I am turning a mild steel doughnut: OD= 4.5", ID 2.125", thickness
0.1875". The purpose is to clean it up and make the two surfaces
parallel.

The process is always the same: Hold the piece by expanding 3-jaw,
face off, turn the edge, reverse, apply a spacer (a smaller doughnut
held on by superglue), face off the second side, deburr edges. Remove
from the 3-jaw. Clamp in 4 jaw on the outside, indicate the jaws to
within 0.001". Bore the hole till it "looks right". Deburr the inside
edges.

Today, when I got to the 4-jaw stage, I found that the orthogonal jaws
could not be set to the same number. For all intents and purposes the
doughnut now seemed to be an ellipse with one axis 0.014" longer than
the other.

Never mind, I thought, I centered both axes and proceeded to bore. I
did not encounter any problems but when I re-clamped on the 3-jaw it
was clear that the piece was not rotating concentrically. When I
measured it there was a variation of 0.024" in the width of the
doughnut (average width=0.960"), i.e. the hole is eccentric to the
perimeter.

Not that it matters with this piece but what are the possible causes?

My thoughts:

1) I have not indicated the 4-jaw properly. Possible, but has not
happened before.
2) Crummy 4-jaw chuck that came with the 9x20. It is of the "old"
style and a pain to use.
3) Should not indicate the jaws but the piece itself (difficult to
adjust the jaws then, though).
4) After facing both sides the piece was only 0.154" thick and as such
thin enough to flex in the chuck jaws.

Thanks,

Michael Koblic,
Campbell River, BC

wrote in news:94g3g65m52r78e46mvfiknjsrntsul4khv@
4ax.com:

I am turning a mild steel doughnut: OD= 4.5", ID 2.125", thickness
0.1875". The purpose is to clean it up and make the two surfaces
parallel.

The process is always the same: Hold the piece by expanding 3-jaw,
face off, turn the edge, reverse, apply a spacer (a smaller doughnut
held on by superglue), face off the second side, deburr edges. Remove
from the 3-jaw. Clamp in 4 jaw on the outside, indicate the jaws to
within 0.001". Bore the hole till it "looks right". Deburr the inside
edges.

Today, when I got to the 4-jaw stage, I found that the orthogonal jaws
could not be set to the same number. For all intents and purposes the
doughnut now seemed to be an ellipse with one axis 0.014" longer than
the other.

Never mind, I thought, I centered both axes and proceeded to bore. I
did not encounter any problems but when I re-clamped on the 3-jaw it
was clear that the piece was not rotating concentrically. When I
measured it there was a variation of 0.024" in the width of the
doughnut (average width=0.960"), i.e. the hole is eccentric to the
perimeter.

Not that it matters with this piece but what are the possible causes?

My thoughts:

1) I have not indicated the 4-jaw properly. Possible, but has not
happened before.
2) Crummy 4-jaw chuck that came with the 9x20. It is of the "old"
style and a pain to use.
3) Should not indicate the jaws but the piece itself (difficult to
adjust the jaws then, though).
4) After facing both sides the piece was only 0.154" thick and as such
thin enough to flex in the chuck jaws.

4) is a possibility. Another is that the material had internal stresses
which were released by the machining, resulting in distortion. I've seen
this happen big time with plastics like Delrin, but not so much with
steel.

If it was me, I'd turn the OD, and then use a "Step collet" for the rest.
They can machined in place to fit the part precisely, so are guaranteed
concentric. They also apply very even force to the OD of the part,
unlike the high point pressure of a bunch of chuck jaws.

http://travers.com/skulist.asp?Reque...&q=block%20id%
20114899

Doug White

Assuming stress isn't the cause of the distortion, another approach
would be to use a longer piece of material. Face, turn ID and OD, then
turn around and machine off the excess. More work removing the excess,
but -should- result in concentric ID/OD leaving only parallelism of the
two faces as an issue for the last operation.


Jon

On 12/09/2010 10:23 PM, wrote:
I am turning a mild steel doughnut: OD= 4.5", ID 2.125", thickness
0.1875". The purpose is to clean it up and make the two surfaces
parallel.

The process is always the same: Hold the piece by expanding 3-jaw,
face off, turn the edge, reverse, apply a spacer (a smaller doughnut
held on by superglue), face off the second side, deburr edges. Remove
from the 3-jaw. Clamp in 4 jaw on the outside, indicate the jaws to
within 0.001". Bore the hole till it "looks right". Deburr the inside
edges.

Today, when I got to the 4-jaw stage, I found that the orthogonal jaws
could not be set to the same number. For all intents and purposes the
doughnut now seemed to be an ellipse with one axis 0.014" longer than
the other.

Never mind, I thought, I centered both axes and proceeded to bore. I
did not encounter any problems but when I re-clamped on the 3-jaw it
was clear that the piece was not rotating concentrically. When I
measured it there was a variation of 0.024" in the width of the
doughnut (average width=0.960"), i.e. the hole is eccentric to the
perimeter.

Not that it matters with this piece but what are the possible causes?

My thoughts:

1) I have not indicated the 4-jaw properly. Possible, but has not
happened before.
2) Crummy 4-jaw chuck that came with the 9x20. It is of the "old"
style and a pain to use.
3) Should not indicate the jaws but the piece itself (difficult to
adjust the jaws then, though).
4) After facing both sides the piece was only 0.154" thick and as such
thin enough to flex in the chuck jaws.

Could it have been as simple as a .014" thick bit of crud on one of the
jaws?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On 2010-12-10, wrote:
I am turning a mild steel doughnut: OD= 4.5", ID 2.125", thickness
0.1875". The purpose is to clean it up and make the two surfaces
parallel.

The process is always the same: Hold the piece by expanding 3-jaw,
face off, turn the edge, reverse, apply a spacer (a smaller doughnut
held on by superglue), face off the second side, deburr edges. Remove
from the 3-jaw. Clamp in 4 jaw on the outside, indicate the jaws to
within 0.001". Bore the hole till it "looks right". Deburr the inside
edges.

O.K. So far, it sounds like a standard independent jaw 4-jaw.

