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I generally put a small nick in the post to mark it but I recently upgraded to a Thomson post and I don't want to nick it. How do you guys mark your posts?
 

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Don't have any ideas for marking the post, but just wanted to advise against purposefully nicking the post. It's a stress riser, and to make it worse the nick is down low where the post enters the frame.
 

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Sorry but I've gotta toss the...

lyndonchen said:
Don't have any ideas for marking the post, but just wanted to advise against purposefully nicking the post. It's a stress riser, and to make it worse the nick is down low where the post enters the frame.
BS flag on this one. Yes putting a gouge in a seat post creates a stress riser or a weak point and is not a good thing. Simply scratching the annodizing or other finish off of the metal does NOTHING to weaken the seat post as long as you don't start digging into the metal itself. Yes you have to be careful, but careful removal of the black finish to create a contrasting reference mark is safe. For a silver seat post it's a different story. Often it's impossible to get enough visibility from a scratch without doing damage to the post. And you are making a scratch as there is usually no finish on a silver seat post. In this case a fine tipped permanent marker (sharpie or similar) works well. If you run you post up and down frequently it will have to be refreshed now and then. For a black seat post that you are opposed to removing the finish from to create a reference mark it can be pretty easy, especially with the Thomson. The milling mards of the Thomson seat post are designed to give the seatpost it's famos grip in the seat tube when clamped in. They also serve quite nicely to hold a bit of paint! Using a fine tipped modelers paint brush dip it in white enamel, you can also use the tip of a tooth pick. Get the smallest drop that you can on the tip and the touch it to the area you want marked. The with a rag wipe the excess quickly. What you end up with is one or two little lines of white down in the machined groves. You can make as large or small a mark as you want. You can even mark just one groove by using the point of a pin or sewing needle dipped in the paint, a magnifying glass and a steady hand. There are other methods out there as well. The only really permanent mark is the remove of a bit of finish from the metal with a black seatpost. Most others need to be refreshed now and then.

Good Dirt
 

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Squash said:
BS flag on this one. Yes putting a gouge in a seat post creates a stress riser or a weak point and is not a good thing. Simply scratching the annodizing or other finish off of the metal does NOTHING to weaken the seat post as long as you don't start digging into the metal itself. Yes you have to be careful, but careful removal of the black finish to create a contrasting reference mark is safe. For a silver seat post it's a different story. Often it's impossible to get enough visibility from a scratch without doing damage to the post. And you are making a scratch as there is usually no finish on a silver seat post. In this case a fine tipped permanent marker (sharpie or similar) works well. If you run you post up and down frequently it will have to be refreshed now and then. For a black seat post that you are opposed to removing the finish from to create a reference mark it can be pretty easy, especially with the Thomson. The milling mards of the Thomson seat post are designed to give the seatpost it's famos grip in the seat tube when clamped in. They also serve quite nicely to hold a bit of paint! Using a fine tipped modelers paint brush dip it in white enamel, you can also use the tip of a tooth pick. Get the smallest drop that you can on the tip and the touch it to the area you want marked. The with a rag wipe the excess quickly. What you end up with is one or two little lines of white down in the machined groves. You can make as large or small a mark as you want. You can even mark just one groove by using the point of a pin or sewing needle dipped in the paint, a magnifying glass and a steady hand. There are other methods out there as well. The only really permanent mark is the remove of a bit of finish from the metal with a black seatpost. Most others need to be refreshed now and then.

Good Dirt
+1 not a stress riser unless you go down about .080. Just use a Sharpie. Even a black one shows up on black as a very light purple mark or use something you ride with as a yard stick (pump, arm, shoe, etc).
 

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Kyle88 said:
+1 not a stress riser unless you go down about .080.
Huh? where does this magical value of .080 come from?

Any scratch, nick, hole, whatever on a smooth surface is a stress riser. You can ask any fatigue analysis engineer.

Oh wait, you already did. ME :thumbsup:
 

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lyndonchen said:
Huh? where does this magical value of .080 come from?

Any scratch, nick, hole, whatever on a smooth surface is a stress riser. You can ask any fatigue analysis engineer.

Oh wait, you already did. ME :thumbsup:
I was guessing the seat post has roughly a .120" wall. .080 would roughly be enough to actually cause premature failure. The seat post I have already has very visible tool marks from a lathe. I'm guessing to help it stay up and not slide down. A small mark wouldn't be much more (percentage wise) than one of those. They're maybe .010-.018ish deep. So you'd really have to lay into it to get deep enough (or use a dremel tool) to get deep enough (I just estimated .080) to do some damage. If they did it right on the post is should have a safety factor of 12 (for impact resistance + vibration). Adding a small mark shouldn't hurt, given the stress risers all the way up and down the tube.

Fatigue Analysis Engineer? Is that architectural, automotive, aerospace?
Wedding Photographer?
 

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I purchased an extra seat post mount for my rear blinking light and use that to mark the height of the seatpost on all my bikes. I think it cost me $2 each. The best thing is its non-permanent and I can move it around if needed.
 

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Kyle88 said:
Fatigue Analysis Engineer? Is that architectural, automotive, aerospace?
Wedding Photographer?
Aeronautical.

I'm currently a wedding photographer, but I was a mechanical engineer before. Got my bachelors in ME, then spent 8 years at a helicopter manufacturer, specializing in stress analysis. In helicopters, as you can probably imagine, it's all about fatigue failure. Same generally with bikes.

A nick, or even a tool mark, creates a stress concentration. The size of the mark matters, but also the "sharpness" of the mark matters. For example, a "U" shaped mark creates a lower stress concentration than does a "V" shaped one. Stress concentrations are most critical at the surface, because that's where the maximum bending stresses occur. Even if a mark is only a couple thou deep, if it's sharp like most nicks, it's a stress riser.
 

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mikeb said:
electrical tape is cheap if you don't intend on lowering the saddle.
Plus one on electrical tape, or any tape for that matter. If its wrinkled, your post is moving.
 

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I weigh 160#, and have broken seat posts before (I know, I'm a hardass). I'll never intentionally notch or scratch my seatpost. Tape is great if you won't be moving it up and down. Just experiment with "permanent" markings until you find one that is.
 

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walter said:
Plus one on electrical tape, or any tape for that matter. If its wrinkled, your post is moving.
This has been my way for a long time, as well.

Black post + black tape = invisible.
 
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