Making a carbon seatpost, any carbon experts about?- Mtbr.com
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  1. #1
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    Making a carbon seatpost, any carbon experts about?

    Has anybody ever made a carbon seatpost?

    I need to make an inline seat clamp to go on this carbon tube (31.7 OD, 2.4mm wall) My initial plan is to make this style of seat clamp, there aren't many parts to it, so I should be able to make it nice and light, and the parts needed i can machine up easily enough.

    My question is,, I've seen a few production items like this. Some have a metal collar around the outside, some not. If i get carried away being all weight weenie, how am i to decide if it needs a metal reinforcement or not?

    Will boring a hole through my carbon and then sliding a metal rod through it be strong enough? This is my first time doing anything carbon, so I'm a blank canvas at the moment. Any input at all is appreciated.

    Edit, for a road bike.

    Making a carbon seatpost, any carbon experts about?-img_1238.jpgMaking a carbon seatpost, any carbon experts about?-img_1239.jpg

  2. #2
    will rant for food
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    I'm sort of in a squishy zone between amateur and expert. What I know is that drilling, even with a proper composite dual-flute-direction bit, will lift the layers in very small amounts over a certain radius away from the cutting zone. Careful drilling can make this damage very small.

    If it were me? I'd sleeve it as in the second picture.

    I have a customer requesting a carbon seatpost, I was going to do the Enve style clamps. You just mold a negative space for the Enve hardware to plug into and away ya go.

    I think there's some papers out there from the US Army about drilling carbon in situations where it is strictly unavoidable
    Disclaimer: I run Regular Cycles (as of 2016). As a profiteer of the bicycle industry, I am not to be taken very seriously.

  3. #3
    pvd
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    I been doing carbon handlebars and I'm currently doing a carbon fiber fork. It's interesting stuff. Very expensive if you order the wrong stuff.

    Most of the cheaper carbon fiber seatposts you see are wrapped over metal.

  4. #4
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    Cheers.

    Iím not overly worried on the hole drilling, I spent about 3 years at work putting holes in carbon, or carbon metallic stack up aircraft skins. Iíd probably use a carbide dagger drill if it was just the carbon tube, or a more conventional 3 flute carbide drill if I had a steel outer collar. I can ďborrowĒ a drill or 2 from my old department and I have enough of an idea on what speed/feed works to prevent de-lam.

    Itís more the strength side Iím worried about, if I cross drilled, and maybe used a 10mm diameter pin, would this damage the carbon when I tighten it? I suppose if Iím worried, then I shouldnít be doing it! I think Iíll go with a steel collar around the tube. I can then shape the end of it to match the rest of my lugged frame.

    Drew, quick question, I need to notch the end of the carbon tube, what rotary hand tools are best to cut it with? Emery cloth style abrasion, or some kind of a die grinding burr?

  5. #5
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    Quote Originally Posted by Cord View Post
    I need to notch the end of the carbon tube, what rotary hand tools are best to cut it with? Emery cloth style abrasion, or some kind of a die grinding burr?
    A little of both. I've seen one dude's setup where he covered a cylinder drum in abrasive, mounted it a little offset from center and ran it low speed on a lathe, and used it as a notcher even though it wasn't really a cutting instrument in the way one would usually think.

    Die grinder type hand held power tool will remove a lot of meat really fast and wants to dig - be very ginger with those. My present frustration is that hand sanding is too time consuming, but machine sanding is far too aggressive. There seems to be little in between.

    And what the heck, you sound like the expert here regarding hole drilling. Especially if you did aircraft. You don't want the fractures to spider.

    Have you given any thought to, like, bonding two posts on to implement those protruding threaded holes?
    Disclaimer: I run Regular Cycles (as of 2016). As a profiteer of the bicycle industry, I am not to be taken very seriously.

  6. #6
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    I wouldnít say Iím an expert, I just applied engineering that somebody else had already proven. I have made a few hundred thousand H7/8 holes, so making another 1 is no big deal!

    I had thought of somehow bonding on the ďearsĒ but other than making holes, Iíve never touched carbon, I donít think this is the project to start experimenting on. Maybe another day.

