Machining Cast Iron Dumb Bells

Allan

Active User
Registered
Joined
Oct 7, 2012
Messages
281
I have collected a bunch of cast iron dumb bels on spec. I pick them up at the thrift store for a buck or less. I have used and tried to use some of them for various projects with mixed results. Some machine beautifully and others are as hard as granite. They must take them out of the mold hot and dump them in the sea. One I used recently made a beautiful face cut and not bad longitudinal cut but the angled cut was just about impossible with HSS.

One I was hoping to use was so hard that a file just slid over it. I put it in a raging fire in backyard. The fire burned 3 feet tall for several hours. I let it cool overnight in the ashes but it is still just as hard. So is there an inexpensive way with minimal cash outlay and no weird chemicals to anneal these things?
 
Mystery metal is just that. The file test can help, but there are also sometimes inclusions that are harder than Hades, and/or porosity and voids. Buying known quality metal with known properties is a safer but more expensive way to buy machining stock. Most of us use mystery metal at times, test it with a file and hope for the best. Sometimes the money saved on the material ends up costing more than that in damaged machines and tooling, not to mention frustration and a finished product that is not as good as it could be. More and more, I stay away from mystery metal and try to get drops of metal stock from known sources at a reduced price or free.
 
The hard ones are probably a mixture of leftovers, with nickel and zinc and who knows what else in it.- probably the cheapest grade of cast iron made.
Good only for weights.
mark
 
Life is too short. And I want a happy ending. My main choices in life nowadays are 12L14, 1144, aluminum, brass & plastics. The days of exotic and mystery metals are gone! Unknown cast iron will be just that “unknown”. Sorry, I don’t want any part of it. Especially the hard spots that it could be hiding inside.
 
Last edited:
Life is too short. And I want a happy ending. My main choices in life nowadays are 12L14, 1144, aluminum, brass & plastics. The days of exotic and mystery metals are gone! Unknown cast iron will be just that “unknown”. Sorry, I don’t want any part of it. Especially the hard spots that it could be hiding inside.
Plus one here. Wasting time on mystery metal and money dulling cuters and broken tooling just is not in my time table any more. Buying more cutters and grinding down your HSS, will cost more in time and money you could use to buy needed known material.
Good luck and God’s Speed
CH
 
Last edited:
Cast iron come in multiple flavors. When you think about the desirable properties of of weight, it needs ti be heavy and to be able to cast into a specific form. Mechanical property needs are all but non existent. There is no reason to expect that weights from different manufacturers or even from different production lots from the same manufacturer will have the same mechanical properties.

White cast iron is inherently hard and brittle. It can be converted to gray cast by heating at around 1,000ºC for an extended period (several days) and cooling slowly over an extended period. While your strategy of heating in a bonfire is on the right track, I doubt that you can say that you held the cast at 1,000ºC for the entire time. Even if you had, the conversion process normally takes about 10x the time. The best way would be to use a muffle furnace that can maintain a controlled temperature for the required length of time.
 
I have worked with cast iron weights mainly barbell, window sash, and medical scales. Found some medical scale weights that were 1" by 3" by 8" with 3 guide holes, These machine beautifully. Barbell weights, if they are bare(no heavy paint or plastic coat), pass the file test, may be okay. Even so I take the first cut on an old carbide bit to see what it will do. Window sash weights,forget it. However, they can still be machined, sort of. Just use a side grinder and figure to a tenth of an inch instead of a thousand. Still, it's not a total loss, these weights still can be used as, DaDa!, weights. Used four of the weights as a counter weight for a machine. ( they're great since the weight is usually cast right on them), Weights to hold down things as I work on them. Weights when gluing two wood panels together. Last of all weights that are put in a box or heavy bag so they won't roll around as a substitute for sand bags for winter driving.
 
Of the two different barbell weights that I tried one was a joy to turn. The other one not as easy but was ok. This is the one that turned real nice:

IMG_0064.JPG
 
Life is too short. And I want a happy ending. My main choices in life nowadays are 12L14, 1144, aluminum, brass & plastics. The days of exotic and mystery metals are gone! Unknown cast iron will be just that “unknown”. Sorry, I don’t want any part of it. Especially the hard spots that it could be hiding inside.

I agree one thing that I do is get scrap drops from my local metal supermarket scrap bin. The CLT store lets us pick through them and sells us the material by weight at scrap price


Sent from my iPhone using Tapatalk
 
What do they charge per lb. scrap price? I pay $1/lb for quality steel remnants, but I 'm thinking its a bit high.
 
Back
Top