Today, when I got to the 4-jaw stage, I found that the orthogonal jaws
could not be set to the same number. For all intents and purposes the
doughnut now seemed to be an ellipse with one axis 0.014" longer than
the other.

Strange. This is not a "universal" (e.g. scroll-back 4-jaw is
it?

Never mind, I thought, I centered both axes and proceeded to bore. I
did not encounter any problems but when I re-clamped on the 3-jaw it
was clear that the piece was not rotating concentrically. When I
measured it there was a variation of 0.024" in the width of the
doughnut (average width=0.960"), i.e. the hole is eccentric to the
perimeter.

Nearly doubling the eccentricity from before.

Not that it matters with this piece but what are the possible causes?

My thoughts:

1) I have not indicated the 4-jaw properly. Possible, but has not
happened before.

Possible.

2) Crummy 4-jaw chuck that came with the 9x20. It is of the "old"
style and a pain to use.

That still should not result in eccentricity -- just greater
difficulty achieving concentricity.

3) Should not indicate the jaws but the piece itself (difficult to
adjust the jaws then, though).

You indicate from the *jaws*? With no certainty that they are
equal sized? This is likely the problem.

4) After facing both sides the piece was only 0.154" thick and as such
thin enough to flex in the chuck jaws.

0.154" thick -- but still about an inch in radial dimension so I
don't think so.

Good Luck,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Dec 10, 1:23*am, wrote:
...
3) Should not indicate the jaws but the piece itself (difficult to
adjust the jaws then, though).
...
Michael Koblic,
Campbell River, BC

Instead of reading runout on the indicator you could feed it in to
zero and read the leadscrew dial. Then you could move the carriage in
and out of position to indicate the work beside the jaws.

This job may justify a spacer plate with slots for the jaws to keep it
in place and standoffs to position the dial plate out past the jaw
ends.

jsw

On Fri, 10 Dec 2010 18:02:41 -0800 (PST), Jim Wilkins
wrote:

On Dec 10, 1:23*am, wrote:
...
3) Should not indicate the jaws but the piece itself (difficult to
adjust the jaws then, though).
...
Michael Koblic,
Campbell River, BC

Instead of reading runout on the indicator you could feed it in to
zero and read the leadscrew dial. Then you could move the carriage in
and out of position to indicate the work beside the jaws.

This job may justify a spacer plate with slots for the jaws to keep it
in place and standoffs to position the dial plate out past the jaw
ends.

jsw
===========
One way around this from the old machining books is to use
what is called a bridge or pump staff.

You can make one out of a piece of stiff wire that you can
clamp in the tail stock chuck or make a bushing. To use,
you bend the free end so that the tip of the bridge rides on
what you are trying to get concentric and you can use a drop
indicator on the bridge to measure the runout. The actual
measurements won't be correct, but generally you are trying
for zero runout with no or minimal needle movement.

You can also fabricate a bridge out of a used hacksaw blade
that you can clamp in either the tail stock or tool post.
Works great for indicating square/hex stock or rough cast
preforms or rough cast bores.

If it would be helpful I can post pictures of the ones I
made on either the drop box or my web site.

Another possibility if you have several of these to do is to
fabricate a holder/fixture that will clamp the donut that
you can bolt to the faceplate.

Let the group know how you make out and what your solution
was.


-- Unka George (George McDuffee)
...............................
The past is a foreign country;
they do things differently there.
L. P. Hartley (1895-1972), British author.
The Go-Between, Prologue (1953).

On Fri, 10 Dec 2010 13:07:29 GMT, Doug White
wrote:

[...]


4) After facing both sides the piece was only 0.154" thick and as such
thin enough to flex in the chuck jaws.

4) is a possibility. Another is that the material had internal stresses
which were released by the machining, resulting in distortion. I've seen
this happen big time with plastics like Delrin, but not so much with
steel.

If it was me, I'd turn the OD, and then use a "Step collet" for the rest.
They can machined in place to fit the part precisely, so are guaranteed
concentric. They also apply very even force to the OD of the part,
unlike the high point pressure of a bunch of chuck jaws.

http://travers.com/skulist.asp?Reque...&q=block%20id%
20114899



I have never seen one of those so I had a look around the Google to
see how they work.

If I understand it correctly for a work piece like mine one would get
a 5" step collet and machine it closely to fit the OD of the work
piece. Presumably the clamping range of these collets is the same as
ordinary 5C collets - rather small. The recess would have to be deep
enough to accommodate the work piece and a spacer to allow boring of
the central hole.

Even at $172 it would be a good investment if one were to make more of
these pieces. Unfortunately I do not think I can use 5C collets on my
lathe.

Michael Koblic,
Campbell River, BC

On Fri, 10 Dec 2010 09:40:01 -0800, Tim Wescott
wrote:

[...]

Could it have been as simple as a .014" thick bit of crud on one of the
jaws?

It's a thought. I do try to be fairly anal about cleaning everything
before clamping.

On 11 Dec 2010 01:41:53 GMT, "DoN. Nichols"
wrote:

[...]

Strange. This is not a "universal" (e.g. scroll-back 4-jaw is
it?

No, it's an independent 4-jaw. Looks like this:
http://www.busybeetools.com/products...OOD-LATHE.html

I bought a similar one for my wood lathe. I refused to believe that it
was a metalworking chuck as some maintained elsewhere until I got one
with the 9x20.

[...]

2) Crummy 4-jaw chuck that came with the 9x20. It is of the "old"
style and a pain to use.

That still should not result in eccentricity -- just greater
difficulty achieving concentricity.

You'd better believe it...

3) Should not indicate the jaws but the piece itself (difficult to
adjust the jaws then, though).

You indicate from the *jaws*? With no certainty that they are
equal sized? This is likely the problem.

I measured the jaws when I got the chuck. I have also used the same
procedure on similar work pieces with nothing like this happening
before.

4) After facing both sides the piece was only 0.154" thick and as such
thin enough to flex in the chuck jaws.

0.154" thick -- but still about an inch in radial dimension so I
don't think so.

Thinking about it I should be able to tell by indicating the face and
tightening the jaws.

