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Seatpost - Seat Tube Clearance - How much is too much?

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Seatpost - Seat Tube Clearance - How much is too much?

Old 11-21-22, 05:56 AM
  #51  
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I know.

Just wanted to check after maddog's claim of Thomsons being undersized and things got out of hand.
The Record Ti gave me a moment's pause but I double and triple checked.
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Old 11-21-22, 03:15 PM
  #52  
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Originally Posted by Mackers View Post
I know.

Just wanted to check after maddog's claim of Thomsons being undersized and things got out of hand.
The Record Ti gave me a moment's pause but I double and triple checked.
it wasn't just a "claim".. note the image i linked....... and i have two thomsons here.. one is .12mm under the stamped size (the 27.2mm)... the other one is ok (the 25.4mm)

the only thing i find "impressive" about thomson Anything is their continued ability to pull money out of people's pockets.
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Old 11-22-22, 08:51 PM
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Well, I took some caliper measurements of the seat tube both above and below the top tube. The tube is round within a couple of thoudandths. The diameter is also pretty consistent within .005-.010" both above and below the top tube. So it looks like some idiot didn't know how to use a reamer.
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Old 11-23-22, 01:15 AM
  #54  
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Originally Posted by Steve_sr View Post
Well, I took some caliper measurements of the seat tube both above and below the top tube. The tube is round within a couple of thoudandths. The diameter is also pretty consistent within .005-.010" both above and below the top tube. So it looks like some idiot didn't know how to use a reamer.
OR.. the thin walled titanium tubing came in a size that made it a poor fit for any standard Seat tube known to man and woman so the Builder slipped a sleeve in and shipped it out the door............. which is what all these posts are saying in weird but wonderful ways....

go to a Well Stocked Hardware store, buy some appropriate shim stock, cut enough to fill the void of your consternation, clamp that sucker up and GO RIDE.

oh, and Reaming Titanium is a real BIG pain, not to be attempted without a specially coated reamer and No Slots in the surface to be violated.

Cutting Titanium makes cutting low nickel Stainless Steel look like aluminum.... the stuff is Stringy, Springy, loves to tear, ruins tool bits, and coils up "chips" in a big damn mess that wants to burn any flesh nearby. '' and, as my friend that worked at Precision Cast Parts (Jet Engine Compressor Blades, Hush hush jobs for NASA, the CIA, etc...) pointed out.. the Dust is Poisonous.. cool, huh?

https://makeitfrommetal.com/tips-for-turning-titanium/

Last edited by maddog34; 11-23-22 at 01:34 AM.
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Old 11-24-22, 03:11 PM
  #55  
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Originally Posted by maddog34 View Post
as my friend that worked at Precision Cast Parts (Jet Engine Compressor Blades, Hush hush jobs for NASA, the CIA, etc...) pointed out.. the Dust is Poisonous.. cool, huh?
Your friend is mistaken:

Effects of Exposure: Titanium is generally considered to be physiologically inert. There are no reported cases in the literature where titanium as such has caused human intoxication. The dusts of titanium or most titanium compounds such as titanium oxide may be placed in the nuisance category.
Acute Effects: -Titanium 2-
Inhalation: Prolonged inhalation may cause mild irritation to the lungs and respiratory tract. I
ngestion: Relatively non-toxic, poorly absorbed from the alimentary tract.
Skin: May cause abrasive irritation.
Eyes: Dust or powder may cause irritation.
Chronic Effects: None known
Medical Conditions Generally Aggravated by Exposure: Any preexisting respiratory problems. Target Organs: Mucous membranes Routes of Entry: Inhalation, ingestion, skin, eyes.
Carcinogenicity: NTP: No IARC: No OSHA: No EPA: No
Other: Questionable carcinogen with experimental tumorigenic data. Experimental reproductive effects.

(SOURCE)
Titanium is widely used for dental implants and joint replacements with no toxic effects.
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Old 11-24-22, 06:17 PM
  #56  
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Why are we arguing about rhe difficulties or toxicity of titanium. No one is calling for machining or even touching titanium. A proper repair would only involve reaming out the aluminum sleeve down to but not into the titanium, fitting a replacement, and reaming to spec.
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Old 11-24-22, 09:10 PM
  #57  
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Not arguing; just fact checking.
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Old 11-24-22, 10:36 PM
  #58  
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There are no reported cases in the literature where titanium as such has caused human intoxication.

except .. umm.. a quick search brings up this first, many others to choose from...

