Gear Dentistry: Repairing Broken Gear Teeth

Added: 2026-05-12

[00:00:07]Hello, Keith Rucker here at vmachinery.org. Guys, today we're back in the shop and we are out here. I've got a gear. I actually got several gears that I want to work on today. I've got two gears that I need to make repairs to, uh, which is probably going to be the content of this video. I've also got another gear I got to make. I'm not sure if that's going to be in this video or a separate video. Just kind of depends on how fast things move. Um, I've got a gear I actually did some brazing and repaired some broken teeth on this a while back as far as filling it in with braise. Today I want to get this gear cut out. I've got another gear that I've got to braise up and do the same type of thing on. It's a different gear pitch.

[00:00:43]And then a third gear that needs to be made from scratch. And again, that may be in a separate video down the road.

[00:00:50]Not sure yet. So, um, I'll show you up close this gear here in just a minute.

[00:00:54]But, uh, this is basically going to be a nine pitch gear. Uh diametrical pitch is nine. It has 16 teeth and uh there were a couple of broken teeth. Again, we went in and brazed it up. I'll zoom you in here. Kind of show you what we got and we'll get started on this project. So, to start with, this is the gear. This came out of a lathe. It's a back gear. I don't remember what lathe this came out of off top of my head, but it is a back gear off of a lathe. There were a couple of broken teeth in here. Again, I had come in and we brazed this up. And the idea here is now we'll machine out uh the waste in between the gears and we should have a couple of new teeth in there. There was a broken tooth, couple of broken tooth on this side and a couple on the other. Again, I don't remember exactly that was in a separate video. But anyway, we got to we got to basically cut that brace out and get it in there. This gear has already been cut, so it's a little bit different than normal. I will come in here and we will actually set up on the original tooth and uh then we will come in and cut out the material. So to hold this gear, this is a little bit unusual gear. It has the long hole through it. I made an arbor uh custom for this uh basically just has a shoulder. This is going to go up into the dividing head. Let me get this in here.

[00:02:22]Like such.

[00:02:25]We will uh put the gear up onto the arbor. And then I've just got a uh real thick washer here on the front. And we knock my And I just threaded the end here for 5/81.

[00:02:46]So, we'll tighten all this up. And that should give us something to work with here. And when I go to actually get this set up on the on the tooth, I can actually loosen that up and move it around and get it lined up exactly right. First thing I want to do is get the arbor centered up on the top. And to do that, I'm just going to use some of this turn surface where I just turned the outside diameter. I'm going to tighten this up.

[00:03:14]And we will slide our um the foottock here in place. Tighten it up. So that's supporting it out there on the end. So that's kind of the fixture that we made to do this in. And now what I need to do, I've already got my arbor set up. I've already got the dividing head set up. I've already got it set for 16 teeth. U putting the right plates in. I've shown how to do that in other videos in the past, so I just kind of skipped over that today. If you want to see that, you can go back and see some of my older videos on gear cutting.

[00:03:47]Let's uh get the uh the cutter centered up onto the arbor or onto the gear and we'll go from there.

[00:03:56]So, I've got you kind of looking straight down the end here, straight in onto the cutter. And you can see I've got I just kind of eyeball the center.

[00:04:04]It's not on center yet, but it's close.

[00:04:06]I've got a surface up here on the top on the braise that's just been turned to that outside diameter. And what I'm going to do is I'm going to raise the table up until it just barely touches the arbor. Then I'm going to slide the table back to forth, make a mark, and uh I'm going to probably adjust my table height, move it in and out a little bit until I get that where I got just a little dot right there. And by moving this back and forth, what you're doing is you're you're finding the top of that and the cutter will make a mark right where the center of the shaft is. And then we can just literally move it back and forth, eyeball it, get right on there. And that has been good enough for most of these gears that I've always done in the past. So, um, I'm going start out here by just raising up until I see just a little chip come off of that.

[00:05:03]Just moving the table up manually real slow.

[00:05:09]I'm going do we'll move in a little bit to start with.

[00:05:18]All right. I got a little mark, little pop mark right there. I'm going to move up until I'm just barely touching right there. Now I'm going to move the table in and out.

[00:05:33]I'm just kind of going across that top.

[00:05:36]I need to move down or move the table up just a thou or two. I'm not quite making contact yet. I just want to make a small mark. So, I'm going to do this a couple of times until I get that small mark.

