Drill Press Repair

I think the angle of the sides of the rack teeth is the pressure angle. Common values are 14-1/2 and 20 degrees.

An old technique for copying gear teeth is to make a crude oversized gear out of thin lead and roll it against the good gear until the center distance is correct. Then grind a shaper bit to fit the gap between lead teeth.

Jim Wilkins

Yes. And the number of teeth per inch is the pitch. If you're lucky it'll be a standard spur gear. In which case I'd buy the proper gear from Boston Gear, Union Gear, or Martin. You can verify you've picked the right gear by comparing the center distance between the shaft and rack with the catalog value. The numbers are also in Machinery's Handbook.

Turn down the shaft a bit below the teeth of the old gear, bore the new gear for a shrink fit onto the shaft, and taper-pin it in place. Or some variation based on the actual design of the shaft.

Cute!

It looks looks like they machined the entire shaft and

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It might be worth taking a closer look. And maybe asking some more specific questions about this part. I would think that even back then they'd have wanted to use a different material for the shaft and for the gear. Take the machine apart, clean up that shaft completely and look at it for a couple of days. Take some pictures and post them. You might find a pin or two that were strategically placed . The head may have been carefully filed to match some other feature, making it hard to see under a lot of grime.

These machines are often called "camelback drill presses". Searching for such a thing may shed a little light on the subject, or give you a clue as to where to go next.

Pete Stanaitis

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Dress a cutter tool to the root shape of a pair of teeth on an unworn area on the rack. Now count the teeth on the gear and measure the diameter. Layout a circle to that diameter and layout the teeth to match the old gear.

As for how to attach it. I would machine the current gear down the a hub in a standard size. Machine the new gear in that size minus a few thousandths. Attach the new gear by heating it in an oven and pressing it on the hub. Once it cools it will be solid, no key or solder involved.

I appreciate all the replies. Here are some photos:

I had thought about the boring an existing gear idea, but as you can see, the whole depth of the gear is only slightly larger than the shaft diameter. I like the shrink fit idea. Maybe I could make it in three pieces? The good news is there is one good tooth profile left.