tool_scrounge
Well-known member
I recently purchased a used Columbian 506 M3 bench vise. For a relatively recent make vise from the Wilton ownership era, the previous owners had abused it a bit. When I picked it up it had a bent handle, some rust, and a broken jaw screw. After cleaning it up and unbending the handle, I still needed to tackle the broken screw.
I needed to drill the broken screw out but not damage the much softer threaded hole in the cast iron. To get this level of accuracy, I needed a drill guide. Well, with a vise jaw, you already have a drill guide - the screw hole in the jaw. But the hole is too big. So you need to make a reducing bushing like I fabricated below.
Just put the bushing in the jaw hole and you are set.
I started with a small hole in the drill bushing and drilled a small hole into the screw. I was centered to 0.010”, which I figured would be close enough. Then I removed the bushing and drilled the bushing for a larger hole. Then I was able to drill a larger hole thru the screw.
I used a hand drill due to the awkward shape shape of the vise casting and trying position it in a drill press. I had to use a lot of force, drilling very slowly with thick pipe tapping black oil. I figure if the drill broke, it would break at the end of the bushing. This would be easy to grasp after the vise jaw was removed. But I was able to drill it with no broken drills.
Unfortunately I did not have the correct sized left handed drill, as the 5/16-18 screw thread would have probably unscrewed while being drilled. I finished the removal easily with a spiral screw extractor. After that I chased the threads carefully with a tap, cleaned the threads well, and reassembled it.
I suspect the screw originally broke off because of the threaded hole depth was slightly too shallow for the screw length. The previous owner found the screw was tight but the jaw was loose. So they gave the screw an extra turn and broke off the screw. I had to retap the holes a little deeper for 2 of the 4 replacement screws.
I needed to drill the broken screw out but not damage the much softer threaded hole in the cast iron. To get this level of accuracy, I needed a drill guide. Well, with a vise jaw, you already have a drill guide - the screw hole in the jaw. But the hole is too big. So you need to make a reducing bushing like I fabricated below.
Just put the bushing in the jaw hole and you are set.
I started with a small hole in the drill bushing and drilled a small hole into the screw. I was centered to 0.010”, which I figured would be close enough. Then I removed the bushing and drilled the bushing for a larger hole. Then I was able to drill a larger hole thru the screw.
I used a hand drill due to the awkward shape shape of the vise casting and trying position it in a drill press. I had to use a lot of force, drilling very slowly with thick pipe tapping black oil. I figure if the drill broke, it would break at the end of the bushing. This would be easy to grasp after the vise jaw was removed. But I was able to drill it with no broken drills.
Unfortunately I did not have the correct sized left handed drill, as the 5/16-18 screw thread would have probably unscrewed while being drilled. I finished the removal easily with a spiral screw extractor. After that I chased the threads carefully with a tap, cleaned the threads well, and reassembled it.
I suspect the screw originally broke off because of the threaded hole depth was slightly too shallow for the screw length. The previous owner found the screw was tight but the jaw was loose. So they gave the screw an extra turn and broke off the screw. I had to retap the holes a little deeper for 2 of the 4 replacement screws.
