Bicycle Mechanics - using dry ice to pull a shallow dent out of a steel frame?
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11-12-04, 04:50 PM
Hi guys, my Fuji that im trying to refurbish has a small, shallow dent in the down tube. Would there be any harm done to the frame by attemting to use dry ice to shrink the dent out?
11-12-04, 07:31 PM
Only to your wallet to the extent of the cost of the dry ice. If it is only a small dent in steel I dont think the structural integrity wiil be affected . Sand off the paint and fill with solder, preferably a low temp solder as you wouldnt want to affect the heat treatment of the steel. If aluminum I would fill with epoxy.
I've worked in shops for a long time, and I've never heard of that method of taking out dents. How does it work? Do they do this for cars?
The dry ice method is one that is supposedly useful for removing dents in car panels. The effectiveness of this is questionable however the theory is that you place a small piece of dry ice directly onto a small dent. The metal in contact with the dry ice contracts which causes it to pull back in place.
Whether this trick works on cars, I cannot say, though I am doubtful. Even if the metal did contract enough to pull up even with the surrounding metal, what happens when the metal warms up and expands? However, if applied to a metal tube the best you could hope for is to pull the metal up far enough to create a flat spot. In order to restore the round shape you would have to pull the metal back up somehow.
Nonetheless, a small piece of dry ice would be pretty inexpensive if you wanted to try it. I doubt that you would damage the paint. You certainly will not damage the tubing with it.
Have you heard of "rare earth" magnets.......you can find them on ebay, that would be a good way to pull the dent out
11-13-04, 06:26 PM
I think I saw someone try this on Monster Garage last year - used heat and cold to try and get the metal to snap back in place. The head guy (Jesse James?) came in, saw the terrible terrible mess it was causing in the sheet metal, yelled a lot, and they ended up cutting out the whole chunk and welding in a new sheet to make up for all the damage it had done.
The guy who was doing it swore it was possible, though.
We did this to the plastic bumper of a Porsche 911 Turbo (996) I was detailing, though we just used standard ice + a heat gun to shrink/expand/shrink/expand to get a crease out of the plastic bumper. Worked very well on the plastic but I'm not sure it would do much for steel. Took a lot of time, finesse and patience.
These are the tools designed to remove small, shallow dents from tubes:
11-13-04, 07:52 PM
Thanks for the feedback guys! I wasn't sure if it was a good idea and well I have my doubts too. The tube forming dies look like a good way to go as I discovered some damage at the seatlug binder. I think it's going to need professional repairs at this point. Thanks for all the help!
11-15-04, 11:57 AM
For others wondering the merits of the dry ice technique, it works for smaller dents in sheet metal, e.g. from hail damage. Its not a miracle cure though. I doubt you could get enough contraction in a bicycle frame tube to pull a dent - the metal thickness & tube shape make it tougher to work than a panel of sheet metal.
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