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Fork crown brazing

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Old 01-12-18, 02:03 PM
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calstar 
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Fork crown brazing

Do you braze your blades and steerer at the same time? Here's a Brent Steelman vid of what I mean:


Also, why are the crown blade openings not fluxed before inserting the blades?

thanks, Brian
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Old 01-12-18, 02:14 PM
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fietsbob 
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He builds Unicrown forks mostly, from what I have seen..
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Old 01-12-18, 02:36 PM
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Originally Posted by fietsbob View Post
He builds Unicrown forks mostly, from what I have seen..
Why would that make a difference?

Brian
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Old 01-12-18, 02:40 PM
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no fork crown at all..
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Old 01-12-18, 03:49 PM
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David Tollefson
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Couple things to note:

* He does have flux in the crown already, along with some brass. He knows when the steerer/crown joint is up to temp when he can see the brass flowing out the crown race seat end (bottom).
* He's using a "big ass tip" (a small rosebud). That's pouring a lot of heat into the crown in a short time.

I think it also depends on how your jigging works. What access you have, etc.

My method: I generally do a two-step process (well, three, because I'll often put a plate on the bottom of the steerer to close that off). Brass on the steerer to crown, and then silver on blades to crown. I use a #4 tip with oxy/propane, and it gets the job done. I like to be able to feed brass into the crown/steerer joint through the blade openings. I also drill the steerer to vent through the crown.
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Old 01-12-18, 05:49 PM
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Originally Posted by David Tollefson View Post
Couple things to note:

* He does have flux in the crown already, along with some brass. He knows when the steerer/crown joint is up to temp when he can see the brass flowing out the (bottom).
* He's using a "big ass tip" (a small rosebud). That's pouring a lot of heat into the crown in a short time.
He states he has flux in the top(crown race seat end) of the crown(points to it) but not where the blades are inserted, no flux is visible on the blades in the insertion area before he applies it externally, it appears there is none in the insertion area, maybe I'm wrong though.

Yes he's using a rosebud, not sure what difference that makes in the brazing sequence, just up to temp quicker.

Thanks, Brian
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Old 01-12-18, 08:51 PM
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I feel like brass is a little less sensitive to the presence of flux, and some probably wicks in there when he is heating it up.

I really like building forks. I have a pile of forks in my shop, waiting for frames.

I do the fork crown first with silver and then the blades. I like to see that the silver has created a fillet in the windows in the crown. I pull the silver through from one side to the other, so there are always fillets, but it makes me happy to see them.

I go back and heat up the first blade when I'm done with the second. It doesn't take that much, I don't get it red or anything. Never had to set a fork or file a dropout either.
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Old 01-13-18, 01:41 AM
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Originally Posted by unterhausen View Post
I go back and heat up the first blade when I'm done with the second. It doesn't take that much, I don't get it red or anything.
Please elaborate! Do you heat just at the crown socket or the whole blade? Front, back, both? Enough to soften the filler or just enough to sort of 'normalize' the cooling? Two of the four I recently built required a touch with the file on the left leg dropout. I had to remove about 0.2-0.3mm to center the wheel after aligning which was annoying.

I have same process as Unterhausen - silver the crown to steerer. I actually leave a bit of extra flux in the sockets when putting the crown on the steerer so I can scoop it out and put more on as I'm going around the crown. I use a #4 which is about the max my tanks will handle. After the crown is on, I cut the headset race, then I flux up the sockets and dropouts and assemble in the jig. Then I do the dropouts and finally the sockets.

Last edited by duanedr; 01-13-18 at 01:47 AM.
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Old 01-13-18, 05:32 AM
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Originally Posted by duanedr View Post
Two of the four I recently built required a touch with the file on the left leg dropout. I had to remove about 0.2-0.3mm to center the wheel after aligning which was annoying.
Do you do the left leg second? My fork fixture allows some movement of the steerer tube in the clamp. I found that the expansion, from brazing the first leg, pushed the crown and steerer up slightly and had the effect of pulling the other leg out of the crown a small amount. This caused the second leg to be slightly longer than the first. The fix was to evenly heat both legs until they were close to brazing temp and then do each one individually.
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Old 01-13-18, 01:06 PM
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Originally Posted by dsaul View Post
Do you do the left leg second? My fork fixture allows some movement of the steerer tube in the clamp. I found that the expansion, from brazing the first leg, pushed the crown and steerer up slightly and had the effect of pulling the other leg out of the crown a small amount. This caused the second leg to be slightly longer than the first. The fix was to evenly heat both legs until they were close to brazing temp and then do each one individually.
Right, that was my thought that something in the sequence is pulling the steerer/crown away from the one leg. My steerer is clamped 'gently' with toggle clamps in 2 axes and the crown is brazed to the steerer. I think Brent mentions something about brazing the crown/legs together at one sitting results in straight forks - it could be to avoid this shifting. I'm building another fork this weekend finishing up another project so, I'll look at this. Thanks
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Old 01-13-18, 05:45 PM
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There are fluxing including torches now too ..
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