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I Forge Iron

Fun with a ball bearing

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I just picked up a 1" diameter ball bearing at a garage sale. Just one ball, presumably made out of hardened steel. It is amazing what a rebound test tells when tried on various grades of anvils:

concrete floor 20%
railroad plate turned over 20%
cast iron vise anvil 40%
railroad track anvil 40%
railroad track anvil (vertical) 70%
good 150 lb. anvil in blacksmith shop 90%
large unmarked 220 lb. anvil, weld repaired spot 70%, off the spot, 80%

So, this gives results that would be reasonably expected. Strength of material matters, weight matters, and mass in line with the impact matters. The weld was ground flat but the color showed striations. Also, it dinged with the edge of a hammer. Possibly interesting to those who wish to weld on the tops of their anvils. There was also a much duller sound over the discolored area. The difference in rebound is real, but the welded surface is still much better than cast iron. The railroad track experiment shows the importance of mass below the blow. Some say that a 120 lb. railroad track set on end is like a 200 lb anvil. According to my test, it is (as long as the anvil is welded). Otherwise, it is not even up to a 150 lb. anvil. So it is not entirely mass under the hammer, but the hardness of the surface as well. Surprising :D

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Hi Apprenticeman. Good point. Most hammers are pretty hard. I tried out a 10 lb sledge hammer sitting on the concrete floor. Got 70%. I think that one can get carried away doing this sort of testing, since mass matters a lot, since a hammer is much more massive than a ball bearing. I would much rather use the railroad track section than a sledge hammer head. The hardness of the surface is important, though, in preserving the rebound energy. It only takes a thin layer of hard face, though, to get the effect, since the deformation is probably something like inverse square or less.

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