|
?
?Hi all,
I am in the process of rehabbing a 3995 lathe. It was free and maybe I now know why. The runout on the spindle inner and outer diameter is really good. Like .0013. Screw on the chuck and chuck up a mandrel and it all goes bad, really bad. You can see it, let alone measure it. The chuck is a Cushing 3 jaw.
So is it worth buying a new chuck, i.e. will it mitigate much of the issue, or is there something else at play here (see what I did there) that I have missed? I am new at lathe details and the ins and outs, but an engineer by background.
Sent From iPad
|
First, disassemble the chuck, clean and lubricate it. Reassemble it making sure the chuck jaws go in the correct slots, and started at the correct times. Then try it again.? A really good ?quality?3-jaw self-centering chuck will still have .003" of run-out. There are a number of schemes to let them be adjusted to better run-out, and both Buck and Cushing use them on some of their more expensive chucks. You may have one of those that has been opened up, and not reset. Or the thing can be incredibly dirty inside. Saw a video yesterday that showed a guy testing a standard non-adjustable Craftsman chuck. Which was over .020" out. He ground the jaws, then disassembled it to clean it out. Cleaned and reassembled, it was right at .003" run-out.? Here it is:?
I'd do the cleaning and such first! I have an atlas chuck of my own that's .014" out. Haven't been able to get mine apart, yet.?
Bill in OKC
William R. Meyers, MSgt, USAF(Ret.)
Aphorisms to live by: Good judgement comes from experience. Experience comes from bad judgement.? SEMPER GUMBY!
Expect in one hand, expectorate in the other. See which one gets full first.
On Wednesday, December 18, 2024 at 04:27:42 PM CST, Guy Edkins <gedkins@...> wrote:
?Hi all,
I am in the process of rehabbing a 3995 lathe. It was free and maybe I now know why. The runout on the spindle inner and outer diameter is really good. Like .0013. Screw on the chuck and chuck up a mandrel and it all goes bad, really bad. You can see it, let alone measure it. The chuck is a Cushing 3 jaw.
So is it worth buying a new chuck, i.e. will it mitigate much of the issue, or is there something else at play here (see what I did there) that I have missed? I am new at lathe details and the ins and outs, but an engineer by background.
Sent From iPad
|
the Sanou 3 jaw scroll chucks are real nice chucks . I bought one
several years back due to my Cushman chuck being all messed up . I
think I got it from These guys
# 0603F0 with soft jaws for @ 120 , ya still need a backplate
unless the one from the Cushman is salvageable . Same folks have
backplatesfrom 40 bucks n up .
animal
On 12/18/24 2:40 PM, Bill in OKC too
via groups.io wrote:
toggle quoted message
Show quoted text
First, disassemble
the chuck, clean and lubricate it. Reassemble it making sure
the chuck jaws go in the correct slots, and started at the
correct times. Then try it again.? A really good ?quality?3-jaw
self-centering chuck will still have .003" of run-out. There
are a number of schemes to let them be adjusted to better
run-out, and both Buck and Cushing use them on some of their
more expensive chucks. You may have one of those that has
been opened up, and not reset. Or the thing can be
incredibly dirty inside. Saw a video yesterday that showed a
guy testing a standard non-adjustable Craftsman chuck. Which
was over .020" out. He ground the jaws, then disassembled it
to clean it out. Cleaned and reassembled, it was right at
.003" run-out.? Here it is:?
I'd do the
cleaning and such first! I have an atlas chuck of my own
that's .014" out. Haven't been able to get mine apart, yet.?
Bill in OKC
William
R. Meyers, MSgt, USAF(Ret.)
Aphorisms to live by:
Good judgement comes from experience.
Experience comes from bad judgement.?
SEMPER GUMBY!
Improvise, Adapt, and Overcome.
Physics doesn't care about your
schedule.
The only reason I know anything is
because I've done it wrong enough times to START
to know better.
Expect
in one hand, expectorate in the other. See
which one gets full first.
On Wednesday, December 18, 2024 at 04:27:42 PM CST, Guy
Edkins <gedkins@...> wrote:
?Hi all,
I am in the process of rehabbing a 3995 lathe. It was free
and maybe I now know why. The runout on the spindle inner
and outer diameter is really good. Like .0013. Screw on
the chuck and chuck up a mandrel and it all goes bad,
really bad. You can see it, let alone measure it. The
chuck is a Cushing 3 jaw.
So is it worth buying a new chuck, i.e. will it mitigate
much of the issue, or is there something else at play here
(see what I did there) that I have missed? I am new at
lathe details and the ins and outs, but an engineer by
background.
