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This is a quick method to check if the head on a knee type milling machine, such as a Bridgeport, is out of tram. Bridgeports do not take kindly to crashes, or or sometimes too heavy a cut. The head mounts on two rotary joints, and they sometimes move a bit when abused. So, you are machining away and make a TINY little mistake. After the shop dog decides that it's not him that you are mad at and comes back inside, the next question is "do I have to re-tram the mill" or is it still close enough that I can do it later.
What I do for a quick check is put a 1-2-3 block in the vice and an edge finder in the spindle. Raise the spindle all the way, and then raise the table until you can edge find a corner on the block. Set your dials or DRO to zero. Then lower the table 3 or 4 inches and again edge find the corner of the block. and see how much difference there is from the zero you set. If the difference is very small, you are probably good to go. What makes this check reliable is that if your mistake is bad enough to disturb the tram, the head will probably have moved enough to show a sizable error, say 10 ro 20 thousands of an inch. Seldom will a Bridgeport style head only move a few tenths.
This is not a way to tram the head, only a quick way to check to see it needs to be trammed.
Gail in NM,USA
What I do for a quick check is put a 1-2-3 block in the vice and an edge finder in the spindle. Raise the spindle all the way, and then raise the table until you can edge find a corner on the block. Set your dials or DRO to zero. Then lower the table 3 or 4 inches and again edge find the corner of the block. and see how much difference there is from the zero you set. If the difference is very small, you are probably good to go. What makes this check reliable is that if your mistake is bad enough to disturb the tram, the head will probably have moved enough to show a sizable error, say 10 ro 20 thousands of an inch. Seldom will a Bridgeport style head only move a few tenths.
This is not a way to tram the head, only a quick way to check to see it needs to be trammed.
Gail in NM,USA
