I just got to wondering about internal stresses in 4140 round stock . I'm
making a part for an oilless compressor , and have it roughed a bit oversize
.. I know that some steels and other metals develop internal stress from
forming operations , and need a few hours to let the stresses equalize
before finishing machining so the finished part doesn't distort . Got to
wondering if 4140 is one of them .
--
Snag

"Terry Coombs" wrote in message
...

I just got to wondering about internal stresses in 4140 round stock . I'm
making a part for an oilless compressor , and have it roughed a bit
oversize . I know that some steels and other metals develop internal
stress from forming operations , and need a few hours to let the stresses
equalize before finishing machining so the finished part doesn't distort .
Got to wondering if 4140 is one of them .
--
Snag


It is generally accepted that all parts have stress, the result of the
manufacturing procedure, as you alluded. Hot rolled materials tend to have
much less.

Good shop practice dictates that one roughs parts, leaving sufficient
material for finish machining, with total cleanup. The less material
remaining, the better, as the piece will more closely represent the finished
object, and the small amount of material removed in the process should make
very little difference in movement of the part. I expect that unless you
have a very critical dimension, less than .0002" tolerance, you should be
fine.

Nice job. I spend a lot of my time trying to have folks understand that
roughing is a very important part of machining. Some don't pay attention
(until they have the pleasure of reviewing the resulting scrap, anyway).

Time can be a factor, but the roughing should release much of the stress.
If you have doubts, allow the part to age a day.

Harold

"Harold & Susan Vordos" wrote in message
...

"Terry Coombs" wrote in message
...

I just got to wondering about internal stresses in 4140 round stock .
I'm making a part for an oilless compressor , and have it roughed a bit
oversize . I know that some steels and other metals develop internal
stress from forming operations , and need a few hours to let the stresses
equalize before finishing machining so the finished part doesn't distort
. Got to wondering if 4140 is one of them .
--
Snag


It is generally accepted that all parts have stress, the result of the
manufacturing procedure, as you alluded. Hot rolled materials tend to
have much less.

Good shop practice dictates that one roughs parts, leaving sufficient
material for finish machining, with total cleanup. The less material
remaining, the better, as the piece will more closely represent the
finished object, and the small amount of material removed in the process
should make very little difference in movement of the part. I expect
that unless you have a very critical dimension, less than .0002"
tolerance, you should be fine.

Nice job. I spend a lot of my time trying to have folks understand that
roughing is a very important part of machining. Some don't pay attention
(until they have the pleasure of reviewing the resulting scrap, anyway).

Time can be a factor, but the roughing should release much of the stress.
If you have doubts, allow the part to age a day.

Harold

I backed off the chuck jaws a tad before I came in , rechucked it after a
couple of hours . After recentering it I found about .002 runout on the last
area I'd machined same setup . Looks like it might have had a bit of
stress . I'll finish it up today .
--
Snag

On 4/12/2013 12:02 AM, Harold & Susan Vordos wrote:

"Terry Coombs" wrote in message
...

I just got to wondering about internal stresses in 4140 round stock .
I'm making a part for an oilless compressor , and have it roughed a
bit oversize . I know that some steels and other metals develop
internal stress from forming operations , and need a few hours to let
the stresses equalize before finishing machining so the finished part
doesn't distort . Got to wondering if 4140 is one of them .
--
Snag


It is generally accepted that all parts have stress, the result of the
manufacturing procedure, as you alluded. Hot rolled materials tend to
have much less.

Good shop practice dictates that one roughs parts, leaving sufficient
material for finish machining, with total cleanup. The less material
remaining, the better, as the piece will more closely represent the
finished object, and the small amount of material removed in the process
should make very little difference in movement of the part. I expect
that unless you have a very critical dimension, less than .0002"
tolerance, you should be fine.

Nice job. I spend a lot of my time trying to have folks understand
that roughing is a very important part of machining. Some don't pay
attention (until they have the pleasure of reviewing the resulting
scrap, anyway).

