Tramming a bench top mill.. Y-Axis

[Pcmaker]

I have a Precision Matthews PM-25MV mill and I've been working on tramming the X axis. I got it to a few thou from end to end of the table. The problem will be the Y Axis.

I put an indicator on the table, and from front to back, it's off by about 6 thou. Pretty much the only way to tram it is to add shims, which I'll be using automotive feeler gauges. The plan is for me to loosen the 4 allen bolts and add .006 worth of feeler gauge in between the front of the Z axis column.

Any useful tips to tramming the Y-Axis of a bench top mill?

 

[Groundhog]

I also used feeler gauges to tram my Syil X4+. However I could get a tenth or so just from torquing the front/rear bolts a little differently. It didn't matter how much planning I did, it took more trial and error to get it right than anything else.

 

[rwm]

How exactly did you measure this?
Robert

 

[Pcmaker]

Im thinking once I get the X axis trammed, I want to tack 4 small welds so it doesn't move again, then I can focus on tramming the Y Axis. I'll never use the adjustable head and even if I did, I can just grind off the tacks.

How exactly did you measure this?
Robert

Spindle indicator, measured the back of the table and moved the table to the back, watching the indicator move 6 thou

 

[rwm]

I don't think that proves you have a error in the square of your column. That is a different problem.
Robert

 

[RJSakowski]

Spindle indicator, measured the back of the table and moved the table to the back, watching the indicator move 6 thou

What you are actually measuring is a non-parallel condition between the y axis ways and the table top. If you think about it, the indicator in spindle is stationary while the table moves under it. The indicator could be mounted on any external surface to make the same reading.

One cause for this type of measured difference is loose gibs. As the center of gravity of the table shifts, it can cause the table to lift and tilt.

 

[rwm]

To check the Y axis squareness with the Z, use a cylinder square or precision ground square. Mount the indicator on the spindle touching the square surface. Then operate the Z axis and note the reading over the travel. If the Z axis is square you can then move the spindle feed and check the spindle squareness as well.
HOWEVER, if your Y axis is not parallel to the table top as RJ mentioned all bets are off. Tighten the Y axis gib and recheck that.
You could use a 2 dial tramming indicator however that will measure the sum of the Z axis error and and spindle error. You could theoretically have (for example) a 5 deg error in the column and a matching 5 deg error in the spindle and that indicator would read 0.
Robert

 

[Pcmaker]

If I'm not mistaken, then does this mean that my work piece will be square even if the Y axis isn't? I'll just not get a good finish?

I don't have a cylinder square, just a regular machinist square. I'll mount an indicator on the headstock and run the Z axis up and down the square to see if the needle moves. Unless I'm misreading your post.

 

[RJSakowski]

I have the problem with table lift on my Tormach 770. I discovered it when I mapped my table surface. The gory details are in post #2 in this thread: https://www.hobby-machinist.com/threads/g0704-accuracy-question.60622/#post-499447

To get around issues like this when tramming a mill, I mount a piece of aluminum to the table and mill the face. If this is done with the table in a fully supported position, in an balanced condition, and with tightened gibs, Table tilt shouldn't come into play. The faced surface should be parallel with the ways. Tramming can then be done in the usual fashion to this surface.

As far as mill alignment goes, it differs with the type of mill. My mill drill has a spindle in a quill for vertical motion. The Tormach has a fixed spindle in a head which moves on vertical ways. The G0755 mil has both vertical ways and a movable quill. Knee mills accomplish vertival motion with the knee and a movable quill. Proper mill alignment requires proper sequencing of the various adjustments.

 

[ttabbal]

I can't offer any advice squaring a bench top mill. However, I would advise against welding, even tacks. The heat is likely to cause some movement, and with a precision surface even a little bit matters.