Adjustments Turn Conversation Pieces into Working Machines

My workshop is a disaster area right now, due to the recent arrival of my compressor, mill, and lathe. The lathe is up and running, although I have not leveled it yet. The other two tools are still waiting for my help. I need to get things squared away, because I moved about half of the stuff in the garage in order to get the additional tools in, and I can’t get to things I would like to use.

Last night I went to Lowe’s and picked up $75 worth of electrical stuff to hook up the mill. I could have gotten out of the store for $33, but I bought two extra parts: a plug and a receptacle, both for the mill.

I have been trying to decide whether to use a VFD on the mill, as I did in the past, or to connect it directly to my 3-phase power supply. The only benefit of the VFD is that it allows me to work without firing up the huge power supply. I have an uneasy, irrational feeling that the power supply (phase converter) is fragile, so I avoid putting unnecessary hours on it. It’s probably bulletproof. It came from a serious company that makes industrial products.

If I use a VFD, I’ll have to run a cord from a wall socket to the VFD, and then I’ll have to run wires to the mill. In Miami, this was an okay setup, because the mill was next to a wall. I was able to put the VFD on the wall, and when I wanted to turn it on and off, I simply reached over and pushed a button. This time, my mill is out on the shop floor, so there is no convenient place for mounting a VFD.

I decided to go with the phase converter, so I have to cut a hole in the cabinet, hook a cord up to the phase converter, and run the cord to the mill. In order to make life simpler in the future, I’m going to put a plug and receptacle on the cord so I can detach and reattach it at will in the future.

I’m going to run the cord over the roof trusses and let it drop down to the mill. This will keep it off the floor.

Once the cord is hooked up, the mill has to be adjusted.

Bridgeport-style knee mills have rotatable heads. They can nod in the xy-plane, and they can turn in the xz-plane. This is a great feature, provided you’re not afraid to use it. In order to use a mill in the vertical orientation, it has to be “trammed,” which means it has to be set up so it’s perfectly perpendicular to the table from every direction. Tramming a mill is a pain in the butt. Generally, people use indicators that measure to within a thousandth of an inch, and they sweep their tables holding the indicators in the spindle. If the reading on the indicator changes when you move the indicator, your head is not perpendicular.

I learned a neat trick for tramming a mill quickly. People get mad at me when I mention it, but it works very well. Even if they can argue that it’s not as precise as a test indicator, which is dubious, it’s a very quick way to get you within half a thousandth.

I have something known as an angle block. It’s a big piece of iron with a handle. It looks sort of like a clothes iron, except it’s rectangular. The sides are square to each other to a high degree of precision. To tram your mill, you put the angle block on the table, lower your quill, and rest the quill against the block. If any light can be seen between the block and quill, the quill is not square to the table, so you adjust it.

My quill is 6″ long. Using this method, I can get it square to the table within half a thousandth over that 6″ length. If you put a light behind an angle block and a quill when they’re pressed against each other, you will be able to detect light coming through when there is less than a half-thousandth gap.

That’s not too shabby for a job that probably takes less than 10 minutes for both axes.

Once you get below a thousandth, it becomes hard to improve things. You’ll get everything lined up perfectly, and then things will move while you’re tightening the mill’s adjustment bolts, and you’ll have to loosen them and start over. How hard you want to work on it depends on how accurate you want to be. The difference between half a thousandth and a quarter of a thousandth (or whatever tiny amount you can manage) is not going to have any measurable effect on your work. No one will ever look at a part you milled and say, “Your mill is off by three tenths of a thousandth.”

Tram problems show up when you use wide tools like fly cutters and face mills. These things put flat faces on parts, and the faces can be two or more inches wide. Let’s see. If your tramming is out by half a thousandth over 6″, it’s off by a twelfth of a thousandth an inch from the spindle’s center of rotation, where a 2″ cutter is going to be most affected by your laziness. Hmm. That’s even more accurate than I thought it was.

To machinists, a twelfth of a thousandth is the same thing as zero. It’s an incredible degree of precision. A machine that can hold a tenth is considered top notch. No one in his right mind tries to do better than that on ordinary machines. Once you drop down close to a tenth of a thousandth, you’re getting into the territory of precision grinders, and you’re leaving mills and lathes behind.

I have used the block to tram my mill and then produced a faced part that appeared to have a perfect finish, so the process seems pretty reliable to me.

According to the video I embedded above, anything within a few thousandths is good, so it looks like the angle plate method is the way to go. The man who made the video is a respected machinist.

I have been told that a real expert will tram his head so it’s not quite square in the xy-plane, to allow for deflection when the work is under pressure, but that’s too much aggravation for me.

Milling machines are usually used with vises, just like drill presses. You can use clamps instead, but they’re a lot of work. Most machinists leave their milling vises on their tables all the time, except for unusual jobs. The big problem with using a vise is that it, like the mill’s head, has to be trammed. You don’t want a vise which is angled to the table.

I don’t know of an easy way to tram a vise. You put your test indicator on your spindle, you rest the tip on the vise’s rear jaw, and you move the vise back and forth while watching the dial. You bop the vise with a soft hammer until the dial stops moving. It’s maybe a 10-minute job. Again, as in the case of the mill’s head, everything will try to move when you tighten the vise down, so sometimes there is a lot of repetition.

I guess it will take 45 minutes to wire the mill up, and I would budget half an hour to get everything trammed.

Once all this is done, I can feel like a machinist again, and I may even have the motivation to start arranging my welding area.