To clamp a device or workpiece onto a part fitted with T-slots requires either bolts fitted with heads that fit the t-slots or with T-nuts. T-nuts are usually fitted with a threaded hole to take a stud.
It is seldom worth making just one or two T-nuts so what is going to be explained is how to make up to half a dozen in one go and made accurately.
It might seem that a T-nut does not need to be very accurate. However unless an attempt is made to make it accurately it is easy to make so inaccurate that it makes it liable to fail in either to hold the workpiece or, worse, to break the T-slot.
The trick, as usual, is to set up the workpiece properly and make as much in one go as possible. In this case, it means machining the T-nuts from one piece of bar and then separating them.
The workpiece starts off as a rectangular bar which is held in the vice. Notice the bar is extra deep so all that needs to be machined accurately is sticking out of the vice.
fig workpiece in vice
The job is made easier if the vice is square to start with but this is not critical.
The idea is that it is possible to machine the bottom of the T’s shank, the two sides of the shank and the two ends of the cross piece all in one setup. It is also possible to center drill the bolt holes.
The critical dimensions are the width of the shank. This is not because it must fit the slot accurately. it is because the size of the bolt that fits the T-slot usually only just fits the slot. If the shank is too narrow or the center drills are off center the thread might show through the side of the shank of the T.
The width of the cross is important because the more it reaches the side of the t-slot the less the stress on the T-slot.
The only bit that in not machined with this setup is the top of the T. However it is easy to do and the height of the cross is not critical. In fact it is useful for there to be a significant gap between the T-nut and the bottom of the T-slot. This means the T-slot does not have to be perfectly clean for the T-nut to fit into it.
When this part has been machined it can be drilled and tapped and sawn into pieces.