What Do You Indicate Off Of When Tramming Mill

[loose nut]

I use an old bearing (cheap/free) outer race, ground all over, since it allows me to cross over the gaps in the bed. It could be placed on blocks to elevate it up above a mill like the fixture in the pictures.

[garyhlucas]

A perfect tram is when the spindle is perpedicular to the X & Y axis ways, not the vise or the table. If you are trammed perfectly to the ways the edge on a cutter will touch perfectly on the leading and trailing edges of a cut. Then you can take trim cut on your softjaws or a sacrifical plate to get the flatest possible support for your part. Of course if the ways are shaped like a banana as on my old Bridgeport then flat won’t be flat.

[MichaelP]

A perfect tram is when the spindle is perpedicular to the X & Y axis ways, not the vise or the table. If you are trammed perfectly to the ways the edge on a cutter will touch perfectly on the leading and trailing edges of a cut. Then you can take trim cut on your softjaws or a sacrifical plate to get the flatest possible support for your part. Of course if the ways are shaped like a banana as on my old Bridgeport then flat won’t be flat.

How do you tram to the ways?