Time can be a factor, but the roughing should release much of the
stress. If you have doubts, allow the part to age a day.

Harold


We call it "Roomalizing"!

On 4/12/2013 8:13 AM, Terry Coombs wrote:
"Harold & Susan Vordos" wrote in message
...

"Terry Coombs" wrote in message
...

I just got to wondering about internal stresses in 4140 round stock .
I'm making a part for an oilless compressor , and have it roughed a bit
oversize . I know that some steels and other metals develop internal
stress from forming operations , and need a few hours to let the stresses
equalize before finishing machining so the finished part doesn't distort
. Got to wondering if 4140 is one of them .
--
Snag


It is generally accepted that all parts have stress, the result of the
manufacturing procedure, as you alluded. Hot rolled materials tend to
have much less.

Good shop practice dictates that one roughs parts, leaving sufficient
material for finish machining, with total cleanup. The less material
remaining, the better, as the piece will more closely represent the
finished object, and the small amount of material removed in the process
should make very little difference in movement of the part. I expect
that unless you have a very critical dimension, less than .0002"
tolerance, you should be fine.

Nice job. I spend a lot of my time trying to have folks understand that
roughing is a very important part of machining. Some don't pay attention
(until they have the pleasure of reviewing the resulting scrap, anyway).

Time can be a factor, but the roughing should release much of the stress.
If you have doubts, allow the part to age a day.

Harold

I backed off the chuck jaws a tad before I came in , rechucked it after a
couple of hours . After recentering it I found about .002 runout on the last
area I'd machined same setup . Looks like it might have had a bit of
stress . I'll finish it up today .


Speaking of which, would you have a piece of 4140 that is 6" x 2" x 3/4"
or thereabouts that you could sell?

"Tom Gardner" Mars@Tacks wrote in message
...
On 4/12/2013 8:13 AM, Terry Coombs wrote:
"Harold & Susan Vordos" wrote in message
...

"Terry Coombs" wrote in message
...

I just got to wondering about internal stresses in 4140 round stock .
I'm making a part for an oilless compressor , and have it roughed a bit
oversize . I know that some steels and other metals develop internal
stress from forming operations , and need a few hours to let the
stresses
equalize before finishing machining so the finished part doesn't
distort
. Got to wondering if 4140 is one of them .
--
Snag


It is generally accepted that all parts have stress, the result of the
manufacturing procedure, as you alluded. Hot rolled materials tend to
have much less.

Good shop practice dictates that one roughs parts, leaving sufficient
material for finish machining, with total cleanup. The less material
remaining, the better, as the piece will more closely represent the
finished object, and the small amount of material removed in the process
should make very little difference in movement of the part. I expect
that unless you have a very critical dimension, less than .0002"
tolerance, you should be fine.

Nice job. I spend a lot of my time trying to have folks understand
that
roughing is a very important part of machining. Some don't pay
attention
(until they have the pleasure of reviewing the resulting scrap, anyway).

Time can be a factor, but the roughing should release much of the
stress.
If you have doubts, allow the part to age a day.

Harold

I backed off the chuck jaws a tad before I came in , rechucked it
after a
couple of hours . After recentering it I found about .002 runout on the
last
area I'd machined same setup . Looks like it might have had a bit of
stress . I'll finish it up today .


Speaking of which, would you have a piece of 4140 that is 6" x 2" x 3/4"
or thereabouts that you could sell?

Nope , all I have is rounds in 1.250 and 1.5" or maybe 1.75 , didn't
measure it because the 1.25 was big enough here in . Now I have some
unidentified bigger 2.375 and 3.125 IIRC rounds in Memphis that machine
and harden like 4140 , but I really don't know for sure what they are .
--
Snag

On Fri, 12 Apr 2013 13:54:57 -0500, "Terry Coombs"
wrote:


"Tom Gardner" Mars@Tacks wrote in message
m...
On 4/12/2013 8:13 AM, Terry Coombs wrote:
"Harold & Susan Vordos" wrote in message
...