Michael Koblic,
Campbell River, BC

On Fri, 10 Dec 2010 18:02:41 -0800 (PST), Jim Wilkins
wrote:

On Dec 10, 1:23*am, wrote:
...
3) Should not indicate the jaws but the piece itself (difficult to
adjust the jaws then, though).
...
Michael Koblic,
Campbell River, BC

Instead of reading runout on the indicator you could feed it in to
zero and read the leadscrew dial. Then you could move the carriage in
and out of position to indicate the work beside the jaws.

I am being slow. Cannot visualize this.

This job may justify a spacer plate with slots for the jaws to keep it
in place and standoffs to position the dial plate out past the jaw
ends.

What I have is a piece that does both. It is smaller than the work
piece and I center it and attach it to the work piece with superglue.

Michael Koblic,
Campbell River, BC

wrote:
I am turning a mild steel doughnut: OD= 4.5", ID 2.125", thickness
0.1875". The purpose is to clean it up and make the two surfaces
parallel.

The process is always the same: Hold the piece by expanding 3-jaw,
face off, turn the edge, reverse, apply a spacer (a smaller doughnut
held on by superglue), face off the second side, deburr edges. Remove
from the 3-jaw. Clamp in 4 jaw on the outside, indicate the jaws to
within 0.001". Bore the hole till it "looks right". Deburr the inside
edges.

Today, when I got to the 4-jaw stage, I found that the orthogonal jaws
could not be set to the same number. For all intents and purposes the
doughnut now seemed to be an ellipse with one axis 0.014" longer than
the other.

Never mind, I thought, I centered both axes and proceeded to bore. I
did not encounter any problems but when I re-clamped on the 3-jaw it
was clear that the piece was not rotating concentrically. When I
measured it there was a variation of 0.024" in the width of the
doughnut (average width=0.960"), i.e. the hole is eccentric to the
perimeter.

Not that it matters with this piece but what are the possible causes?

My thoughts:

1) I have not indicated the 4-jaw properly. Possible, but has not
happened before.
2) Crummy 4-jaw chuck that came with the 9x20. It is of the "old"
style and a pain to use.
3) Should not indicate the jaws but the piece itself (difficult to
adjust the jaws then, though).
4) After facing both sides the piece was only 0.154" thick and as such
thin enough to flex in the chuck jaws.

Thanks,

Michael Koblic,
Campbell River, BC

I think a faster and easier way to make this part would be to start
with .187 plate, use a hole saw or tram cutter in the drill press to
cut the ID and then trim the corners with a shear or saw and then
finish the OD by mounting the piece on a mandrel.

You could also make a fly cutter / tram that would cut the ID and the
OD in one op. Here it would probably be best to have the ID cut first
and then have the od cut as you might need to have a speed chang

If for some reason you need to use bar stock rather than plate, Then
I would face one end, drill/boar the ID part or cut off the blank and
then use the mandrel to face and size the OD.

As I see it the disadvantage top the way you are doing it now is that
it requires a whole lot of set up changes and having to reestablish
center each time.

Roger Shoaf

On Dec 10, 10:53*pm, wrote:
On Fri, 10 Dec 2010 18:02:41 -0800 (PST), Jim Wilkins
..
Instead of reading runout on the indicator you could feed it in to
zero and read the leadscrew dial. Then you could move the carriage in
and out of position to indicate the work beside the jaws.

I am being slow. Cannot visualize this.

Michael Koblic,
Campbell River, BC

And I need to practice writing clear descriptions.

When centering work in a 4-jaw you normally turn the chuck while
watching the indicator dial, right?

You can't do this when the jaws grab the OD, and moving the carriage
out of the way to turn past a jaw means you have to slide the
indicator point back onto the work afterwards without shifting it.

I suggest initially advancing the crossfeed until the indicator reads
zero (close to a jaw) and then perhaps zeroing the crossfeed dial.
Then you can back it out and slide the carriage to the right so the
jaws clear the indicator. Rotate the work half a turn, return the
carriage and advance the crossfeed to a zero indicator reading again.
Adjust the jaws to remove half of the difference between the new and
previous crossfeed readings. If you zeroed it and the new one is 30
then move the jaws to make it 15. At this point I reset the zero.

This works with a lever test indicator with a cosine error because you
only read it at one point, its zero.

Rotate the chuck a quarter turn and repeat. The work should now be
nearly centered.

HTH
JSW

On Sat, 11 Dec 2010 15:16:53 -0800 (PST), Jim Wilkins
wrote:

[...]

And I need to practice writing clear descriptions.

When centering work in a 4-jaw you normally turn the chuck while
watching the indicator dial, right?

You can't do this when the jaws grab the OD, and moving the carriage
out of the way to turn past a jaw means you have to slide the
indicator point back onto the work afterwards without shifting it.

I suggest initially advancing the crossfeed until the indicator reads
zero (close to a jaw) and then perhaps zeroing the crossfeed dial.
Then you can back it out and slide the carriage to the right so the
jaws clear the indicator. Rotate the work half a turn, return the
carriage and advance the crossfeed to a zero indicator reading again.
Adjust the jaws to remove half of the difference between the new and
previous crossfeed readings. If you zeroed it and the new one is 30
then move the jaws to make it 15. At this point I reset the zero.

This works with a lever test indicator with a cosine error because you
only read it at one point, its zero.

Rotate the chuck a quarter turn and repeat. The work should now be
nearly centered.

HTH
JSW

OK, now I get it, thanks. What you are doing is attaching the
indicator in such a manner that it need not be touched by human hand
while doing the series of measurements except to re-set the zero. You
are also indicating next to the jaws.

If I thought about it I should have done that or something similar
then. I shall be aware of it with the next piece.

I am more and more convinced that the issue is the flexing of the work
piece: All the previous ones I had done I only faced off one side.
Also, the recent batch I bought were definitely thinner than the ones
I bought in the past. I said so much in the shop at the time.

Recession is hitting everywhere. Even baby bum-wipes are smaller and
thinner these days...

Michael Koblic,
Campbell River, BC

On Fri, 10 Dec 2010 21:27:43 -0600, F. George McDuffee
wrote:

On Fri, 10 Dec 2010 18:02:41 -0800 (PST), Jim Wilkins

[...]

One way around this from the old machining books is to use
what is called a bridge or pump staff.

