Differences in supposedly same material

[marfaguy]

I'm pretty new to this so I don't know if it's something I'm doing or of it's the
material. I'm making 4 screwless vice clamps. More or less like these;
http://littlemachineshop.com/Projects/Drawings/ScrewlessViseClamps.pdf
I bought 4 pieces of 1018 cold rolled steel 1.25" square x 2.0" long ( should have
have had them cut 1.5" long but that's my bad). Got'em squared up at about 1.18"
or so on the mill on four sides. One of them didn't seem to "cut" the same as the other
three and was quite a bit more out of square/dimension than the other three when I started.
By out I mean 4-5 thousands. Mentally I dubbed that piece my "problem child".

Anyway, once I got them square I started mounting them on the lathe with my 4 jaw chuck
to start wasting off material to get the length in the neighborhood of 1.6" or so. I could take
off about .025" at a whack with no problem, accept for one piece. Granted it was late in the
day and I can't be absolutely sure my "problem child" piece from the milling operations was
the same one that gave me so much grief on the lathe. That one piece on the lathe was really
NOT happy with more than about 10-13 thousands. Bucking, trying to if not chattering, all in
all not the same experience I had with the other pieces. I think they were all cut from the same
bar. I'm lucky enough to have a very close supplier so I can call in an order and go pick it up
within the hour. I did watch the last piece fall off the horizontal bandsaw when I went to pick
them up so I wouldn't think the first piece was from a different bar BUT it may have been the
first cut from THAT bar. Is it possible, or possibly common for the first inch or so from a new bar
stock to have different properties from material further along in the bar?

 

[Brian Rupnow]

Yes, it is very possible. I have experienced that myself. I have a peice of 4" diameter cold rolled that I got very cheap at my metal supplier to make flywheels from.--It is an end peice, and it is harder than a diamond. It will immediately turn an HSS cutter blue, and make a carbide cutter squeal like a pig. I think its pretty common practice when they build something from large cold rolled shafting, that they cut off the first 2 or so inches from the uncut ends of 20 foot lengths and sell that bit as scrap.

 

[marfaguy]

Hi Brian,
Very interesting. In visualizing how cold rolled is formed I can see where the initial compression could
affect the steel's properties but I'm not sure how the end of the bar could be affected. I'm trying to think
how compression differences would change when approaching the end of a bar. I wouldn't think there could be
much difference beyond the radius of the compression bars. I'm visualizing a sort of standing wave just in front
of the compression bar.
So it's possible my theory is correct, but just the wrong end of the bar as it was rolled. Or is it possible that
we both ended up with the first cut as it was rolled from the manufacturer? In other words, what was the end of
the bar as your supplier sold it was actually the lead in to the rollers at the manufacturer.

Edit:
Or I've got it the wrong way around and we both ended up with the tail end of the stock. ;D

Anyway, a good demonstration of why it's a good to make an extra or two when milling the same part. I'm still working
my problem child but if it gives me any problems I'll set it off to the side with a great big flag on it.

 

[nfk]

Hi,
My metal supplier is the father of a close friend of me, so all my metal is free (or almost free)
Usually my free metal are end or beginning of bars.
I found the beginning of aluminum bars harder than the bottom (6160 mostly) and on steels, the opposite.
I once broke 2 carbide cutters with the end of a cast iron bar (a heavy deformed one), it was very hard. I`ve en up throwing it away and getting a piece from the middle.

So far, it work for me that way, replacing a cutter once in a while is cheaper than the metal i got.

Regards,
Norberto

 

[Tin Falcon]

inconsistency happens in metal. There is a large supplier in the area that sells mostly steel but some aluminum heap. The company has the rep of stocking mill seconds. I did find that when i was doing some scroll bending that some pieces were softer than others. The guys brother also sells steel. if you want the good stuff of known alloy go to him a much smaller place but known for quality.
Tin

 

[f350ca]

Hot and cold rolled steel is formed in continuous sections from the billet, then sheared to lengths. The ends may be stressed from the shearing action but the rolling stresses should be even all along.

Greg

 

[quinette7]

Marfaguy -

The specifications for 1018 are pretty wide, allowing for a lot of variations within the same piece. I don't know how to verify if this is still current information, considering changes in the American steel industry, but I was told the following about 10 years ago by an Iscar Product Manager from Arizona, in whom I have a lot of respect. He (and others) said that most steel mills in the Eastern US produce 1018 from raw materials, so the product is pretty consistent from one end of the bar to the other. But steel mills in the Western states commonly make 1018 from remelted scrap metal, so hardness and machinability can vary dramatically from inch to inch. He has seen 1018 containing not-quite remelted ball bearings, making it impossible to predict tool life. Personally, I don't use much 1018. Maybe somebody with more knowledge of our steel industry practices can shed more light on this.

Bob G