"Terry Coombs" wrote in message
...

I just got to wondering about internal stresses in 4140 round stock .
I'm making a part for an oilless compressor , and have it roughed a bit
oversize . I know that some steels and other metals develop internal
stress from forming operations , and need a few hours to let the
stresses
equalize before finishing machining so the finished part doesn't
distort
. Got to wondering if 4140 is one of them .
--
Snag


It is generally accepted that all parts have stress, the result of the
manufacturing procedure, as you alluded. Hot rolled materials tend to
have much less.

Good shop practice dictates that one roughs parts, leaving sufficient
material for finish machining, with total cleanup. The less material
remaining, the better, as the piece will more closely represent the
finished object, and the small amount of material removed in the process
should make very little difference in movement of the part. I expect
that unless you have a very critical dimension, less than .0002"
tolerance, you should be fine.

Nice job. I spend a lot of my time trying to have folks understand
that
roughing is a very important part of machining. Some don't pay
attention
(until they have the pleasure of reviewing the resulting scrap, anyway).

Time can be a factor, but the roughing should release much of the
stress.
If you have doubts, allow the part to age a day.

Harold

I backed off the chuck jaws a tad before I came in , rechucked it
after a
couple of hours . After recentering it I found about .002 runout on the
last
area I'd machined same setup . Looks like it might have had a bit of
stress . I'll finish it up today .


Speaking of which, would you have a piece of 4140 that is 6" x 2" x 3/4"
or thereabouts that you could sell?

Nope , all I have is rounds in 1.250 and 1.5" or maybe 1.75 , didn't
measure it because the 1.25 was big enough here in . Now I have some
unidentified bigger 2.375 and 3.125 IIRC rounds in Memphis that machine
and harden like 4140 , but I really don't know for sure what they are .

Keep in mind that mechanical stresses will be relieved right away. If
it changes over time, it's the result of improper heat treatment, with
delayed martensite conversion. That's a lot less common.

BTW, do you still want to know what metallurgists say about casting
7075 aluminum? I came across a couple of things, but they mostly
dismiss it without getting into measured results.

--
Ed Huntress

"Ed Huntress" wrote
BTW, do you still want to know what metallurgists say about casting
7075 aluminum? I came across a couple of things, but they mostly
dismiss it without getting into measured results.

--
Ed Huntress

Shirley I do . More knowledge is almost always a good thing .
--
Snag

On 4/12/2013 2:54 PM, Terry Coombs wrote:
"Tom Gardner" Mars@Tacks wrote in message
...
On 4/12/2013 8:13 AM, Terry Coombs wrote:
"Harold & Susan Vordos" wrote in message
...

"Terry Coombs" wrote in message
...

I just got to wondering about internal stresses in 4140 round stock .
I'm making a part for an oilless compressor , and have it roughed a bit
oversize . I know that some steels and other metals develop internal
stress from forming operations , and need a few hours to let the
stresses
equalize before finishing machining so the finished part doesn't
distort
. Got to wondering if 4140 is one of them .
--
Snag


It is generally accepted that all parts have stress, the result of the
manufacturing procedure, as you alluded. Hot rolled materials tend to
have much less.

Good shop practice dictates that one roughs parts, leaving sufficient
material for finish machining, with total cleanup. The less material
remaining, the better, as the piece will more closely represent the
finished object, and the small amount of material removed in the process
should make very little difference in movement of the part. I expect
that unless you have a very critical dimension, less than .0002"
tolerance, you should be fine.

Nice job. I spend a lot of my time trying to have folks understand
that
roughing is a very important part of machining. Some don't pay
attention
(until they have the pleasure of reviewing the resulting scrap, anyway).

Time can be a factor, but the roughing should release much of the
stress.
If you have doubts, allow the part to age a day.

Harold

I backed off the chuck jaws a tad before I came in , rechucked it
after a
couple of hours . After recentering it I found about .002 runout on the
last
area I'd machined same setup . Looks like it might have had a bit of
stress . I'll finish it up today .