You can make one out of a piece of stiff wire that you can
clamp in the tail stock chuck or make a bushing. To use,
you bend the free end so that the tip of the bridge rides on
what you are trying to get concentric and you can use a drop
indicator on the bridge to measure the runout. The actual
measurements won't be correct, but generally you are trying
for zero runout with no or minimal needle movement.

You can also fabricate a bridge out of a used hacksaw blade
that you can clamp in either the tail stock or tool post.
Works great for indicating square/hex stock or rough cast
preforms or rough cast bores.

If it would be helpful I can post pictures of the ones I
made on either the drop box or my web site.

Yes please. I am having a hard time visualizing it: How do you get
around the jaws with the bridge?

Another possibility if you have several of these to do is to
fabricate a holder/fixture that will clamp the donut that
you can bolt to the faceplate.

Right. That's where that 5C step collet would have been so nice, too.
Up to now the pieces have been all different as I am experimenting. At
some stage I would like to develop a method where the edge, one face
and the hole in the middle can be all done in one clamping.

Let the group know how you make out and what your solution
was.

Next time I do a similar piece I shall take notes and do a few extra
measurements.

It is not impossible that Santa will drop a new 4-jaw down the
chimney, too.

Michael Koblic,
Campbell River, BC

On Dec 11, 8:28*pm, wrote:
...
I am more and more convinced that the issue is the flexing of the work
piece: All the previous ones I had done I only faced off one side.
Also, the recent batch I bought were definitely thinner than the ones
I bought in the past. I said so much in the shop at the time.
...
Michael Koblic,
Campbell River, BC-

Do you standardize the size of these dials? If so, maybe you could
find a chuck with removeable top jaws and make your own pie jaws, with
short protrusions on both ends to clamp either the ID or OD and an
undercut so you can cut across the unclamped edge.

/'''|__---------------__|'''\

jsw

On Sat, 11 Dec 2010 13:29:15 -0800 (PST), RS at work

[...]

I think a faster and easier way to make this part would be to start
with .187 plate, use a hole saw or tram cutter in the drill press to
cut the ID and then trim the corners with a shear or saw and then
finish the OD by mounting the piece on a mandrel.

Interesting. You think it would be faster doing the pieces from
scratch rather than using prefabricated items as I am doing now? Also
what is the advantage of a mandrel as opposed to a 3-jaw chuck?

You could also make a fly cutter / tram that would cut the ID and the
OD in one op. Here it would probably be best to have the ID cut first
and then have the od cut as you might need to have a speed chang

If for some reason you need to use bar stock rather than plate, Then
I would face one end, drill/boar the ID part or cut off the blank and
then use the mandrel to face and size the OD.

As I see it the disadvantage top the way you are doing it now is that
it requires a whole lot of set up changes and having to reestablish
center each time.

Again, I am not sure of the advantage of doing it from scratch rather
than finishing the pre-fabs. The only hassle part of the procedure is
the 4-jaw chuck to get the ID concentric with the OD.

Michael Koblic,
Campbell River, BC

On 2010-12-11, wrote:
On 11 Dec 2010 01:41:53 GMT, "DoN. Nichols"
wrote:

[...]

Strange. This is not a "universal" (e.g. scroll-back 4-jaw is
it?

No, it's an independent 4-jaw. Looks like this:
http://www.busybeetools.com/products...OOD-LATHE.html

I bought a similar one for my wood lathe. I refused to believe that it
was a metalworking chuck as some maintained elsewhere until I got one
with the 9x20.

O.K. This does not show the back side. Is this, by any chance,
the chuck with studs sticking through the backplate, and a nut and
washer holding it in, and tightened after you get it adjusted?

I have read descriptions of these with people who got them on
metalworking lathes saying that they are only good for woodworking. :-)

I see a hint at the bottom of the page that if you are
interested in this chuck -- you should also be interested in this chuck
(again) at the bottom of the page. :-)

[...]

2) Crummy 4-jaw chuck that came with the 9x20. It is of the "old"
style and a pain to use.

That still should not result in eccentricity -- just greater
difficulty achieving concentricity.

You'd better believe it...

Sounds like the type with the nuts on the back holding the jaws,
then.:-)

3) Should not indicate the jaws but the piece itself (difficult to
adjust the jaws then, though).

You indicate from the *jaws*? With no certainty that they are
equal sized? This is likely the problem.

I measured the jaws when I got the chuck. I have also used the same
procedure on similar work pieces with nothing like this happening
before.

O.K. But *never* trust the jaws to be right -- measure the
workpiece, even if it is more difficult.

4) After facing both sides the piece was only 0.154" thick and as such
thin enough to flex in the chuck jaws.

0.154" thick -- but still about an inch in radial dimension so I
don't think so.

Thinking about it I should be able to tell by indicating the face and
tightening the jaws.

O.K.

Good Luck,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

wrote in message
...
On Sat, 11 Dec 2010 13:29:15 -0800 (PST), RS at work

[...]

I think a faster and easier way to make this part would be to start
with .187 plate, use a hole saw or tram cutter in the drill press to
cut the ID and then trim the corners with a shear or saw and then
finish the OD by mounting the piece on a mandrel.

Interesting. You think it would be faster doing the pieces from
scratch rather than using prefabricated items as I am doing now? Also
what is the advantage of a mandrel as opposed to a 3-jaw chuck?

You could also make a fly cutter / tram that would cut the ID and the
OD in one op. Here it would probably be best to have the ID cut first
and then have the od cut as you might need to have a speed chang

If for some reason you need to use bar stock rather than plate, Then
I would face one end, drill/boar the ID part or cut off the blank and
then use the mandrel to face and size the OD.

As I see it the disadvantage top the way you are doing it now is that
it requires a whole lot of set up changes and having to reestablish
center each time.

Again, I am not sure of the advantage of doing it from scratch rather
than finishing the pre-fabs. The only hassle part of the procedure is
the 4-jaw chuck to get the ID concentric with the OD.

