Quill Seat Posts

[fausto99]

Came across this https://www.youtube.com/watch?v=4TkjA41tJ78 today.

Made me wonder why the scheme was not more common given all the aggro that you can get with binder bolts and clamps.

[freeflow]

Quill seatposts are the wrong solution to the problem as you would be putting forces on the seattube in a direction for which the seattube is not designed.

Like many things in life, the fact that you can does not mean you should.

[fausto99]

Quill seatposts are the wrong solution to the problem as you would be putting forces on the seattube in a direction for which the seattube is not designed.

a bold statement indeed with little justification or clear explanation

Not obvious to me how the forces from a seatpost onto a seattube differ from the forces from a handlebar stem onto a steerer tube
Are some frame seat tubes internally butted? Now I can see that would cause problems...

[KM2]

The form column is considerably thicker than a seat tube and more able to withstand such forces.

[SimonCelsa]

Some good comments on this thread;

viewtopic.php?f=5&t=123718&hilit=quill+seatpost

The one I made is still holding good & hasn't seen any seat tube mishaps as yet!!

[9494arnold]

Might be stating the obvious here, further to what Fausto and KM2 said:
Conventional Seat Tubes (Reynolds 531) are Butted, that is thicker at the ends than the middle.
So if you used a "quill" seatpost in prefference to a conventional one, on a frame not designed for it, there's a danger the wedge bit is going to impinge on the thinner gauge tubing and potentially deforming same. (It happens on steering columns too which are uniform thickness i.e. Not butted)
(The Quill design is actually a cheaper way of doing Stems, old school stems had a tapered bung with a slot that spread the end of the stem uniformly so contact inside the steerer was uniform, wedge style actually tilt the stem , the longer part of the wedge pushes against the front /rear face of the coulumn, the lower back part of the stem is pushed back against the opposite side of the tube) ( and really old school stems didn't have a bung or a wedge, the stem went around the column and clamped externally via a bolt in the upper Headset race) ( a bit like an aheadset but it did actually deform the column slightly. )
I am assuming the tubes in frames designed for quill stems are thicker in the relevant area. If you have broken your seat clamp I would suggest you might be better sawing the seatbolt retaining loop off and use a separate clamp . Or getting a framebuilder on the case.

And if your issue is simply seatpost slip with no obvious reason :
1/ Check your seatpin size .
2/ Get a decent bike shop or a framebuilder to clean/ ream /measure your seat tube (Reynolds 531 frames are usually 27.2 mm. , but according to one of the framebuilding books a really well built 531 frame will be 27.4 mm seatpin, )
I had a French built 531 Peugeot that had a very odd seatpin size , my tame Cycle mechanic from the LBS said Peugeot were notorious for putting seattubes in upside down !
Seat clamps get crushed and I have lost count of the secondhand frames I have seen with the wrong size seatpin in them.
Generally too small (you need a very big hammer to fit an oversize pin without reaming first) (I wouldn't recommend this approach by the way )
3/Double check the size of your seatpin. Is it the correct size? Is it worn? Replace it if nessescary.
4 / If that doesn't sort it get a machine shop to lightly mill the pin in the clamp area. This will slightly increase the nominal diameter . (This process doesn't lose any material off the pin, it makes a small raised diamond pattern , the displaced metal actually marginally increases the diameter. )
Hope this makes sense !

[tatanab]

Conventional Seat Tubes (Reynolds 531) are Butted, that is thicker at the ends than the middle.
So if you used a "quill" seatpost in prefference to a conventional one, on a frame not designed for it, there's a danger the wedge bit is going to impinge on the thinner gauge tubing and potentially deforming same.

Pedant alert - in a double butted frame Reynolds seat tubes are single butted with the thick end at the bottom bracket
http://www.equusbicycle.com/bike/reynol ... -sizes.jpg

[rjb]

I had a French built 531 Peugeot that had a very odd seatpin size , my tame Cycle mechanic from the LBS said Peugeot were notorious for putting seattubes in upside down !

And not only Peugeot, I spent my first wages on a Holdsworth Pro frame in 1970. 2 years later in the gallop at the end of a road race the seat tube snapped, I was a lightweight hill climber not a sprinter.

I posted this on this forum maybe 2 years ago and several other members reported an identical failure. It transpired that Holdsworth had also built a batch of frames with the seat tubes upside down with the butting at the top instead of the bottom bracket.

[rjb]

4 / If that doesn't sort it get a machine shop to lightly mill the pin in the clamp area. This will slightly increase the nominal diameter . (This process doesn't lose any material off the pin, it makes a small raised diamond pattern , the displaced metal actually marginally increases the diameter. )
Hope this makes sense !

I think you mean Knurling not milling.

[9494arnold]

Yes knurling thats the one. Brain fade. (It was about 51 years ago I was doing metalwork at school)!
I honestly thought that double butted was different thicknesses both ends, compared to the middle. But I will stand corrected .
Never forget the definition of an expert (and I do not categorise myself as one)!
I am an enthusiastic amateur.
Ex. Former
Spurt. Drip under pressure.

[freeflow]

What's not clear about

putting forces on the seattube in a direction for which the seattube is not designed

[Brucey]

I honestly thought that double butted was different thicknesses both ends, compared to the middle. But I will stand corrected .

IIRC there are double-butted seat tubes made for some welded frames; the top of the seat tube is externally butted so the ID remains constant and yet there is enough 'meat' to weld to at the top end of tube.

cheers

[NickJP]

Quill seatposts are the wrong solution to the problem as you would be putting forces on the seattube in a direction for which the seattube is not designed.

a bold statement indeed with little justification or clear explanation

Not obvious to me how the forces from a seatpost onto a seattube differ from the forces from a handlebar stem onto a steerer tube
Are some frame seat tubes internally butted? Now I can see that would cause problems...

Considering only steel frames/forks, the wall thickness of a 1" steerer is more than twice that of a seat tube (1.6mm vs 0.7mm), so the steerer can withstand a considerably greater force trying to expand the tube from within.

In addition, once you have a saddle on top of the seatpost, getting to the bolt needed to loosen/tighten a quill would be difficult unless your saddle has a fart slot.

[Brucey]

in this version the bolt is readily accessible. I think it would be easy to overdo it and to overstress a thin-walled seat tube though; this is probably why this arrangement isn't more popular.

cheers

[webber]

I have a moser leader tk1 which has a quill seatpost and never had any issues