Yesterday I installed the "Large Table Assembly" and the "Air Spring Kit" from LittleMachineShop.com, so today was the time to tram the column and the head. I've seen some people tramming the column by attaching a dial indicator to the quill and adjusting the column unti the reading on both end of the table are equal. There is one huge flaw with this method: it doesn't tram the column, it trams the spindle. If you look carefully, the head is composed of two castings. The part that holds the bearings and the spindle is held by grou long bolts, and, you guessed it, is not always parallel to the dovetails. A tell-tale sign that your mill has this problem is when you jobber drill bits miss the spot that you started with the started drill bit. Essentially the head is perpendicular to the table but the column being at the angle offsets the head in the X axis as you move it up and down.
Tramming The Column
|Square Secured on The Table|
The best way I found to tram the column is to use a good machinists square and a dila test indicator. I secured my best square to the table, locked the column and mounted the dial test indicator usina a quill-style holder (so the indicator is offset enough to the side to avoid the head hitting the square). On the setup is secured, I loosened the giant nut at the bottom of the column, leaving it just snug enough to hold the column in place. From that point on the method works as follows:
- move the head all the bottom
- zero out the dial test indicator
- move the head to the top of the square
- adjust the column until the indicator reads zero again
- repeat a few times
Now, the tricky part is that the squares aren't perfect. My "good" square is certified to have .0001" runoff over 6", but the price tag was over $100 (and I still don't trust it 100%). Fortunately, the problem is easy to solve: after the column is trammed, turn the square around, turn the spindle 180 degrees. and repeat steps 1-3. [you need to turn the square, not just read the other side]. If you don't ged a zero reading, your square is off. At this point simply adjust the column to read zero at the bottom and 1/2 of your reading at the top. At this point all that's left to do is to tighten the nut and double check the tramming.
Note: in most cases the column on the Harbor Freight/Grizzly mini mill doesn't need to be trammed, and chances are, yours is spot on. My original setup was spot on, but when I first installed the table, the column was really crooked. If yours has this problem, unbolt the 3 screws holding the column pivot to the tabe and see if the surface is clean and burr free. Take a look at the previous post describing the alignment problem I had.
Tramming The Head
|Head Tramming Along X Axis|
Once I confirmed that the column is perpendicular to the X axis, I moved on to tramming the head. This procedure is a bit tricky, since the bolts holding the front casting are normally hidden. I removed the column, loosened the bottom two bolts completely and left the top two bols just snug enough to prevent the head from easily twisting. After reinstalling the head on the column, I attached the dial test indicator using a quill-style holder.
The tramming method works on the principle of isosceles triangle theorem, or more precisely, on the property of the altitude of isosceles triangle... OK, just kidding. The method is as follows:
- swing the indicator to one side of the table.
- zero out the indicator
- swing the indicator 180 degrees
- note the difference between the reading
- adjust the head until the indicator reads 1/2 of the difference
After repeating this a few times, I had to move the head high enough that the top two bolts become accessible. I tightened the two bolts as to almost full torque, removed the head and tightened all 4 bolt to full torque. Once the head was reinstalled, I rechecked everything one more time, just in case. The whole process took a solid evening, but good portion of that was caused by the unexpected disassembly (to fix the base casting problem). The column is aligned to within 0.0005" in the Y axis and spot on on X axis. The head is close to .002" off when measured over 13" (swinging the indicator). This is as close as I could get without drilling out the holes, but at this point this is pretty darn good for Harbor Freight mini mill.