Tramming Tool Idea From Mr Pete

[Oldvetteman]

Mr Pete just posted this. It's so simple, I wonder why nobody thought of this before. I will make the collars for the Dial Indicator and also try for a smaller set for a DTI.

I

I just unscrew my dial indicator setup from the magnetic base, put the threaded end of the shaft in a collet in the vertical mill spindle. A few adjustments of the clamps, rods and indicator and Robert is your mother's brother.

 

[RJSakowski]

Here's maybe a stupid question. I've watched this video, and others. I made something a few years back for dual indicators, but lost it or threw it away. I didn't trust it, because I don't trust myself. So here's the maybe stupid question. Nobody talks about there being any requirement for the drilled holes to be perfectly perpendicular to the horizontally suspended portion. Is that because there isn't a precision requirement? If not, why not? Thanks guys.

It is not a requirement as long as the holes aren't so far out as to invoke a cosine factor. The dial indicators are zeroed on the same point 2hich calibrates them. If you had an error of 5º in the angle, the cosine factor would be .996. Assuming your head were out of tram so you had a .010" difference in the tram readings, that error would only amount to ,00004". As you make your tram adjustments the difference in readings should be less than .001" so the error would be less than 4 microinches. And a 5º out of square condition would be highly noticeable.

What is more important is that the ends of the probe on the dial indicators be the same distance from the spindle axis. The reason for that is when to calibrate thedial indicators, you want the contact point to be as close to the same as possible to reduce the possibility of having different calibration heights. But even that isn't all that critical. In most cases, being within .1" should be sufficient and that would be some fairly sloppy machining.

 

[RJSakowski]

I should point out that the proper way to calibrate the dual dial indicator is to use the same point to calibrate each. Mr Pete did a video some time ago where he was using a dual dial tramming indicator and he zeroed the dials by resting the indicator on a flat surface. This is wrong for multiple reasons. Firstly, if there happened to be a divot or burr in the surface that would affect the calibration. Secondly, if for some reason, the tramming tool shank was not perfectly square to the beam, there would be a calibration error. And lastly, even if the tramming tool was perfectly made, if there was angular runout in the spindle chick or collet, it would result in a calibration error.

 

[jwmay]

Not too important, but I should qualify my concern I guess. Way back when I bought my mill/drill, I had read that you probably would have to shim the column/base interface in order to make it right. So I made the indicator thing, and got to work shimming. After a few multi hour days, I thought I had it perfect. Then I spent three years making crooked parts, and filing them to fit, and assuming I just sucked at this, or the vise had a problem.
Long story shortened: When I moved, I took the shims out during disassembly and decided to leave them out. After all, everything I make is crooked anyways. What did it matter? Ha!
The mill is more accurate without my interference/indicator thing/shims. The end.

 

[RJSakowski]

Not too important, but I should qualify my concern I guess. Way back when I bought my mill/drill, I had read that you probably would have to shim the column/base interface in order to make it right. So I made the indicator thing, and got to work shimming. After a few multi hour days, I thought I had it perfect. Then I spent three years making crooked parts, and filing them to fit, and assuming I just sucked at this, or the vise had a problem.
Long story shortened: When I moved, I took the shims out during disassembly and decided to leave them out. After all, everything I make is crooked anyways. What did it matter? Ha!
The mill is more accurate without my interference/indicator thing/shims. The end.

An assumption which is commonly made is that the surface of the mill table is flat and parallel to the x and y ways. This can be false for a number of reasons. The table can be worn from use or it simply could have been improperly manufactured. A third cause is loose gibs. At extreme positions, a loose table can pivot due to the center of mass extending past the support. This will lift the table closer to the mill head , having the same effect as a non parallel table or a worn table. This is more of a problem with CNC mills as the gibs have to be loose enough to permit free travel.

Tramming a mill head will not compensate for an issue with cutting non parallel parts. Tramming to a table whose surface is not parallel to the x and y ways will not be a accurate tram. Consider a mill whose table is perfectly parallel to the ways. Now put a poorly machined vise on the table and mount a bar and tram to the bar. Since the bar is tilted, the head will now be tilted to match. If a facing cut is made, the table will move parallel to the ways and the bar will now have a taper. Additionally, the faced surface will have a slight dish. Not really noticeable with small end mills but more so with a facing mill or fly cutter.

When tramming. I first mount a sacrificial plate and skim cut a circular path to match the tramming tool using a small diameter end mill. Using a small diameter end mill will minimize any effect of an out of tram condition. This ensures that the tram path is parallel to the ways. On a manual mill, the circular path would be difficult to cut so just having freshly milled pockets at the four compass points would be sufficient. The condition of the surface of the table can best be assessed by sweeping the surface of the table with a dial indicator or test dial indicator. A series of parallel sweeps will identify any problems.

 

[gard]

I think you are correct. Tramming only shows that the spindle axis is perpendicular to a line defined by the 2 points that indicators set on (or the plane of the circle if you are rotating the indicator thru 360 degrees). Next put the indicator directly on the table (or a parallel sitting on the table) and crank the table in that direction. This will show if the top of the table is parallel with the V ways on the bottom. If its not you will be cutting tapered parts.
I had not thought about milling a sacrificial part to use for tramming. I did tram my mill once by indicating one spot on my part then rotating the spindle 180, cranking the X axis to bring that point under the indicator. That was a lot of cranking back and forth but I had a large part fixtured to the table so it seemed like my only option.