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Braze-on seat tube binder/clamp

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Braze-on seat tube binder/clamp

Old 02-15-23, 11:26 AM
  #1  
Xyphota
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Braze-on seat tube binder/clamp

I was planning on using one of these braze-on seat tube binders, but I cant find a lot of information on others having used them, so now I'm less confident in my decision. Have others successfully used these before?

I haven't made enough posts yet so I can't post links or pictures, but the one I had in mind is called "SEAT/STEM BINDER M6x1.0" at bikefabsupply


The current plan is to use a Reynolds 853 seat tube, externally butted 1.0 wall thickness for a 27.2 seat post, I plan on tig welding most of the frame, but brazing the drop-outs and potentially this seat tube binder.
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Old 02-15-23, 12:18 PM
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unterhausen
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Lots of people use those, although they are possibly a little more old-school. Scanning the internet for framebuilding pictures it seems like a lot of people are still using them though. They are also very useful to make fixturing. Some people prefer external clamps, because there are a couple of failures that can happen with the braze on version.

OP's link https://www.bikefabsupply.com/seat-b...m-binder-m6x10
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Old 02-15-23, 03:35 PM
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I don't like those from BikeFabSupply (though they are a good vendor in general) because the slit is too wide for my taste, and the miter is too shallow. Also the fact that they're pre-slitted makes it harder to miter them more deeply, as I am used to doing with all the cylidrical binders I've used, which is many hundreds.

I used to use generic binders from bike frame sundries suppliers, but the mild steel ones are noticably weak; they distort under higher bolt tension. That should never happen on a quality frame IMHO, so I started making my own on a lathe from 4130 Cr-Mo. But then Paragon started selling theirs in Cr-Mo, so no need to make them anymore. (Except when PMW is out of stock, as they frequently are.)

A deeper miter is a win-win: more wetted area for the braze, combined with lower bending leverage. The leverage is the offset of the screw from whatever's being clamped, say a seatpost, steerer or handlebar. My ideal, which you may not like 'cuz it's extra steps, is to miter them so deep that the miter breaks through into the interior where the screw goes. If your seattube is 1.0 mm thick, you can miter 1 mm past where the miter just starts to break through into the screw space. That results in zero offset between the screw and the post/steerer/h-bar. That results in max clamping force per torque on the screw, and least bending force on the "ears".

The extra step is that you have to re-drill the clearance hole and chase the thread after brazing, because braze will get in there, and there's that 1 mm of seat tube intruding on the screw space. If this is too much of a pain, then only deepen the miter just short of breaking through into the screw space. But the advantage of deepening the miter is too great to put up with the shallow miters that generic binders come with.

The pre-slitted ones like Bike Fab shows are harder to hold in a vise for mitering. Whether you do it on a mill with a hole saw or just with a half-round file, you need to hold it by the ends of the cylinder, and the slitted ones will just close up the slit if you clamp them tightly that way.

There is one possible downside to making the miter as deep as possible, but only if you wanted to use the type of centerpull housing stop that hangs off the binder screw. Those need some space between the screw and the post.
But I consider those hangers a kluge and a bad compromise. Acceptable if the frame is already made (and made wrong IMHO) there's no way to fix the excessive offset after the frame is made, so you might as well use that space for a hanger, right? But to me, it just calls attention to the incorrect design of the binder.

I'm aware that I'm being crotchety and inflexible, and this is a minor point for most people. But "seatpost binder ears bending in" is not a rare problem it is practically a given on cheap old steel frames, and a key differentiator for a quality frame IMHO.

Mark B
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Old 02-15-23, 07:44 PM
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Crotchety is good a lot of the time.
Is the bending really in the braze on? I've never been too close to one that bent.
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Old 02-15-23, 08:48 PM
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I'll agree with mark in that a bent binder barrel is a sad thing, although i do prefer a wider slot than most do. I will pre bend a commercially available barrel slightly the opposite way the bolt will act on the barrel. This way the slight pull up (yes, a well done seat tube won't have much...) when tightening the post will have the barrel straighten out and the bolt won't be bent and under tension. To my eyes most of the closed up binder slots with a brazed on barrel are from the tube bending and not the barrel though.

Many of my bikes use a brazed on collar with a cast in binder to reduce the chance of the tube bending at the barrel's brazing.

What i really dislike for this area are sheet steel formed lugs with unreinforced lug ears. I am continually amazed by the number of "good" bikes that lack this and suffer from lug ear deformation. Andy
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Old 02-16-23, 08:52 PM
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I just make my own on a minilathe. Turn down a little cylinder the full width, drill and thread it with M6 the whole way through. Then flatten it a bit with the grinder. Then I TIG braze it on. Then cut the slot through the seat-tube and the cylinder in one go. Then drill out one half so the bolt just goes through and only screws into the far side. They work like a charm.
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