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Thread: Broken bevel gear tooth repair
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15th Aug 2017, 11:44 PM #1Golden Member
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Broken bevel gear tooth repair
Hi all,
The patient is a bevel gear with a broken tooth. There is enough tooth root left for it to actually work. When mated with other bevel gear and rotated things seems smooth enough - but using it as is just don't seem right. Know what I mean? Pics:
IMAG1648.jpgIMAG1647.jpgIMAG1645.jpg
I am happy to defer to greater experience in "just use it as it is you noob idiot" but if it is to be repaired then I am considering my options. Given there is a good root there I was figuring I might be able to put a pin either side of the tooth 'crest' you see in the pics and then build up some material around it then file it back - using the other (quite worn) mating gear for bluing to get a reasonable contact.
If so, would this 'silver solder' be okay for building up material?
IMAG1649.jpgIMAG1650.jpg
(apols if pics are sidewards, I did rotate them on my machine and they look upright locally)
All help and advice appreciated.
Greg.
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16th Aug 2017, 12:13 AM #2Golden Member
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I don't think that will do it. Maybe something like this https://youtu.be/YWaF_QhcxA0
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16th Aug 2017, 12:51 AM #3Most Valued Member
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Hi Greg, what you have there is commonly called soft solder, mainly used for galvanized iron, copper etc.
If you used a brazing rod with flux, you'd also need an oxy acetylene or similar to heat the gear and melt the brazing rod, I don't think the MAP torches put out enough heat to melt the brazing rod. Silver solder, is a combination of various metals, whereas what you have, is a combination of lead and tin, plus a few other minor amounts of metal.
I have some offcuts of cast iron, if you need some, to make a new tooth, then braze it on, you could also pin it if you wanted extra strength.
That video is an excellent how to. A few things that I'd change, is that instead of heating it in the vise, I'd sit it on some fire bricks or similar, as the vise will draw the heat away from the gear, and another is to heat the whole gear, you'll probably have noticed that the gear when he was machining the sides, had misses in it on the areas not heated sufficiently, last thing is to bury the gear in some DRY sand, which will slow down the cooling of the gear, otherwise there'll be hard and soft spots in it.
KrynTo grow old is mandatory, growing up is optional.
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16th Aug 2017, 09:46 AM #4Most Valued Member
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Build up with hard braze, file to fit. Not rocket science, just requires persistence. This was one of the things we had to do as part of the oxy-acetylene welding course back in the day. Then we got to do the same thing only using cast iron rod for filler instead of brazing rod.
Brazed repair is heaps strong enough and the material will cold-flow a little to work in, with no risk of white iron forming due to a too fast cooling rate.
PDW
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16th Aug 2017, 10:04 AM #5Golden Member
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I have had success with brazing castiron before, the trick is to heat it up prior and cool it down slowly afterward. I am guessing the gear is not big enough and the carbon level is not as high in this particular gear to be concerned?
I am guessing arc weld with castiron electrode will do the trick too. I have some and I am in Melbourne if you need them? PM me your portal I can send them to you.
IMG_6547.jpg
IMG_6563.jpgLast edited by jackaroo; 16th Aug 2017 at 10:15 AM. Reason: Add photos
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16th Aug 2017, 10:46 AM #6Golden Member
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There are many ways to skin this cat. I am dealing with the same problem at the moment with a bevel gear off my hulse planer. Unfortunately it has 2 teeth missing that are together so a little more complicated.
The easy method is as Peter describes. For low speed,low stress gears this is the easiest, quickest and generally more than adequate end result. But you would generally need access to oxy/acetylene which not everyone has. I've not used oxy/LPG or one of the MAPP torches with propane and i'm not sure if that would be adequate.
Cast iron welding especially with nickel rods (or other cast iron specific rods)can be done and I think (although no solid proof) would gives a more solid tooth. Welding cast iron is not for the uninitiated but remember clean well, prepare the site by grinding a suitable base, preheat and slow cool and should be fine.
Both these approaches would then involve using a file to shape the tooth profile.
Generally don't need holding pins or other structural supports unless it is under a far amount of stress. More common on bigger spur gear repairs.
