From: Robert Bastow <teenut@home.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Why Cold-Rolled?
Date: Mon, 18 Oct 1999 08:56:16 GMT

Engineman1 wrote:
> When something like you described
> happened my fellow machinists would say "oops, there's a ball bearing".

I had almost come to think that that was a thing of the past...'Til I ran into
exactly thet..a ball bearing inclusion in a 4140 barrel blank I was turning down
to finish size.

As the barrel (.505 cliber) had already been threaded chambered and headspaced,
I was NOT a happy camper!

Close examination showed no sign of it in the bore, and a bit of careful
measurement of exposed diameter vs distance to go showed it would all come out
just before I hit finished muzzle diameter (it was about 4" from the muzzle end)
so I pressed on.

THAT was a long night!!

teenut

From: Robert Bastow <teenut@home.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Why Cold-Rolled?
Date: Mon, 18 Oct 1999 22:36:19 GMT

A voice of reason here from Mike...with sound advice!

I forget sometimes that the hot rolled I use, comes from a reputable supplier
(Metal Supermarkets) and is NOT the hot rolled "steel" (???) one finds at the
Ace Hardware or Home Despot.

"Good" hot rolled steel is a joy to machine..Unfortunately a LOT of steel
suppliers will ship A36 on all hotrolled orders unless you tell them not to..in
which case you may be SOL because it is all they have!

There is NOTHING wrong with A36 for the purposes for which it is
intended...Fabrication, and in particular for boiler work.  Problem is, to be
good for boilers it has to be very ductile, elongation up in the 27-30% range
IIRC.

But that ductility makes it a ROYAL PITA to machine...those chips will NOT break
and the usual rats nest will ruin your whole day...especially on an enclosed cnc
machine with a chip conveyor!!  Anyone who has had to deep hole drill it on a
production basis..as I have, will have few good things to say about its
machineability!!

By comparison, cold rolled steel (Non FC) has locked in stresses and work
hardening, that not only make it dimensionally unstable..even if you  DON'T
machine it sometimes!!..but also make the material so variable in texture and
character, that it is impossible to get a decent finish on it without resorting
to subterfuge.

One of the reasons for this, is that a piece of say 7/16" diameter CRS will go
through a whole different sequence of dies and draws etc, than a piece of 1/2"
diameter that came from the same melt on the same day!! So far as machining is
concerned it may as well be a different material, from a different Planet!

Where I came from, CRS was for near-net finished shapes and "For Pretty"

Any Draftsman that spec'ed CRS on a fully machined part would be LAUGHED out of
the Drawing Office, BOOED out of the Cost Office and BOOTED out of the Machine
Shop!!

teenut

mikoberg wrote:

> in a fit of sanity, EVERYBODY (net somewhere@some time.net) snatched up
> their respective keyboards and typed:
>
> ---snip--- snip---
> --somthin somthin somthin---Cold rolled, is much better/worse than
> --somthin somthin somthin--- Hot Rolled.
>
>    Ok My 2c:
>   I think that one of the things that confuses most amateur is the
> different steel qualities and how to tell them out of the scrap pile. Tool
> steel unless it still has it's wrapper and/or end paint is impossible to
> distinguish between 01 02 A1 W1 etc. and hot rolled can be anything under
> the sun. (usually it's just structural crap that is REAL fun to machine.
> Cold rolled's minimum quality on the other hand is usually pretty good. It
> as a minimum is fairly easy (in comparison to the usual hot rolled scrap)
> to machine.
>   I have found that cold rolled, if _just_ turned threaded etc and lightly
> milled, holds its shape pretty well.
>   Now if I was telling a person what to pick up new from the metal yards I
> would say go with 1118 hot rolled if he wanted to color case harden it
> (even 11L18 color cases okay) and probably go with 12L14 if hardening was
> not an issue. If I figured that the machinist was a beginner and would find
> his stuff in the scrap yard; for the project outlined I would suggest the
> cold rolled.
>
>    -mikoberg

Newsgroups: rec.crafts.metalworking
Subject: Re: Why Cold-Rolled?
From: Robert Bastow <teenut@home.com>
Date: Wed, 20 Oct 1999 13:00:43 GMT

"Fitch R. Williams" wrote:

> Maybe I've had bad hot rolled, don't know, but most of it is so gummy
> it is terrible to machine and I end up taking the last pass with a
> Mill Smooth.


Sounds like the A36 plague is becoming endemic!

It seems to me that, because A36 is an absolute requirement for some
applications and because it will meet spec. on almost any other HR application,
that is all that a lot of steel stockholders carry.

The fact that it drives the poor machinist nuts, doesn't seem to figure, and I
suspect that a lot of users really don't suspect that this material is
shortening their life spans!

Ask your local stock holder what grade of steel he would NORMALLY supply in say
1" to 6" dameter HRS

I'll bet when you pin him down, it is A#^...sorry Freudiand slip...A36.

Ask him WHY?

teenut