Michael Koblic,
Campbell River, BC

I'm in late on this conversation, and have not read all the responses.
However, a ready solution, if it hasn't been mentioned, is to run the part
in soft jaws. Turn the OD to size, then fashion pie shaped jaws that will
encompass the major portion of the diameter. By creating a step of the
proper depth, you'll be able to face the item parallel and bore the hole
concentric. Used properly, you shouldn't have any problem holding a half
thou in concentricity and parallelism. Facing should be the last
operation, and it should be done by taking equal amounts off each side, to
rough, then equal amounts off each side to finish, flipping the part over
for each pass. Leave a few thou only for the finish cuts

Harold

This type of chuck isn't ideally suited for most large lathes, but it's
sufficiently adequate for use on a generic 9x20 model.
I don't know if the chuck is a good choice for thin rings, though, as jaw
pressure could easily distort the ring (much like thin tubing).. the flat
faceplate may be a better choice (with some fittings added).

I've used the same type 4-jaw on my own 9x20, and it isn't substantially any
more difficult to use than a heavy duty 4-jaw chuck.
Like many pieces of tooling from China/elsewhere, it was kinda rough as
supplied. After deburring all the parts and edges, and smoothing the sliding
surfaces, I replaced the soft flat washers under the nuts with hardened,
ground flat washers. That may not seem like a major issue, but those
original soft washers don't give a good feel of when a fastener is tight.

Backing off the jaw nuts just enough to allow for minor adjustments may be
the key to ease of use with these chucks.

Hardened/ground washers offer a significant improvement in feedback of
tight/just-snug within a short wrench swing.. I generally install them where
repeated use is common.
When a fastener has 90+ degrees of swing from tight-to-snug (backing off),
something is wrong.. the bolt isn't stretching, and the cast iron isn't
compressing, so it's the soft flat washer.
Another cause of wrench "overswing" could be that the threaded hole in the
nut isn't perpendicular with the flat sides, which is a fairly frequent
occurrence with Chinese hardware.

A HD 4-jaw will have other issues, such as the correct spindle thread and
matching register seat for the 9x20 models with metric thread spindles.
Another issue with a HD 4-jaw is the workpieces will always be supported
further away from the spindle nose bearing, which will most likely result in
more tool chatter when not using tailstock center support.

--
WB
..........


wrote in message
news

No, it's an independent 4-jaw. Looks like this:
http://www.busybeetools.com/products...OOD-LATHE.html

I bought a similar one for my wood lathe. I refused to believe that it
was a metalworking chuck as some maintained elsewhere until I got one
with the 9x20.

Michael Koblic,
Campbell River, BC

On Sun, 12 Dec 2010 10:06:02 -0500, "Wild_Bill"
wrote:

This type of chuck isn't ideally suited for most large lathes, but it's
sufficiently adequate for use on a generic 9x20 model.
I don't know if the chuck is a good choice for thin rings, though, as jaw
pressure could easily distort the ring (much like thin tubing).. the flat
faceplate may be a better choice (with some fittings added).

Agreed.


I've used the same type 4-jaw on my own 9x20, and it isn't substantially any
more difficult to use than a heavy duty 4-jaw chuck.
Like many pieces of tooling from China/elsewhere, it was kinda rough as
supplied. After deburring all the parts and edges, and smoothing the sliding
surfaces, I replaced the soft flat washers under the nuts with hardened,
ground flat washers. That may not seem like a major issue, but those
original soft washers don't give a good feel of when a fastener is tight.

Backing off the jaw nuts just enough to allow for minor adjustments may be
the key to ease of use with these chucks.

Hardened/ground washers offer a significant improvement in feedback of
tight/just-snug within a short wrench swing.. I generally install them where
repeated use is common.
When a fastener has 90+ degrees of swing from tight-to-snug (backing off),
something is wrong.. the bolt isn't stretching, and the cast iron isn't
compressing, so it's the soft flat washer.
Another cause of wrench "overswing" could be that the threaded hole in the
nut isn't perpendicular with the flat sides, which is a fairly frequent
occurrence with Chinese hardware.

Sounds like a cheaper solution to try before getting a whole new
chuck.

A HD 4-jaw will have other issues, such as the correct spindle thread and
matching register seat for the 9x20 models with metric thread spindles.
Another issue with a HD 4-jaw is the workpieces will always be supported
further away from the spindle nose bearing, which will most likely result in
more tool chatter when not using tailstock center support.

I had no problem with the spindle thread, unlike the face plate that
came with the 9x20. I could not get it on the spindle. The vendor sent
a replacement which they swore fitted OK on one of their spindles.
Same problem. I had to re-thread both plates and it was not a subtle
process of a few thou. I had to take a fair bit off.

Michael Koblic,
Campbell River, BC

On 12 Dec 2010 03:52:29 GMT, "DoN. Nichols"
wrote:

On 2010-12-11, wrote:
On 11 Dec 2010 01:41:53 GMT, "DoN. Nichols"
wrote:

[...]

Strange. This is not a "universal" (e.g. scroll-back 4-jaw is
it?

No, it's an independent 4-jaw. Looks like this:
http://www.busybeetools.com/products...OOD-LATHE.html

I bought a similar one for my wood lathe. I refused to believe that it
was a metalworking chuck as some maintained elsewhere until I got one
with the 9x20.

O.K. This does not show the back side. Is this, by any chance,
the chuck with studs sticking through the backplate, and a nut and
washer holding it in, and tightened after you get it adjusted?

I have read descriptions of these with people who got them on
metalworking lathes saying that they are only good for woodworking. :-)

Barely...There are much better chucks for woodworking.

I see a hint at the bottom of the page that if you are
interested in this chuck -- you should also be interested in this chuck
(again) at the bottom of the page. :-)

They have two versions - one which needs inserts and one which is
threaded 1"-8.

[...]

O.K. But *never* trust the jaws to be right -- measure the
workpiece, even if it is more difficult.

Oddly enough I do it because of advice I received on this very group
from someone about two years ago :-)


Michael Koblic,
Campbell River, BC

On Sat, 11 Dec 2010 17:50:18 -0800 (PST), Jim Wilkins
wrote:

On Dec 11, 8:28*pm, wrote:
...
I am more and more convinced that the issue is the flexing of the work
piece: All the previous ones I had done I only faced off one side.
Also, the recent batch I bought were definitely thinner than the ones
I bought in the past. I said so much in the shop at the time.
...
Michael Koblic,
Campbell River, BC-

Do you standardize the size of these dials? If so, maybe you could
find a chuck with removeable top jaws and make your own pie jaws, with
short protrusions on both ends to clamp either the ID or OD and an
undercut so you can cut across the unclamped edge.

