Goodell-Pratt Bench Drill Cleanup
by Isaac Smith
This article first appeared in a thread on theWoodNet woodworking forum. It was compiled and reproduced here for easier public consumption. All Text and Images are the property of Isaac Smith.
I recently found a GP 9 1/2 bench drill. It was in good shape, with some wear and a feed screw that had been separated from the spindle. I'd never seen one of these before in real life, so I decided to try repairing it. Along the way, I decided to document the process. I did not take pictures of the disassembly, but it is the reverse of assembly. Just a few drive pins hold everything together.
First, here is what was broken on it (the spindle should be attached to the feed screw, yet remain able to rotate independently).
Having neither a complete nor working model, I had to make an educated guess as to how to proceed with repairs. What I came up with was a retaining spring that fits in the groove at the end of the feed screw. When the end of the feed screw (with the retaining spring) is inserted into the end of the spindle, the spindle remains free to rotate. Finally, two pins are inserted thru the end of the spindle, locking both parts together. Hard to explain, but hopefully the pictures make this a little clearer. I have no idea if this is how it was originally made, but it seems to make sense (and it works).
Making the spring from music wire.
The spring, before cutting off.
The finished retaining spring, installed on the end of the feed screw.
We'll come back to this assembly later. First, here are all of the parts, cleaned and ready to assemble.
Chuck parts, and the assembly process. When assembled, the chuck is tightened by the piece I am holding (in the third picture below) being forced down by the end of the spindle, which in turn pushes the chuck jaws further into the cone of the chuck shell.
This is the speed selector mechanism. The two C-shaped pieces seat in the slots in the spindle, transmitting power from the gears to the spindle, while allowing the spindle to slide up and down. The knob on the frame (at the top of the fourth and fifth pictures below) has an off-centered tab at the end that rides in the groove of the piece that holds the two C-shaped pieces (in the center of the second and third pictures below). Rotating the knob slides this piece up or down, engaging either the slow or fast gear. Even though it is a fairly simple mechanism, make sure to note how all of the pieces came off, and reassemble them in the same way.
Installing the drive gear. The gear is attached to the crank handle with a pin, which was quite easy to remove. The wooden crank handle (not shown) is held on with a nut. This nut is left handed, so take care not to strip it by trying to remove it in the wrong direction.
Now, time for the hardest part. Hopefully you can see how the feed screw and the spindle will be coupled together. There are two pins that are parallel to each other (you can only see the front one below). Because the pins were worn out, I had to make new ones. They were not a common size, so I chucked an oversized piece of steel rod in the drill press and filed it to the proper diameter while running. Once the pins are installed, the spindle and feed screw are locked together (although they are still able to rotate independently). To disassemble the drill, these pins need to be removed, or the spindle will not slide thru the selector gears.
Almost done, but first, the pins need to be filed flush to the spindle. It was interesting to see file marks on the spindle from the first time this was done at the factory.
The reason these pins must be filed flush: the feed screw needs to enter the spindle housing to allow the full range of travel:
And the finished bench drill, ready for work once again. Not quite all of it's former glory, but it has aged gracefully. There is some play between the spindle and it's housing, but this was never meant for precision work. For most purposes, it has sufficient accuracy. It drills surprisingly fast, and must have been quite a boon to the home woodworker.
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