Braze Welding Gear Tooth Repair

[David MountainParticipant @davidmountain83941]

Hi all

I need to braze weld a gear tooth repair on a boxford lathe. I'm wondering if I'll get enough heat output from the likes of this

https://www.bunnings.co.nz/tradeflame-tf-ultra-gas-turbo-blow-torch-kit_p5910235

or do I need to get a bigger unit?

Any suggestions?

I do have some cast-iron stick welding rods that I could use. Is this an option?

[David MountainParticipant @davidmountain83941]

[larry phelan 1Participant @larryphelan1]

Would love to hear the feed back on this one !

I have a similar gear waiting for repair.

[Brian WoodParticipant @brianwood45127]

I have done inserted teeth repairs on both cast iron and steel gears using oxy-acetylene for SIF_Bronze brazing. The same method has been used to repair other cracked cast iron components..

You do need a high temperature locally to melt the braze for the process to be successful, I am not sure propane torches alone would raise the joint temperature enough for the braze to flow.

Brian

[not done it yetParticipant @notdoneityet]

I would say you don’t need a bigger unit but it would be better, and much easier, with a larger heat output.

Clearly it gets hot enough to braze (not weld), but the heat output will be the limiting factor.

Is it a CI or steel gear? I would not be trying to weld cast iron and then machining afterwards, but others might.

Braze is the way to go. Or just set in some grub screws and file to shape. That type of repair has worked for me, but I prefer to insert screws, fill with braze, then machine to profile.

[Dave HalfordParticipant @davehalford22513]

It depends on how big the gear is, you have a finite time to heat it before the flux dies.

Do you know the composition of the rods? 99.5% nickel Ok, otherwise you might have to shape you new tooth with the angle grinder. Don't ask how I know .

What is the condition of the rest of the teeth?

I'm guessing this is one of the backgear train, you can turn off all the old teeth, bore out a bought in gear (or cut your own) to match and Loctite them together, then drill and tap the joint for a screw then cut the heads off.

[Simon Williams 3Participant @simonwilliams3]

Good Morning all,

There are two different though related processes being discussed here, and hence the debate over the heat input.

Brazing is where you heat the whole item – or enough of it locally – to get the bronze filler to flow into the work. This implies you have a general temperature suitable to get the filler to melt and flow. Very difficult to control where the filler goes, other than a thin layer on the surface of the hot area, or pulled by capilliary action into a fit-up gap. A Sievert or a Bullfinch gas torch would be suitable for this process, provided the burner was chosen appropriately.

Bronze WELDING, where the heat input is very localised (though possibly with the use of a pre-heat to control distortion etc.) This uses the heat of the flame to melt the filler metal locally, so it fuses but by manipulation of the heat you can build up a fillet or an insert of bronze material locally. This is the process you can see Adam (Aborn 79) or Keith Rucker use for the task being discussed.

The necessity for a significant localised heat input makes bronze welding the territory of oxy-acetylene, though you can do it with oxy-propane if needs must. But you need the small intense heat source to locally melt the filler deposit as you add more to build up the weld metal in layers. The skill is in manipulating the heat input so as to melt enough but not too much.

TIG brazing is the same process – the terminology is very confused. However the visibility difficulties with having to use a welding mask to see anything at all means that using a TIG torch as the heat source is a whole lot more difficult.

Having built up the filler sufficiently then you machine it back appropriately to give the gear tooth profile. You might well end up with a gear tooth of bronze amongst a whole lot of iron ones.

Keith Rucker does exactly this job in one of his planer restoration videos, he makes the point that you need to grind the parent metal out to get back to good material to which the bronze weld will adhere.

The tooth resulting looks a bit odd; provided the process is done without overheating the silicon bronze filler rod and burning off the alloy constituents the filler is potentially stronger than the parent cast iron.

HTH Simon

Edited for typo

Edited By Simon Williams 3 on 01/06/2020 10:38:01

[HopperParticipant @hopper]

You won't get enough heat out of one of those Bunnings propane torches to successfully bronze braze or weld. You need oxy acetylene to get the local area hot enough to successfully do that. Where the Bunnings marketing spiel says you can "braze" copper pipe with that torch, they are referring to silver brazing, (aka silver soldering) which requires a much lower temperature that brazing with a bronze rod. It's a plumber's torch and that's about all.

Bunnings used to do a mini oxy-Mapp gas two-bottle set that was a hotter flame, but only a small torch for small jobs so also wouild struggle to heat a large gear up enough for such a bronzing job.

Might be one of those instances where it is cheaper to pay a local welding expert to build the gear up for you, given the cost of oxy acetylene kit these days. Bottle rental alone is prohibitive for home use in most cases.

[J HancockParticipant @jhancock95746]

Nothing wrong with good bodge but I would think a tapped to plain shank Allen screw(s) filed to tooth profile is about equal to all the heat damage to adjacent teeth by brazing/welding ?

[Peter SansomParticipant @petersansom44767]

To Bronze braze you need either Oxy acetylene or Oxy LP gas. The LP Gas of any form without Oxy are good for silver brazing. Acetyle is required to Oxy weld.

Back in the early 70's that was what we were taught by the boiler making apprentice instructors. Where i was working at the time, repairing gears by bronze brazing to repair broken cast iron gears was regulary performed.