Speaking of which, would you have a piece of 4140 that is 6" x 2" x 3/4"
or thereabouts that you could sell?

Nope , all I have is rounds in 1.250 and 1.5" or maybe 1.75 , didn't
measure it because the 1.25 was big enough here in . Now I have some
unidentified bigger 2.375 and 3.125 IIRC rounds in Memphis that machine
and harden like 4140 , but I really don't know for sure what they are .

Thanks anyway. I need to make an arm that holds a carbide square like
an arm on a pair of scissors. The current one is cold-roll and is
flexing too muck under pressure. Ya' think 4140 would be a better choice?

"Tom Gardner" Mars@Tacks wrote in message
...

Thanks anyway. I need to make an arm that holds a carbide square like an
arm on a pair of scissors. The current one is cold-roll and is flexing
too muck under pressure. Ya' think 4140 would be a better choice?

Probably not.
The modulus of elasticity will be the some. The yield will go up, so it will
bend farther before it takes a set, but it will flex just as far with the
same load.
Redesign the part to have more meat in it.

Paul K. Dickman

On Fri, 12 Apr 2013 20:02:37 -0400, Tom Gardner Mars@Tacks wrote:

On 4/12/2013 2:54 PM, Terry Coombs wrote:
"Tom Gardner" Mars@Tacks wrote in message
...
On 4/12/2013 8:13 AM, Terry Coombs wrote:
"Harold & Susan Vordos" wrote in message
...

"Terry Coombs" wrote in message
...

I just got to wondering about internal stresses in 4140 round stock .
I'm making a part for an oilless compressor , and have it roughed a bit
oversize . I know that some steels and other metals develop internal
stress from forming operations , and need a few hours to let the
stresses
equalize before finishing machining so the finished part doesn't
distort
. Got to wondering if 4140 is one of them .
--
Snag


It is generally accepted that all parts have stress, the result of the
manufacturing procedure, as you alluded. Hot rolled materials tend to
have much less.

Good shop practice dictates that one roughs parts, leaving sufficient
material for finish machining, with total cleanup. The less material
remaining, the better, as the piece will more closely represent the
finished object, and the small amount of material removed in the process
should make very little difference in movement of the part. I expect
that unless you have a very critical dimension, less than .0002"
tolerance, you should be fine.

Nice job. I spend a lot of my time trying to have folks understand
that
roughing is a very important part of machining. Some don't pay
attention
(until they have the pleasure of reviewing the resulting scrap, anyway).

Time can be a factor, but the roughing should release much of the
stress.
If you have doubts, allow the part to age a day.

Harold

I backed off the chuck jaws a tad before I came in , rechucked it
after a
couple of hours . After recentering it I found about .002 runout on the
last
area I'd machined same setup . Looks like it might have had a bit of
stress . I'll finish it up today .


Speaking of which, would you have a piece of 4140 that is 6" x 2" x 3/4"
or thereabouts that you could sell?

Nope , all I have is rounds in 1.250 and 1.5" or maybe 1.75 , didn't
measure it because the 1.25 was big enough here in . Now I have some
unidentified bigger 2.375 and 3.125 IIRC rounds in Memphis that machine
and harden like 4140 , but I really don't know for sure what they are .

Thanks anyway. I need to make an arm that holds a carbide square like
an arm on a pair of scissors. The current one is cold-roll and is
flexing too muck under pressure. Ya' think 4140 would be a better choice?

The flexing -- that is, the spring rate without taking a set -- is the
same for all grades on steel, within a couple of percent. More
correctly, they all have about the same Young's Modulus, and it
doesn't matter how they're heat treated or work-hardened. The modulus
will be the same.

That is, except for stainless, which is a little springier (lower
Young's Modulus).

--
Ed Huntress

On 4/12/2013 9:16 PM, Paul K. Dickman wrote:
"Tom Gardner" Mars@Tacks wrote in message
...

Thanks anyway. I need to make an arm that holds a carbide square like an
arm on a pair of scissors. The current one is cold-roll and is flexing
too muck under pressure. Ya' think 4140 would be a better choice?

