# Seat Post Slot Ignorance



## G-reg (Jan 12, 2004)

This is something I've always wondered, and as I gather ideas for frame #1 feel the need to ask the forum. Why are most slots for the seatpost binber cut at the back of the tube. In my head having the slot at the front of the seat tube vs. the rear would have it in a lower stressed part of the tube and out of the line of fire from the rear tire.

Given that saying _most_ frames have the slot at the back is a generalization, but I can't can't think of a reason to have it at the back at all.


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## Clockwork Bikes (Jun 17, 2006)

It's on the back side because it's easier to put there. It does make more sense to put it on the front.


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## Smokebikes (Feb 2, 2008)

This may sound kinda "joyous".........................but I think it looks better to have it facing in the direction of the stem.......that is, binder bolts leading away from the direction of the bike. Unless your fixed and like to ride backwards. Style/design/function hand in hand. 
On the subject......how do you all apply the slot? I use an angle grinder and cut the slot down to the pre-drilled "key-hole"......for me, this method never looks as clean as the bikes I see in a LBS.


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## marks_bike (Aug 22, 2006)

I prefer my personal bikes with the slot facing forward. In my head it helps keep dirt, mud, and water that is thrown up from the tire out of the slot. It probably doesn't help at all but that's why I prefer it forward. --Mark


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## Linnaeus (May 17, 2009)

There are also bikes with multiple slots (3) cut in the ST, although they use a traditional seat clamp binder.


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## CharacterZero (May 19, 2004)

I was told that cutting it in the front allows it to be stronger/more durable/longer lasting (having had a frame fail at this point).


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## Rody (Sep 10, 2005)

Always in the front as this is the lower stress point and keeps dirt/grit/water from rear tire kick up from seeping in as readily.

I slot all posts on the mill with a slitting saw for accurate, repeatable results.

cheers,

rody


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## Smokebikes (Feb 2, 2008)

That accuracy stuff makes a huge difference..........mine have NEVER looked that nice. I suck......:madman:


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## febikes (Jan 28, 2011)

Rigid holding on a milling machine is the key to getting the nice clean sharp edges. Mine are done with hand using drill, dremel, and final cleanup with needle files but they will never look as sharp as what a milling machine produces. 

A milling machine is out of my current budget so I remind myself that I enjoy working with simple tools.


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## Citizen Kane (Aug 12, 2007)

I like forward facing. Small slot drill just shy of breaking through, still allows for reaming and the jig cone to work. Final cut is easy.


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## blackgt (May 27, 2010)

Smokebikes said:


> This may sound kinda "joyous".........................but I think it looks better to have it facing in the direction of the stem.......that is, binder bolts leading away from the direction of the bike. Unless your fixed and like to ride backwards. Style/design/function hand in hand.
> On the subject......how do you all apply the slot? I use an angle grinder and cut the slot down to the pre-drilled "key-hole"......for me, this method never looks as clean as the bikes I see in a LBS.


I've built 4 frames so far, and only had a good look on one of them... the first one I built. I used a hacksaw with 2 blades mounted in it, and sawed my way down to the drilled hole. the second time I tried this it did not work as planned, and I quickly abandoned it as each blade was going in tis own direction, instead of cutting one wide-ish slot. I'm now using the angle grinder with a cut-off wheel mounted in it, cutting down to the pre-drilled hole. Same way you are SMOKE.

Jeremy


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## wizzer16 (Sep 9, 2010)

on my first (and only) I clamped the frame to the mill table and keyway cut to my hole. I was happy with the results.

Rody, do you drill and slit prior to mitering/welding?


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## 18bikes (Jan 15, 2007)

I use an end mill like so


Slotting the seat tube by 18bikes, on Flickr

and then finish it like this to prevent damage to the seatpost


Seat Tube slot by 18bikes, on Flickr

I prefer forward facing and do the slot before welding, I just cover the slot with masking tape when purging the frame

Matt


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## Rody (Sep 10, 2005)

wizzer16 said:


> Rody, do you drill and slit prior to mitering/welding?


Yes, the seat tube is the backbone of the frame, so it needs to be dead on from the beginning. After cutting a 12 degree angle cut from the top of the tubing, the binder is then tacked in place at the peak/dead center of the forward aspect of the seat tube. The binder is then utilized for insuring the tube is both square to the table/in phase for all of the subsequent processes...mitering for the bb, H2O bolts, and of course, slotting for the relief.

The seat tube gets a heat sink for support and purging during welding to protect it's integrity.

Here is the rest of the blog post the pics came from...

http://groovycycleworks.blogspot.com/2010/08/chads-frame-melted-together.html

cheers,

rody


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## JaquesN (Sep 14, 2009)

I'm glad this thread got started, since I've messed up cutting the seat post slot in every frame I've ever done. It's usually one of the last steps and I hate it when it comes out all crooked. Thanks for all the tips.


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## dr.welby (Jan 6, 2004)

Rody said:


> Always in the front as this is the lower stress point and keeps dirt/grit/water from rear tire kick up from seeping in as readily.
> 
> I slot all posts on the mill with a slitting saw for accurate, repeatable results.


I luvvvv the way you do your seat tubes, but what makes it the lower stress point? Maybe I'm overthinking it, but most failures coming off of the slot are fatigue failures, and the front and back should have similar cyclical loading, even though the absolute stress is different.

FWIW, I put them in the front for the already covered water reasons.


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## chuggboy (Jan 10, 2005)

In regards to aesthetics, my frame has a forward facing slot and I run the collar 'right way around'. just put a smear of grease under the collar and tighten. Holds just fine and dandy..

C


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