    If I bond a metal collar on, I then have to set up to drill a hole, then reset to cut a radius at 90į. Maybe Iím making this job more complicated than it needs to be. I could just weld 2 tubes together and use an Enve style seatclamp. And simply bond this onto my carbon tube? Hmmm I seem to be coming up with more options, not narrowing it down!!!

    I like the idea of abrasive and a lathe, I could just glue emery cloth onto a wooden dowel of the correct diameter, then run it nice and slow to make my notch. Thanks for that.

  7. #7
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    This style, then i can shape to match my jugs, and bond it onto the carbon tube?

    I've not seen 1 in the flesh, but assume its just a plain tube that the clamp slides inside?
    Making a carbon seatpost, any carbon experts about?-img_1240.jpg

  8. #8
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    Quote Originally Posted by Cord View Post
    This style, then i can shape to match my jugs, and bond it onto the carbon tube?

    I've not seen 1 in the flesh, but assume its just a plain tube that the clamp slides inside?
    Click image for larger version. 

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    The inside is cone shaped as is the aluminum bits. They wedge as you tighten the bolt. Had to use carbon paste to keep mine tight.
    Salsa Carbon Bucksaw- Trek Farley 8

  9. #9
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    The inside of the tube that houses the clamp is conical? Hmm, more complicated than meets the eye! Thanks for that.

  10. #10
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    Why not just bond an existing head inside the tube?

    "Too easy" is an acceptable answer !

  11. #11
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    A perfectly good idea, and a 27.2 will fit with only a tiny tidy up of the ID. (Iíve already tried it!) Iíve offered up an in-line Thomson, but there is quite an ugly step where the carbon finishes, and it leaves the bolt heads VERY close to the outside diameter of the tube. So if desperate I could do this, just not sold on the aesthetic. Iím definitely more interested in a tube slipping over the carbon, then I can shape this to match the lug work on the rest of my frame.

    And no, Iíve not got a 34.9 post lying around to test slipping it over the outside! Or Iíd have tried that too!

  12. #12
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    I've built titanium seatposts using that IRD method but I found that the cross-rod would slowly creep towards one side. So if I was making a carbon post I'd think about bonding some tabs around the outside of the tube. I wonder if you cold take the top piece of an existing clamp, cut off the rail channels, bore a hold in the center, and flip it over?

  13. #13
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    Working with carbon I'd super easy. It's just the same as working with standard fiberglass.

    If you want extra wall thickness where you drill the hole simply sand back and wrap some carbon around the area you want to increase strength.

    Sanding, drilling, adding more carbon later is all easy.

  14. #14
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    Ah, so the ears/cross rod thing can creep forwards through the hole over time if not secured and hence loosen the clamps, thanks for that. I could braze the ears on to a steel tube and bond that onto the top of my seatpost.

    You lost me on the last bit, can you explain again please.

  15. #15
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    Quote Originally Posted by plummet View Post
    Working with carbon I'd super easy. It's just the same as working with standard fiberglass.

    If you want extra wall thickness where you drill the hole simply sand back and wrap some carbon around the area you want to increase strength.

    Sanding, drilling, adding more carbon later is all easy.
    Cheers, Iíll give you a shout when Iím elbow deep in glue and making a dogs dinner of it!

  16. #16
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    Quote Originally Posted by Cord View Post

    You lost me on the last bit, can you explain again please.
    So take the top of a something like a Thomsen post.

    Bore a 31.8 hole through it

    Bond it on your post upside down.

    You now have two tabs.

    (You could do the same by waterjetting some plate, of course)

  17. #17
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    Quote Originally Posted by dr.welby View Post
    So take the top of a something like a Thomsen post.

    Bore a 31.8 hole through it

    Bond it on your post upside down.

    You now have two tabs.

    (You could do the same by waterjetting some plate, of course)
    Ah, I get it. I shall investigate further. I have a fair few old posts knocking about.

  18. #18
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    Sounds to me like your reluctant to layup additional carbon. It's not too hard. Yes give me a should out if you want more indepth info.

    I've been working with carbon for years and years.

    I reckon if your going to make a carbon post you might as well make the whole thing out of carbon, use titanium bolts/nuts and make it lighter than most production carbon posts.