Sent From iPad
|
I will see if I can get it apart. Tried earlier. Backing plate is on tight. Thank you for the info. Not giving up yet.?
toggle quoted message
Show quoted text
On Dec 18, 2024, at 6:00?PM, mike allen <animal@...> wrote:
?
the Sanou 3 jaw scroll chucks are real nice chucks . I bought one
several years back due to my Cushman chuck being all messed up . I
think I got it from These guys
# 0603F0 with soft jaws for @ 120 , ya still need a backplate
unless the one from the Cushman is salvageable . Same folks have
backplatesfrom 40 bucks n up .
animal
On 12/18/24 2:40 PM, Bill in OKC too
via groups.io wrote:
First, disassemble
the chuck, clean and lubricate it. Reassemble it making sure
the chuck jaws go in the correct slots, and started at the
correct times. Then try it again.? A really good ?quality?3-jaw
self-centering chuck will still have .003" of run-out. There
are a number of schemes to let them be adjusted to better
run-out, and both Buck and Cushing use them on some of their
more expensive chucks. You may have one of those that has
been opened up, and not reset. Or the thing can be
incredibly dirty inside. Saw a video yesterday that showed a
guy testing a standard non-adjustable Craftsman chuck. Which
was over .020" out. He ground the jaws, then disassembled it
to clean it out. Cleaned and reassembled, it was right at
.003" run-out.? Here it is:?
I'd do the
cleaning and such first! I have an atlas chuck of my own
that's .014" out. Haven't been able to get mine apart, yet.?
Bill in OKC
William
R. Meyers, MSgt, USAF(Ret.)
Aphorisms to live by:
Good judgement comes from experience.
Experience comes from bad judgement.?
SEMPER GUMBY!
Improvise, Adapt, and Overcome.
Physics doesn't care about your
schedule.
The only reason I know anything is
because I've done it wrong enough times to START
to know better.
Expect
in one hand, expectorate in the other. See
which one gets full first.
On Wednesday, December 18, 2024 at 04:27:42 PM CST, Guy
Edkins <gedkins@...> wrote:
?Hi all,
I am in the process of rehabbing a 3995 lathe. It was free
and maybe I now know why. The runout on the spindle inner
and outer diameter is really good. Like .0013. Screw on
the chuck and chuck up a mandrel and it all goes bad,
really bad. You can see it, let alone measure it. The
chuck is a Cushing 3 jaw.
So is it worth buying a new chuck, i.e. will it mitigate
much of the issue, or is there something else at play here
(see what I did there) that I have missed? I am new at
lathe details and the ins and outs, but an engineer by
background.
Sent From iPad
|
I found if you loosen the cap screws on the back and tap them sequentially with a brass hammer or even a ball peen hammer you can usually split the chuck. ?
toggle quoted message
Show quoted text
On Dec 18, 2024, at 3:40?PM, Guy Edkins via groups.io <gedkins@...> wrote:
? I will see if I can get it apart. Tried earlier. Backing plate is on tight. Thank you for the info. Not giving up yet.?
Guy Sent From iPad On Dec 18, 2024, at 6:00?PM, mike allen <animal@...> wrote:
?
the Sanou 3 jaw scroll chucks are real nice chucks . I bought one
several years back due to my Cushman chuck being all messed up . I
think I got it from These guys
# 0603F0 with soft jaws for @ 120 , ya still need a backplate
unless the one from the Cushman is salvageable . Same folks have
backplatesfrom 40 bucks n up .
animal
On 12/18/24 2:40 PM, Bill in OKC too
via groups.io wrote:
First, disassemble
the chuck, clean and lubricate it. Reassemble it making sure
the chuck jaws go in the correct slots, and started at the
correct times. Then try it again.? A really good ?quality?3-jaw
self-centering chuck will still have .003" of run-out. There
are a number of schemes to let them be adjusted to better
run-out, and both Buck and Cushing use them on some of their
more expensive chucks. You may have one of those that has
been opened up, and not reset. Or the thing can be
incredibly dirty inside. Saw a video yesterday that showed a
guy testing a standard non-adjustable Craftsman chuck. Which
was over .020" out. He ground the jaws, then disassembled it
to clean it out. Cleaned and reassembled, it was right at
.003" run-out.? Here it is:?
I'd do the
cleaning and such first! I have an atlas chuck of my own
that's .014" out. Haven't been able to get mine apart, yet.?
Bill in OKC
William
R. Meyers, MSgt, USAF(Ret.)
Aphorisms to live by:
Good judgement comes from experience.
Experience comes from bad judgement.?
SEMPER GUMBY!
Improvise, Adapt, and Overcome.
Physics doesn't care about your
schedule.
