View Full Version : Checking a mill head 90 Deg to table

Mike Hunter
01-21-2009, 11:36 AM
Ok, probably a very dumb question from a guy that owns a couple of Bridgeports.

How to you check to ensure that your head is 90 degrees to the table. Not talking about simple tram, but 90 deg to X axis, since the top ram can rotate 360.

Guess another question is Does it matter, since the head is stationary.

Thanks for not laughing too hard


01-21-2009, 11:46 AM
I've never had occasion to check and wouldn't think it matters. In theory, if it really was important, I'd put a large angle plate on the table, make sure it was straight with the X axis, then rotate (sweep) the head to check for squareness that direction. Then, of course, I'd have to reset squareness (verticality) with the table.

In most instances I can imagine, if I were relocating the ram and head I would recheck location on my work so it wouldn't matter. I suppose one could hypothesize about a job too big for the Y axis travel in which one might machine part of the job, then relocate the ram and the saddle and carry on, but that's pretty far fetched.

OTOH, since this is a creative forum, maybe others can come up with jobs where ram movement during the job, and squareness would be important.

01-21-2009, 11:49 AM
mike i would either put a 123 or some other machined block in the
vice or clamp to table. make sure it has a good square 90 and
indicate the x to be 0 then check the y if its not 0 then you will
have to swing the head around till it is.hope this helps and i am
some one with more knowledge will be able to tell you better than me

Mark Hockett
01-21-2009, 12:30 PM
The 360 degree rotation of the entire top of a BP is important to have perpendicular to the table only when you are setting the head at an angle. If you angle the head and the ram is not square it will have a compound error, I think that would be the correct term.

I use a DTI mounted to the table, move the table in the Y axis to indicate the dovetail slide on the ram, and adjust it square.

01-21-2009, 12:39 PM
Gee Mike, thats a blast from the past and the exact thing that one of my Bridgeport Mentors lost the Fiver for (About eight dollars now but worth a lot more 45 years ago.)

Our machines had Rotabs(UGH) on the X -Y slides, and co-ord tables on the rotarys which for normal co-ordinate machineing was OK, but sometimes we had to swing the head round on the vertical axis cos we had the slotting attachment on the other end of the "Ram". When the slide was rotated back, bringing the milling head back into operation although you could "Tram" the edge of an angle plate square front to back using the machine slides and clamping the plate, if there was any chance of having to move the Ram out to clamp a large job, you should then clamp the slide and adjust the angular position of the Ram by tramming the edge of a previously squared and clamped plate using the ram jacking bolt. Game, set and five pounds please. Although he insisted, I couldn't take it from him, for a skilled man,that was a third of his wage.

Regards Ian.

Mike Hunter
01-21-2009, 02:47 PM
Thanks for all the feedback,