/'''|__---------------__|'''\


This sort of thing?

http://www.busybeetools.com/products....-11.0IN..html

On Sun, 12 Dec 2010 09:35:37 GMT, "Harold & Susan Vordos"
wrote:

[...]

I'm in late on this conversation, and have not read all the responses.
However, a ready solution, if it hasn't been mentioned, is to run the part
in soft jaws. Turn the OD to size, then fashion pie shaped jaws that will
encompass the major portion of the diameter. By creating a step of the
proper depth, you'll be able to face the item parallel and bore the hole
concentric. Used properly, you shouldn't have any problem holding a half
thou in concentricity and parallelism. Facing should be the last
operation, and it should be done by taking equal amounts off each side, to
rough, then equal amounts off each side to finish, flipping the part over
for each pass. Leave a few thou only for the finish cuts


Jim Wilkins mentioned pie jaws.

A quick flit through Google turned up more questions than answers:

1) Pie jaws are available only for chucks with 2-part jaws, right?
2) The reason for soft jaws is ease of machining to fit the part?
3) What is the minimum size of the step that will hold a 3/16" part
securely (in aluminum)?
4) Should one be able to get pie jaws that will hold larger OD than
the regular external jaws in a 3-jaw chuck? The current 4" 3-jaw chuck
is just too small to hold the 4.5" piece on the outside (hence the
4-jaw use).

Michael Koblic,
Campbell River, BC

On Dec 9, 11:23*pm, wrote:
I am turning a mild steel doughnut: OD= 4.5", ID 2.125", thickness
0.1875". The purpose is to clean it up and make the two surfaces
parallel.

The process is always the same: Hold the piece by expanding 3-jaw,
face off, turn the edge, reverse, apply a spacer (a smaller doughnut
held on by superglue), face off the second side, deburr edges. Remove
from the 3-jaw. Clamp in 4 jaw on the outside, indicate the jaws to
within 0.001". Bore the hole till it "looks right". Deburr the inside
edges.

Today, when I got to the 4-jaw stage, I found that the orthogonal jaws
could not be set to the same number. For all intents and purposes the
doughnut now seemed to be an ellipse with one axis 0.014" longer than
the other.

Never mind, I thought, I centered both axes and proceeded to bore. I
did not encounter any problems but when I re-clamped on the 3-jaw it
was clear that the piece was not rotating concentrically. When I
measured it there was a variation of 0.024" in the width of the
doughnut (average width=0.960"), i.e. the hole is eccentric to the
perimeter.

Not that it matters with this piece but what are the possible causes?

My thoughts:

1) I have not indicated the 4-jaw properly. Possible, but has not
happened before.
2) Crummy 4-jaw chuck that came with the 9x20. It is of the "old"
style and a pain to use.
3) Should not indicate the jaws but the piece itself (difficult to
adjust the jaws then, though).
4) After facing both sides the piece was only 0.154" thick and as such
thin enough to flex in the chuck jaws.

Thanks,

Michael Koblic,
Campbell River, BC

I believe your eccentricity is due to one edge of the ring being
lifted up, you then get an angular section of a cylinder instead of a
circle, an ellipse in other words. Has been a kink written up in old
machinists' books to bore elliptical holes.

What you list as workflow wouldn't be my choice if I wanted concentric
inside and outside. I'd start with flat stock, roughing out a blank
on the 4x6 first. If your flat stock is that much out or you need
machined surfaces, face off both sides first. Precision ground stock
isn't that expensive, saves facing and possible "wedgies". With the
blank still stuck in the chuck, bore your hole to whatever limit you
care to. Make up a mandrel for between centers to fit your hole, I'd
make up one with a shoulder and a retaining sleeve. Now finish off
the outside to size. If you're doing multiples, make your mandrel
long enough to put a bunch on and finish them all at the same time.

It always bugs me when somebody reverses the process. It's always
much easier to get a precision hole bored and finished FIRST, then
reference everything from that. You get much better results from
putting a part on a mandrel between centers than trying to indicate a
part in a chuck. Concentricity is pretty much guaranteed that way.

I've not seen any metal lathe supplied with such a flimsy 4 jaw chuck,
even the 7x has a better chuck than that. Didn't cost as much,
either. Reminds me of some of the faceplate add-ons I saw in The
Model Engineer ads circa 1899 for treadle lathes. I wouldn't trust it
on a wood lathe, either.

Stan

wrote in message
...
On Sun, 12 Dec 2010 09:35:37 GMT, "Harold & Susan Vordos"
wrote:

[...]

I'm in late on this conversation, and have not read all the responses.
However, a ready solution, if it hasn't been mentioned, is to run the part
in soft jaws. Turn the OD to size, then fashion pie shaped jaws that
will
encompass the major portion of the diameter. By creating a step of the
proper depth, you'll be able to face the item parallel and bore the hole
concentric. Used properly, you shouldn't have any problem holding a half
thou in concentricity and parallelism. Facing should be the last
operation, and it should be done by taking equal amounts off each side, to
rough, then equal amounts off each side to finish, flipping the part over
for each pass. Leave a few thou only for the finish cuts


Jim Wilkins mentioned pie jaws.

A quick flit through Google turned up more questions than answers:

1) Pie jaws are available only for chucks with 2-part jaws, right?

Generally, yes, but creativity can provide a way to use soft jaws that are
inserted on hard jaws. Not the best of all worlds, but a solution to a
difficult problem.

2) The reason for soft jaws is ease of machining to fit the part?

Correct, but there are more reasons that just that. For one, if you are
running volumes of parts, they offer the ability to remove and replace parts
on a continuing basis without losing registration with tooling. They are
also capable of holding concentricity and parallelism to a half thou, or
less. That often isn't close enough for critical work, but is within
acceptable guidelines for the vast majority of work one will encounter.
Not to detract from acceptable standards, but a half thou is virtually
nothing. The human eye can't discern .003" runout---so it's very good in
the scheme of things.