[00:05:48]Let me come up another thou or two.

[00:05:52]All right, there we go.

[00:05:58]And I'll move my cutter in and out. And I don't know whether you can see it or not. Let me uh move the camera where hopefully you can see that little mark on there.

[00:06:12]I don't know whether this is showing up in the camera or not, but right up underneath the tooth right there, there's a little bitty mark that I can see. And now I'm just going to move the table in and out until the center of my cutter is right over that mark. And I will have the part centered up. I'm gonna have to move the camera because I have to get my head right there where it's in the way to see what's going on.

[00:06:34]Uh, but I'm going to get that done and we'll be back. All right, we have got our part centered up here. Now, I need to get the part kind of onto the a tooth here. I'm going to start by loosening up this gear where I can kind of move it around. And um I'm going to kind of pull that tooth in there. And I I zeroed out my height on when we touched off there. I know from my calculations that uh we should need to go uh 240,000 deep on this uh particular cut. That's how deep it needs to be cut. So I can kind of raise my table up and kind of find that where it needs to be. And I'm just going to get it lined up on one of the teeth. Uh, what I want to kind of do is get my cutter where I got a tooth going straight up and down. Um, I may put it in neutral and kind of manually move it around. And then I can raise my table up and move this back and forth until it locks into place on the on the envelope shape inside the gear. And then I'll tighten this down and I should be lined up to match the gears going around. That's the plan.

[00:07:51]All right. But I got my arbor where I can just kind of turn it by hand. It's disengaged. I'm going to put a tooth kind of right down there in the bottom.

[00:07:59]I've raised this up 200,000.

[00:08:02]Still got about 30,000. You can see the gear kind of rocking back and forth. I'm going to go ahead and u go up 10 more.

[00:08:16]20 more.

[00:08:23]30 more.

[00:08:26]Still got a little bit of rocking going on there.

[00:08:31]I'm going to raise this table up until I kind of feel it.

[00:08:36]Some interference between the cutter.

[00:08:41]All right. I kind of feel something right there.

[00:08:47]I need just a little bit more.

[00:08:58]And I'm going to tighten up the uh nut here on the end.

[00:09:07]We snug that right now.

[00:09:22]That's about where it's at right there.

[00:09:26]It's a little bit deeper than what the u the measurements call for, but that's where it's at. So, we're going to tighten it down. So, now I've got this centered up onto the part. And I've also got my cutter centered up into the um radially centered up onto the cutter.

[00:09:50]So, we should be able to come off of that.

[00:09:56]I'm going to mark here where we are on the depth so that I kind of know how deep I need to go based on um the original teeth.

[00:10:07]Uh like I said, 200 It's calling for 20 240,000 and I'm at 258,000 is where I the old one was. So, it looks like they may have gone a little bit deeper originally, but uh we'll we'll play that by ear and uh get it figured out where we need to be. All right, I think we are ready to start cutting here. I'm going to h let me think about this. I don't think I want to cut those teeth out at the whole depth. I think I want to uh maybe do about half of that.

[00:10:43]So, let's see. We'll probably just back off a 100 thou so I can take a 100,000 pass to clean these up. So, let me go to I'm going to go to around go about right there.

[00:11:06]And that should leave me 100,000 in the bottom. I should be making about 130 140,000 cut on the first pass.

[00:11:13]Uh, and I'm going to go ahead and move over a couple of teeth here.

[00:11:18]So, I'm going to move my index index my head over.

[00:11:23]That should be lined up on the next tooth. And it is.

[00:11:27]And I'm going to Yeah, we'll we'll do it on the next pass. Run it down through there. It's not going to touch on this pass, but I need to make my first cut here.

[00:11:38]on that tooth.

[00:11:40]Let me get my mill back re-engaged and we'll make our first cut.

[00:11:46]All right, I think we're ready. We're going to make our first pass through here.

[00:11:54]See, I'm on 7 and 5/8 in per minute. I think it would cut fine there, but I am going to slow it down just a little bit.

[00:12:02]Be on the conservative side. We're at uh 5 and 78 now.

[00:12:25]come out. I'm going to index my head around Make our next pass.

[00:13:06]All right, go to our next tooth.

