Is my seatpost safe with a hole? update: we're good.

[hillzofvalp]

I need to make about a 2.35mm diameter hole in my seat post head, in order to route wires through for my rfid board. I'm a perfectionist about my build, and I'm trying to keep it very clean (only external wires are throttle and phase). If I have to, I can try to use magnet wire so the hole is even smaller. Key thing is that I don't want to create a huge stress point on one of the lightest seatposts made.

Here are some pictures of my 150ish gram alien USE seatpost. I plan on putting it on my surly 29er hard tail for primarily road/commuting use. Here are some pics. Feel free to comment on the safety aspect of my intention on going 25-30mph on a 29er with front reba and 2.35" Big Apples and this potential carbon seat post hazard, with or without the hole.

It's probably no big deal, but I wanted the material engineers and physicists of ES to help me out...
Thanks!

 

[liveforphysics]

Round holes are rarely problems for things, as they have no stress riser edges on them to propagate cracks.

Making slots or notches in light things is the no-no.

 

[MadRhino]

Yep. a small hole won't be a problem.
It is a carbon seatpost though, I would edge the hole with epoxy to prevent further fibre separation.

 

[Alan B]

Probably need to drill it with very high speed carbide or diamond bit to avoid starting cracks.

 

[hillzofvalp]

I wanted to do it in the aluminum head... rather than risk the carbon fiber.. is that okay?

and you guys are pretty cool about carbon seatposts for this application? When do carbon seatposts ever break?

 

[biohazardman]

I used my dremel with a small abrasive point unit on it for drilling carbon tubing it seemed to werq well and did not need any dressing up when I was done. You might be able to drill down through the aluminum top of the seatpost as well. The angle would not really matter. What's the wire for external power? I have been trying to figure out how to turn one of those into a brake light as well as keep the flashing stock. But things are tight inside for a solder iron.

 

[hillzofvalp]

It's for powering the rfid board, as well as for serial output and enable lines. The idea is that I will unlock the bike by sitting on the bike, and it will effectively scan for my ass. I will go straight down about 3-4 mm from the edge of diameter of the flat part of the aluminum. I hope that it isn't very thick.

 

[MadRhino]

"it will effectively scan for my ass...

After the advent of thumb and eye scanning security,
here comes the ass scanning anti-theft for ebike.

 

[biohazardman]

I would expect the aluminum would be 1-1.5 inches thick but it's soft so should not be a problem. Ass scanning, that's a new thing I will have to think about that for a bit. ;^)

 

[Hillhater]

Modern bike thieves dont bother to ride them away .. they simply load them into a van and haul ass !
your best bet is a hidden GPS tracker.

 

[hillzofvalp]

I'm going for more of a seamless experience than to ward off thieves. Sit on the bike.. it powers on and senses for light levels and turns lights accordingly. The RFID implementation will also add to the minimalist dashboard concept and possibly allow for a ass-off-the-seat-"uh oh!" safety mechanism. LAstly, I might use my second rfid tag for programming purposes (for example, when letting a friend ride I will give him a separate tag.. so whenever he gets on the bike a governor takes effect). He'll never know I was limiting it.

GPS is another thing I'd like to implement.

 

[AussieJester]

Perhaps drill it very close to the top if your worried? so it goes through the aluminum that is seated
in the top part of the tube? small hole though wont make a beez dick of a difference to strength..

KiM

 

[Drunkskunk]

I would drill the hole at the top, in the aluminum, going down in. Not from the side. That area isn't structrual.

 

[hillzofvalp]

thanks guys. See my 29er build thread for updates if you're interested in butt scanning

 

[hillzofvalp]

uh oh. I started drilling it closer to the edge.. stopped when I realized I was too close. only 1/8" of aluminum. Moved inward.. only 1/8" of aluminum again. Keep drilling... carbon keeps coming out for over 1.25" depth of cut. Tested it by actually measuring through the other end and there is indeed a whole bunch of somerthing in the middle for about 1.25". if aluminum goes down farther it must be right dead on in the middle.. and probably around .5" in diameter.


I led the hole towards the outside of the post cause I miss judged the actual width of the carbon tube (cause the aluminum head is 29.3mm in diamater compared to 27.2mm)---- so I think I ruined it. I imagine the very tip of the bit is about 1/8" away from perimeter of tube...

FROCK!!such an IDIOT!
Maybe I'll have to inject some jb weld in there to fill it up and then start over from a more centered point. Good plan? Safe? encouragement?

 

[MadRhino]

Forget the seat mount, the end of the carbon fiber tube is fragile and more likely to start fibre separation.

I would drill in the carbon tube, in the rear. then cover the edge of the hole with epoxy, maybe an eyelet...
Just fill what you've done with epoxy

 

[Drunkskunk]

I would fill that hole up with epoxy and not worry about it, then drill your hole right down the center of that trigger shaped rail so it goes down the center of the seatpost tube. You won't pull the wire through the seat rail part, but through the underpass part at the top of the tube.

 

[biohazardman]

I would have drilled in the middle of the aluminum as you said. Might even have to drill deeper than 1.5 inches hard to say for sure. If you can get some epoxy down there it would be good but might prove difficult without some kind of syringe and a more liquid type of epoxy. Good luck

 

[Gordo]

My first thought it to drill thorough the center of the side of the brake light bracket. The bracket clamp will be transferring any stress at the hole, above and below the edges of the bracket.

 

[LI-ghtcycle]

You can get some of the epoxy that comes in a syringe and just inject it in there, and drill your new hole as close to the center of the aluminum cap going down, or like DS said, just through the top of the middle of that trigger shaped portion and feed the wire through where it first exits the cap and you should be fine.

 

[hillzofvalp]

This sounds very reassuring. The middle of the big top part is very thin.. I'm not sure how integral it is for support. Its a mm thick. I can still go at this closer than in the picture.. Just need long enough bit. Would 6mm from center be acceptable? I feel like this thing has been engineered for minimal weight and probably needs that thinner middle section. They definitely had a good opportunity to Cnc mill all the way through

 

[Alan B]

Measure twice, drill once. I thought you were going to drill the center.

The RFID scanners generally have very little range, most have to be nearly in direct contact. Is this going to work anyway?

 

[hillzofvalp]

It's about 3 inches for a good read. I'll have play around with it for sure. There may a closer moment when the bike is just being mounted... Which is all that is necessary for enabling the bike

There are some other boards with a little more distance but I paid $10 for this guy. The engineers are already prototyping much larger distances, but for this application 3-6 is just fine

 

[hillzofvalp]

I put in some 6 minute epoxy. I kinda just dripped each part it in separate (alternating drips) and then agitated it a bit to get out the air bubbles. I drilled a proper hole down the middle and it was only about 3/16" thick aluminum and no carbon. The carbon must be a little bit beefed up towards the sides on the top.. maybe by about 30% tube wall thickness.

I looked over my post and the drill bit had caused a small bulge. Hopefully there is still enough material left to support me. Worst comes to worst, the seat post breaks and I have to stand up. I suppose I'll be more cautious when hitting curbs or other bumps.

 

[amberwolf]

When do carbon seatposts ever break?

http://www.google.com/search?q=broken+carbon+seatpost&btnG=Search&oe=utf-8&rls=org.mozilla%3Aen-US%3Aofficial&client=firefox-a&um=1&hl=en&tbm=isch&source=og&sa=N&tab=wi