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PostPosted: Thu Aug 10, 2017 9:30 pm 
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So I'd finally built the new frame (Emonda 2018) and was just setting the correct height on the seatmast, torquing up....with the supplied torque key (5nm). Wasn't anywhere near the 5nm when I heard it go. Right down where the slit is in the seatmast. It's the SLR 10 seatmast.

Is this just poor tolerances on the seatmast? Reading around it doesn't seem like it's the first time this has happend particularly with the SLR 10 seatmast.

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PostPosted: Thu Aug 10, 2017 9:41 pm 
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Location: Madison, WI USA
That is bizarre.

The seat mast is molded, so its outer diameter will be the same on every frame. I think you're referring to the tolerances on the cap (the female portion). But that's molded too, and should hold very tight tolerances.

Going by the photos Calnago posted in this thread ( viewtopic.php?t=142809&start=26 ) it looks like the fact that the slot in the clamp lines up exactly with the slot in the single-slot cap creates line contact (and a resulting stress concentration) along the edges of the cap slot.

Did your cap have one slit or two? Can you post photos of it?


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Posted: Thu Aug 10, 2017 9:41 pm 


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PostPosted: Thu Aug 10, 2017 9:42 pm 
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Someone else on here had a thread with exactly the same thing happen I believe. And it certainly does seem that the design of the SLR seatmast can contribute to that. But even on the regular seatmast, I don't like that they've bonded the collar to the actual mast. In my opinion, that collar should be free to "float", and wrap around the whole thing evenly as opposed to being bonded and essentially squeezing the parts together at the bond. Not sure that makes sense in writing. I've actually tried talking to TREK about that, but I only got to the first level of Customer Support and they didn't seem to understand what I was talking about. I didn't bother after that. On the mast on my SL Emonda I was able to break that bond free so the collar works more like a normal wrap around collar.

That's gotta be incredibly frustrating when assembling your brand new frame and that happens. I think in the other case Trek warrantied the frame. Good luck and keep us posted. Do you have a picture of the seat mast and clamp that caused the crack?

_________________
Colnago C60 - PR99
C59 Five Years Later
My Special Colnago EPQ
Trek Emonda SL Campagnolo SR


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PostPosted: Thu Aug 10, 2017 9:47 pm 
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For what it's worth, I'm certain that Trek will take care of the OP.

Calnago, your unbonding of the collar would help diminish the stress concentration I described. So would rotating the unbonded collar 180 degrees, though it might look goofy. Trek's fix seems to be two slots, which means that the edges of the single slit are not directly lined up with the edges of the collar. I'm really curious about whether the OP got one-slot or two-slot cap. If the former, I wonder why Trek shipped the frame with the earlier (potentially flawed) cap).


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PostPosted: Thu Aug 10, 2017 9:50 pm 
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The SLR 10 Seatmast has two slits, rather that the single slit I have one my Domane SLR. The clamp is different too. I don't have a photo to hand. It's this one

Image

The one on the right but with a different clamp.

Image


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PostPosted: Thu Aug 10, 2017 10:04 pm 
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Is it this clamp?
Image

That one is pretty good at minimizing stress concentrations.

Looking at the location of that crack, you may have gotten unlucky with a discontinuity between plies. Still, I'd expect a lot of tangential layers in that area to deal with the clamping force and to prevent radial buckling. (Your mast buckled radially).

From the information I see here, this is most likely a clear-cut warranty issue. But doing forensic engineering on an internet forum is a little like practicing medicine on an internet forum: it's no substitute for being there in person. Caveats aside, I would be shocked if Trek didn't give you a new frame pretty quickly.


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PostPosted: Thu Aug 10, 2017 10:22 pm 
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Yeah that's the clamp.
It's a project one frame too


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PostPosted: Thu Aug 10, 2017 10:23 pm 
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Yes, that's the SLR clamp and I really don't like how those two barrels concentrate stress on their tangents. But I still really don't understand why they bond the collar to the mast itself. Imo that clamp should be free to slide around the surface of the mast and thus provide a more even pressure around the whole thing. Years ago, that was the reason that Campy came out with their excellent seatpost collar. Their carbon seatposts, which at that time were often put in steel and ti frames were subject to a more "squeezing" at the edges of the seatube slot that would get clamped. Wasn't good.
I'm sure Trek will take care of you but still very frustrating.