Inhaling titanium dust particles is bad for your lungs. Also, Titanium exposure may be harmful to your brain. Titanium nano particles can enter directly into the hippocampus region of the brain through the nose and olfactory bulb. Research found that titanium dioxide had a toxic effect on glial cells in the brain, suggesting that exposure to titanium dioxide may cause brain injury and be a health hazard

https://prestivac.com/blog/how-to-sa...factory%20bulb.

The dust is also an explosive combustible.

My friend is correct.

I have two titanium plates in my chest right now so this is a subject very close to my heart! ... It's the Dust that gets you, not the larger Metal.

If your toothpaste is bright white, it almost assuredly has Titanium Oxide in it.
cool, huh?

Last edited by maddog34; 11-24-22 at 10:46 PM.
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Old 11-24-22, 11:17 PM
  #59  
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This thread has officially going off the rails.
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Old 11-24-22, 11:25 PM
  #60  
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Originally Posted by Koyote View Post
This thread has officially going off the rails.
Hopefully they're not titanium rails, or we'd be in trouble.
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Old 11-24-22, 11:34 PM
  #61  
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Oh, but if those rails were magnesium...
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Old 11-25-22, 04:27 AM
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Originally Posted by base2 View Post
Oh, but if those rails were magnesium...
That would certainly have the potential to make this a really hot thread . . . .
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Old 11-25-22, 07:59 AM
  #63  
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Originally Posted by maddog34 View Post
My friend is correct.
I stand corrected; here's the most recent information I could find: 2022.
My source was ~20 years old. One take-away here is that nanoparticles of materials that are normally biocompatible can behave in very different ways.
I'm not arguing!
We now return you to our regular programming...
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Old 11-25-22, 01:25 PM
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Originally Posted by base2 View Post
Oh, but if those rails were magnesium...
Originally Posted by Hondo6 View Post
That would certainly have the potential to make this a really hot thread . . . .
Well, since the seatpost thing seems to have run its course, I'll just add this regarding magnesium burning...
When I was a kid, my parents got me a subscription to something called Things of Science, which came once a month and had stuff that was interesting to science nerd types. One of these kits had a strip of magnesium metal in it. I don't remember the topic of this particular kit, but I do remember it involved setting the magnesium on fire. The strip was about 2mm x 0.25mm and a couple inches long. It took a while to get the Mg to ignite, but once going, holy spotlight, Batman! It was such an intense white light you couldn't look at it. I got several burns out of it; my friends were impressed. I always wondered how safe it was for aircraft to have magnesium parts in their landing gear.
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Old 11-25-22, 02:43 PM
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Originally Posted by sweeks View Post
I always wondered how safe it was for aircraft to have magnesium parts in their landing gear.
when I was part of a training team for shipboard firefighting & mass casualty events the policy was any class Delta fire was jettisoned. Period. If that was a $30,000,000 aircraft, so be it. Better than burning a hole through the deck all the way through the keel catching everything ablaze all the way down.

The standard procedure on land was to drown it in a wide nozzle mist to remove heat from everything around it until it burned itself out. Hitting it with a solid stream would cause it to explode & have bunches of little Delta fires everywhere, including on yourself. Not recommended.

Class Delta fires create their own O2 & burn hot enough to crack the water to H & O2 before it even reaches the flame. There's not much anybody can do about it once it's started. On the plus side, they're really hard to get started.
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Old 11-25-22, 02:50 PM
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Originally Posted by Steve_sr View Post

In the meantime if anyone can show instances of frame failure on a TI frame caused by this defect. I would be interested.
Just recall one Ti frame problem years (and years) ago - Merlin off road frame - and it was at the top of the seat tube (near seatpost clamping area)

many Ti frames (if not most ?) do not have additional material or a lug type reinforcement at the top of the seat tube
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Old 11-26-22, 09:15 PM
  #67  
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Originally Posted by Mackers View Post
I know.

