TIG Braze Welding Tooth Back onto Gear...PING Ernie

I have torch brazed back gears of two Raglan lathes years ago as well as several other slow moving gears on machine tools in school shops. Certainly the silicon bronze or even aluminum bronze alloys would be superior but I got many years further service just with torch brazed alloy. I used a shaper to reform the tooth by grinding a tool bit to match the gear profile. Randy

wrote: (clip) I assume I should pre-heat the gear to about 400 degrees and then weld it? Allow to cool in vermiculite overnight. (clip) ^^^^^^^^^^^^^^ The preheat/postcool procedure is critical if the cast iron forms a loop of any sort, which will result in shrinkage stresses. A gear tooth sticks out from the gear, but does not reconnect back to the main body. Therefore, it can expand and shrink without stress. You should be able to build it up and then just let it cool.

To form the gear profile, I have been successful by rolling the gear against its mating gear, and removing material until I could not feel any "lumpiness" as it rolled through engagement. I would only do this for non-critical applications. What gets you by is the fact that gear teeth go through double and triple tooth contact, so the repaired tooth never carries the load alone. (For this reason, I would never do an adjacent pair of teeth.)

Before brazing, you might consider threading in pins to provide some support, then build the bronze over them. I have several gears, large and small, with repaired teeth, and pinning helps it hold up when the tooth is substantially missing.

snipped-for-privacy@aol.com wrote:

solid.

Aluminum bronze would be the best choice for filler since it wears so much better than silicon bronze

Aluminum bronze will give better results-no hot short and ductile enough to minimize cracking.

Good Luck