_________________
Colnago C60 - PR99
C59 Five Years Later
My Special Colnago EPQ
Trek Emonda SL Campagnolo SR


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PostPosted: Thu Aug 10, 2017 10:33 pm 
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The clamp does move round the mast. It doesn't seem bonded in any way.


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PostPosted: Thu Aug 10, 2017 10:43 pm 
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Oh, well that's good at least. So you could slide the clamp completely off the mast then. I wonder if the clamp is still glued to the regular mast found on the SL's etc.

_________________
Colnago C60 - PR99
C59 Five Years Later
My Special Colnago EPQ
Trek Emonda SL Campagnolo SR


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PostPosted: Thu Aug 10, 2017 10:56 pm 
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Location: Madison, WI USA
Calnago wrote:
Yes, that's the SLR clamp and I really don't like how those two barrels concentrate stress on their tangents.


Sorry, what? Can you clarify? Where do you see a stress concentration in that clamp?

Fair warning: I'm a mechanical engineer, and I live and breathe this stuff. I'm not trying to catch you in a mistake; I'm just trying to follow what you're saying. You've seen this clamp in person and I haven't, so you might be picking up on something I've missed.


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PostPosted: Thu Aug 10, 2017 11:16 pm 
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Yes, certainly.... I understand. The clamp itself is smooth. But when it's mounted on the double slotted seat mast, the barrels seem to wanted to push right down on the edges of the two slits, so it's actually the edges of the two slits that I believe creates a stress point on the mast itself. This one seems to have cracked in the same place as the other one, which appears to be right where one of the slits is. With the regular mast, the clamp is a more regular type of collar and the opening edges clamp on the larger piece in the middle of the two slits, so it's much more of an even force all the way around with no extra pressure on the two slits themselves. Don't know if I've explained it very well, and the pics in that other thread that you linked to are gone now, but that's the only explanation I can think of for these failures, unless the mast itself is just so thin in the interest of weight savings that it's on the edge of what's feasible, but I would hope that TREK has thought all that stuff through and this is a very rare occurrence. I've also only heard of this happening with the SLR type collar around the double slotted seatmast. Not sure how long the double slotted seatmast has been used... my Emonda was an early one purchased in 2014 and it has the single slot. But the last two SL's I built both had the double slotted seatmast, however, they had the regular seat collar, of a more standard design which wraps completely around and over both of the slots. The collar itself has a slot where the tightening bolt goes through, and that slot is fully supported by the middle tab between the two slots on the seat mast. Oh geez... hope you can follow that as I can see it being a little confusing to read. In any case, I think the regular seat clamp collar is less stressful on the double slotted seat mast than the SLR clamp appears to be. Just my opinion.

_________________
Colnago C60 - PR99
C59 Five Years Later
My Special Colnago EPQ
Trek Emonda SL Campagnolo SR


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PostPosted: Fri Aug 11, 2017 12:00 am 
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I did not get the weight weenie seatmast cap with my 2018 Project One Emonda SLR. I got the single-slot version.


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 Post subject: Cracked Brand New Emonda
PostPosted: Fri Aug 11, 2017 12:03 am 
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That's interesting, which clamp did you get with it? Although I don't think the double slot mast is necessarily a weight weenie version, just double slotted. It's the one that has come standard on the last two emonda SLs I've built. I thought they were all double slotted now?

_________________
Colnago C60 - PR99
C59 Five Years Later
My Special Colnago EPQ
Trek Emonda SL Campagnolo SR


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 Post subject: Cracked Brand New Emonda
Posted: Fri Aug 11, 2017 12:03 am 


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PostPosted: Fri Aug 11, 2017 1:07 am 
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Ouch! Let us know how Trek deals with the situation.


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