Probably not.
The modulus of elasticity will be the some. The yield will go up, so it will
bend farther before it takes a set, but it will flex just as far with the
same load.
Redesign the part to have more meat in it.

Paul K. Dickman



I was afraid of that but I can add 20%-25% where it counts. What about
hard D-2?

On 4/12/2013 10:17 PM, Ed Huntress wrote:
On Fri, 12 Apr 2013 20:02:37 -0400, Tom Gardner Mars@Tacks wrote:

On 4/12/2013 2:54 PM, Terry Coombs wrote:
"Tom Gardner" Mars@Tacks wrote in message
...
On 4/12/2013 8:13 AM, Terry Coombs wrote:
"Harold & Susan Vordos" wrote in message
...

"Terry Coombs" wrote in message
...

I just got to wondering about internal stresses in 4140 round stock .
I'm making a part for an oilless compressor , and have it roughed a bit
oversize . I know that some steels and other metals develop internal
stress from forming operations , and need a few hours to let the
stresses
equalize before finishing machining so the finished part doesn't
distort
. Got to wondering if 4140 is one of them .
--
Snag


It is generally accepted that all parts have stress, the result of the
manufacturing procedure, as you alluded. Hot rolled materials tend to
have much less.

Good shop practice dictates that one roughs parts, leaving sufficient
material for finish machining, with total cleanup. The less material
remaining, the better, as the piece will more closely represent the
finished object, and the small amount of material removed in the process
should make very little difference in movement of the part. I expect
that unless you have a very critical dimension, less than .0002"
tolerance, you should be fine.

Nice job. I spend a lot of my time trying to have folks understand
that
roughing is a very important part of machining. Some don't pay
attention
(until they have the pleasure of reviewing the resulting scrap, anyway).

Time can be a factor, but the roughing should release much of the
stress.
If you have doubts, allow the part to age a day.

Harold

I backed off the chuck jaws a tad before I came in , rechucked it
after a
couple of hours . After recentering it I found about .002 runout on the
last
area I'd machined same setup . Looks like it might have had a bit of
stress . I'll finish it up today .


Speaking of which, would you have a piece of 4140 that is 6" x 2" x 3/4"
or thereabouts that you could sell?

Nope , all I have is rounds in 1.250 and 1.5" or maybe 1.75 , didn't
measure it because the 1.25 was big enough here in . Now I have some
unidentified bigger 2.375 and 3.125 IIRC rounds in Memphis that machine
and harden like 4140 , but I really don't know for sure what they are .

Thanks anyway. I need to make an arm that holds a carbide square like
an arm on a pair of scissors. The current one is cold-roll and is
flexing too muck under pressure. Ya' think 4140 would be a better choice?

The flexing -- that is, the spring rate without taking a set -- is the
same for all grades on steel, within a couple of percent. More
correctly, they all have about the same Young's Modulus, and it
doesn't matter how they're heat treated or work-hardened. The modulus
will be the same.

That is, except for stainless, which is a little springier (lower
Young's Modulus).



My cousin told me that, I was hoping he was wrong. I could make it out
of Ti and/or go from 5/8" to 3/4" or a scooch more.

On Sun, 14 Apr 2013 00:43:43 -0400, Tom Gardner Mars@Tacks wrote:

On 4/12/2013 10:17 PM, Ed Huntress wrote:
On Fri, 12 Apr 2013 20:02:37 -0400, Tom Gardner Mars@Tacks wrote:

On 4/12/2013 2:54 PM, Terry Coombs wrote:
"Tom Gardner" Mars@Tacks wrote in message
...
On 4/12/2013 8:13 AM, Terry Coombs wrote:
"Harold & Susan Vordos" wrote in message
...

"Terry Coombs" wrote in message
...