The only reason I know anything is
because I've done it wrong enough times to START
to know better.
Expect
in one hand, expectorate in the other. See
which one gets full first.
On Wednesday, December 18, 2024 at 04:27:42 PM CST, Guy
Edkins <gedkins@...> wrote:
?Hi all,
I am in the process of rehabbing a 3995 lathe. It was free
and maybe I now know why. The runout on the spindle inner
and outer diameter is really good. Like .0013. Screw on
the chuck and chuck up a mandrel and it all goes bad,
really bad. You can see it, let alone measure it. The
chuck is a Cushing 3 jaw.
So is it worth buying a new chuck, i.e. will it mitigate
much of the issue, or is there something else at play here
(see what I did there) that I have missed? I am new at
lathe details and the ins and outs, but an engineer by
background.
Sent From iPad
|
Before you even take it apart, verify the the jaws are in the right slots (each jaw and each slot is numbered)? Also verify that each jaw was started sequentially at the right time when assembled.? Good luck?
toggle quoted message
Show quoted text
On Dec 18, 2024, at 5:11?PM, David Ghilarducci via groups.io <daveghil@...> wrote:
? I found if you loosen the cap screws on the back and tap them sequentially with a brass hammer or even a ball peen hammer you can usually split the chuck. ? On Dec 18, 2024, at 3:40?PM, Guy Edkins via groups.io <gedkins@...> wrote:
? I will see if I can get it apart. Tried earlier. Backing plate is on tight. Thank you for the info. Not giving up yet.?
Guy Sent From iPad On Dec 18, 2024, at 6:00?PM, mike allen <animal@...> wrote:
?
the Sanou 3 jaw scroll chucks are real nice chucks . I bought one
several years back due to my Cushman chuck being all messed up . I
think I got it from These guys
# 0603F0 with soft jaws for @ 120 , ya still need a backplate
unless the one from the Cushman is salvageable . Same folks have
backplatesfrom 40 bucks n up .
animal
On 12/18/24 2:40 PM, Bill in OKC too
via groups.io wrote:
First, disassemble
the chuck, clean and lubricate it. Reassemble it making sure
the chuck jaws go in the correct slots, and started at the
correct times. Then try it again.? A really good ?quality?3-jaw
self-centering chuck will still have .003" of run-out. There
are a number of schemes to let them be adjusted to better
run-out, and both Buck and Cushing use them on some of their
more expensive chucks. You may have one of those that has
been opened up, and not reset. Or the thing can be
incredibly dirty inside. Saw a video yesterday that showed a
guy testing a standard non-adjustable Craftsman chuck. Which
was over .020" out. He ground the jaws, then disassembled it
to clean it out. Cleaned and reassembled, it was right at
.003" run-out.? Here it is:?
I'd do the
cleaning and such first! I have an atlas chuck of my own
that's .014" out. Haven't been able to get mine apart, yet.?
Bill in OKC
William
R. Meyers, MSgt, USAF(Ret.)
Aphorisms to live by:
Good judgement comes from experience.
Experience comes from bad judgement.?
SEMPER GUMBY!
Improvise, Adapt, and Overcome.
Physics doesn't care about your
schedule.
The only reason I know anything is
because I've done it wrong enough times to START
to know better.
Expect
in one hand, expectorate in the other. See
which one gets full first.
On Wednesday, December 18, 2024 at 04:27:42 PM CST, Guy
Edkins <gedkins@...> wrote:
?Hi all,
I am in the process of rehabbing a 3995 lathe. It was free
and maybe I now know why. The runout on the spindle inner
and outer diameter is really good. Like .0013. Screw on
the chuck and chuck up a mandrel and it all goes bad,
really bad. You can see it, let alone measure it. The
chuck is a Cushing 3 jaw.
So is it worth buying a new chuck, i.e. will it mitigate
much of the issue, or is there something else at play here
(see what I did there) that I have missed? I am new at
lathe details and the ins and outs, but an engineer by
background.
Sent From iPad
|
I have successfully torn down the chuck fully, quite a bit of chips in the small bevel gears that drive the scroll threads that close the jaws. Chips elsewhere, but not a large number, (only takes one in the right spot) so it maybe that this cleaning will help. I do know the jaws are numbered and they only go in a certain slot. The jaws have discernible numbers, but the slots in the chuck only show where number 1 jaw goes. The other two are at best, vague. When installing the jaws sequentially into the scroll thread does # 1 go first followed by #2, etc. or do they start at the same time?
toggle quoted message
Show quoted text
On Dec 18, 2024, at 9:21?PM, Ray Daniels via groups.io <rmdaniels47@...> wrote:
? Before you even take it apart, verify the the jaws are in the right slots (each jaw and each slot is numbered)? Also verify that each jaw was started sequentially at the right time when assembled.? Good luck? Ray On Dec 18, 2024, at 5:11?PM, David Ghilarducci via groups.io <daveghil@...> wrote:
? I found if you loosen the cap screws on the back and tap them sequentially with a brass hammer or even a ball peen hammer you can usually split the chuck. ? On Dec 18, 2024, at 3:40?PM, Guy Edkins via groups.io <gedkins@...> wrote:
? I will see if I can get it apart. Tried earlier. Backing plate is on tight. Thank you for the info. Not giving up yet.?
