Bicycle Mechanics - cnc vs non-cnc rim wall
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01-14-13, 08:18 AM
I want to buy a set of black rim. The rim I want doen't have cnc braking surface. It seems to me that there a braking surface but they paint/powder coated over. Can I simply remove the paint with a flat file, sand paper or something. It will be to install on a singlespeed bike.
01-14-13, 08:21 AM
If the rim genuinely has a braking surface (a close-up picture will help us determine that), you should be able to sand off the paint and use it. Don't file it, files are for removing metal.
Not all rims intended to be used with a brake have CNC-machined brake surfaces anyway, it doesn't make much of a difference once the rim's had a few miles to wear in.
01-14-13, 08:32 AM
It would be helpful to know the particular rim you are wanting. Though there are a few rims designed with a "brake track" for rim brakes that don't aren't "shiney," most rim brake rims exhibit a machined surface.
Then there are rims for disc only which for the most part are not machined, and are not meant to be used with rim brakes. They are different in their sidewall design.
If you want a black rim with a machined brake track, they are available.
01-14-13, 08:39 AM
depends on the rim.
01-14-13, 10:40 AM
Or you can buy a really abrasive brake pad, and let the friction of braking do the work for you..
I did this with the hard anodized Mavic ex 721 on my Koga trekking bike..
01-14-13, 11:13 PM
Alright thanks guys. I'll go the sand paper option i'll send you picture when I have 1 minute
machined rims are quite a new thing, we ran rim brakes for decades on smooth rims with out any machining.
01-15-13, 12:43 PM
people Thought the pinned rim seams were weak, and so the companies started welding the joint,
then you have to clean up the weld bead..
Also keep in mind that some rims are hard anodized in various colors, including black and silver...
indeed, hard anodized stuff will survive 1000s of miles of riding as long as you don't use really abrasive pads, and still clean up looking like new.
01-15-13, 08:42 PM
I have a Velocity Dyad with dark gray reflective paint (sent to replace out-of-stock Freedom Ryder 23 with the same ERD, though I had to pay the difference in price). And one guy at smartbikeparts.com told me on his, the paint just scrapped off by using V-brakes. I was kind of hoping my Jagwire brake pads don't wear off the reflective paint though. I haven't tried it yet.
By the way, I did my best to measure by hand the ERD of the Velocity Dyad and Freedom Ryder 23. As far as I can tell, it's only 1mm difference. If the spokes go 1mm farther into the nipples, I don't see an issue there (although the wheels are not built yet lol).
01-15-13, 08:57 PM
indeed, hard anodized stuff will survive 1000s of miles of riding as long as you don't use really abrasive pads,
and still clean up looking like new.
I found the braking performance Improved once I got through the CD Anodizing..
Rim: Mavic EX 721 CD, Brake: Magura HS 33, Abrasive pad: Cross Country Racing 'Greenfrog' ,
then back to standard Black compound pad, Now I use Magura Red/Salmon compound ,
Insert made in Oregon, by Kool Stop, shipped in bulk to Germany where they glued the pad in the holder,
then packaged them in sets of 4 for distribution.
I'll go the sand paper option
Best not to, IMO. Unless maybe the rims are powdercoated rather than anodised.
An anodised finish should last a long time before pad wear eats through it, at which point wear accelerates, eventually leading to a shagged rim.
If it's normal anodising as opposed to the thicker and slipperier hard anodising, it shouldn't hurt braking enough to remove it.
Break out the sandpaper when most of the anodising is gone, and remove what's left for aesthetics' sake if you don't like the worn look.
01-17-13, 03:44 PM
as you can see on the not-so-clear picture that there's a braking surface cover with paint. I beleive that it's powder coating not anodize. If it was my wheels I would try to brake on it and see how long the paint last and then sandpaper it to a clean braking surface. It's not my wheel and the guy agreed that sandpaper it to have a clean surface. I'll try first to sandpaper the inside of the rim to see what happen.
Yeah, I'd use it as is until it starts looking crappy, then there'll be less paint to remove.
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