I just got to wondering about internal stresses in 4140 round stock .
I'm making a part for an oilless compressor , and have it roughed a bit
oversize . I know that some steels and other metals develop internal
stress from forming operations , and need a few hours to let the
stresses
equalize before finishing machining so the finished part doesn't
distort
. Got to wondering if 4140 is one of them .
--
Snag


It is generally accepted that all parts have stress, the result of the
manufacturing procedure, as you alluded. Hot rolled materials tend to
have much less.

Good shop practice dictates that one roughs parts, leaving sufficient
material for finish machining, with total cleanup. The less material
remaining, the better, as the piece will more closely represent the
finished object, and the small amount of material removed in the process
should make very little difference in movement of the part. I expect
that unless you have a very critical dimension, less than .0002"
tolerance, you should be fine.

Nice job. I spend a lot of my time trying to have folks understand
that
roughing is a very important part of machining. Some don't pay
attention
(until they have the pleasure of reviewing the resulting scrap, anyway).

Time can be a factor, but the roughing should release much of the
stress.
If you have doubts, allow the part to age a day.

Harold

I backed off the chuck jaws a tad before I came in , rechucked it
after a
couple of hours . After recentering it I found about .002 runout on the
last
area I'd machined same setup . Looks like it might have had a bit of
stress . I'll finish it up today .


Speaking of which, would you have a piece of 4140 that is 6" x 2" x 3/4"
or thereabouts that you could sell?

Nope , all I have is rounds in 1.250 and 1.5" or maybe 1.75 , didn't
measure it because the 1.25 was big enough here in . Now I have some
unidentified bigger 2.375 and 3.125 IIRC rounds in Memphis that machine
and harden like 4140 , but I really don't know for sure what they are .

Thanks anyway. I need to make an arm that holds a carbide square like
an arm on a pair of scissors. The current one is cold-roll and is
flexing too muck under pressure. Ya' think 4140 would be a better choice?

The flexing -- that is, the spring rate without taking a set -- is the
same for all grades on steel, within a couple of percent. More
correctly, they all have about the same Young's Modulus, and it
doesn't matter how they're heat treated or work-hardened. The modulus
will be the same.

That is, except for stainless, which is a little springier (lower
Young's Modulus).



My cousin told me that, I was hoping he was wrong. I could make it out
of Ti and/or go from 5/8" to 3/4" or a scooch more.

Not titanium! It's MUCH springier than steel. The Young's modulus for
steel runs around 30 (don't worry about the units). For titanium, it's
around 16 -- about the same as gray cast iron (14) . Aluminum is
around 10.

Tungsten is a little over 60. Tungsten carbide is close to 70.

On the other hand, stiffness is a function of the *cube* of thickness
(called "plate stiffness"). So making your part a little thicker will
improve its stiffness by a lot more than you might think.

In your example of going from 5/8 to 3/4, the part would be 1.2 times
thicker but 1.73 times stiffer.

--
Ed Huntress

Tom Gardner Mars@Tacks wrote in
:

snip
The flexing -- that is, the spring rate without taking a set -- is
the same for all grades on steel, within a couple of percent. More
correctly, they all have about the same Young's Modulus, and it
doesn't matter how they're heat treated or work-hardened. The modulus
will be the same.

That is, except for stainless, which is a little springier (lower
Young's Modulus).

My cousin told me that, I was hoping he was wrong. I could make it
out of Ti and/or go from 5/8" to 3/4" or a scooch more.

I'm a little rusty on this stuff, but for a simple rectangular bar, I
believe the stiffness goes up as the cube of the dimension. You
shouldn't have to add much to make it significantly stiffer. 5/8" to
3/4" would almost double the stiffness (halve the deflection). Adding a
rib could do a lot, if there is room.

Doug White

On Sun, 14 Apr 2013 13:56:06 GMT, Doug White
wrote:

Tom Gardner Mars@Tacks wrote in
:

snip
The flexing -- that is, the spring rate without taking a set -- is
the same for all grades on steel, within a couple of percent. More
correctly, they all have about the same Young's Modulus, and it
doesn't matter how they're heat treated or work-hardened. The modulus
will be the same.