Guy Sent From iPad On Dec 18, 2024, at 6:00?PM, mike allen <animal@...> wrote:
?
the Sanou 3 jaw scroll chucks are real nice chucks . I bought one
several years back due to my Cushman chuck being all messed up . I
think I got it from These guys
# 0603F0 with soft jaws for @ 120 , ya still need a backplate
unless the one from the Cushman is salvageable . Same folks have
backplatesfrom 40 bucks n up .
animal
On 12/18/24 2:40 PM, Bill in OKC too
via groups.io wrote:
First, disassemble
the chuck, clean and lubricate it. Reassemble it making sure
the chuck jaws go in the correct slots, and started at the
correct times. Then try it again.? A really good ?quality?3-jaw
self-centering chuck will still have .003" of run-out. There
are a number of schemes to let them be adjusted to better
run-out, and both Buck and Cushing use them on some of their
more expensive chucks. You may have one of those that has
been opened up, and not reset. Or the thing can be
incredibly dirty inside. Saw a video yesterday that showed a
guy testing a standard non-adjustable Craftsman chuck. Which
was over .020" out. He ground the jaws, then disassembled it
to clean it out. Cleaned and reassembled, it was right at
.003" run-out.? Here it is:?
I'd do the
cleaning and such first! I have an atlas chuck of my own
that's .014" out. Haven't been able to get mine apart, yet.?
Bill in OKC
William
R. Meyers, MSgt, USAF(Ret.)
Aphorisms to live by:
Good judgement comes from experience.
Experience comes from bad judgement.?
SEMPER GUMBY!
Improvise, Adapt, and Overcome.
Physics doesn't care about your
schedule.
The only reason I know anything is
because I've done it wrong enough times to START
to know better.
Expect
in one hand, expectorate in the other. See
which one gets full first.
On Wednesday, December 18, 2024 at 04:27:42 PM CST, Guy
Edkins <gedkins@...> wrote:
?Hi all,
I am in the process of rehabbing a 3995 lathe. It was free
and maybe I now know why. The runout on the spindle inner
and outer diameter is really good. Like .0013. Screw on
the chuck and chuck up a mandrel and it all goes bad,
really bad. You can see it, let alone measure it. The
chuck is a Cushing 3 jaw.
So is it worth buying a new chuck, i.e. will it mitigate
much of the issue, or is there something else at play here
(see what I did there) that I have missed? I am new at
lathe details and the ins and outs, but an engineer by
background.
Sent From iPad
|
They start differently , turn all 3 jaws over next to each other
& ya can see how their clocked . If I took my 3 jaws & put
then next to each other the tallest steps were different
thickness's . One of these days I'll get then setup in my mill
vise & get them all the same size & then see how far their
out & tune them up with the toll post grinder . Did ya run a
indicator on the outside of the chuck before ya dissected it .
Porbably should have mentioned that before .
animal
On 12/18/24 7:15 PM, Guy Edkins wrote:
toggle quoted message
Show quoted text
I have successfully torn down the chuck fully, quite a bit of
chips in the small bevel gears that drive the scroll threads that
close the jaws. Chips elsewhere, but not a large number, (only
takes one in the right spot) so it maybe that this cleaning will
help. I do know the jaws are numbered and they only go in a
certain slot. The jaws have discernible numbers, but the slots in
the chuck only show where number 1 jaw goes. The other two are at
best, vague. When installing the jaws sequentially into the scroll
thread does # 1 go first followed by #2, etc. or do they start at
the same time?
Thanks, ?
Buy?
Sent From iPad
?
Before you even take it apart, verify the the jaws
are in the right slots (each jaw and each slot is
numbered)?
Also verify that each jaw was started
sequentially at the right time when assembled.?
Good luck?
Ray
On Dec 18, 2024, at
5:11?PM, David Ghilarducci via groups.io
<daveghil@...> wrote:
?
I found if you loosen the cap
screws on the back and tap them sequentially
with a brass hammer or even a ball peen
hammer you can usually split the chuck. ?
