Monostay seat tube join
 

I've just started building a track frame for a friend who seems insistent on having a monostay compact rear triangle. This would obviously situate the monostay/seat tube join a good few inches down from the trad seat cluster position. Is this doable with a 0.5mm seat tube or am I asking for trouble? I have it in mind to reinforce the join with a piece of scrap tube (so kinda like a semi lug) or am I better off just using plain gauge for the seat tube?

Thanks as ever.

probably not a good idea without some kind of sleeving or externally butted seat tube

Hmm. Pretty much as I thought. I should say the ST I've got is actually 0.6 not 0.5 like I said in my OP (it's the single butted zona) - but I don't suppose this alters things significantly. Do you think I'd still need some form of sleeving with a plain gauge ST?

The externally butted sections (certainly on the zona e/b seat tube) wouldn't be long enough unfortunately - I'd want a 120mm reach at least - not sure if there's a ST out there with that length of ext. butt?

Re. sleeving - is internal sleeving (oxymoron?) possible that far down a tube? Can't imagine how I'd get in there to clean it sufficiently.

I had intended brazing a piece of half tube (cut out to match the lugset) to the top end of the stay to 'spread the load' at the join, but I guess if this isn't encircling the ST it's not really adding a great deal of structural support to the tube? I've seen this method employed on a couple of frames but can't for the life of me remember where :mad:

the half tube would still keep the tube wall from buckling, just not as well. It's fairly common on older fillet brazed fastback seat stays

Llewelyn Cadenzia seat lugs have about 21mm of metal below the slot. The design looks like some metal could be added pretty easily to extend that quite a bit. That would give you a design similar to the seat lug on the Raleigh Professional from the 70's. Nova has the double oversize lug set. If you want OS, you will need to get them straight from Llewelyn. The lugs are very well designed and manufactured. Very nice to work with.

Thanks for the heads up. They do indeed look very nice - possibly a little pricey for this particular build though. I did initially consider the '514' seatlug (from Ceeway) which has a similar deep rear section design to the Cadenzia, but it didn't come down quite far enough. I'll prob end up just talking him 'round to having a standard config. rear triangle :lol:

Check out the frames English Cycles does. Rob does road frames with exactly what your looking for. You could look at his build cause one member here has a very detailed thread to the build of his frame. All I have to say is very cool and very light. I do have to say it looks really delicate as the seat stays look like the size of pencils. He still builds them like this so they must be holding up.
http://www.englishcycles.com/bikepics/cam/cam2.htm
http://www.englishcycles.com/bikepics/cam/camroad10.jpg

well one way of doing it, thats if it doesn't interfere with the seat tube, is to go right through the seat tube. Just lay a find silver bead around both orifices, **** you could even braze a spike on the end of the monostay so it looks like it was just jabbed through.

Aww yeah that's what I'm talking about. Can you post a link to that thread you mention if it ain't too much trouble? Intrigued to know what seat tube he's used 'cos that is one tiny monostay (prob a bit spindly for me).

I'm familiar (ie I've scanned his website) with English cycles, so that's possibly where I saw that config. initially. His 'weight weenie' philosophy I find quite interesting, in that it seems to fly in the face of what a lot of contemporary steel framebuilders espouse. I'm particularly intrigued by the style of his fillets, which almost look like welds they're that small. There's no doubt in my mind they're not as aesthetically pleasing as a fuller fillet, but obv that's not his game - he's all about saving weight. I'd be interested to know whether this has any (detrimental) effect on the strength of the join though?

Now this is one method that hadn't occurred to me. Suddenly options. Thanks.

he hasn't been around that long, so I don't think you can make any judgments based on what's on his web site. I don't see much reason to be a weight weenie with steel frames. It's really not that hard to build carbon if you want to be a weight weenie.

As far as small fillets go, if you are getting full penetration, then a small fillet is just as strong and durable as a large fillet.

If you build the frame with an extended seat mast, you have all sorts of options for the seat stay join.

Actually I broadly agree with your sentiment. I meant interesting in the sense that I personally haven't come across anyone who places quite such an emphasis on that aspect of building with steel (no doubt others exist) - I'm not suggesting he's rewriting the rulebook or suchlike.

Re. small fillets - is there any weight advantage to be gained over a welded join?

For some reason I thought I saw it here but after about 30 minutes of searching I turned up nothing and did a google search and found the thread on...weight weenies. But it's very indepth and loads of pictures which should answer your questions. I'm going to be building my first frame and loved his take on a lightweight steel frame.
http://weightweenies.starbike.com/fo...p?f=10&t=76055

Henry

that's a pretty cool thread, even though many of the techniques are somewhat inadvisable.

Why are they inadvisable? It's nice to see something different and pleasant on the eyes. I don't think he would be using that rear stays on pretty much all his bikes if they didn't work or weren't safe.

Many parts of bicycle frames are constructed with an eye towards longevity and so might be considered overbuilt. But when you start underbuilding those same parts....well, let's just say fate is being tempted. This isn't a slight towards English, however.
Isn't it common sense that ultralight bikes (of any material) aren't meant to last?