Civil Engineering Reference
In-Depth Information
Fig. 7.4 Using a slot drill with a worn end will create a stepped keyway. This diagram
is greatly exaggerated. Always use a new cutter for each different depth of keyway.
Machining T-nuts
You can buy T-nuts, but they are a simple exercise in machining so I suggest
you make a dozen or so.
First, measure the T-slot and make a cross section view. Cut some lengths
of bar sufficient to make four or five T-nuts from each length of bar, leaving
sufficient material to hacksaw the individual T-nuts off when they are ma-
chined.
Machine the bottom face of the T-nut - this is the bit that ends up at the bot-
tom of the slot. Machine both sides so the bar is the finished width required.
Drop the bar sideways onto a parallel with sufficient above the vice jaws to
make the side cutouts. Rough the first side cut-out out and turn the bar over
and rough out the second side.
Measure the overall width of the remaining centre of the bar. Take note of
the size of the bar and lower the cutter by half of the difference to bring it to
size; say the middle of the tee nut needs to be 12mm wide and the bar meas-
ures 13.5, the difference is 1.5 so we need to raise the table by 0.75mm and
remove this from each side. We do need a bit of clearance so I would remove
about 0.9mm leaving a little bit of clearance at each side.
We also need to finish the thickness of the T-head, so measure this as
well and move over the required amount taking the thickness of the tee about
0.2mm thinner than required. You now have a bar of the correct shape of the
