Messy fillet brazing and (bad?) solution...

[christo]

It took me some time but i finally finished this project, for a good part thanks to your advise. I scraped the initial frame and used it to practice more on fillet brazing. I think that part of the distorsion was due to poor miters. As I don't have much time to practice hand mitering until it gets perfect, I build an abrasive mitering machine that works pretty well.

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I then practiced on scrap tubing (the picture only shows a little part of the practice) until i feel more comfortable with heat control and also fillet finishing.

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I then went back to the frame with a new tube set. When done, I couldn't resist to assemble the bike without paint, to see if the geometry fits me well. So far so good, it just needs a seatpost with more setback and a slighlty longer stem.

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My only concern (and question to you guys) is about a few tiny holes in some fillets .

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It didn't show up during practice brazing, but I think I was a little nervous with the real thing and my heat control wasn't always perfect. Question is : does it matter if I leave those holes as they are knowing that the frame will get powder coating ?

Thank you for reading

Christophe

[Chauncey Matthews]

Congrats on finishing your first!
Yeah you can leave the holes and the bike will be fine, but be forewarned, if you think are noticeable now they will be twice as glaring after powdercoating.
Also, it looks like you have your seat clamp on the .6 part of the seat tube, its going to crack right along the stress riser at the top of the sleeve. Get a bigger clamp that fits the sleeve and cut the slot a little longer...easy to do now that it's not painted.

[einreb]

Question is : does it matter if I leave those holes as they are knowing that the frame will get powder coating ?

You can fill them with JB Weld before powder coating.

[David Tollefson]

You can fill them with JB Weld before powder coating.

Or silver.

[steve garro]

Yeah you can leave the holes and the bike will be fine

You can get porosity to porosity cracking, actually.

- Garro.

[Chauncey Matthews]

You can get porosity to porosity cracking, actually.

- Garro.

True, I should've added "because its your first frame and its not like you'll be riding it for years and years..."

[christo]

Many thanks for the feedback and the advises. It seems that I can find some JB Weld here in France, so I'll fill those holes as soon as I receive this product.
Chauncey, about the seat tube, I get your point on the weakness of this configuration. I should have put more thoughts on it. The sleeve is just above 30mm diameter and I can easily find a proper seat clamp. For the modification your are advising, I don't know if I have enough space to extend the slot.

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What do you think about brazing some more 30mm sleeve around the 28.6 portion of the seat tube ?

Again, many thanks for your feedback

Christophe

[duanedr]

I found my porosity holes didn't even show up before powder coating but afterwards surprised me by showing up in a couple places and being quite visible.

What causes that? I don't recall the brass boiling which comes to my mind as a potential cause. Could it be impurities? I hand miter, sand with 100 grit and then wipe with rubbing alcohol before applying flux.
Thanks as always

[Will Neide]

I found my porosity holes didn't even show up before powder coating but afterwards surprised me by showing up in a couple places and being quite visible.

What causes that? I don't recall the brass boiling which comes to my mind as a potential cause. Could it be impurities? I hand miter, sand with 100 grit and then wipe with rubbing alcohol before applying flux.
Thanks as always

I'm assuming you dropped off at the powdercoater and they sandblasted it. This will remove any dust/etc from the pinholes and make them more visible. As far as preventing them, I've found the more I braze, the better/quicker I get with control, the less they appear (or just flat out don't appear). I think going slower and hanging around in one area too much (too much heat) increases the frequency of the "bubbles."

[dbohemian]

We can all get a unexplained pinhole from time to time. Being a painter it is a normal occurrence to fill these. It is one of the disadvantages of powder. With powder you can have a very small pinhole but it will look huge after cure because the air in the pinhole can expand and pop out the top making a crater that looks quite a bit larger than the original. You have to fill the holes preferably with a conductive filler (aluminum doped) any high temp epoxy will work on small ones. It is hard to sand this stuff smooth so it is no fun.

As far as preventing them, I am sure it has been discussed alot here but in addition to all the normal stuff (dirt, overheating) you may consider a very, very, very slight oxidation to your flame. When I say this I cannot emphasize how small I really mean. Students routinely over-oxidize which is a big no no. I mean like a 20th of a turn extra. What does this do? With most of the bronzes we use there is some zinc in them. The zinc oxidizes (zinc oxide) and this in turn creates a film on the fillet during brazing that helps to cut down on porosity. Of course you have to have your other bases covered (clean, clean and clean again) but this little trick sometimes helps.

[Mark Kelly]

Dave, what about silver solder as a filler? The Harris Stay Brite, available as a small cheap kit , has a solidus / liquidus of 220 / 280 so it can be worked at temps that won't touch the primary braze alloy but will survive powder coat.

[Mark Kelly]

And another thought: if you dope an ordinary epoxy with enough carbon it becomes conductive and it's pretty easy to sand. You can get milled carbon from many composite suppliers.

[duanedr]

The zinc oxidizes (zinc oxide) and this in turn creates a film on the fillet during brazing that helps to cut down on porosity.

Ah, is this the light gray stuff I see after I finish a joint? Here's a recent practice joint that I found a light gray film around - which is I suppose fairly common for me. The gray film is from the joint on the left of the picture, not the central joint.

anything else look wrong in this picture while I have your collective attention?

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Thanks