Take 1in square stock and chamfer the edges. Take a slot punch and move it about an 1in from the corner - this is the hammer end. Line the slot punch up very carefully, so that its straight and divides the stock in the middle. Hit it a couple times to get a registration. Now, get the stock nice and hot, align the slot punch with the registration, hit it hard three times, cool the slot punch in water, rotate it by 180 degrees and repeat. At some point, the slot punch is almost through, flip the stock over and use the slot punch to punch out the remaining piece of metal. Now, use a drift to open up the hole to the desired size. Start the drift from the other side of the slot. Doing this over the hardy hole is a good idea. With the slot still inserted, dress up the faces. Then chamfer the corners. Cut off the other side for the length of the tenon and drill a hole of the right size.
That’s it. Out of the four holes I drifted only two came out sort of in the middle 