[00:13:18]All right. So, I've got those cut on that side, but there are another brace area in here. So, I'm just going to kind of index around until I get to it.

[00:13:29]I'm not going to cut each one of those teeth because there's nothing to cut.

[00:13:36]We go one more and we'll make a cut on that one.

[00:14:04]All right, we got them all roughed out.

[00:14:06]Now I'm going to go ahead and go back around kind of where I started at.

[00:14:20]I'm barely touching right through there.

[00:14:23]I can hear it just touching in a couple little places.

[00:14:39]My next tooth.

[00:14:44]This will be cutting this one to the final depth.

[00:15:31]This is the last braise tooth, but I am going to hit the next one beside it because there's some flux and u stuff that kind of went down into that in blue. So, we'll u just clean it up with the cutter, but one more pass and we will be done.

[00:15:51]All right, this one will be it.

[00:15:57]Like I said, this is mostly here just cleaning up some flux and stuff that's gotten in that in there. Barely touching it.

[00:16:20]That's it.

[00:16:23]We're done with this one. Well, there we go. We got our gear uh cleaned up. We recut that brace out and we've got our envelute pattern back in there. So, this uh gear I think is ready to go back.

[00:16:39]I've mentioned in my previous video on this that guys, you know, brazing up a tooth like this, it works pretty good kind of in light duty use. Uh, however, if you got a lot of stress on one of these teeth, it can that softer bronze can can tear out over time. It's sometimes this kind of repair will last a really long time. Sometimes it won't, just depending on how hard your gears are being used. These are on the back gears on the lathes. So, really the only time they get used is when the lathe is in the back gear mode. And honestly, what happens on these lays is a lot of people, they'll lock their back gears in place while the uh before they they pull the little pin on it so that they can't the spindle is is stuck and then they will put pry on their chuck to get their chuck to unscrew when their chuck gets stuck. And it's when they're prying on it, sometimes the the weakest link is this tooth right here. It'll just break the tooth out. If uh the chuck gets stuck and he gets on one of these uh braced up teeth when he's doing that, it's probably going to knock it right out. But for just using the uh lathe in back gear mode, it'll probably hold up quite a while. But hopefully this will get him back in in uh where he can use this machine and hopefully it'll last a little long a long time. Like I said, I have done this and it has I've got gears running right now in my shop that I've done this on and they're still running fine. Have held up fine. But uh again, if you put a lot of pressure on them, not the ideal solution, but it is a uh fix that you can do kind of an emergency situation or to get a machine back up and going.

[00:18:24]So, I've got my teeth up here that are broken out. Uh first thing I want to do is I want to kind of notch out an area.

[00:18:30]I like to actually have the braids go down in below the surface, not just right on the top. It just I feel like gives a little bit more strength. So, I'm just going to use an angle grinder here and just kind of nibble that out.

[00:18:56]And I'm going to leave some of that original tooth on that one, I think. Uh, and we'll come back and just fill that in with braze now. So, let me um already got the other one done. I'm going to go ahead and get out the torch. We'll braze those up and we'll let that cool down.

[00:19:12]And we'll come in here and we will heat this up to about a cherry red color. And then just using a regular flux brazing rod, I'll just kind of fill those gaps in.

[00:19:28]All right, we are ready to start putting a little brace down in here.

[00:19:34]And I'm just going to basically just fill in this cavity with bronze.

[00:19:50]I think that one's pretty well filled in.

[00:19:54]Maybe just a tad back here in the back.

[00:20:01]Let me get the one next to it now.

[00:20:09]All right, that one is pretty well filled in. Let me rotate this around and I'll get the other one done, too.

[00:20:19]you know, with this brazing, you know, right now, basically the braise is going to become the new tooth. And by notching that out down there in the bottom, it just kind of gives a little bit of of the braise material a little extra bite kind of down up into the casting.

[00:20:37]uh rather than just brazing it right on top of the of the the broken tooth. Uh this just gives a little bit more surface area for it to kind of grab a hold of in that tooth. Uh and I've just had a little bit better luck doing it this way. We've got some color in there, so I think we're ready to go ahead and start putting some braids in.

[00:21:00]Yep, it's sticking just fine.

[00:21:03]And I'm just kind of filling this in.

[00:21:09]I'm just filling that cavity in just like the dentist does.

[00:21:14]Maybe not just like, but very similar to how the dentist does it.