Just wanted to check after maddog's claim of Thomsons being undersized and things got out of hand.
The Record Ti gave me a moment's pause but I double and triple checked.
I also wanted to check his claim

placed a new battery in my calipers and had a small measurement party

Thomson seatposts - measured outside diameter

26.6 x 330 Elite silver - 26.58
26.6 x 330 Elite black - 26.58

26.8 x 330 Elite silver - 26.77
26.8 x 330 Elite black - 26.75
26.8 x 410 Elite silver - 26.78

27.0 x 330 Elite black - 27.0

27.2 x 250 Elite black - 27.18
27.2 x 240 MP black - 27.18
27.2 x 330 MP black - 27.27
27.2 x 330 Elite black - 27.24
27.2 x 330 MP silver - 27.28
27.2 x 410 Elite silver - 27.18

31.6 x 350 MP black - 31.6
31.6 x 410 Elite black - 31.55

.
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Old 11-27-22, 02:51 AM
  #68  
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Originally Posted by t2p View Post




I also wanted to check his claim

placed a new battery in my calipers and had a small measurement party

Thomson seatposts - measured outside diameter

26.6 x 330 Elite silver - 26.58
26.6 x 330 Elite black - 26.58

26.8 x 330 Elite silver - 26.77
26.8 x 330 Elite black - 26.75
26.8 x 410 Elite silver - 26.78

27.0 x 330 Elite black - 27.0

27.2 x 250 Elite black - 27.18
27.2 x 240 MP black - 27.18
27.2 x 330 MP black - 27.27
27.2 x 330 Elite black - 27.24
27.2 x 330 MP silver - 27.28
27.2 x 410 Elite silver - 27.18

31.6 x 350 MP black - 31.6
31.6 x 410 Elite black - 31.55

.
Once again, it was not just a "claim", as witnessed by the image i posted to try and slow down the trolling on this forum.. lord knows it will never cease completely. Glad they seem to have gotten their QC issue under control. The Thomson Pricing is still WAY out of line....i guess those bags are really expensive? I spotted an XTR box on CL the other day... no part, just a der. box... $17, but Free shipping... someone should snap it up!

Update: did some checking on Thomson .. they state that the alloy is 7000 aluminum... Can't find that specific alloy listed Anywhere except in relation to their parts... It seems the closest commonly manufactured aluminum 7000 SERIES alloy is 7005... then 7010... next is 7021, 7030, then 7050, 7070... and 7075 is the Normal alloy for demanding applications.... variations exist, as some applications may call for specific characteristics not covered by the production mixes. 7005 is used by multiple Bicycle Frame builders, as is 7075... the 7075 is preferred for it's strength but tends to be more easily fatigued into failure. Boeing uses a lot of 7075... i'll ask my buddy that works there if they specify careful Heat Treating/annealing, and/or stress relieving on the parts she's made for a few decades now...

ever seen the "Thrust Link" on a 707? it holds the engine to the wing.... it's aluminum.... and one 4" long grade 5 bolt rated at 275,000lbs. shear strength.... grade 8 bolts crack easier under high frequency vibrational loads... i'd imagine those thrust links and bolts were regularly inspected and replaced... my neighbor worked for Alaska Airlines for 30 years... i'll ask him next time i run into him...

Thomson's "Masterpiece" posts have a weight Limit of 200lbs. listed On Thomson's Site..... didn't read much past that weight limit spec...... Heads-up, Clydesdale Class! YIKES. I wonder if their steering stems call out a Weight Limit too... hmmmm... pretty sure I won't bother looking... i have a Thomson stem on my Commencal right now, and i'm a definite Clyde-class rider.... sharply machined diameter changes create stress risers in any material... even a tiny radius at a diameter change improves the durability... just sayin'...

As to the Pricing.. Thomson punishes anyone that sells their products below their pre-determined retail price.................. NEXT!

Last edited by maddog34; 11-27-22 at 04:31 AM.
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Old 11-28-22, 12:39 AM
  #69  
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Sure looks like an unsubstantiated claim to me.


If Thomson were (as you claim) known for producing undersized stuff, you'd think we'd do worse than 1 sample out of 18.

(not going to count the image you found as the guy took it from another site and I can't find its context)


But it's nice to see that you've moved the goalposts to now include Thomson's metallurgy, machining and pricing policies.