On Dec 18, 2024, at
3:40?PM, Guy Edkins via groups.io
<gedkins@...>
wrote:
?
I will see if I can get it apart. Tried
earlier. Backing plate is on tight. Thank
you for the info. Not giving up yet.?
Guy
Sent From iPad
?
the Sanou 3 jaw scroll chucks are
real nice chucks . I bought one
several years back due to my
Cushman chuck being all messed up
. I think I got it from These guys
# 0603F0 with soft jaws for @ 120
, ya still need a backplate unless
the one from the Cushman is
salvageable . Same folks have
backplatesfrom 40 bucks n up .
animal
On
12/18/24 2:40 PM, Bill in OKC too
via groups.io wrote:
First,
disassemble the chuck, clean
and lubricate it. Reassemble
it making sure the chuck
jaws go in the correct
slots, and started at the
correct times. Then try it
again.? A really good ?quality?3-jaw
self-centering chuck will
still have .003" of run-out.
There are a number of
schemes to let them be
adjusted to better run-out,
and both Buck and Cushing
use them on some of their
more expensive chucks. You
may have one of those that
has been opened up, and not
reset. Or the thing can be
incredibly dirty inside. Saw
a video yesterday that
showed a guy testing a
standard non-adjustable
Craftsman chuck. Which was
over .020" out. He ground
the jaws, then disassembled
it to clean it out. Cleaned
and reassembled, it was
right at .003" run-out.?
Here it is:?
I'd
do the cleaning and such
first! I have an atlas chuck
of my own that's .014" out.
Haven't been able to get
mine apart, yet.?
Bill
in OKC
William
R. Meyers, MSgt,
USAF(Ret.)
Aphorisms
to live by:
Good
judgement comes
from experience.
Experience comes
from bad
judgement.?
SEMPER
GUMBY!
Improvise,
Adapt, and
Overcome.
Physics
doesn't care about
your schedule.
The
only reason I know
anything is
because I've done
it wrong enough
times to START to
know better.
Expect
in one hand,
expectorate in
the other. See
which one gets
full first.
On Wednesday, December
18, 2024 at 04:27:42 PM CST,
Guy Edkins <gedkins@...>
wrote:
?Hi all,
I am in the process of
rehabbing a 3995 lathe. It
was free and maybe I now
know why. The runout on
the spindle inner and
outer diameter is really
good. Like .0013. Screw on
the chuck and chuck up a
mandrel and it all goes
bad, really bad. You can
see it, let alone measure
it. The chuck is a Cushing
3 jaw.
So is it worth buying a
new chuck, i.e. will it
mitigate much of the
issue, or is there
something else at play
here (see what I did
there) that I have missed?
I am new at lathe details
and the ins and outs, but
an engineer by background.
Sent From iPad
|
Yes, I did indicate backing plate od. Right about .0034. I had to avoid marking dimple for alignment to chuck itself. This leads me to believe it's a jaw issue with huge jump in runout.
Thanks, ?Guy Sent From iPad
toggle quoted message
Show quoted text
On Dec 18, 2024, at 11:10?PM, mike allen <animal@...> wrote:
?
They start differently , turn all 3 jaws over next to each other
& ya can see how their clocked . If I took my 3 jaws & put
then next to each other the tallest steps were different
thickness's . One of these days I'll get then setup in my mill
vise & get them all the same size & then see how far their
out & tune them up with the toll post grinder . Did ya run a
indicator on the outside of the chuck before ya dissected it .
Porbably should have mentioned that before .
animal
On 12/18/24 7:15 PM, Guy Edkins wrote:
I have successfully torn down the chuck fully, quite a bit of
chips in the small bevel gears that drive the scroll threads that
close the jaws. Chips elsewhere, but not a large number, (only
takes one in the right spot) so it maybe that this cleaning will
help. I do know the jaws are numbered and they only go in a
certain slot. The jaws have discernible numbers, but the slots in
the chuck only show where number 1 jaw goes. The other two are at
best, vague. When installing the jaws sequentially into the scroll
thread does # 1 go first followed by #2, etc. or do they start at
the same time?
Thanks, ?
Buy?
Sent From iPad
?
Before you even take it apart, verify the the jaws
are in the right slots (each jaw and each slot is
numbered)?
Also verify that each jaw was started
sequentially at the right time when assembled.?
Good luck?
Ray
On Dec 18, 2024, at
5:11?PM, David Ghilarducci via groups.io
<daveghil@...> wrote:
?
I found if you loosen the cap
screws on the back and tap them sequentially
with a brass hammer or even a ball peen
hammer you can usually split the chuck. ?
