The pins capturing the SHCS heads will mount the 123 blocks to the Sherline’s table or tooling plate, but attaching things to the blocks or joining them requires threaded pins on the other end of the screws:
Optical illusion: those two pins are the same length.
I grabbed a length of 3/8 inch aluminum rod in the Sherline vise, center-drilled four holes spaced 7/8 inch apart, then drilled them with a #20 drill for E-Z tapping.
Space the holes with manual CNC command entry:
GO X[0*0.875*25.4]
GO X[1*0.875*25.4]
GO X[2*0.875*25.4]
GO X[3*0.875*25.4]That’s LinuxCNC on a Sherline with hard-inch leadscrews and G21 active. I normally use millimeters, but inch dimensions make more sense for these pins.
Transfer the rod to the lathe for hand tapping:
Not shown here: stick a transfer punch in one of the holes and eyeballometrically align tap with punch to get straight threads.
Then, for each pin:
- Chuck rod so the whole pin sticks out
- Turn OD to 8.4 mm
- Face to 3/8 inch rightward from hole center
- Chamfer edge with file
- Part off a little more than 3/8 inch leftward from hole center
- Find pin in chip tray
- Rechuck the other way around
- Face to 3/8 inch rightward from hole center
- Chamfer edge with file
- Ease thread entries with a round file
- Done!
Again, I can’t believe I’m the first person to think of these pins; aim me at the commercial offerings I can’t find anywhere.
Update: The keywords “cross dowel nut” and “furniture bolt” will turn up useful products intended for woodworkers. Thanks to blaz for the suggestion.
The Smell of Molten Projects in the Morning 
Does a search for “barrel nut” find anything useful. I find similar things, I’m not sure if close enough.
Good find!
Long ago and far away, we scratch-built our bookshelves with “furniture bolts” through the uprights into “cross dowel nuts” fitted into blind holes. I never made the connection, even though the shelves stand next to the bed. [sigh]
Looks like a choice between 10-24 threads and M5 in the size I’d need, as furniture folks aren’t into fine-pitch threads.
Thanks for the right keyword!
Robin Renzetti (Robrenz on youtube) has a different solution to the problem. Tom at oxtoolco has a video making a set and demonstrating them: https://www.youtube.com/watch?v=FxVPM08jnGM
Ah-ha! That’s a detailed look at the “more complex” blocks I’d seen a hint about.
Now, if only I had a power hacksaw, a real mill, a surface grinder, a heat-treating oven, and … leet machinist skillz. [grin]
Aaaaand a link to a video about making nearly the same pins I did: https://www.youtube.com/watch?v=65fXIuBRWUE