramming a Milling Machine

February 4, 2020 2:51 pm

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 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.

Tools needed:

Step-by-step process

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.

Cylinder Square

Magnetic Cylinder Square

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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23 Comments

  • Don says:

    Use a large bearing cup from a tapered bearing as the surface to indicate thereby avoiding any interruptions from the slots in the table

  • Greg says:

    Quick and easy. I use a calibrated block clamped in the vise (clamp the mating block on the other side). 2-4-6 blocks work well. Using the quill, indicate the x and y sides of the block. Adjust and the quill will be aligned with the vise. For table mounts, I’ll use gage stacks.

  • Morphine says:

    That big bearing race method is how I’ve done it for years. Good one Don

  • rudd says:

    So a couple of dial indicators maybe 6″ apart are more accurate than set up blocks a foot apart and a DTI? Horse hocky.

  • willray says:

    Cheapest method with surprisingly good accuracy – a bent coat-hanger and a sheet of paper: Bend coat-hanger into a “squarish Z” shape. Hold one end in a collet or chuck, raise the table/lower the quill until the coat hanger just contacts a sheet of paper placed on the table on the left or right (pick one) side. Rotate the spindle 180 to the other side and see if there is a gap. If there is no gap, lower the table, move the paper to that side, and raise the table/lower the quill again until you just contact. Rotate the spindle 180 again, check the gap. If it’s the thickness of your paper, you’re good. If not, adjust the tram until you contact the paper equally on both sides. Rotate the spindle 90 degrees and do the other axis.

    Most annoying part of this approach is waiting for the !#[email protected]$ coat hanger to stop vibrating, but, it’s cheap and because you can use a really long coat-hanger, you get the error-magnifying feature of using a really long radius arm.

  • Larry says:

    On knee and column machines:
    Ram must be indicated square with x axis
    On all machines:
    Quill must be fully extended
    And, of course, the indicator set up must be rigid

  • Bob says:

    Another way is a new brake disc. Both surfaces are ground parallel.

  • […] Spindle Square was mentioned in a great article on Practical Machinist on 2/4/19. The article discusses different mechanisms for tramming a machine and links to a video of Keith […]

  • Murph says:

    It all sounds easy, but I watched guys get so frustrated trying to tram a BP
    In. Especially in older machines, keep the head bolts snug and tap it in with a
    Soft hammer one axis at a time.

    • Chip Burns says:

      Murph,
      It is easy. It just takes time and practice. I have been doing this for over fifty years, and have found better(maybe not the best) ways to lessen the frustration and improve the accuracy and speed..
      The X axis basically a mirror image teeter-totter deal as the pivot point is in line with the quill/spindle center line. When the right side is raised .001″, the left is lowered .001″.
      The Y axis is where the fecal material can get in the high speed fan. In this case the pivot point is behind the spindle. This causes both the front and rear readings to raise or lower together, but as a ratio that is set by the radius of the swing.
      Let’s concentrate on the toughest axis(Y). Try to start with the front higher than the rear. Lock the quill and raise the table to add .005″ to the indicator. Swing to the front and pivot the head down to contact the table. Lower the table, swing to the rear, raise and repeat this process until you are square. At each adjustment, the angle decreases.
      You can establish the ratio for the Y axis with a bit of trial and error. On the 9″ table I believe it is somewhere around 1.3:1. Once that is confirmed, Rotate the indicator to the rear and zero on the table. Zero the elevation crank dial, and rotate the indicator to the front(high, remember). Raise the table to contact the indicator, observing the total amount on the dial, Let us use .033″ for an example. .033″x1.3=.043″ Now lower the table .043″. Use the Y axis worm to lower the indicator to the table. Lower the table to clear the indicator, and raise the table to the indicator. Swing to the front and check your results. I showed this to a group of juniors and seniors at a local vocational school. They set the mill at five degrees up. I was within ten thousanths on the first try. Then they started to pay attention and ask questions.
      Good luck

    • Chimera says:

      Yes, my 1958 M head can be a pain to tram on the X axis. Tightening the bolts just so, and tapping it in can be frustrating. I bolted a stop to the head collar and a block with a fine thread set screw to the ram, now it’s pretty easy to tram.

  • Ron says:

    I use a 6×6 granite plate and that provides enough area to suit my needs. If I feel that I need more area then the square granite plate becomes a diamond. I still prefer to use a single test indicator.

  • Wayne says:

    A good message, but, seriously, proofread your work.”It never hurts to use a brown”? What does that even mean?