That is, except for stainless, which is a little springier (lower
Young's Modulus).

My cousin told me that, I was hoping he was wrong. I could make it
out of Ti and/or go from 5/8" to 3/4" or a scooch more.

I'm a little rusty on this stuff, but for a simple rectangular bar, I
believe the stiffness goes up as the cube of the dimension. You
shouldn't have to add much to make it significantly stiffer. 5/8" to
3/4" would almost double the stiffness (halve the deflection). Adding a
rib could do a lot, if there is room.

A rib, or better yet use U-Channel so the face and stiffening ribs are
all one integral piece, and a chunk of thick bar at the top to bolt
your inserts to - go as physically big as you can. Modify the machine
to make room if need be.

If this is one of those gidges you have mentioned in the past where
you're using the carbide inserts as a hard-faced guillotine and
anvil-blade to chop wire to length, don't count on the machine and
mount rigidity to keep it aligned...

I'd have a finger from the upper jaw extend below the lower jaw where
they overlap, and a few roller bearings with a fine-threaded gap
adjusting method. And a jam nut to keep it there.

Physically keep the upper and lower blades from crashing, even if the
machine gets out of alignment.

-- Bruce --

On 4/14/2013 9:43 AM, Ed Huntress wrote:
On Sun, 14 Apr 2013 00:43:43 -0400, Tom Gardner Mars@Tacks wrote:

On 4/12/2013 10:17 PM, Ed Huntress wrote:
On Fri, 12 Apr 2013 20:02:37 -0400, Tom Gardner Mars@Tacks wrote:

On 4/12/2013 2:54 PM, Terry Coombs wrote:
"Tom Gardner" Mars@Tacks wrote in message
...
On 4/12/2013 8:13 AM, Terry Coombs wrote:
"Harold & Susan Vordos" wrote in message
...

"Terry Coombs" wrote in message
...

I just got to wondering about internal stresses in 4140 round stock .
I'm making a part for an oilless compressor , and have it roughed a bit
oversize . I know that some steels and other metals develop internal
stress from forming operations , and need a few hours to let the
stresses
equalize before finishing machining so the finished part doesn't
distort
. Got to wondering if 4140 is one of them .
--
Snag


It is generally accepted that all parts have stress, the result of the
manufacturing procedure, as you alluded. Hot rolled materials tend to
have much less.

Good shop practice dictates that one roughs parts, leaving sufficient
material for finish machining, with total cleanup. The less material
remaining, the better, as the piece will more closely represent the
finished object, and the small amount of material removed in the process
should make very little difference in movement of the part. I expect
that unless you have a very critical dimension, less than .0002"
tolerance, you should be fine.

Nice job. I spend a lot of my time trying to have folks understand
that
roughing is a very important part of machining. Some don't pay
attention
(until they have the pleasure of reviewing the resulting scrap, anyway).

Time can be a factor, but the roughing should release much of the
stress.
If you have doubts, allow the part to age a day.

Harold

I backed off the chuck jaws a tad before I came in , rechucked it
after a
couple of hours . After recentering it I found about .002 runout on the
last
area I'd machined same setup . Looks like it might have had a bit of
stress . I'll finish it up today .


Speaking of which, would you have a piece of 4140 that is 6" x 2" x 3/4"
or thereabouts that you could sell?

Nope , all I have is rounds in 1.250 and 1.5" or maybe 1.75 , didn't
measure it because the 1.25 was big enough here in . Now I have some
unidentified bigger 2.375 and 3.125 IIRC rounds in Memphis that machine
and harden like 4140 , but I really don't know for sure what they are .

Thanks anyway. I need to make an arm that holds a carbide square like
an arm on a pair of scissors. The current one is cold-roll and is
flexing too muck under pressure. Ya' think 4140 would be a better choice?

The flexing -- that is, the spring rate without taking a set -- is the
same for all grades on steel, within a couple of percent. More
correctly, they all have about the same Young's Modulus, and it
doesn't matter how they're heat treated or work-hardened. The modulus
will be the same.