On Dec 18, 2024, at
3:40?PM, Guy Edkins via groups.io
<gedkins@...>
wrote:
?
I will see if I can get it apart. Tried
earlier. Backing plate is on tight. Thank
you for the info. Not giving up yet.?
Guy
Sent From iPad
?
the Sanou 3 jaw scroll chucks are
real nice chucks . I bought one
several years back due to my
Cushman chuck being all messed up
. I think I got it from These guys
# 0603F0 with soft jaws for @ 120
, ya still need a backplate unless
the one from the Cushman is
salvageable . Same folks have
backplatesfrom 40 bucks n up .
animal
On
12/18/24 2:40 PM, Bill in OKC too
via groups.io wrote:
First,
disassemble the chuck, clean
and lubricate it. Reassemble
it making sure the chuck
jaws go in the correct
slots, and started at the
correct times. Then try it
again.? A really good ?quality?3-jaw
self-centering chuck will
still have .003" of run-out.
There are a number of
schemes to let them be
adjusted to better run-out,
and both Buck and Cushing
use them on some of their
more expensive chucks. You
may have one of those that
has been opened up, and not
reset. Or the thing can be
incredibly dirty inside. Saw
a video yesterday that
showed a guy testing a
standard non-adjustable
Craftsman chuck. Which was
over .020" out. He ground
the jaws, then disassembled
it to clean it out. Cleaned
and reassembled, it was
right at .003" run-out.?
Here it is:?
I'd
do the cleaning and such
first! I have an atlas chuck
of my own that's .014" out.
Haven't been able to get
mine apart, yet.?
Bill
in OKC
William
R. Meyers, MSgt,
USAF(Ret.)
Aphorisms
to live by:
Good
judgement comes
from experience.
Experience comes
from bad
judgement.?
SEMPER
GUMBY!
Improvise,
Adapt, and
Overcome.
Physics
doesn't care about
your schedule.
The
only reason I know
anything is
because I've done
it wrong enough
times to START to
know better.
Expect
in one hand,
expectorate in
the other. See
which one gets
full first.
On Wednesday, December
18, 2024 at 04:27:42 PM CST,
Guy Edkins <gedkins@...>
wrote:
?Hi all,
I am in the process of
rehabbing a 3995 lathe. It
was free and maybe I now
know why. The runout on
the spindle inner and
outer diameter is really
good. Like .0013. Screw on
the chuck and chuck up a
mandrel and it all goes
bad, really bad. You can
see it, let alone measure
it. The chuck is a Cushing
3 jaw.
So is it worth buying a
new chuck, i.e. will it
mitigate much of the
issue, or is there
something else at play
here (see what I did
there) that I have missed?
I am new at lathe details
and the ins and outs, but
an engineer by background.
Sent From iPad
|
Here’s a YouTube video on converting a 3-jaw chuck into a ‘set-tru’ type:
|
On 12/18/24 15:22, Guy Edkins wrote: ?
?Hi all,
I am in the process of rehabbing a 3995 lathe. It was free
and maybe I now know why. The runout on the spindle inner
and outer diameter is really good. Like .0013. Screw on
the chuck and chuck up a mandrel and it all goes bad,
really bad. You can see it, let alone measure it. The
chuck is a Cushing 3 jaw.
So is it worth buying a new chuck, i.e. will it mitigate
much of the issue, or is there something else at play here
(see what I did there) that I have missed? I am new at
lathe details and the ins and outs, but an engineer by
background. Well, there are several possibilities.? First, see if there is wobble on the outside of the chuck body.? If not, then the problem is in the jaws.? If the outside of the chuck has wobble or runout, then the backplate needs to be faced true.? Possibly the register on the chuck side of the backplate also needs to be trued.? If you do that, then there will be looseness between the register and the chuck.? You might be able to put a shim in there, or make the "poor man's adjustable chuck".? Leave the chuck mounting bolts slightly loose, indicate a bar in the chuck, bump the chuck body until the bar runs true and then tighten the bolts. For severe runout, the chuck jaws may have been inserted into the wrong slots.? The jaws are numbered to match numbers on the slots.? If you put the wrong jaws in the wrong slots you will have huge runout.? If that is not the issue, the jaws may be "bell-mouthed", meaning worn more at the tips than farther back. This makes it hard to hold long stock securely.? The fix is to grind the inner faces of the jaws.? Usually some sort of "spider", putty or rubber bands are used to hold the jaws against the scroll face as it would be if holding a piece of work. One other gotcha is the possibility of a loose scroll.? Some chucks have a circular shim that centers the scroll in the body. If that had been lost, then the scroll will move around and the jaws won't hold anything on center. And, finally, if you can't find the source of this issue, then the chuck may have been crashed, and the grooves for the jaws may be bent.? There's really no way to fix that. Jon
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On 12/18/24 21:15, Guy Edkins wrote: do know the jaws are numbered and they only go in a
certain slot. The jaws have discernible numbers, but the
slots in the chuck only show where number 1 jaw goes. The
other two are at best, vague. When installing the jaws
sequentially into the scroll thread does # 1 go first
followed by #2, etc. or do they start at the same time? With all jaws out, crank the pinions until the outer scroll tooth approaches slot one.? Back off a bit.? Insert jaw #1, hold against the scroll and advance the pinion until it grabs jaw 1.? Advance pinion until scroll tooth approaches next slot, that is #2. Insert jaw # 2, repeat for next slot and jaw # 3.? Really, there is no need to have slots 2 and 3 numbered, they just follow after slot #1.? And, the only reason to have slot 1 marked is to make sure you have the jaws in the same slots they were in when the initial jaw grinding was done. Jon
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Hi all,?
