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rebrazing repaired crack in cast steel?


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Hi everyone,

I made my first attempt at brazing some cast steel today. It's a blade guide off a horizontal bandsaw made in Taiwan, so I'm not really sure what type of metal it is. The part was broken in three places and I think the brazing was reasonably successful, but it was a bit sloppy with too much bronze puddled in some spots and not enough in others. In the pic below you can still see part of the crack at the top of the part and a partially filled hole drilled by the previous owner as part of a xxxx  poor repair with a corner bracket. I'm not too worried about this piece, but if I wanted a better looking job would it be ok to reheat the part and add some more bronze to fill that crack and hole better? Or could reheating potential weaken all the joints on this piece?

Thanks.

P_20200923_130253.jpg

P_20200923_171539 (1).jpg

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That doesn't look like a bad job. Sure you can try to improve what you have now and YES heating it to brazing temp WILL soften, maybe melt the bronze there now. Were it me I'd mount it up and see how it works. Pretty it up if it breaks again, maybe even reinforce it some.

Frosty The Lucky.

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Thanks Frosty. I'll take your advice and leave this piece alone unless it breaks again. I was just wondering what I might do if it was an item where appearance was more important. I also wondered if I bevelled the edges of the crack too much? Maybe with a smaller bevel it would have been easier to fill that gap without the bronze running out.

 

p.s. My apologies for the inappropriate language in my original post.

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I honestly don't know if it's iron or steel, but it's definitely cast. I'm a total noob when it comes to this stuff, but I thought I read that it can be difficult to tell the difference with metal like this of Chinese origin.

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Next time don't bevel for a brazed join, aggressive wire brushing is plenty. The thinner the layer of braze the stronger the joint. We used to tin one side, that's applying a THIN layer of brazing rod to one side then wipe it with a clean dry rag. Fit the pieces together with a DUSTING of flux and heat both sides to brazing temp. A touch with the brazing rod indicates when they are at the proper temp. 

The break says cast iron to me, casting steel is expensive and it's not needed for band saw guide rolls. It was probably broken originally by someone hitting it while putting stock in the saw to cut or by a mumbledy mumble knothead trying to adjust it with a hammer. The world is full of idjits.

Frosty The Lucky.

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7 hours ago, Frosty said:

Next time don't bevel for a brazed join, aggressive wire brushing is plenty. 

Thanks for the tips. I was looking for some flux before I did this job, but there was nothing available locally. Is powered flux the way to go? I've seen both powder and paste on Amazon. Below is an example of the powder flux. Would it be a good choice? I've got a broken Langdon Mitre Box from the 1800's that I'd like to try repairing next and will try and follow your suggestions for that one.

Remove commercial link per TOS.

 

 

hot max brazing flux.jpg

Edited by Mod30
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That one does not have any fluorine compounds, so I say it is a good choice for a general braze flux. Keep away from the ones containing fluorine compounds unless you know exactly why you need it, and have good enough ventilation (1st) and PPE (2nd, and necessary but no substitute for active ventilation) where you and others around won't be breathing it. Keep in mind where the vented stuff goes, too. 

https://www.hotmaxtorches.com/download/msds/24000%20Brazing%20Flux%20Powder%20MSDS.pdf

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  • 2 weeks later...

Hey everyone. I put the guides back in service and they seem to be holding up all right so far. First big test was pressing the pins back in that hold the back bearings in place. I was half expecting the pins to not go back in or the welds to blow apart. So it was a big relief when they went in smooth and snug.

I know this started as a welding question, but I'm wondering if someone could tell me about the proper orientation of the side bearings that are on eccentric bushings on these 4x6 bandsaws? Are they both on the outside of the blade? That's where they are now, but this machine was poorly repaired in the past and I don't know if they were put back correctly. 

Thanks.

 

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