Weld repair of hardened gear teeth?

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I have two gears that are inside a 13x40 lathe (headstock gear box) and they are missing a couple of teeth. They are made from steel, not cast iron, and they are hardened according to the specs.Is it possible to build up the teeth with weld beads and then machine them? If it is possible, how would one go about the welding part of it? I assume the gears have to be annealed first?BTW, I have no clue what kind of steel the gears are made of but I guess it would be the cheapest kind that would get the job done.Any ideas or anyone that done something similar perhaps?Last edited by Pete.S.; 12-03-2014 at 06:30 PM.
Reply:I can't answer your question but won't welding hardened steel take the temper out of it and just make it more prone to damage,
Reply:Sounds like a fun project Pete.I Don't think I would worry about the hardening part. Gear cutters are not cheap though.I wonder what kind of results a guy could get making his own single point gear cutter. It supposes you have all the other goodies required though. I also wonder what kind of results a guy could get with a quick braze and file. Probably good enough for me. You could also contact a gear maker with your woes. What kind of lathe is it?
Reply:I know it's been done before because I've read about it on the machining forums.   It was probably on http://bbs.homeshopmachinist.net/forums/3-General  or  http://www.practicalmachinist.com/vb/general/An involute cutter is usually cheaper than a custom gear, or one from the manufacturer.    Anyway, that's what I recall.General process was to clean up the damaged area, build up weld with a tough rod, mill or file the excess weld, hog out the tooth profile, index properly and cut with the cutter.   Case harden if necessary.Dan----------------------------Measure twice.  Weld once.  Grind to size.MIG:  Lincoln SP100 TIG/STICK:  AHP Alphatig 200X
Reply:You can anneal , repair and harden your gears. This guy does an awesome job explaining and demonstrating heat treatingLast edited by NinjaRay; 12-03-2014 at 08:49 PM.
Reply:not sure how old your lathe is, but some of todays gears are made of 8620.    Not real up on the heat treating, when they get done, the outer skin is very hard, and the innet part is softer has some ductility to it.   That way, when the gears crash, or something goes dont mesh right under a load, they are impact resistant, the outer hardened skin is thin enough to flex w/o going to heck.   My guess is that they pack them in carbon while heat treating to get that effect.
Reply:a gear on our south bend lathe lost a couple teeth a while back. i built the area up with 7018. no weld pre or post heat. it's been several months and working good so far. Attached Imagesi.u.o.e. # 15queens, ny and sunny fla
Reply:lol, nice.  what did you cut the teeth w/?
Reply:Why don't you make an attempt to contact the manufacturer and get a replacement?  I did that with  Taiwan company and they about fell all over themselves to help out.  The US importer however were jerks. I had to go to the source.
Reply:Originally Posted by 123weldlol, nice.  what did you cut the teeth w/?
Reply:Originally Posted by docweldera milling machine then a file.
Reply:How did they break in the first place? If it happened during normal use one might assume the new teeth may need to be hardened to last any significant time, if they broke due to something out of the ordinary, such as a sudden stop, Another piece of metal caught between the gears or such, they are much more likely to hold up without hardening.Another factor would be how much they'll be used. If the stock piece is good for 40h running a week for 20 years straight and you only use the machine for the odd little project every third weekend you're unlikely to wear anything out.
Reply:Cool repair on that gear docwelder!
Reply:To answer some of your questions. The lathe is import (chinese I think) and it's fairly new so no real wear to speak of. The importer seems to have problems sourcing parts from the (to me unknown) manufacturer of the lathe.The teeth broke when the lathe was stopped with the emergency foot brake (to avoid a real mishap). I don't think it should break like that but I can understand why - the brake is located on the pulley to the motor so when you hit the break you stop the motor real quick but then you have all the mass of the spindle with the chuck and workpiece wanting to keep on turning, and the gears are in between.If we can't source the original spare parts we have a few options.1) Try to find the same parts from somewhere else and hope they are actually identical. (Hit or miss)2) Sending out the gears and have someone make us new gears. (100% success but expensive I imagine).3) Abandon the gears and run it from a VFD instead. (100% doable but a lot of work).4) Repair the gears ourselves - if possible.If we do it ourselves we only have to buy the correct gear cutter or make it with other tools and if it doesn't work we're back to square one. Hopefully a little wiser. I don't know the rpm of these gears but top spindle speed is 2000 rpm and the motor is around 1500 rpm so somewhere around these numbers.There is actually option no 5 too. Do nothing, and just avoid using the gears that have brooken teeth.Last edited by Pete.S.; 12-04-2014 at 09:27 AM.
Reply:Can you post pic's of the broken gear and of the lathe?  And the brand? The importer should be able to tell you where it came from and the contact info.  Since it is a newer machine there should be info on it- is there an owners group?  You might try a search "broken gear on brand x when using emergency stop" or something like that- rest assured you are not the only guy in the world with this problem.
Reply:Heck man, I'd just weld it up and see how it does.  No harm in that.If it were mine, it would get welded, cut to fit with an angle grinder by eye, and then touched up with a die grinder and file 'till I got tired of doing it Doc's looked really good.Good luck on the repair Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Originally Posted by MinnesotaDaveHeck man, I'd just weld it up and see how it does.  No harm in that.If it were mine, it would get welded, cut to fit with an angle grinder by eye, and then touched up with a die grinder and file 'till I got tired of doing it Doc's looked really good.Good luck on the repair
Reply:The only problem I see with the cutter is that you'd better be sure and anneal the gear or you'll ruin it.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply:Originally Posted by Pete.S.Yeah, I was thinking along the same lines. But I think I'll order the right gear cutter after I find out what size it is. They are not that expensive if you only need one. Keith Fenner just cut a new cast iron gear for an older lathe in one of his videos and in this one he's braze repairing the old gear and then he'll recut the missing teeth in the next upcoming vid.
Reply:I would contact maybe Boston gear and talk them about the gear, I'm pretty sure they have something to replace it.Jeff
Reply:Use a filler that will stick to the hardened steel without cracking, i.e. tig it with 312 stainless.Welding/Fab Pics: www.UtahWeld.com
Reply:Originally Posted by MikeGyverUse a filler that will stick to the hardened steel without cracking, i.e. tig it with 312 stainless.
Reply:Use the teeth that are in tact and make yourself a cardboard template of the profile using three or four teeth.  Preheat the teeth to about 500 and build up weld with 11018. Post heat to at least 700 degrees and slow cool with a FR blanket or lime bath. Once cooled use a mill/grinder/file or whatever means you have to restore the teeth to their original shape and timing. I used to work for a machine shop who did this kind of work all the time on gears of all shapes and sizes. Good luck