[mattford1]

Hi Guys-

I'm a bit confused about tramming on the tormach and I'm sure it's something silly I'm missing...

I'm using the Edge Technologies tramming device. I currently have a Kurt vise in the middle that I'm not to keen to remove so I looked at the tram in X on either side of the table. The thing that I don't get is that if I measure on either side it gives me what I'm taking as opposite results. Pics are attached.

Essentially when I'm measuring at the left side of the table, it shows the right side needs to come up 1 thou. When I jog it and measure on the right it shows that the right side of the mill needs to come down 2.5 thou.

Same error in Y when measuring at opposite ends of the table. Shouldn't the error be consistent across the table?

Pic 252 is measuring at the left side of the table, 253 is on the right side of the table.

What am I missing here?

Matt

[MFchief]

Far from an expert on tramming, but at first blush, it sounds like the table is sagging, maybe a loose gib?
Terry

[tmarks11]

Spin that tool around in 90 degree increments and track what one of the dial indicators say.

[CountrySmith]

What you are missing is that the table is not necessarily flat or that the table may be lifting when extended to the far left due tothe center of gravity of the table now extended past the support point and loose gibs or flex in the mill lifting the table.

My 770 experiences both. I was able to improve the error by 50% by adjusting my gibs. If the purpose of tramming is to make the spindle perpendicular to the x-y plane, as determined by the x and y ways, you should skim a sacrificial plate with a small diameter end mill at the points of measurement contact. This provides surface which is running true to the x-y plane. The small diameter end mill is used to minimizs any error caused by improper tram.

In tramming the mill, I would want to use the central area of the table. On a 770, the center of gravity of the table is about 10" from the home position in the x direction. Also note that a CNC mill has to be somewhat loose in the gibs to prevent lost motion due to increased friction. Given the geometry of the gibs, the mill has about.0015" of vertical play for every .001" of horizontal play. Working on the far right hand side of the table will see a lift from the cantilevered weight. This would show exactly that you are observing. If it were me, I would remove the vise. It isn't that hard to re-register it..

If your reason for tramming is to determine whether your table surface is perpendicular to the spindle axis then you would do what you're doing and see what you are seeing.

R J

Edit: BTW, I would suspect loose gibs as well, given the size of the difference.