[00:21:23]I've got to have a crown done at the dentist here in a couple of weeks. And uh I hope he doesn't pull out a torch. All right, I think we're done. I'm going to get out a welding blanket, wrap this up, and just let it cool down probably overnight, and we'll work on machining that tomorrow.

[00:22:01]So guys, I got this brazed up. It did cool down overnight. I took this to the wire wheel and just kind of cleaned it up a little bit. You can see the braise on there. Um, we need to take this to the lathe now and get it cleaned up and then we can go to the milling machine and cut those new teeth back in.

[00:22:20]So guys, I made a arbor here off camera.

[00:22:24]I've shown this before. I just took a piece of scrap metal. We turn an outside diameter over here. Just whatever to chuck in the chuck. There's a collar here for that to kind of go up against.

[00:22:35]Then we got a shoulder here for the gear to go up on and a nut to tighten it all up on. And our gear basically just fits right up on this like such. I've got a big washer here on the end that I'm going to use to tighten it down with. And that's just a one inch eight pitch nut that we'll tighten up on the end to hold it all in place. And this just gives us something to support and hold the gear while we're working on it.

[00:23:10]Now I'm going to bring my tailtock in with a live center on there. That's just going to give some added support to this. And now we can spin this around. That gear should be turning true to the inside bore. And we can just clean up. I need to um just face the outside of this on either end to get it ted up and then get the diameter uh cut in there as well on that braise. So, let me get a tool and we'll get that done.

[00:23:42]Just going to make it flush with the rest of the gear.

[00:23:49]This is just going to kind of reach right there on the back side and do the same thing.

[00:24:05]Just kind of doing this by hand right now. When I get down a little bit closer, I'll use the speed.

[00:24:13]All right, that's got the tops of those gears, tops of that brace just not back again flush with the outside diameter.

[00:24:32]So, this is now ready to go over to the milling machine and we'll cut those uh teeth back out.

[00:24:42]We're just going to take the whole arbor and everything over there because we'll have to put it in the chuck on the dividing head and that'll hold it.

[00:24:49]Little fixture here will hold it over on the mill machine as well.

[00:24:53]So, need to get this set up over here in the dividing head. I'm just getting my little um piece up here. I can get my chuck key in.

[00:25:04]Open up the chuck. I'm going to take this arbor out.

[00:25:09]I'm always having to make these little arbors to hold stuff. And when I do, I've got a little drawer over there that I keep them in. And often times, uh, I can find one that fits something I'm already doing that's got the same diameter or whatever in it. So, I can save myself some time and trouble uh, and just use an existing arbor or modify an old arbor. Uh, sometimes that works, too.

[00:25:37]So, I'm going to go ahead and get that in there. In this case, I had to make a new one from scratch, but I ever have to do this job again, I can just grab an old arbor. So, it's nice to have those handy.

[00:25:51]I'm going slide my foot stock in and we'll tighten that up to give some support.

[00:25:58]All right, this is set up. Now, I need to get the right figure out what plate I need and hole pattern to do this. U particular gear which has what is it? 76 uh teeth in it. So, let me figure that out. I'm probably going to have to change out the plate or at least put it in a different hole pattern. So, let me figure out what I need and we'll go from there.

[00:26:20]Got my manual here for the dividing head. And there's some charts in here that tells you what plates you need for different hole patterns. I'm just going to look up here. 76 which is right here.

[00:26:32]And there's only one option and that is a 76 holes plate and you go five holes and uh this uh dividing head is a 5 to1 ratio. So that kind of makes sense. U if you got 76 holes uh you would go five holes and you do that 76 times and it makes a 76 pattern. So u I need to go look and see what plate is in there. And if I don't have the 76 hole plate, I'll have to find that and get it installed on there.

[00:27:08]So, I'm over here at the dividing head now, and I'm looking at the plate that's in here. Each one of these circles has a certain number of holes in it. And it's actually stamped in here. I might have to put a little light on there. Y'all might be able to see it in the camera, but I can't. But this was 100 96 92 84 72 66 and 60 depending on which row you're in.

[00:27:34]Uh so that one's got a what was it? 72 and we need a 76. So I'm going to have to find the plate that has 76 holes.

[00:27:42]This one actually has holes on the other side that's a different pattern. And I got three different plates for a total of six different options for hole patterns. And I just have to take this apart and put the right plate in there depending on which one I need.