  19. #19
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    I am indeed shying away from adding carbon, I like the current look and will hopefully keep it. If I can do that by just adding simple metal hardware, all the better. At some point in the future I want to get more involved in trying carbon stuff. Iíll be pestering for more information then!

  20. #20
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    Found a used Enve clamp on ebay for £12, bonus! So thought i'd have a whirl. OD of Enve clamp is round, and 30 diameter, so just going to braze a "T" from 2 tubes. Clamp will slide into the cross tube, the vertical tube i will shape to match the lugs on my frame and then bond onto the carbon.

    Just had a quick go with some left overs, think it will work a charm. If anything, too easy!!! The internet tells me that these clamps can be prone to moving, so after brazing I'll put it in the lathe and clean it up, make sure i have maximum surface area in contact.

    Making a carbon seatpost, any carbon experts about?-img_1244.jpgMaking a carbon seatpost, any carbon experts about?-img_1246.jpg

  21. #21
    pvd
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    Those round binding systems are terrible. They always slip.
    They may be fine for super light roadies but for real off road use, they suck hard.

  22. #22
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    Yep, I have read some bad things about them. Am hoping with some attention to detail I can get the mechanics of it working correctly. if I can get the ID of the tube it sits in to be actually round, the OD of the clamp to be the correct shape and then lube on the ramped surfaces so it can clamp properly, I see no reason for it not to work, it seems viable in theory. It is for road use, and I am a feather weight. So fingers crossed. Failing that itís another lesson learnt!!!!!

  23. #23
    pvd
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    It 'might' work for road. For MTB, I've never been able to get them to work and I'm willing to do the work for a proper setup.

  24. #24
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    Those designs often suffer due to two similar assumptions:

    If the parts are split into a top and bottom, they only combine into a round assembly if the seat rail material is perfectly toleranced. It isn't, so you will likely end up with an oval.

    If the assembly uses a wedge, as soon as it's tightened it's also an oval.

    It's probably worthwhile to ream out the high spots, but don't worry about getting it perfectly round.

  25. #25
    pvd
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    A long time ago in a galaxy far far away,

    https://www.peterverdone.com/wiki/in...ottom_Brackets

  26. #26
    will rant for food
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    *scratches chin*

    Hmm, thanks for the heads up on why not to use the Enve clamps. I'm all for making things easy in terms of the composite portion, but if it makes the result suffer, then, no thanks.
    Disclaimer: I run Regular Cycles (as of 2016). As a profiteer of the bicycle industry, I am not to be taken very seriously.

  27. #27
    pvd
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    This is one of the nicest post tops being done right now:


  28. #28
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    Iím a few weeks away from finishing the frame that this is going on, but Iíll be sure to post up my results (good or bad) with this clamp.

  29. #29
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    Quote Originally Posted by pvd View Post
    Those round binding systems are terrible. They always slip.
    They may be fine for super light roadies but for real off road use, they suck hard.
    Carbon paste and it won't slip. I'm 244# and it's a cheapo Chinese post.
    Salsa Carbon Bucksaw- Trek Farley 8

  30. #30
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    Stick an aluminium sleeve in the top of the carbon (peo it) then that will take the load from the hole for the tension pin the saddle will be an aluminium running face just like the USE from a quick calc it will add 4g to the carbon you could use a carbon plug

    to be fair if your not selling these any of the methods outlined above will work

  31. #31
    pvd
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    Quote Originally Posted by bcriverjunky View Post
    Carbon paste and it won't slip. I'm 244# and it's a cheapo Chinese post.
    I demand more professional setups. If you're using 'carbon paste' for a mechanical system to work, it's a garbage system.

  32. #32
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    Quote Originally Posted by compositepro View Post
    Stick an aluminium sleeve in the top of the carbon (peo it) then that will take the load from the hole for the tension pin the saddle will be an aluminium running face just like the USE from a quick calc it will add 4g to the carbon you could use a carbon plug

    to be fair if your not selling these any of the methods outlined above will work
    Thanks for that, Iím going with a sleeve over the outside so I can shape it to match the rest of the lugs in the frame.

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