The handles on the cross slide on the South Bend lathe are held on with a new to me type of screw. The head is similar to a slotted head, but the slot is interrupted. This type of screw requires a pin wrench, which could be purchased but seemed straightforward to make. The nut is 1/2" diameter. The pin holes are 1/16" X 1/8" and separated by 1/4".
The first attempt at making this pin wrench used a length of 1/2" hex bar stock. A 1 1/4" piece was cut off with a hacksaw. Both ends were faced in the lathe. One end was reduced to 0.497" for 1/4". This was placed in a vise in the mill and this same end was cut crosswise with a 1/4" cutter to a depth of 0.080" in eight passes. This cut was repeated on the other side after rotating the workpiece 180°. The same end mill was then used to cut a slot in this thinned section to a depth of 1/8". The part was then cross drilled in the vise with a 1/8" drill bit for a tommy bar. After cleaning with a file attempted to use the wrench to remove a nut holding the cross slide handle. Unfortunately, both pins simply twisted in the process! Clearly the pin wrench needs to be hardened prior to use. A second pin wrench was now called for.
This wrench was to be made a little differently. Dimensions were captured from the a photo of a wrench for sale on eBay. The hex end was made first. A 1 1/2" length of 1/2" steel round bar stock was faced on both ends in the lathe. One end was reduced to 5/16" for 1". The "Calc Hex Dimensions" tool was used for determining depth of cut. The 4-jaw chuck was attached to the rotary table set up vertically on the bed of the mill. The part was placed in the 4-jaw chuck. Run out was reduced to less than 0.001". The edge was located and 0.019" was removed with a 5/16" end mill for a length of 0.5". The table was rotated 60° and the cut was repeated. After all sides were finished bit fit was checked in a hex bit holder. A bit of filing was required as the fit was quite tight.
The part was moved to the vise and 0.222" was removed with a 5/16" end mill in 0.005" passes to a depth of 0.312". The part was rotated 180° and repeated the cut on the opposite side. The width at the thinnest part measured 0.065" so removed 0.005" from each side.
Probably getting flex as part is thinned.
Set in the vise with the blade parallel to the table. Located the center and used a 1/4" bit to cut a slot across the thin part to a depth of 1/8". Then switch to a 3/16" bit to wide the slot to 0.188". Then removed 0.016" from each side to get to the final slot dimension. The pin wrench worked without hardening.