Peter

[Simon Williams 3Participant @simonwilliams3]

And if you are interested to see it in practice, here's the Keith Rucker video I referenced

**LINK**

As you can see, apart from the fact that the finished article is multicoloured, it makes a very workable repair.

Best rgds Simon

[BazyleParticipant @bazyle]

You have to meet the temperature to melt brass but not to melt cast iron. Plus you need enough heat provision at that temperature to overcome heat loss due to inadequate insulation.
Plain propane-air does reach the necessary temperature so it is then a matter of volume in proportion to the size of your part and the insulation you have. So use a good arrangement of vermiculate type boards not heavy hearth bricks.
Oxy-Acetylene concentrated risks thermal shock cracks.

[David MountainParticipant @davidmountain83941]

Posted by Simon Williams 3 on 01/06/2020 10:35:56:

Good Morning all,

There are two different though related processes being discussed here, and hence the debate over the heat input.

Brazing is where you heat the whole item – or enough of it locally – to get the bronze filler to flow into the work. This implies you have a general temperature suitable to get the filler to melt and flow. Very difficult to control where the filler goes, other than a thin layer on the surface of the hot area, or pulled by capilliary action into a fit-up gap. A Sievert or a Bullfinch gas torch would be suitable for this process, provided the burner was chosen appropriately.

Bronze WELDING, where the heat input is very localised (though possibly with the use of a pre-heat to control distortion etc.) This uses the heat of the flame to melt the filler metal locally, so it fuses but by manipulation of the heat you can build up a fillet or an insert of bronze material locally. This is the process you can see Adam (Aborn 79) or Keith Rucker use for the task being discussed.

The necessity for a significant localised heat input makes bronze welding the territory of oxy-acetylene, though you can do it with oxy-propane if needs must. But you need the small intense heat source to locally melt the filler deposit as you add more to build up the weld metal in layers. The skill is in manipulating the heat input so as to melt enough but not too much.

TIG brazing is the same process – the terminology is very confused. However the visibility difficulties with having to use a welding mask to see anything at all means that using a TIG torch as the heat source is a whole lot more difficult.

Having built up the filler sufficiently then you machine it back appropriately to give the gear tooth profile. You might well end up with a gear tooth of bronze amongst a whole lot of iron ones.

Keith Rucker does exactly this job in one of his planer restoration videos, he makes the point that you need to grind the parent metal out to get back to good material to which the bronze weld will adhere.

The tooth resulting looks a bit odd; provided the process is done without overheating the silicon bronze filler rod and burning off the alloy constituents the filler is potentially stronger than the parent cast iron.

HTH Simon

Edited for typo

Edited By Simon Williams 3 on 01/06/2020 10:38:01

Thanks. This is exactly what I needed. I thought it was still called brazing

[Ady1Participant @ady1]

I've been giving it a go with CI and so far no disappointments

As long as it's good quality CI you can get a nice join

Have welded a vertical steel tube to a vice anvil and a bearing to the end of my drummond leadscrew with 2mm sticks and a Lidl inverter 80Amp welder

No doubt these are not to any "standard" but they seem to be fine for hobby standard

Wish I'd known about this before I sorted out my backgear, which took many weeks to complete via more manual methods

Other bits you really need to make the job fast and simple are an angle grinder and drill with a wire brush

I find that a small ball end peening hammer is much better than a pointy hammer for removing slag with gentle taps

Edited By Ady1 on 02/06/2020 09:35:39

[Simon Williams 3Participant @simonwilliams3]

Does anyone know if the deposit and the heat affected zone from using cast iron welding rods – presumably nickel based – are machinable? I'd hate to hit a hard patch at the interface between the weld and the parent material and knock the edge off one of my gear cutters.

Rgds Simon

Edited for the obligatory typo

Edited By Simon Williams 3 on 02/06/2020 11:03:19

Edited By Simon Williams 3 on 02/06/2020 11:03:51

[not done it yetParticipant @notdoneityet]

They would need to be very high nickel content (99%?), not just ‘nickel-based’. Steel plus all the carbon in the cast iron cooling quickly will be like chilled cast iron castings and very high carbon steel.

I simply machine the broken tooth/teeth area, insert the reinforcing screws, screw on a couple of ‘side bars’ to retain the braze, fill with braze, machine off the side bars and recut the teeth. Quite simple and relatively straightforward, with no worries of hard machining, weld falling off, overheating the gear, etc,etc.

[David MountainParticipant @davidmountain83941]

Posted by not done it yet on 02/06/2020 12:07:29:

They would need to be very high nickel content (99%?), not just ‘nickel-based’. Steel plus all the carbon in the cast iron cooling quickly will be like chilled cast iron castings and very high carbon steel.

I simply machine the broken tooth/teeth area, insert the reinforcing screws, screw on a couple of ‘side bars’ to retain the braze, fill with braze, machine off the side bars and recut the teeth. Quite simple and relatively straightforward, with no worries of hard machining, weld falling off, overheating the gear, etc,etc.

I have a Tauco drill press with a terrible smile-of-shame from years of use before I got it. I tried the cast iron welding rods to fill weld it and it welds alright, but the weld is very HARD. File just skates right over it. I was going to have to spend ages grinding it down, and probably make more of a mess than just leaving it like that. Plus there was a strong possibility of warping the table so I gave it a miss.

I have however had good success in welding up a cast iron handle so I would not dismiss the whole cast iron arc welding idea.

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