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Rotate
09-27-2002, 01:37 PM
Hi is this done? Does it actually reduce the surface area and thicken the metal? This seems inconsistent with the hammer action, which normally thins and spreads the metal. I have zero experience with sheet metal fabrication so this has always puzzled me.

Albert

Thrud
09-27-2002, 03:26 PM
Albert
My experience with sheet metal stops at autobody hammer dolly stuff - never needed to know that for office funiture, cabinets, and electrical gear.

alsinaj
09-27-2002, 03:45 PM
Mechanical shrinkers grab the metal in two sets of serrated jaws. At the beginning of the stroke, the jaws are separated by a small distance. The stroke then moves the jaws toward each other, forcing the metal to thicken without wrinkling. Hand shrinking works the same way. Think of a piece of corrugated metal. If you restrain two adjacent low spots so they can't move, and then smash down the high spot, the metal will thicken - there's no place else for it to go unless it wrinkles. The trick is to prevent wrinkling. So the process is, put wrinkles in (which draws in the outer edges), then take the wrinkles out again while restraining the outer edges. In hand work, inertia and friction against the dolly do the restraining. You are right that you can't whack the metal between the hammer & the dolly - that stretches it. You have to hit only on the unsupported high spots.

docsteve66
09-28-2002, 12:18 AM
Body and fender men (before bondo) used to shrink metal that was stretched in a accident. They had "shinking hammers but most just heated the metal to dull red in one spot, hit it with a wet rag and it shrunk. done wrong, it made the metal brittle. I under stand its a forbidden practice on unibody construction. Lead (40/60 or cheaper solder) was used to cover the blemishes. Even new cars had considerable lead work straight from the factory. I have no idea ratherthe metal became thicker or not.

abn
09-28-2002, 02:34 AM
Have to make another plug for metalshapers.org here...there is a nice album there where you can see the process of putting in tucks (wrinkles) and taking them out with a hammer. I don't have a link right now but it worth the time to check out the available albums.



<font face="Verdana, Arial" size="2">Originally posted by Rotate:
Hi is this done? Does it actually reduce the surface area and thicken the metal? This seems inconsistent with the hammer action, which normally thins and spreads the metal. I have zero experience with sheet metal fabrication so this has always puzzled me.

Albert</font>