That is, except for stainless, which is a little springier (lower
Young's Modulus).



My cousin told me that, I was hoping he was wrong. I could make it out
of Ti and/or go from 5/8" to 3/4" or a scooch more.

Not titanium! It's MUCH springier than steel. The Young's modulus for
steel runs around 30 (don't worry about the units). For titanium, it's
around 16 -- about the same as gray cast iron (14) . Aluminum is
around 10.

Tungsten is a little over 60. Tungsten carbide is close to 70.

On the other hand, stiffness is a function of the *cube* of thickness
(called "plate stiffness"). So making your part a little thicker will
improve its stiffness by a lot more than you might think.

In your example of going from 5/8 to 3/4, the part would be 1.2 times
thicker but 1.73 times stiffer.

--
Ed Huntress



That'll do. The part's 10 years old but the new wire it cuts is higher
tensile.

On 4/14/2013 9:56 AM, Doug White wrote:
Tom Gardner Mars@Tacks wrote in
:

snip
The flexing -- that is, the spring rate without taking a set -- is
the same for all grades on steel, within a couple of percent. More
correctly, they all have about the same Young's Modulus, and it
doesn't matter how they're heat treated or work-hardened. The modulus
will be the same.

That is, except for stainless, which is a little springier (lower
Young's Modulus).

My cousin told me that, I was hoping he was wrong. I could make it
out of Ti and/or go from 5/8" to 3/4" or a scooch more.

I'm a little rusty on this stuff, but for a simple rectangular bar, I
believe the stiffness goes up as the cube of the dimension. You
shouldn't have to add much to make it significantly stiffer. 5/8" to
3/4" would almost double the stiffness (halve the deflection). Adding a
rib could do a lot, if there is room.

Doug White


Room for another 1/8", 5/8" to 3/4". Thanks!

On 4/14/2013 9:53 PM, Bruce L. Bergman (munged human readable) wrote:
On Sun, 14 Apr 2013 13:56:06 GMT, Doug White
wrote:

Tom Gardner Mars@Tacks wrote in
:

snip
The flexing -- that is, the spring rate without taking a set -- is
the same for all grades on steel, within a couple of percent. More
correctly, they all have about the same Young's Modulus, and it
doesn't matter how they're heat treated or work-hardened. The modulus
will be the same.

That is, except for stainless, which is a little springier (lower
Young's Modulus).

My cousin told me that, I was hoping he was wrong. I could make it
out of Ti and/or go from 5/8" to 3/4" or a scooch more.

I'm a little rusty on this stuff, but for a simple rectangular bar, I
believe the stiffness goes up as the cube of the dimension. You
shouldn't have to add much to make it significantly stiffer. 5/8" to
3/4" would almost double the stiffness (halve the deflection). Adding a
rib could do a lot, if there is room.

A rib, or better yet use U-Channel so the face and stiffening ribs are
all one integral piece, and a chunk of thick bar at the top to bolt
your inserts to - go as physically big as you can. Modify the machine
to make room if need be.

If this is one of those gidges you have mentioned in the past where
you're using the carbide inserts as a hard-faced guillotine and
anvil-blade to chop wire to length, don't count on the machine and
mount rigidity to keep it aligned...

I'd have a finger from the upper jaw extend below the lower jaw where
they overlap, and a few roller bearings with a fine-threaded gap
adjusting method. And a jam nut to keep it there.

Physically keep the upper and lower blades from crashing, even if the
machine gets out of alignment.

-- Bruce --



Yep, you must have seen it! The cutter uses a 1" shaft riding in Timkin
tapered roller bearings that this arm is attached. I use 3/4" square x
1/4" thick, coated HSS inserts. I've tried every grade of carbide, even
custom made they get tiny chips and and they all self destruct in very
short order. The HSS works great and they are only $5 and I get 8
cutting edges on each.

I think the arm sometimes gets too much pre-load pressure from the
mechanism that tightens the stationary blade. It gets readjusted every
time we do a blade change.