Chainstay repair Questions

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Chainstay repair Questions

Author	Message
cookeaa	cookeaa posted 11 Years Ago HOT Topic Details
Group: Forum Members Posts: 7, Visits: 58	I have a cracked, Triangular cross-section, Chainstay on a road bike which I'm looking at repairing at the moment. I have Rubbed down the tube and looking at it I have a transverse crack going most of the way through two of the three sides of the profile, my original plan was to remove the material around the cracks, leaving the one original back wall still intact and then infill the tube profile, possibly with a sleeve of some sort, to provide support and then over-wrap the section to reinforce it and transfer loads across the damaged area. however I've watched a few different youtube repair videos/read a couple of "how to's" and seen some people simply 'fix' a cracked area from the outside of the tube with a thickened gelcoat type epoxy and then just over-wrap the area... My instinct is that this isn't the way to do things, that your not really binding the fibres al lthe way through the crack, and that further de-lamination could occur without you really knowing about it, but it is tempting as it requires no significant removal of the original material and is quicker and easier... am I being a bit too cautious? My other question is on layup for the repair, being a seat stay its subject to cyclical loading in a few different axis'. I have 200g UD and 200g 90/90* Plain Weave (PW) fabrics to choose from. My initial (rather lazy) plan was to simply use the PW at 45* to the tube axis and wrap that 5 or 6 times in a single go, but reading about further I think I might be wiser to use a combination of the PW fabric and UD to try and better align fibres to possible load paths so I have several possible configurations under consideration now: Config 1 (7 layers): 1-PW @ 0* 2-UD @ +30* 3-UD @ -30* 4-UD @ 0* 5-UD @ +45* 6-UD @ -45* 7-PW @ 0* Config 2 (5 layers): 1-UD @ 0* 2-UD @ +30* 3-UD @ -30* 4-PW @ 45* 5-PW @ 0* Config 3 (4 layers): 1-PW @ 45* 2-UD @ +30* 3-UD @ -30* 4-PW @ 0* Config 4 (4 layers): 1-PW @ 45* 2-PW @ +30* (-60?) 3-PW @ -30 (+60?) 4-PW @ 0 Ideally I don't want the repair to be too bulky, just from an aesthetic point of view, its not critical, but it would be nice if repair looked "minimal" when finished... I'm also keen to keep the ride of the frame comfortable so I'm thinking too much added material (especially aligned with the tube @ 0) might make for a harsher ride? Config 1 is a bit of a belt and braces approach, lots of layers, possibly too many @ 0 but I'd maybe be more confident in it, Config 2 is paired down from that a bit and Config 3 and 4 are intended as much more 'minimalist' options, based on the assumption that the repair doesn't need lots of extra material as the extant tube will still be taking a fair bit of the load already and that only one layer addressing each axis would be sufficient... Sorry for the rambling post, but this isn't something I've dealt with before... Any advice/input? Thanks in advance.
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progetto	progetto posted 11 Years Ago HOT Post Details
Group: Forum Members Posts: 6, Visits: 231	5 layers of 200gsm will give you a solid enough repair. Scarf back damaged tube, I have filled with a piece of styrene foam (closed cell foam is better) if tube shape is compromised, it will give you something to lay up onto. Use the ud, 0,+30, 0, -30, 0* or a variation of above would work fine. Be careful with your vacuum that you don't crush the foam. You may need to do it in a couple of goes to get the aesthetics right. Jump in and see where it takes you. Edited 11 Years Ago by progetto
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cookeaa	cookeaa posted 11 Years Ago HOT Post Details
Group: Forum Members Posts: 7, Visits: 58	Cheers for that, So there's no real need to align any layers to 45* or 90*?
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progetto	progetto posted 11 Years Ago HOT Post Details
Group: Forum Members Posts: 6, Visits: 231	No, I've built bikes with chain stays with layup similar ( nothing greater than 30*), they are designed just fine. The rear end is triangulated when the wheel is attached so most of the twisting force is nearer the bottom bracket.
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cookeaa	cookeaa posted 11 Years Ago HOT Post Details
Group: Forum Members Posts: 7, Visits: 58	Just realized I typed Chainstay throughout my first post when I meant Seat Stay... But I assume the same holds true, axial and +/-30* as that is the primary loading. The damage is almost exactly at the mid point of the tube. took the damaged section out last night and I've made up a support piece which I'll epoxy in tonight, I' was quite surprised at just how thin the tube walls are 5 or 6 layers will about double the wall thickness for the repair section.. Cheers again for the help.
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progetto	progetto posted 11 Years Ago HOT Post Details
Group: Forum Members Posts: 6, Visits: 231	Yes, much the same only a lot less loading except at the brake bridge. The wall thickness on modern frames is ridiculously thin, beefy enough for stiffness and strength but not good during a crash. A 1kg frame has a lot more accident protection than a 750gram frame generally speaking, providing they put the weight in the right places.
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cookeaa	cookeaa posted 11 Years Ago HOT Post Details
Group: Forum Members Posts: 7, Visits: 58	I weighed it before I started, 1092g bare, I didn't actually crash it, I bought it as a repair project from the original owner knowing I already had the materials to repair it (not necessarily the expertise)... Its quite silly but I started totting up a weight estimate for the reinforcements, I've not had such a light frame before and obviously the repair will add some mass, but now I'm wanting to minimize it... Maybe when I'm done I'll take all the paint off the rest of the frame, see if that pulls it down to 1kg...
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