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Bauer (NZ) Repair Thread

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Bauer (NZ) Repair Thread

Old 12-14-22, 07:33 PM
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Bauer (NZ) Repair Thread

This post is just a marker. I pretty much lack all the tools necessary to effect the complete repair. I am also a complete novice, having done just enough work building a frame in Doug's shop to be dangerous. That said, Mad Honk gifted me a busted Bauer (NZ) Momentum frame. (I'd never heard of the company before and can find very little about them online.) I figured while I might completely muff the repair, it would still be good experience and others who come after can learn from my mistakes and questions. I will acquire tools as I go. Call it a winter project. It might turn out to be a two winters project, who knows? I'm sure I will have questions as time goes on, but for now, I will just describe the problem.

The frame has two significant problems, a bad dent on the LHS of the top tube and a LHS seat stay which has come apart from the seat tube. There are two smaller dents, one on the RHS of the top tube, one on the down tube. As one would expect with the dents and the broken joint, it's also a bit misaligned. I spent a bit of time with a scraper, some sandpaper, and a tubing block to clean things up a bit today.



It will be cold here next week, so I'm going to try freezing water in the top tube to see if it improves the bad dent.

The rear triangle needs to be aligned before I can do much with LHS seatstay. That's just as well, as I don't currently have a torch. I just cleaned up the area a bit.

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Old 12-14-22, 08:28 PM
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Looks like the post binder ears need some attention too Good project for learning on a few levels.

One path would be to do an alignment (with the LH dropout location left "loose", alignment based on RH side that's still intact) then install in a jig to have geometry trapped so to speak. Do one aspect at a time, replace or fill the tube/dents. next replace/reattach the LH SS. I hope the seat lug was done with brass/bronze as this will make the repair of the lug ears easier. Andy
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Old 12-15-22, 03:23 AM
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When it comes time to tack the loose left seatstay to the seat tube, I recommend pinning it. Otherwise as soon as you start heating it to tack it (say, with brass) it will thermally expand and creep further up on the ST. Then shrink on cooling, making it too short, so the wheel doesn't sit straight. Apologies if this explanation is too obvious, I'm pitching it at beginner level for any beginners reading. After pinning, take it out of any rigid fixture and braze with it free to move a little, so the forces from thermal expansion don't force the stay to slide up on the seat tube. Even with a pin, some creep is possible if the forces are high. A dummy axle joining the two dropouts is fine, but not more rigid than that.

My preferred way: 1/8" taper pins, 1/2" long, like these.
They're nominally .115" at the small end of the taper. I drill with a #32, nominal .116" (coincidence?) There are tapered reamers to make the hole fit the taper pin along its whole length, but I don't use one, I just hammer 'em in to the plain #32 drilled hole. There's enough elasticity and/or yielding (in the pin and the hole both, in some proportion) so the pin ends up tightening into both of the pieces being pinned. Even with such a tight fit, I've always gotten braze penetration through the hole, by what miracle I don't know, but it's been 100% reliable over literally thousands of pins. You see a tiny ring of filler come through from underneath. Talking mostly lugs here but I've used them on lugless joints like this too. I used to put at least 2 of those into every lug — more in the seat lug, because each seatstay got one.

You wouldn't necessarily have to drill the seatstay too, if you put the pin in the seat tube only, right at the top of the seatstay, but I think it'll be more reliable to put the hole through the stay as well. Very close to the top of the stay, to keep the pin itself short, and minimize the leverage that the stay has for moving the pin.

You nip off any extra pin sticking out the outside, after brazing, with big dikes or a small bolt-cutter. Any pin sticking through on the inside will need to be dealt with, probably by reaming, so keep the stickout on the inside to a minimum. Not much comes though when you drill with a #32, but you still might want to grind the tip back a little, if there's a lot of poke-through. Don't leave too much for the reamer to do.

BTW those pins come in SS too, if you're building a SS bike that won't be painted. You don't want little circles of rusty steel appearing later.

I'd probably avoid the ones in 12L14 steel, because that alloy contains lead. I've been warned not to weld or braze on that stuff due to toxicity, but I don't know how much it matters with such little pins. "How dangerous could it be?" <— famous last words? There might be other problems with it too that I don't know about. The ones I have all the experience with are plain carbon steel and SS, never tried 12L14 (which is apparently what McMaster sells)

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Old 12-15-22, 08:27 AM
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It will be interesting how you get along on this repair. It already is. Thanks for posting.
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Old 12-15-22, 09:39 AM
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Mark- How does one pin a fastback/shot in stay attachment? Would a tacking hold against the heat forces if not melted during the flow in the other side of the joint? Andy
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Old 12-15-22, 05:24 PM
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Originally Posted by Andrew R Stewart
Mark- How does one pin a fastback/shot in stay attachment? Would a tacking hold against the heat forces if not melted during the flow in the other side of the joint? Andy
Tacking with brass you mean? I think it can hold, but even a quick tack gets some themral expansion so by the time you have it tacked , it's already moved up the seat tube a little. The faster you tack the better and someone real good can keep the thermal expansion to a minimum, but maybe at the expense of the strength of the tack.

And then when the tack gets "kinda warm" as you braze the joint, it can squirm some even before it reaches the melting point. It gets really weak at temperatures that are are hot but still below solidus. Anyway, do-able, but I still like steel pins.

