Seat tube options

[Gef]

I'm building my 3rd bike and I want to put an external sleeve on the seat tube.  I've struggled with cleaning up over penetration on my last build and was going to get the paragon seat tube extension,  but figured I'd try this.  I have a piece of 4130 in 1 1/4" od, 1 1/8" id that is a tight slip fit.  

My question(s) are:  is this a dumb idea?  If it's not, how do I affix it?  Right now it's too tight to just slip on,  so probably freeze the seat tube to get on there.  If I try to braze it after welding the top tube and seatstays I'm not sure how well it'll penetrate. 

Second,  any advantage/  disadvantage to leaving the rest of the seat tube high and not trimming it down? 

Thanks, 

Geffrey Moy

Springfield,  Virginia 

[good friend]

With a fit as tight as this sounds like, your unlikely to get much braze
material in between the tubes ...     what is the OD of the seat-tube
you are looking to use (and wall thickness?) ? And it sounds like a
thick-wall collar, too, it would take some heat to get that together.

I'm not clear just what you mean when you talk of "leaving the seat-tube
high".
Do you mean for the process of brazing on the collar?   Or after ?

It sounds like you are thinking of brazing the butt section onto the
seat-tube after you weld (weld?) the rear triangle to the collar/butt,
with the butt tacked in place on the seat tube.    Is this what you are
thinking?

noMadic  Thomas

[Andy Walker]

A lathe would make quick work of thinning that sleeve but you might try some hand filing, sanding over a piece of wood on the inside,  adjustable reamer?

I have done a few brazed sleeves with silver for penetration but noticed when welding seatstays some silver ran out. Still worked ok but not ideal and I couldn't really tell if I got the silver all the way through the sleeve although it will still be super strong mostly through.

The really nice thing about the paragon seat collars is that in some (not all) the center section is relieved so that the welded/brazed tubes have extra room on the inside so cleanup is less of an issue . The upper and lower portions are where the seat tube makes contact so will not be affected by the welds ( as long as you don't weld on those portions).

[Jon Norstog]

That is how I sleeve all my seat tubes.  I use 1/8" over the ST diameter x .058" wall for an EZ slip fit.  Be aware there is also an .065" wall chrome moly tube that is NOT a slip fit.  Clean up the burrs on your cuts to make sure you have the right size. This is overkill for reinforcing the seat cluster, but unless you have a way to reduce the sleeve tube OD, the way Garro does his, you are stuck with it. 

This is what it looks like.

jn

"Thursday"

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[Gef]

Thanks for the input.

Andy, thanks for the input, that's what I'm worried about, the silver running out if I braze it before, but wouldn't be able to get the flux in there if I braze it after unless I figure a way to slip the seat tube back out after welding the seat stays and top tube.

Jon, I did confirm it's 0.058 and it slips, but is a little tight, I might have to sand it a bit more, maybe turn it. How do you join it to the seat tube?

Thomas, 1.125" OD seat tube, for 27.2 seatpost, 1 1/4" sleeve 0.058 wall thickness. I could turn it down, but feel like it'd be marginal weight savings. Yes, I think if I brazed it first the weld would reheat everything, so try to braze after the weld, but that's a long section for the braze to penetrate. Second, I haven't cut the seat tube to length yet, so thinking about leaving it long (about 7cm above the TT) then putting the collar up there. No real reason besides something different.

[Jon Norstog]

" Jon, I did confirm it's 0.058 and it slips, but is a little tight, I might have to sand it a bit more, maybe turn it. How do you join it to the seat tube?"

For a long time I Oxy-acetylene welded the bottom of the sleeve to the ST. I was usually using 1.25" x .035" ST on my BMX bikes and brazing it to the 31.8 x.9-.6 mm seat tubes I preferred on MTBs and some road bikes.  On the welded down sleeves I would finish them out by drawing brass down from the top joint. I doubt that I ever got a perfect fill throughout the joint, but it was pretty good and none of them ever gave the clients any trouble.  Both methods of joining introduce some heat distortion and are a bitch to ream out.

As for the tightness, it is normal. Use a half-round bastard (fie) to clean the edges of the cuts. 

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[good friend]

hum, "a little tight but it slips" sounds different to me than "have to freeze it to get it on"   =)
     anyway, no need to turn it down, it should fit well enough   =)

I might consider fillet braze top and bottom of the sleeve after, tho I'm curious about your statement of welding, what kind of welding?    How about braze the collar on, then braze the seat/top/stays assembly ?

Fine to leave the seat-tube long in my opinion.   and if you leave it long, you could even drill a couple windows in the sleeve, to aid braze material addition, and claim it as decorative   =}
some will say the seat-post needs to extend into the seat-tube deeper/past the top-tube/rear-stay connection
and a long extension above the top tube makes it tempting to use too short a seat post...   

noMadic   T

[Duane Draper]

I usually start with .058” tubing for my sleeves but turn them down to about .040” wall thickness so they don’t look quite as bulky.  That’s a personal preference thing. 

You only need to soak the filler down between the sleeve and tube about 1” on each end. You don’t need to fill it completely as I understand it. 

I use 56% silver and flow it through the whole sleeve feeding from the bottom to the top of the seat tube focusing on the bottom shore line and drawing any extra out to the top where it will be cut off and finished.  Hold the seat tube ‘upside down’ so gravity helps you. 

If you are getting spill over you are adding filler too soon probably. 

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From: frameb...@googlegroups.com <frameb...@googlegroups.com> on behalf of good friend <tho...@kokopedli.com>
Sent: Sunday, September 24, 2023 10:43:20 AM
To: frameb...@googlegroups.com <frameb...@googlegroups.com>
Subject: Re: [Frame] Seat tube options

 

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[Marc Pfister]

In my experience once you do the top tube joint the heat distortion locks the sleeve in place and you only need to send a little filler down the ends to seal it up.

-- Marc

[Michael F.]

I'm curious why no one has mentioned simply using a bulge-butted seat tube ?

Mf in SF

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[Duane Draper]

I like the look of a sleeve and add them to the externally butted tubes as well. 

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From: frameb...@googlegroups.com <frameb...@googlegroups.com> on behalf of Michael F. <eme...@gmail.com>
Sent: Monday, September 25, 2023 4:42:35 PM
To: Marc Pfister <marc.p...@gmail.com>
Cc: Framebuilders <frameb...@googlegroups.com>
Subject: Re: [Frame] Re: Seat tube options

 

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[Gef]

Marc- How do you flux it? I don't have any experience with sleeves or lugs, but my understanding is silver will flow where flux is and if the seat tube is locked in place by the heat distortion I can't think of how to get flux down there.

Michael- The legend Andy Newlands did suggest that, but I am trying to not order anything right now. Maybe for the next frame.

Also, I did turn the inside and take a shave off of it, and now it slides easily on the seat tube.