I cracked my lugged gravel frame a few days ago. It split the paint along the HT-DT lug shore line at the head tube. I hit a little 4" tall curb going about 5mph, but it threw my weight forward weirdly and I heard a loud “PING!”
This was the 2nd frame I built, honestly I never felt 100% that the silver flowed perfectly on the one lug joint… guess I should have trusted my gut. It’s been ridden kind of hard but obviously a lug probably shouldn’t fail this way if correctly braised.
Anyway looking for tips and recommendations on the procedure for repair. I would think I would want to pull the head tube off completely? Or maybe just de-braze the bottom lug?
I don’t do repairs and I’m pretty inexperienced, but I’d first check the alignment. While the crack you see is obvious, there may be some other alignment issues that aren’t as obvious. Making some measurements will help you to know if the damage is isolated to that location. My concern would be that there is also some deformation and stress in the whole head tube junction, including the top tube. Post the results of your findings and repair.
Correct, the crack is in the tube, not in the braze. Clear enough if you zoom in. The braze penetration or lack thereof had nothing to do with that crack.
I have seen enough of those, in that very spot, and from reputable builders, that I prefer lugs that have a point there pointing forward. Think “Nervex Professional” if you’re old enough to remember those, or Pacenti Artisan.
Obviously millions of bikes have been made without such points and they didn’t break, most of 'em, but I’d like to eliminate even those rare failures, even for heavy, strong and high-mileage riders, and the one gram (or whatever) those points weigh is worth it. You don’t need to weld them to the lug, brazing them on is fine. Ugh, just realized I don’t have a pic of a lug that I did that way, sorry.
The TT lug doesn’t need them, but you might as well add them there too for thematic consistency.
@bulgie thanks for the insight. I see what you mean with the extended lugs. Any thoughts on the best method for repair? I’m surprised the headtube itself cracked considering how low speed the impact was.
I’ll put the bike on a surface plate and check alignment.
I see that now. Apologies for mistakenly saying the HT cracked. Unless it did also? But your evidence for a fail in the braze is convincing.
Did you clean off the cast surface of the lug on the inside, so you were brazing to shiny metal? Though you can get away without doing that step on some lugs, or areas of lugs that are less highly stressed, your lugs don’t have enough safety margin right there. The surface area of contact between lug and tube is at a minimum there, so I consider removing the as-cast surface there a must.
You might have something similar to this fail going on:
Not my frame! I grabbed this pic from the web. But you can see how little surface area there is in contact right there where yours failed.
Yes, I clean up the surfaces inside and out on all the lugs. I think my failure was just getting the lug too hot and burning off flux, then struggling to get everything to flow. Basic new framebuilder failure. I built this frame a few years ago so my memory is a bit fuzzy.
I’m thinking my plan will be do de-braze the bottom lug and separate (looking similar to the pic above). Then inspect and clean up the whole joint. Then stick it back in the jig and redo the joint.
I’m not saying don’t do it, but that’s a pretty difficult repair. Added to the question of whether the HT is also cracked — I think it might be.
It’d be a shame to go through all that trouble only for that crack to come back and propagate. Though you’ll be able to answer that question more reliably after the lug is off, at that point you’ve already invested a fair bit of effort (and breathing burning paint).
I don’t currently have a dye-penetrant kit for crack finding, but they’re not too expensive and you’ll get plenty of uses out of it. Spray the dye inside the HT only, and the developer on the outside, and you’ll quickly see if any crack goes thru. Or the poor man’s version of the, sandblast it and put some penetrating oil inside, see if it weeps thru. Oil darkens the sandblasted surface, pretty easy to spot.
It’s stupid of me to disagree with @bulgie (his monthly units were greater than my lifetime production!) but, I wouldn’t put it through another heat cycle. Cut out the center section of the headtube and then grind or peal out what’s left inside the top and downtube lugs. You’ll have a better chance of saving the rest of the joint - especially for folks who don’t have Pro level heat control.
Once you’ve cleaned it all out, slide a new headtube through the lugs and braze away! It’s actually not a terrible job if you have the right grinding tools. If you just have files, it’s a bit of a drag.
Some things to watch for:
-As you grind out/pull away the remains of the headtube from the lug, you’ll see what your penetration was and what cracked.
-Careful to not grind away too much of the lug or top or down tube. Big gaps can contribute to silver not filling the joint well.
-try to strip the paint back a ways to minimize how much fumes you breathe.
Got it. I see what you mean putting it all through another heat cycle. I never thought to just replace the head tube. I suppose it is probably faster as well to cut out the tube.
I will be stripping and blasting the whole frame so no worries on fumes. I will also be able to do the poor man’s dye penentant with oil.
I’m a bit worried about over grinding the lug ID. Has anyone done this before. I’m wondering how difficult it will be to keep the lug IDs concentric and circular?
I am pondering doing some crazy work holding and trying to bore out the headtube on the mill until it’s very thin.
I have done it several times. I used a pneumatic die grinder with pretty aggressive sanding roll. A burr bit would work too but it will remove material faster and makes those little shards that frankly scare me. You’ll need to grind through about 1mm all the way around the ID of the lug so you have plenty of time. Just go slow, be patient, check your fit regularly.
In fact, here’s a series of photos that show my approach on an old Trek MTB that actually has a cast headtube and sockets to make it look like lugs. The approach is the same.
Here’s another way to do it (not for the faint of heart!):
Wow @Duanedr, thanks for the pics. I feel much better seeing someone actually do it. I was thinking I could use the mill like you did, start with a 1-3/8" holesaw then finish up with a boring head or burr grinder.
At a certain point I wonder if it starts to make more sense just pulling off the lugs and replacing them? If I’m going to order a new 36mm head tube anyway, I could just get new lugs, throw it back on the jig and redo the headtube?
I think using the mill, even with an ATI hole saw as shown, is a bit challenging and results were borderline acceptable. Steel bikes aren’t straight at the level of detail we’re talking about here. So, when you drill through the lug, even when indicated really well, you may find the lug is pretty thin in certain areas where the cuts were off-center. In other words, lug thickness is like .040" so, if you’re off by .010", that’s 25% impact.
I usually use a grinder to remove material slower so I know i’m getting a good fit and maintaining as much good material as possible.
In this case, I would leave the TT and DT lugs intact and simply deal with the HT replacement.
I have instances of replacing back almost to the SEattube and that’s more challenging. We can discuss in a more private way if you want. DM me.
Started doing some more paint removal. It looks like the Top Tube lug is also cracked!?! DT-HT lug appears to also have a small crack between the down tube and the lug.
With the down tube-lug joint also needing repair I am wondering if it’s time to cut my losses (literally) and grind off the lugs and just put new lugs on…?
Getting the lugs off of the tubes is a pain - in my experience. it’s hard to get and keep the whole socket to the temp where silver (or brass) melts so you can pull the socket off the tube. It’s easy to damage the tube that you want to keep. Good luck.