A proper bevel gear tooth profile can really only be generated by a bevel gear cutting machine. A rough but mostly adequate profile can be generated on a manual milling machine but requires some homework to calculate the lateral and rotational offsets, some way of indexing the gear while at the appropriate angle, a cutter that will do the job. There are entire books devoted to cutting a bevel gear.
Personally I have built up the area of the tooth with nickel welding rod and plan to recut the tooth profile on my milling machine. It seems like a good challenge and will post some pictures when I do it. Have had some issues with the retaining mechanism for my horizontal arbor on the SHW mill which has delayed progress along with the fact that I have two jobs and trying to build two sheds at the same time.
Mark
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16th Aug 2017, 11:19 AM #7Banned
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Not sure what material it is but if it's not cast you can get stick rods for welding up gears. I've done it with a ride on gearbox I've made and it worked well. Only problem I had was machining the gear afterwards and the rods were something like $150 a packet, so I bought a couple of rods from a local engineering shop..
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16th Aug 2017, 03:26 PM #8Golden Member
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This used to be a project when learning Oxy at tech, build a tooth in cast iron and then dress it with a file. It is a long time ago but I seem to remember we did it both with CI filler and Bronze filler.
CHRIS
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16th Aug 2017, 09:07 PM #9Golden Member
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Wow. Thank all for responses. Sorry for late reply.
jackaroo: I reckon I've watched every gear repair video on youtube. ) On that second posting of yours with pics - nice repair indeed.
I don't have a welder (though I did a great and fun TAFE course in welding a few years back). I also don't have an oxy/acetylene setup. But maybe have access to one.
Kryn, thanks. I kind of doubted that stuff would do the trick, but it have 'silver' and 'solder' on it and so I was speculating that it might be hard solder ... but doubted that as it was coiled. )
That video is a cool repair, though as this is a bevel, I'd not be able to machine it out unless, as Mark says, you do lot of hard work with bevel specifics.
Mark - do post pics when you get there. )
So, it sounds like maybe pin it to be sure, build it up as PDW & Chris describe with some hard brazing material suitable for cast iron (sacc51 - yes, it is cast) using oxy/acetylene, let it slow cool (maybe in some dry sand) and then file it to shape.
Easy. At least if I stuff it up, it can always just be filed back re-brazed and done again.
Thanks again all,
Greg.
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16th Aug 2017, 09:49 PM #10but it have 'silver' and 'solder' on it and so I was speculating that it might be hard solder ... but doubted that as it was coiled.
Dean
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17th Aug 2017, 06:44 AM #11
Hi Guys,
If it is real silver solder/silver braze, it will have the percentage silver mentioned somewhere on the packaging. The higher the silver content the more it costs.Best Regards:
Baron J.
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17th Aug 2017, 04:27 PM #12Most Valued Member
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You can use a TIG torch as a heat source rather than O-A but my results have been pretty mixed. OK to good on a flat surface lapped/butt type joint, lousy for an internal tight fillet. I simply couldn't stop the arc from going sideways and not into the root. Don't know why, I've done lots of joints on 316 pipe and the like. The thing I had trouble with was a broken iron casting in the T&C grinder. After deciding I was wasting time I used the O-A setup and had it done without further problems.
PDW
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18th Aug 2017, 08:09 PM #13Golden Member
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I am interested in thoughts and experience on this guy:
https://www.machineryhouse.com.au/K075
The "Professional Oxyset Mobile Brazing & Welding System". I know it is not O/A and have read about hydrogen embrittlement when welding - but, this is for brazing and heating. It ain't too expensive and could be handy.
Also, anyone used a "weed burner" torch for brazing? Likely with a smallish head/jet I guess.
Greg.
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19th Aug 2017, 12:28 AM #14
Hi Greg,
That setup is basically Oxy propane. Very heavy on oxygen though. With the correct regulators you could use it with acetylene. I used to have one similar but it got stolen some time back. Ok for fairly small work and brazing.Best Regards:
Baron J.
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19th Aug 2017, 12:51 AM #15Most Valued Member
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This is a possibility, look at either borrowing an Oxy Acetylene set or buying one. For the bottles, use the small ones, "D" I think they are. You'll be asked to pay a years rental and for the contents, use them up and return the bottles ASAP or within the month, and get a refund for your rental.
KrynTo grow old is mandatory, growing up is optional.
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