3) What is the minimum size of the step that will hold a 3/16" part
securely (in aluminum)?
Hard to say, but you can hold a part with 1/16" of surface, assuming you
don't crowd the cut. The nice thing with soft jaws is you can hold the
part as deep as you wish, leaving only the amount of material showing that
might require an edge break. For a 3/16" thick part, I'd feel very
comfortable holding it by 1/8", and taking the cuts that may be required.
Remember, that part is held captive---it can't do anything but come out--so
it's very stable, even with modest chucking pressure. With pie jaws, you
can get down on the part quite nicely without fear of distortion, although
it is possible to bow the part outward in the center from excessive chuck
pressure.

4) Should one be able to get pie jaws that will hold larger OD than
the regular external jaws in a 3-jaw chuck? The current 4" 3-jaw chuck
is just too small to hold the 4.5" piece on the outside (hence the
4-jaw use).

The big problem you'd have with soft jaws is that small chucks normally do
not have what I call master jaws---those two piece jaws that make it all
possible. If you do have them, you can design a soft jaw that will hold
the maximum swing of your machine---all without trouble. That's the beauty
of soft jaws. They can be built to conform to your needs, so long as they
don't exceed the capacity of the machine on which they're used. A good
example is a set I made to turn some 4" aluminum tubing. Fairly heavy wall
at about 1/2", but the pieces were more than a foot long. Made 8" long
jaws, installed a stiffener to prevent the ends from springing and ran the
job with no issues.

Hope some of this helps.

Harold

On Dec 12, 9:09*pm, wrote:
...
Jim Wilkins mentioned pie jaws.
...
Michael Koblic,


I just uploaded a photo of mine:
http://picasaweb.google.com/KB1DAL/T...64293268785794

They are made from scrap as the tool mark shows. The jaws cam in only
0.050" when the dark grey outer ring is turned, so it requires top
jaws fitted to the workpiece. The three hardened and lapped disks are
my drilling jig.

This shows the standard mounting geometry for top jaws:
http://www.lathe-chucks.com/BISON/BI...-SOFT-JAWS.htm

You could mill the mortice and tenon in the back of the jaw blanks.
The radial mortice is about 1/4" deep so I'd look for at least 3/4"
thick stock.

If your initial jaw depth isn't enough to hold the work you just turn
the recess deeper. As long as the bit pushes the work against the
chuck you don't need much. Just don't forget and make a cut towards
the right.

jsw

On Sun, 12 Dec 2010 19:15:27 -0800 (PST), wrote:

[...]

I believe your eccentricity is due to one edge of the ring being
lifted up, you then get an angular section of a cylinder instead of a
circle, an ellipse in other words. Has been a kink written up in old
machinists' books to bore elliptical holes.

It is a thought, however, to get a 0.007" error on 4.5" that way
(without any flexion) the disk would have to be tilted over 3 degrees.
Even I would have seen that :-)

I am still voting for the "lay chips" pattern :-)

What you list as workflow wouldn't be my choice if I wanted concentric
inside and outside. I'd start with flat stock, roughing out a blank
on the 4x6 first. If your flat stock is that much out or you need
machined surfaces, face off both sides first. Precision ground stock
isn't that expensive, saves facing and possible "wedgies". With the
blank still stuck in the chuck, bore your hole to whatever limit you
care to. Make up a mandrel for between centers to fit your hole, I'd
make up one with a shoulder and a retaining sleeve. Now finish off
the outside to size. If you're doing multiples, make your mandrel
long enough to put a bunch on and finish them all at the same time.

Roger Shoaf suggested something essentially identical. I can see the
benefit of doing the ID first even using pre-fabricated blanks as I
do. I am still confused as to the benefit of a mandrel vs. 3-jaw
chuck.

It always bugs me when somebody reverses the process. It's always
much easier to get a precision hole bored and finished FIRST, then
reference everything from that. You get much better results from
putting a part on a mandrel between centers than trying to indicate a
part in a chuck. Concentricity is pretty much guaranteed that way.

I am not sure why the need to indicate if the piece is clamped inside
the hole by the 3-jaw self-centering chuck. Concentricity within
0.003" is fine for this application.

I've not seen any metal lathe supplied with such a flimsy 4 jaw chuck,
even the 7x has a better chuck than that. Didn't cost as much,
either.

Which I guess is the reason they throw it in with the lathe. It is of
comparable quality to their face-plates and the stand the lathe comes
with for that matter. Not to mention the work one has to do on the
lathe itself.

Michael Koblic,
Campbell River, BC

On Mon, 13 Dec 2010 07:12:28 GMT, "Harold & Susan Vordos"
wrote:

[...]

1) Pie jaws are available only for chucks with 2-part jaws, right?

Generally, yes, but creativity can provide a way to use soft jaws that are
inserted on hard jaws. Not the best of all worlds, but a solution to a
difficult problem.

Hm. I am not sure I am *that* creative...

2) The reason for soft jaws is ease of machining to fit the part?

Correct, but there are more reasons that just that. For one, if you are
running volumes of parts, they offer the ability to remove and replace parts
on a continuing basis without losing registration with tooling. They are
also capable of holding concentricity and parallelism to a half thou, or
less.

Would steel jaws not do the same?

That often isn't close enough for critical work, but is within
acceptable guidelines for the vast majority of work one will encounter.
Not to detract from acceptable standards, but a half thou is virtually
nothing. The human eye can't discern .003" runout---so it's very good in
the scheme of things.

Good enough for me.

3) What is the minimum size of the step that will hold a 3/16" part
securely (in aluminum)?
Hard to say, but you can hold a part with 1/16" of surface, assuming you
don't crowd the cut. The nice thing with soft jaws is you can hold the
part as deep as you wish, leaving only the amount of material showing that
might require an edge break. For a 3/16" thick part, I'd feel very
comfortable holding it by 1/8", and taking the cuts that may be required.
Remember, that part is held captive---it can't do anything but come out--so
it's very stable, even with modest chucking pressure. With pie jaws, you
can get down on the part quite nicely without fear of distortion, although
it is possible to bow the part outward in the center from excessive chuck
pressure.