Here's my super-professional technical drawing for where I'd pin it, right at the very top of the seatstay:

Not to scale! I just realized I drew the pin too small, relative to the seatstay. Pin is about 3 times as thick as the wall thickness of the stay, and almost as long as the OD of the stay.

Since drilling the stay at that angle will be tricky, I'd start by drilling just the stay from the back (mitered) side, with a smaller pilot drill. I like a #2 center drill, 3/16 shank with 5/32" point, they don't wander as much as a normal drill that small would. (everyone here knows that trick, right?) Then say 7/64", then open up to #32. Just flex the stay out to the side to get access to the back side for drilling. With the frame not held in a jig, there's enough flex in the rear triangle to do that without yielding anywhere. Once you have a #32 hole thru the stay, you can put it back in position and drill the doubler and seat tube to #32, using the existing hole in the stay as the guide. Don't let it squirm while drilling, clamp everything rigidly for this operation. This is your one chance to nail the stay down in precisely the right spot. When brazing (free of the jig), I'd probably start at the pin, solidify that area first.

Note on jargon, a #3/0 pin is not the same as a #3, which is much larger. #3/0 should be read as "triple aught". Needlessly confusing, so hopefully your supplier will just call them 1/8" at the larger end or some such.

Just found this pic showing the inside of the DT at the BB on one of my old frames. You can see the little fillet around the inside of the pin showing it is fully brazed in place.



Bonus: it doesn't hurt as much as a nail if you snag your finger on it.

We tried smaller pins too but settled on this size for ease and practicality.

Last edited by bulgie; 12-15-22 at 05:30 PM.
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Old 12-15-22, 08:16 PM
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Skip,
You do have your hands full with this one! I doubt the freezing water will help much without doing a bit more damage. You have used frame blocks on the dent to round it out correct? If so I would use some brass filler and leave it after getting it round again. As for the rear, I would try aligning the back and then do the pin thing and repair the seat stay normally. It looks like you have got a good start on it. Smiles, MH
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Old 12-19-22, 07:56 PM
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Why not use an extension from the seat lug ear to manually hold the tube in position?
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Old 12-19-22, 08:11 PM
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I spent a bit more time with sandpaper and scraper the other day. Here's what things look like on the seat tube at the moment. It seems the joint for the right side seat stay is also a bit sketchy. I wonder if the joints were ever in great shape. I'm not able to get a very good picture in my somewhat dim basement shop, and it's too dang cold to take it outside for better pictures right now. (Click the image to go to the photo on Flickr.)

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Old 12-19-22, 09:38 PM
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Originally Posted by smontanaro
I spent a bit more time with sandpaper and scraper the other day. Here's what things look like on the seat tube at the moment. It seems the joint for the right side seat stay is also a bit sketchy. I wonder if the joints were ever in great shape.
Yeah both stays should have a small fillet added for more strength and to hide the original work, which is not the worst, but kinda poor.

That seat lug slit is crying out for a round hole at the bottom. Debateable whether it's strictly necessary structurally, but it looks like caca without it.

Good photography, I felt like I was right there and with my reading glasses on!

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Old 12-20-22, 09:40 AM
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As long as I was working this area with a torch I might also remove the lug's binder ears and attach a more solid binder barrel. I assume the lug and stays were joined with a brass/bronze. Andy
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Old 12-20-22, 06:02 PM
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I've experimented a bit trying to use freezing water to pop dents out frame tubing. Tape off vent holes on one end of the tube, add water to a few inches below your dents and let that freeze into an internal ice plug. With lower solid ice plug in place, add more (unfrozen) cold water covering a few inches above the dent and add ice chips to float on top of the water column. Wrap the lower dented portion of the tube with insulation so it is slowest to freeze, leaving the top of the water column & ice chips protruding several inches above the dent & insulation. Idea is to get the ice chips on top of the water column to freeze first and form another (top) plug, instead of just slowly freezing the entire water column inside the tube. It would probably work well to use application of CO2 spray to speed up formation of the top ice plug. With ice plugs at top and bottom of the column, leave the trapped water in the insulated area to freeze last. Challenge is that if you were to entrap too large of a volume of unfrozen water, the large expanding volume could generate enough expansion force to split the tube. Start by experimenting with a relatively small volume of trapped expanding water. Give it a long time (24hours at 20°F) to complete freezing, always takes longer than it seems it should. Check progress then thaw and repeat process for a gradual repair as needed if it does not complete in one try.
Looking at the tube dents on the Bauer in this thread, I would expect that those dents are probably creased too sharply for the ice-fix to fully repair. Filling the dents with bronze would work fine and will be plenty strong here.
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Old 12-20-22, 06:18 PM
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Looking at both seat stay I think I would pin them and then build up the entire area of the heart with brass and finish with the extra around the stays cleaned into a nice finish. As for the seat post lug, the last one I repaired we actually welded a washer on top of the lug and then ground it down to a finished look. It turned out even stronger than the original lug. Smiles, MH
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Old 12-26-22, 04:24 PM
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Here’s the way I like to reinforce these older pressed lug binder bolt ears. Find a piece of tubing the right size to hold a Campy-style seatpost binder bolt, drill out the lug to allow the tubing to slip through, left a little over-long, braze it in, over-filling the squished ends, and sculpt back to shape.

https://www.flickr.com/photos/markbe...77720302485208

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