OT- help with metal work

[aragorn723]

Hi,

This has nothing to do with electronics, but does anyone have experience with fixing deep scratches on a bike?  I have a bicycle that was locked to another, and someone decided to creatively acquire one of them :-p and accidentally hit the other with an angle grinder.  I want to paint up the bike (its chromoly steel) but don't know how to fill in the scratches / how to smooth it out.  Any suggestions?  Thanks,

Dave

[galyons]

Depends on how deep the grinder cut. Superficial...bondo/body filler.  Deep, but no threat to structural integrity JR Weld or similar 2 part high strength adhesive.  Deep enough to possibly affect structural integrity, have it brazed and then sand to level. All will have to be finish sanded to profile then primed and painted.

Cheers,
Geary

[aragorn723]

Hi Geary,

It looks superficial (it seems like enough to need filling but not deep enough to affect the integrity of the steel).  Attached is a picture.  Is bondo easy to work with / sand?


Thanks!

Dave

[2wo]

Bondo makes a "glazing putty" for touch up work. Comes ready to go in a tube and very easy to use. Ask for it at the auto parts store. Sand the wound smooth, with maybe some 220 grit paper apply the putty and sand smooth again maybe with finer paper this time, up to you how far you want to take it before painting...John         

[galyons]

Hard to tell the depth of the cuts.  Glazing putty is for filling pin holes and other minor blemishes. The pics make the cuts seem more drastic than I would recommend for glazing putty, but hard to tell.  If you sand down the blemishes and the metal incursions are minor and quite shallow then glazing compound would likely work.

Bondo is easy to work.  Sand off the burrs and the paint finish to bare metal around the damaged area. Mix the bondo and hardener per directions.  Smooth on with a flexible plastic applicator that will somewhat conform to the tubing's profile.  Let is set up and then sand to smooth and feather into the rest of the tubing. (Google & You Tube will be your friend!  )

Cheers,
Geary

[aragorn723]

The gashes look worse than they are- I found some 100 grit metal sandpaper laying around, and sanded the area smooth.  The deep part is maybe a millimeter or 2, so not too bad.  Maybe a couple of quick passes with the bondo will do it!  How about this for the repair?

http://www.homedepot.com/p/3M-32-fl-oz-Lightweight-Body-Filler-PN0262/202077782

Dave

[Paul Birkeland]

Good old bondo ought to do the job.  Your local auto repair shop may have smaller sizes. 

-PB

[Doc B.]

With all due respect to the knowledge base here, I'd be asking this on some hardcore bicycle frame maker's forum. Depending upon how hard you plan to ride there could be a weak point in the frame from the damage. If you're putt-putting around the neighborhood no biggie, but if you're riding balls out down a mountain or jumping a BMX - just sayin'.

[aragorn723]

Doc,

The bike is a singlespeed racing bike, so it won't see any jumping or anything like that.  I think the fastest i've ever ridden it is 20mph.  Most of the time I ride it around town and sometimes or on shorter rides (less than 10 mi since its very hilly). ,The scratches are a millimeter or 2 deep, so its not much more than cosmetic.

Dave