[00:27:57]So I'll start here by pulling this um handle off.

[00:28:10]It just kind of goes up onto a taper and there's a couple of bushings that come out. This uh scepter plate comes out and then there are some screws that hold all this in. Let me go grab a screwdriver.

[00:28:28]So, we'll just pull these three screws out here.

[00:28:57]All right. So, if I turn this plate over, there's a different hole pattern over here. And we have the 76 right here. So, I don't have to go find another one. This one will um go on here.

[00:29:18]Let's try that again.

[00:29:26]All right.

[00:29:29]Now, put my screws back in. That little outer ring on here basically clamps this plate. Right now, with that ring loose, you can actually rotate the plate and everything and that u will turn the dividing head. So, if you're doing a spiral gear, uh you can use that feature. Uh but if you're not doing spiral gears like we are, what you'll do is just clamp it down. And I will um get it where I in the position that I want before I clamp it, though.

[00:30:10]All right. There's one row right here where everything's lined up and that's where the numbers are. So, I'm going to rotate that up to the top. I like to have that at the top where I can see it.

[00:30:20]And now we'll just clamp this in place.

[00:30:24]And with that clamped in place, it won't turn.

[00:30:29]Um, so again, we're doing straight uh spurgears, so no need to do the helical stuff. So, we'll just clamp that in place. And we'll go ahead now and put this back together. I'm going to go ahead and put my scepter back on.

[00:30:44]And before I get too far here, I'm going to actually adjust this. It's easier to adjust it here. There's a little screw or little bolt right here. You loosen that up. And I want to go five holes.

[00:31:00]So, let me see. This is the 76 hole.

[00:31:06]Yep. So, this row right here is a 76 hole. I'm going to put this one on that one. and we'll go over five holes and we'll stop. So, one, two, three, four, five. Right there. This will just help me find those five holes each time without having to count them each time.

[00:31:28]This is just you slide this up against your pin and then you can move it over.

[00:31:34]One, two, three, four, five. And then slide that one over, move it over five.

[00:31:37]Slide that one over, move it over five.

[00:31:39]just makes it easy uh to do that without having to count each time. And now we can go ahead and start putting this back together.

[00:31:54]Nut on the front.

[00:31:59]I'm going to loosen this up. This is the pin and I want it to go into the 76 hole pattern.

[00:32:11]Make sure I'm in the right one again.

[00:32:14]So that's this row right here.

[00:32:26]Right there.

[00:32:28]Tighten that one up. This is just you can adjust it for whichever hole pattern you want to use.

[00:32:37]And we can go five holes.

[00:32:41]Go five holes and just work our way around. All right, the dividing head is set up and ready to roll. So now I need to get my cutter changed, get it centered up on there, and we can start.

[00:33:20]And I'll actually get the first fully brazed tooth here.

[00:33:43]Next one.

[00:33:52]And this is it.

[00:33:56]All right.

[00:34:10]And I believe with that and we are done with this uh gear. So, let me get it out of there. I'll check it out and we'll bring you back. And just like that, we got this one done, too. One brace tooth there. And there's two braised teeth in there. And again, as long as uh they don't abuse these teeth, those should hold up fine. Uh they decide to go prying off a chuck on that tooth again is probably going to disappear on them once again. But uh just like when you go to the dentist, that uh false tooth they put in isn't quite as good as the original. It's usually good enough, at least to get you by for a while. So uh we're going to let this dentist job head back to its owner and hopefully uh get his lathe back up and running.

[00:34:53]And with that, guys, uh I think that's going to be a wrap for today. I do have one more little small gear I need to make. But this one's going to be a little bit different. I'm going to have to actually totally remake a new gear.

[00:35:04]So, uh I'm going to probably do that in a different video. I just don't have time to fit it all in this one, I think, more than anything else. And since the process is a little bit different, it probably does deserve a uh dedicated video on its own. So, we'll be doing that one coming up soon. But in the meantime, I'm going to get these two repaired teeth uh gears out uh to the rightful owners and hopefully let them be able to get back up and running. So, with that guys, that is a wrap. As always, thanks so much for watching.

[00:35:29]Please subscribe to the channel if you haven't already. Those thumbs up and comments are always greatly appreciated.

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