Great news. Tore down chuck completely. Ugly in there. Not any more. Clean as a whistle. Greased. Carefully reassembled. Viola! ?TIR is .0032! ?I am very pleased. Thank you all for the help and advice.?
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On Dec 19, 2024, at 12:51?PM, Jon Elson <elson@...> wrote:
?On 12/18/24 21:15, Guy Edkins wrote: do know the jaws are numbered and they only go in a
certain slot. The jaws have discernible numbers, but the
slots in the chuck only show where number 1 jaw goes. The
other two are at best, vague. When installing the jaws
sequentially into the scroll thread does # 1 go first
followed by #2, etc. or do they start at the same time? With all jaws out, crank the pinions until the outer scroll tooth approaches slot one.? Back off a bit.? Insert jaw #1, hold against the scroll and advance the pinion until it grabs jaw 1.? Advance pinion until scroll tooth approaches next slot, that is #2. Insert jaw # 2, repeat for next slot and jaw # 3.? Really, there is no need to have slots 2 and 3 numbered, they just follow after slot #1.? And, the only reason to have slot 1 marked is to make sure you have the jaws in the same slots they were in when the initial jaw grinding was done. Jon
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On 12/19/24 14:30, Guy Edkins wrote: Hi all,
Great news. Tore down chuck completely. Ugly in there. Not
any more. Clean as a whistle. Greased. Carefully
reassembled. Viola! ?TIR is .0032! ?I am very pleased.
Thank you all for the help and advice. Glad to hear it!? Some chucks are fixable, and some are not. Glad yours was. Jon
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Yay!?
Hoo Boy, there's a cautionary tale there about maintenance. I never have enough time to make stuff, but stories like this keep reminding me that I need to take the machines apart and clean them out more often.
Tim
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Now you can afford to buy yourself a 4-jaw chuck, if you don't already have one, or possibly a collet chuck. Both are handy if you need better TIR than your 3-jaw will give you.?
?
Bill in OKC
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First, try Bill's advice to disassemble and clean the chuck. Second, disabuse yourself of the mistaken notion held by most hobbyists that a three-jaw chuck is precise. Beginning apprentices used to be taught that a three jaw cannot be relied upon for precision.
That's why we have four jaw chucks that can be indicated to a within a few tenths, or precision ground collets, or turning between centers. A three jaw should be used so that all the diameters and faces of the job are turned without loosening the chuck. Everything
will be within the tolerances of the spindle. Once you remove the workpiece all bets are off. When you re-insert it into the chuck you just bought all the inaccuracies of the chuck. A good one might be within a few thousanths... A not so good one might be
.005 to .020 off. You pays your money and takes your chances...
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Good advice. ?I agree that - in general - three jaw chucks are less accurate than four jaw chucks. ?It is important to note, however, that the question of accuracy is related not to the number of jaws but to the mechanism by which those jaws are actuated. ?
Almost all three jaw chucks are simple scroll chucks, in which all jaws can be moved simultaneously by a single pinion. ?Convenient and quick, but as stated they are usually off by several thousandths when new, and with wear can get worse. ?The great majority of four jaw chucks have each of the jaws controlled independently. ?Work held in one of these - even in an old and worn chuck - can be dialed in to run perfectly concentrically with the spindle. ?Less convenient and much slower, but for fine work much more accurate.
There are, however, some important exceptions to this.
There are three jaw scroll chucks of the Adjust-Tru type, in which the chuck body can be shifted slightly on the backplate after tightening on the workpiece. ?Convenient and quite accurate when used with workpieces of the same size, although they may require re-adjusting for different sized workpieces due to manufacturing inaccuracies in the scroll and to wear.