  • jfischer says:

    Please consider
    The cutting path normal to the XY plane of a mill is defined by the bearing ways, and not defined by the table surface.
    The table surface is only a convenient place to mount fixtures and parts to be machined.
    The 3 methods described by PM as well as the methods described in the comments do not consider the surface of the machine table may not be parallel with the X Y plane due to manufacturing tolerances or wear.
    The desired result is when the spindle axis of rotation is orthogonal to the X Y plane.
    The following method is effective, doing that with high precision, negating any error in parallelism between the table surface and the X Y plane.
    This method may be used without removing parts or fixtures.

    The tool:
    • Fabricate a bar with two parallel holes placed with a center distance of less than ½ the travel of the cross slide, or the shortest axis of travel.
    • Press fit a 3/4″ dowel pin in one hole, ream the other hole 3/8” for DTI
    • cross drill into the 3/8” hole and tap for soft tip set screw to secure the DTI.
    (My manual mill has a more than 15” cross slide travel so my bar is aluminum 1.5″ wide x .75″ thick x 9″ long with 7.5” center to center on the holes)
    The procedure:
    • Mount the 3/4″ dowel pin of the bar in the spindle.
    • Use a marker to put a dot on the table or horizontal surface of an object on the table.
    • place the bar parallel with the axis, locate the indicator point on the dot then zero the dial.
    • Move the table 2 times the center distance of the pin and DTI
    (I move the table 15” for my bar).
    • Rotate bar to locate indicator point on the dot again.
    • Apply adjustments to remove any difference between the two positions.
    • Repeat for both axis in the plane.
    I use this same method even for the largest CNC machine tools.

    Jaime TSI

  • Larry Schweitzer says:

    Count me as one of the frustrated. I have an older Jet 9 X 49. Typical of used machines the ways are more worn near the most used areas. On my mill this is very apparent on the knee. The result is when I lock the knee the table tilts back. If I tighten the gibs the table binds or becomes loose depending on where I started. At least that is my excuse for somewhat variable results in my projects. I like the large bearing cone idea.

    • Chip Burns says:

      Hello Larry,
      I have made parts on Bridgeports that have had 1200# mold bases clamped to their tables. The underside of the flat table ways will wear away over time. I have tried to eliminate this on the new J2 that I bought around twenty years ago. I try to “move” the work envelope along the X axis, and by moving the ram in and out to force me to use as much of the 12″x36″ work area as possible. Another thing that was ground into my mind by the “old farts” that were thirty years younger than I am now, is that grease and oil is cheaper than cast iron.
      Another point that will extend the life of any machine tool, is to keep the spindle register tapers clean. On a Bridgeport, or any machine using split collets is prone to chips getting to the taper and sticking. The next collet will press the chips as flat as possible and the begin to create “dent burrs” in the mating surfaces of the collets and spindle. There are cleaning tools for the various mill tapers. This is not a recommendation(!) but I use a clean finger tip at at a low rpm, while being aware of the driving lug that is left in some machines. OUCH!!!!
      Always use the rear edge of the table as your zero point and then lower the head slowly to a zero at the front. Lower the knee to save buying extra test indicators, and the repeat this first cycle with the indicator at the rear. I have heard this movement called “nodding”.
      If there are any questions, send a pm and I will try to help with the steps.

  • Rando says:

    This is all fine-and-dandy for mills that can be adjusted with the mere turn of a knob/knut. What about these confounded CNC routers? From everything I’ve seen, some claim to have adjustable bearings/etc., but they never seem to actually talk about them. There certainly seems to be no standard “place” they can do that. Is tramming something router users just never bother with? That somehow every machine at every level is always fully and exactly constructed, assembled and calibrated? That’s strange, ’cause mine ain’t ;-).

    Thanks!

  • Mike says:

    TO: PRACTICAL MACHINIST/S……..Before any tram procedure, no matter how, the machine table(complete mach base)
    MUST BE LEVEL…..Use a “B&S Precision Level” to do the Leveling 1ST!………You/who won’t regret it……Mike Degaetano
    40+ years as a Journeyman, Machinist, Tool Maker and Machine Repairman, NYS Dept of labor Certified circa 1983-1988 to present, card # 8333.(480 861 1895, anytime for any Q’s). Great article… by the way….keep up the great work.

  • Chuck says:

    I use a new car or truck brake rotor. It’s flat within .001″ and about 12″ diameter. Just stone the top of the table and lay the rotor on top and indicate it. Work great!

  • Geof says:

    I found a 12 in ring with a 8 in hole, had it heat treated for toughness and ground it flat! Clean the table, set the ring roughly center
    then i use an Interapide indicator on an Indacol holder, then just rotate the spindle, usually gets you within .0005 or less, close enough for most Bridgeport work! I think the ring is about 3/4 thick, I like it better than 123 blocks because your indicator is always in contact!

    Geoffrey

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