Thanks for the details. Interesting info.
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Castings
of all materials contain residual stresses. ?Welded
fabrications contain residual stresses, to the extent that
when conducting stress calculations, you assume that the welds
are already at the yield stress. ?Surface hardening, where a
large temperature difference is induced between the surface
and interior produces what is usually a beneficial residual
compressive stress in the surface. ?Interference fits produce
what are effectively residual stresses. ?
?
Residual
stresses can be overcome prior to machining by either soaking
at a temperature at which creep or yielding occurs, or by
initial over stressing. ?This is why pressure vessels are all
proof tested to a considerably higher pressure than their
working pressure. ?It is to make the highly stressed areas
yield, so that upon removal of the proof pressure, the
residual stress is either much lower or even reversed.
?Residual stresses are also overcome by in service stresses
over a long period. ?I have experience of this occurring and
resulting in fabricated Diesel engine crankcases distorting
and wrecking main bearings or causing leaks around the liner
seat, and axle drive gearboxes on trains distorting to the
extent that bevel gears misalign. ?Incidentally the historic
procedure of leaving castings out in the yard for 6 months
prior to further work is almost entirely ineffective unless
your yard temperature reaches 500C from time to time. ?(500C =
932F, for those still stuck with that system.)
?
For
a tool such as described in this string, I wouldn't worry
about distortion or how soft you can make it. ?Pretty well any
steel will end up soft enough to machine almost as soft as
mild steel if you take it up to temperatures in the high red -
low orange range and cool it slowly enough. ?It is the
re-hardening & tempering I would worry about, as it is
very easy to overdo it and end up with something that either
cracks in service or even at quenching. ?Different alloys want
different hardening & tempering treatments. ?
?
I
rather suspect that a high speed cutter run slow with cutting
oil would last sufficiently to trim down a tool holder. ?Me,
I'd use carbide because I have an indexable cutter, but if I
hadn't, I'd give HSS a try.
?
Eddie,
Chartered Mechanical Engineer, UK
?
------ Original Message ------
From: creswick@...
To: [email protected]
Sent: Monday, April 29th 2024, 03:39
Subject: Re: [SouthBendLathe] Insert Holder Alloy
?
As I understand it, cold formed steels (cold-rolled) have
inherent stresses, as do extruded aluminum/brass/etc... and
as such, they will warp due to material removal alone.
?
Hot rolled do not, or at least to much, much
smaller degree.
?
I would expect that your annealed holders will
not warp a measurable amount due to machining (so you can
likely take all the material off of one side without
worrying about it).
?
I have not gotten around to machining them yet, but I
would expect some warping after hardening. Being that it
is an insert holder, any warping should not matter as
the QCTP holder can be adjusted accordingly. It is hard
to imagine that warping could cause the insert to not
fit, which is the only thing that I see as a problem. I
will chase the retaining screw threads to clear out the
scale.
One point regarding warping: Machining can cause warping
too. I do not know if hardened steel is more or less
likely to warp when machined compared to low carbon (I
would guess less likely), but I have seen low carbon bow
or twist while machining it. I think there is some sort
of stress relief process to prevent it that I have never
investigated.
?
On 4/28/2024 11:20 AM, Andrei via wrote:
?
Mike,
did they warp at all during annealing or subsequent
machining?
?
I
am also curious whether they will warp when you harden
them back.?
?
If
they do, you will have to grind them back to
straight.?
?
They stayed in the oven at 1550 about an hour. I
shut the oven off and left them in overnight to cool
slowly. I did clean the scale off before testing
hardness, but I am still skeptical of it being
softer than 1018. An online source claims 4140
annealed is 12 HRC, so maybe it is plausible.
I have used carbide to cut hardened steel, but it is
not very enjoyable to do on a Clausing 8520 without
coolant. The mill does not have the girth to support
the necessary tool pressure. The risk of breaking
endmills is high. I would rather save my carbide for
when I have no other options.
?
On 4/28/2024 12:16 AM, mike allen via
wrote:
?
Good deal . How long did ya cook them ?
thanks
animal
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On 4/27/24 8:45 PM, Mike Poore wrote:
?
Just an update in case anyone is interested. I
annealed the tool holders at 1550 F. Before
annealing, they tested at 45 HRC. After
annealing, they tested at 8 HRC. I have read I
should use a B scale tester, but I do not have
one. A scrap piece of 1018 tested at 15 HRC, so
these holders should be easy milling.
?
On 4/25/2024 11:37 AM, Mike Poore via
wrote:
?
I did a search for that number. The indicates
that is the Swedish equivalent to 4340.
Sorry for wasting everyone's time. I hate when
people ask easily answered questions and I am
guilty. I found this that
lists the HT specs for most alloys. 1550F is
within the annealing range of almost every
alloy on the list. 1500F is within the
hardening range for almost all alloys. I will
have to do more research on tempering, but for
an insert holder there should be a wide
tolerance.
?
On 4/25/2024 1:17 AM, Andrei via wrote:
?
Found a reference online to
SS2541 being used for tool bit holders.
Maybe check that.?
The problem is I do not know the alloy. I
guess I will use the 4140 specs.
?
On 4/25/2024 12:59 AM, Andrei via
wrote:
?
That is definitely a great
option. I don't have one so my go-to was
carbide and coolant.youbare in great
shape with the oven
I have a heat treating oven right
next to my mill, so I would rather use
the oven.
?
On 4/24/2024 11:02 PM, Andrei via
wrote:
?
Are short of squirter
bottles or endmills?
Not an option for me.
?
On 4/24/2024 9:43 PM, Andrei
via
wrote:
?
Use a carbide
endmill and coolant. No need to
anneal
Anyone happen to know the
alloy most likely to be used for
carbide insert tool holders? My
guess is 4140. I have four that
I need to mill down to work in
an AXA holder. They test at 45
HRC. Thinking about annealing
them before milling and then
heat treating again, so I would
like specs to use.
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