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Feasible to sandpaper seatpost receptacle?

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Feasible to sandpaper seatpost receptacle?

Old 01-15-12, 12:33 AM
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Feasible to sandpaper seatpost receptacle?

Hello, I measured wrong my old 1981 Peugeot road bike seatpost and bought a 25 mm. seatpost, and in fact is 24.9, the thing is it doesn't fit, so would be possible to sandpaper the receptacle? I don't know what kind of material is, I guess that the best answer would be to try myself, but I would like to know also if there is some type of sandpaper best suitable for this, many thanks for any help.
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Old 01-15-12, 12:37 AM
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you can modify the seatopst but it takes time and skill.

this morning i happened to stumble upon a seatpost that my dad took .2mm of off many years ago. i had a pair of caliper handy and checked his work. it was shockingly close in all 6 or so places i measured. he couldnt remember the exact method he used but recalled it taking a while.
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Old 01-15-12, 03:42 AM
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Originally Posted by mindundi
Hello, I measured wrong my old 1981 Peugeot road bike seatpost and bought a 25 mm. seatpost, and in fact is 24.9, the thing is it doesn't fit, so would be possible to sandpaper the receptacle? I don't know what kind of material is, I guess that the best answer would be to try myself, but I would like to know also if there is some type of sandpaper best suitable for this, many thanks for any help.
Does "receptacle" mean the seat tube? I presume the seat post you have is 0.1mm too large for the seat tube. If so, I'd sand down the seat post rather than enlarge the seat tube. IMHO it is always preferable to leave the frame intact and do the machining/sanding on the parts to fit them to the frame.
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Old 01-15-12, 04:53 AM
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Thank you both, I'll sand down the seat post then.
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Old 01-15-12, 09:53 AM
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Did you determine the size with calipers or with a insertable sizing rod? 25mm is the typical size for French bikes and I think the smallest diameter you can get. Seat tubes are typically honed or reamed at the initial build to fit the specified size of post. This takes care of brazing material, burrs, and any deformation that occurs during construction. It's remarkable how many times the "correct" post does not fit. If you are off just a tenth of a mm (about the thickness of a dollar bill), by all means look in the tube to see if there are any issues that should be taken care of. You may be able to find a shop that could hone it, but small files would work. Feel inside with your finger and attack any rough spots. This will also help avoid scratches on your seat post.

If you don't see any deformation, burr, rust, or other issues, then you should work on the post as suggested.

Good luck

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Old 01-15-12, 10:09 AM
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I agree with gmt13. find a shop with sizing rods and triple check the size. if the post was missing a long time or something bogus was stuck in there the seat tube could just be slightly out of round. what the binder bolt tight?

a mild honing never hurt but you really need the correct type of hone.

a 25mm flex or ball hone would be the correct way to go



I use a brake cyclinder hone on just about every new to me frame.



but these are mostly, as pointed out, just to clean the inside of the tube not to remove material to resize it


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Old 01-15-12, 10:21 AM
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Thanks, the new seat post doesn't even initially enter, remeassuring again I'm almost sure that the peugeot post it's 24.9 or 24.85, I guess by then they weren't very accurate in their works, for me it's not easy to get the hone or to take the bike to a shop so I guess I'll have to see what I can do with the sanding, although I'm afraid that the post will get too thin.
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Old 01-15-12, 10:27 AM
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0.1mm is less than 0.004 inch. I highly doubt the tolerance of either your seatpost or the seat tube is that tight. If you can't get it to fit there is probably another issue.
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Old 01-15-12, 10:34 AM
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Take some time to get an understanding of what can impact the integrity of the seat tube cavity. Perhaps spending a bit of time looking through Frame Cavity Preparation will help with some ideas as to what the problem is and how to deal with it.

As often as not, the seat tube cavity is damaged, even though the damage might be very slight. I would be very careful with how I clean out the seat tube. Ensure that the cavity is round at the top by measuring in several spots. If slightly off, then round the cavity out again. However...

What kind of Peugeot does the OP have? A 25mm seat post would immediately suggest a lugged aluminum frame, but I could be wrong. Perhaps a picture of the seat post and the seat post cavity would prove helpful to those of us who are trying to help out. To be honest, this does not make a heck of a lot of sense to me, without a bit more information. That was not intended to offend.
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Old 01-15-12, 10:41 AM
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As mentioned, the most likely culprit is an ovalized opening on the seat tube. I wouldn't even bother measuring several places to confirm this -- just spread the ears on the seat lug a little bit and see if that works.
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Old 01-18-12, 05:08 AM
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Really sorry, I was really absentminded when I measured the seatpost, it's 24 mm. and not 24.9. I've checked there are many posts about the 24 mm. peugeot seat post, gonna read them now. Thank you all.
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Old 01-18-12, 05:18 AM
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I also use a Flex Ball hone on every bike that pass through my hands. Some need more clean up than others. I also use a half round file to clean up any sharp edges around the Seat tube and Steer tube. I hate gouging seat posts or stems.
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Old 01-18-12, 05:51 AM
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Originally Posted by Michael Angelo
I also use a Flex Ball hone on every bike that pass through my hands. Some need more clean up than others. I also use a half round file to clean up any sharp edges around the Seat tube and Steer tube. I hate gouging seat posts or stems.
I do the same thing for the same reasons, I use a sanding drum on a drill bit extender with a fine sandpaper roll then I take a file and put a slight bevel on the seat tube slot making sure there are no sharp edges left to gouge the post.
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Old 01-18-12, 06:58 AM
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Old 01-18-12, 07:14 AM
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Originally Posted by Michael Angelo
I also use a Flex Ball hone on every bike that pass through my hands. Some need more clean up than others. I also use a half round file to clean up any sharp edges around the Seat tube and Steer tube. I hate gouging seat posts or stems.
I concur.
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Old 01-18-12, 07:20 AM
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+1 I use the brake hone style, I need to pick up one of those ball style hones. I don't use it to enlarge the tube, I use it to clean up any burrs.
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