Old Atlas lathe shear pin for lead screw

[Brian Rupnow]

My friend who purchased the old Atlas10-42 lathe asked me a question today and I haven't been able to answer it. The reversing gear box which reverses the direction which the lead screw turns is in good condition, and the gear which drives the lead screw has a 3/16" hole thru it. However, the end of the lead-screw has a 3/16" keyway on one side, but no hole thru it to match the hole thru the gear. What did they do for a shear pin? If the lead-screw had a hole thru it to match the hole in the gear, then a 3/16" brass pin thru the gear and the lead screw would be in double shear. I can't imagine a brass pin going thru one side of the gear and into the keyway in the shaft to act as a single shear pin. I am unable to find a video that answers my question. Can anyone help clear this up please.---Brian

 

[Brian Rupnow]

Okay, I got my answer. There are two gears that rotate in opposite directions in the gearbox. Neither gear has a key. There is a slider which can be manually moved to mesh with either gear, and that moveable slider is what has the key to the lead screw. ---Brian

 

[TSutrina]

The manual speed change by installing gears has as said above a box in line with the screw. Within it is three gears and a lever that move a ring with square teeth that fit into a mate. Moved to the back the teeth connect to the output of the gears. and move towards the front connect to a mate spinning in the opposite direction due to the three gears. the ring transfers through a slot in the screw shaft to that screw. So there is no shear device in the drive. Grab CAD has the model built of my Atlas F lathe.
Now I purchase a change gear box and a reverse direction device. The output of the gear box to the lead screw has a square key slot in both the shaft and the female output shaft. The square key is a shear device to prevent damage. I am using wood and fill the whole length. If I used a soft metal or a square tube soft metal a shorter shear pin may be needed. I am not sure if i put the gear box model on the GrabCAD site.
Note it was created on FreeCAD ~ 0.15 And the parts were also saved as step parts.