Help out a newbie TIG welding a gear

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Hi, I have a gear that came out of a lathe, the gear is made out of 4140 chromoly and is cased hardened.  A couple of the teeth are chipped about a 1/4 of the tooth is missing.  I was wondering if anyone knows if I can weld an already cased harden gear, or will it just cause more problems trying to fix it?   Thanks  Larry
Reply:Hi, the short answer despite what some will tell you is.......if you attempt to weld the said gear you will have to heat treat it or the "renewed" teeth material will just flake off the hardened base material in small pieces.The worst case scenario is if you do weld it with a Tig, you will have a zone of soft material that you can file or re-machine to tooth profile, but you'll need to re-case harden the gear.Looking at the photo of the gear, I'd just use it as it is.....you still have a complete tooth on the gear even if about 1/4 of it is missing.The chipping is caused by engaging the gear, while it is still running, with the gear it meshes with.You probably have another gear in the box that also has some chips knocked off of it......provided they're only chipped to the extent you show, it will still work, but don't apply too heavy a load.ian.
Reply:Yes, you can weld it.Use AH-3, or SuperMissleweld filler. Weld can be dremel ground. Flame stress relieve afterward.Last edited by shovelon; 09-12-2013 at 08:02 AM.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:I recently welded up a gear in a coot and it has been working fine. Complete missing teeth.  Just a chip I would weld up without hesitating at all.
Reply:Case hardening is pretty easy as long as you have a method of getting it up to temp and keeping it there for a couple hours.Lincoln precision TIG 275Millermatic 140 MIG
Reply:Preheat to around 600*f, weld with a chrome moly rod. Next, draw it back with an o.a. torch (to relieve stress). Grind to finished dimensions, then flame harden with an o.a. torch ( with a water quench following the flame. You need to exercise care while flame hardening. When the gear surface begins to look shiney / sweaty, start moving the torch / HAZ, and creep the water quench along, behind the moving HAZ.http://www.facebook.com/LockhartMetalArthttp://www.facebook.com/pages/Grumpy...44306259043484
Reply:Hi,  Just want to say Thanks for all the feed backs, lot's of great information.  Larry