As noted, there are some four jaw scroll chucks around which are scroll chucks. ?Convenient and quick and hold a bit better than three jaw chucks, but subject to the same inaccuracies as all of the scroll chucks.
And then there are the combination chucks. ?I have an ancient Skinner combination chuck - four jaws that can be adjusted independently or that can be controlled simultaneously by a ring and pinion mechanism as can a scroll chuck. ?Once the jaws are individually adjusted, it will be reasonably accurate over a range of sizes. ?More common years ago, these are tough to find new these days.
Exceptions to every rule.
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On Dec 20, 2024, at 12:03 AM, rfmarchi1 via groups.io <rfmarchi@...> wrote:
?
First, try Bill's advice to disassemble and clean the chuck. Second, disabuse yourself of the mistaken notion held by most hobbyists that a three-jaw chuck is precise. Beginning apprentices used to be taught that a three jaw cannot be relied upon for precision.
That's why we have four jaw chucks that can be indicated to a within a few tenths, or precision ground collets, or turning between centers. A three jaw should be used so that all the diameters and faces of the job are turned without loosening the chuck. Everything
will be within the tolerances of the spindle. Once you remove the workpiece all bets are off. When you re-insert it into the chuck you just bought all the inaccuracies of the chuck. A good one might be within a few thousanths... A not so good one might be
.005 to .020 off. You pays your money and takes your chances...
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This has turned into a really informative thread, especially for someone that is new to much of the machining world. Thank you all again.
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On Dec 21, 2024, at 8:25?AM, jmartin957 <jmartin957@...> via groups.io <jmartin957@...> wrote:
? Good advice. ?I agree that - in general - three jaw chucks are less accurate than four jaw chucks. ?It is important to note, however, that the question of accuracy is related not to the number of jaws but to the mechanism by which those jaws are actuated. ?
Almost all three jaw chucks are simple scroll chucks, in which all jaws can be moved simultaneously by a single pinion. ?Convenient and quick, but as stated they are usually off by several thousandths when new, and with wear can get worse. ?The great majority of four jaw chucks have each of the jaws controlled independently. ?Work held in one of these - even in an old and worn chuck - can be dialed in to run perfectly concentrically with the spindle. ?Less convenient and much slower, but for fine work much more accurate.
There are, however, some important exceptions to this.
There are three jaw scroll chucks of the Adjust-Tru type, in which the chuck body can be shifted slightly on the backplate after tightening on the workpiece. ?Convenient and quite accurate when used with workpieces of the same size, although they may require re-adjusting for different sized workpieces due to manufacturing inaccuracies in the scroll and to wear.
As noted, there are some four jaw scroll chucks around which are scroll chucks. ?Convenient and quick and hold a bit better than three jaw chucks, but subject to the same inaccuracies as all of the scroll chucks.
And then there are the combination chucks. ?I have an ancient Skinner combination chuck - four jaws that can be adjusted independently or that can be controlled simultaneously by a ring and pinion mechanism as can a scroll chuck. ?Once the jaws are individually adjusted, it will be reasonably accurate over a range of sizes. ?More common years ago, these are tough to find new these days.
Exceptions to every rule. On Dec 20, 2024, at 12:03 AM, rfmarchi1 via groups.io <rfmarchi@...> wrote:
?
First, try Bill's advice to disassemble and clean the chuck. Second, disabuse yourself of the mistaken notion held by most hobbyists that a three-jaw chuck is precise. Beginning apprentices used to be taught that a three jaw cannot be relied upon for precision.
That's why we have four jaw chucks that can be indicated to a within a few tenths, or precision ground collets, or turning between centers. A three jaw should be used so that all the diameters and faces of the job are turned without loosening the chuck. Everything
will be within the tolerances of the spindle. Once you remove the workpiece all bets are off. When you re-insert it into the chuck you just bought all the inaccuracies of the chuck. A good one might be within a few thousanths... A not so good one might be
.005 to .020 off. You pays your money and takes your chances...
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I’ve said this before, don’t know if in this group or not.
It doesn’t matter how much runout a lathe spindle chuck has IF (underline IF) you use a piece of rough stock larger in diameter than the largest finished diameter on your project, and IF you turn ALL diameters on your project in the same chucking and then part it off, all turned diameters will be concentric within the accuracy of your spindle bearings. IF you need to remove the project from the chuck to turn it around to face etc, and additional turning work needs to be done that needs to be concentric, then best to use a 4-jaw independent chuck and dial the work in with a dial indicator for the additional turning work that needs to be done during the second and subsequent chuckings.
Steve Haskell
Troy, MI
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Bill in OKC too
Steven H