We get it though, you don't like Thomson.
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Old 11-28-22, 01:46 AM
  #70  
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As far as Thomson stuff goes I have probably 5 of their seatposts and a bunch of stems and love their stuff. I am a bigger rider and have had zero issues with any of their products. I don't use the Masterpiece or their road stems (just because I do prefer a four bolt face plate for various reasons) but plenty of companies have lightweight stuff for lighter riders so nothing new or exciting there.

In terms of pricing yeah companies need to have some pricing control otherwise someone can sell them at or below cost screwing over a lot of dealers it is not an uncommon practice and not a bad thing. I get it they make pricey stuff I won't deny that but it is good quality stuff. I could buy any stems and seatposts I want pretty much but I do like Thomson a lot and happily buy their stuff. I mean my first post is over 10 years old and I think it was $80 at the time so $8 a year at this point and will end up getting cheaper per year and has had zero problems and will last for a long time.

If you don't like Thomson that is fine plenty of other companies out there making posts and stems and such.
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Old 11-28-22, 08:06 AM
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Originally Posted by Mackers View Post
Sure looks like an unsubstantiated claim to me.

If Thomson were (as you claim) known for producing undersized stuff, you'd think we'd do worse than 1 sample out of 18.
FWIW: 1 in 18 is a bit over 5.55%. While that's not a statistically valid random sample taken from new items off the production line, it's enough to be of concern.

How would you like it if 5.5+% of the parts you bought from a particular vendor were out of spec so far they wouldn't work properly? Would you continue to do business with them long-term?

I have no "dog in this fight"; I don't think I own anything made by Thomson. But IMO an out-of-spec rate of >5% is far too high. If that defect rate (more than 1 in 20) is representative of past items clearing QC and shipped to customers, it should indeed lead to a reputation for producing out-of-spec products.
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Old 11-28-22, 10:23 AM
  #72  
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I've used Thomson seat posts since they were first available (sometime around the mid 90's ?)

High quality product - work well and are durable ; among the best bike components I've purchased
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Old 11-28-22, 04:29 PM
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Originally Posted by Steve_sr View Post
....The nominal seatpost diameter is 31.8mm. The hole diameter is .020" (0.5mm) oversize.
My thought is that is too much play. The issue is that the locking pinch will only be at the top and the post will be free to wobble around by that 0.5mm towards the lower end of the bushing. And that is going to permit the seat tube to walk it's way in. It might take an hour or perhaps two. But if the pinch isn't tightened extremely firmly you are likely to get that "sinking feeling" sooner rather than later.

Ever frame I've ever had or played with the seat post is a light push fit or a slip fit but with no detectable rocking play. What you have at present would see me cutting up a pop/beer can to make a sleeve shim to fit between the post and the insert to remove any detectable rocking of the post.
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Old 11-28-22, 07:11 PM
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Originally Posted by BCRider View Post
My thought is that is too much play. The issue is that the locking pinch will only be at the top and the post will be free to wobble around by that 0.5mm towards the lower end of the bushing. And that is going to permit the seat tube to walk it's way in. It might take an hour or perhaps two. But if the pinch isn't tightened extremely firmly you are likely to get that "sinking feeling" sooner rather than later.

Ever frame I've ever had or played with the seat post is a light push fit or a slip fit but with no detectable rocking play. What you have at present would see me cutting up a pop/beer can to make a sleeve shim to fit between the post and the insert to remove any detectable rocking of the post.
Or.. head to a hardware store for a proper Shim material, cut and bend as needed, as i suggested a few dozen posts ago... sadly, people became too enthralled with protecting an overpriced seat post, and a titanium frame.... which was bought "new" then sat around for a long time for an undisclosed reason.

General message... have fun... go ream out Seat tube sleeves that are already oversized, as was suggested earlier.... i've got a Fox Float shock to clean thief paint off of... same color as my old Rally Car, actually, a lovely shade of blue.. i really miss that car.......later.

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Old 11-28-22, 07:50 PM
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Originally Posted by BCRider View Post
Ever frame I've ever had or played with the seat post is a light push fit or a slip fit but with no detectable rocking play. What you have at present would see me cutting up a pop/beer can to make a sleeve shim to fit between the post and the insert to remove any detectable rocking of the post.
First I see a mistake on my part. The nominal post hole should be 31.6mm NOT 31.8mm.

I thought about the beer/pop can angle but today's coke cans are only .003" thick!
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