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Milling – the difference between T-slots and dovetails

T-slots and dovetails seem very similar in that they are both used to hold two separate parts together. In both cases the two parts can move relatively to each other. They are each made using a cutter specially made for making them. They can both be used for aligning the two parts involved very accurately.

But there is a very important difference. On a T-slot the two parts are only held sufficiently against each other when the bolts are done up.When the bolts are loose, one part, for example, a vice can move against the, other part, for example, the milling table in the x and z directions. This means the vice held in the t-slot on the milling table cannot hold a part which can be machined. But when it is bolted done it cannot moving in any plane and the part can be machined.

On the other hand, on a dovetail the two parts are always are held precisely against each other, hopefully in three dimensions but at least in two, and, yet can be made to move. This is the situation between the table of the milling machine and the knee of the milling machine.