OK

4) Should one be able to get pie jaws that will hold larger OD than
the regular external jaws in a 3-jaw chuck? The current 4" 3-jaw chuck
is just too small to hold the 4.5" piece on the outside (hence the
4-jaw use).

The big problem you'd have with soft jaws is that small chucks normally do
not have what I call master jaws---those two piece jaws that make it all
possible. If you do have them, you can design a soft jaw that will hold
the maximum swing of your machine---all without trouble. That's the beauty
of soft jaws. They can be built to conform to your needs, so long as they
don't exceed the capacity of the machine on which they're used. A good
example is a set I made to turn some 4" aluminum tubing. Fairly heavy wall
at about 1/2", but the pieces were more than a foot long. Made 8" long
jaws, installed a stiffener to prevent the ends from springing and ran the
job with no issues.

My Taig 3-jaw has two-component jaws. I have turned the aluminum ones
to suit a similar job on a much smaller scale. I do not think I have
seen 4" 3-jaw scroll chucks with two-component jaws at the usual
vendors. I have not looked elsewhere.

Hope some of this helps.

Very much so.

Michael Koblic,
Campbell River, BC

On Mon, 13 Dec 2010 06:34:13 -0800 (PST), Jim Wilkins
wrote:

On Dec 12, 9:09*pm, wrote:
...
Jim Wilkins mentioned pie jaws.
...
Michael Koblic,


I just uploaded a photo of mine:
http://picasaweb.google.com/KB1DAL/T...64293268785794

Am I looking at pie jaws which have been made but not finished to any
particular work piece?

They are made from scrap as the tool mark shows. The jaws cam in only
0.050" when the dark grey outer ring is turned, so it requires top
jaws fitted to the workpiece. The three hardened and lapped disks are
my drilling jig.

Won't the master jaws move *out* to give you more range? Am I missing
something?

This shows the standard mounting geometry for top jaws:
http://www.lathe-chucks.com/BISON/BI...-SOFT-JAWS.htm

You could mill the mortice and tenon in the back of the jaw blanks.
The radial mortice is about 1/4" deep so I'd look for at least 3/4"
thick stock.

I had a look through the site and a couple of others. I see no
two-component jaws available for anything smaller than a 5" 3-jaw
chuck. So I guess the two immediate questions a
1) In the overall scheme of things is a 5" 3-jaw chuck with master
jaws and a suitable back plate a better investment than a good quality
4-jaw independent chuck (with a back plate)?
2) Is a 5" scroll chuck too big for a 9x20? I do not mean the swing
but the weight, inertia, load on the headstock spindle etc.

If your initial jaw depth isn't enough to hold the work you just turn
the recess deeper. As long as the bit pushes the work against the
chuck you don't need much. Just don't forget and make a cut towards
the right.

I take it you are talking about a cut along the z-axis? I guess that
would occur if I was backing the boring bar out of the ID...

A thought occurred to me:
Say one wants to turn something close to the swing of the 9x20
(actually 8.75") - say 8" disk. If I get pie jaws that just clear the
bed (8.5") would a rim of only 1/4" be enough to hold such a piece?
Just thinking ahead to the next project...

Michael Koblic,
Campbell River, BC

On Dec 13, 8:40*pm, wrote:
...
My Taig 3-jaw has two-component jaws. I have turned the aluminum ones
to suit a similar job on a much smaller scale. I do not think I have
seen 4" 3-jaw scroll chucks with two-component jaws at the usual
vendors. I have not looked elsewhere.

Michael Koblic,

I didn't see any smaller than 5" with separate top jaws.

FYI in case you trip over one used as a doorstop, 2 jaw chucks adapt
well to custom top jaws. At their simplest a left+right hand screw
operates the two jaws, but having made a 4 jaw out of a slotted rotary
table faceplate I think making a chuck is too much trouble.

jsw

On 2010-12-13, Harold & Susan Vordos wrote:

wrote in message
...
On Sun, 12 Dec 2010 09:35:37 GMT, "Harold & Susan Vordos"

[ ... ]

4) Should one be able to get pie jaws that will hold larger OD than
the regular external jaws in a 3-jaw chuck? The current 4" 3-jaw chuck
is just too small to hold the 4.5" piece on the outside (hence the
4-jaw use).

The big problem you'd have with soft jaws is that small chucks normally do
not have what I call master jaws---those two piece jaws that make it all
possible. If you do have them, you can design a soft jaw that will hold
the maximum swing of your machine---all without trouble. That's the beauty
of soft jaws. They can be built to conform to your needs, so long as they
don't exceed the capacity of the machine on which they're used. A good
example is a set I made to turn some 4" aluminum tubing. Fairly heavy wall
at about 1/2", but the pieces were more than a foot long. Made 8" long
jaws, installed a stiffener to prevent the ends from springing and ran the
job with no issues.

There actually is a small 3-jaw scroll-back chuck with two-piece
jaws. Not quite as nice as the larger ones, but satisfactory for a lot
of things. This chuck comes with the Taig (or Peatol in the UK) lathe.

This web page shows everything about it except the mating
surface of the master and top jaws.

http://www.cartertools.com/chuck.html

And on *this* page:

http://www.cartertools.com/catalog.html

Scroll down to part number 1050 (the chuck with un-machined jaws).

Scroll a little further (to 1051) and you will see a second set of jaws.

And yet a bit farther (to 1052) and you will see jaws which make a good
pie jaw setup. (Extruded aluminum for those).

The one disadvantage of all of these is that they only have a
single groove milled the length of the underside of the top jaws, which
keeps it from twisting -- but does not form truly precise repeatability
of grip. The bigger ones have a second groove at right angles to the
first on one part, and a matching projection on the other part to set
the radial spacing as well.

The total diameter of the chuck is 3-1/4", with a 3/4-16 thread
for screwing onto the spindle.

So -- the question is whether this is large enough for your
needs. The prices are certainly reasonable.

Oh -- in item # 1060, they have a 4-jaw universal (scroll-back)
chuck. That is new to me.

If you back up to 1030 (the 4-jaw independent chuck) -- I've
taken one of these and modified it to mount on a different lathe (The
Emco-Maier Compact-5/CNC) with a very different mounting system.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On 2010-12-14, wrote:
On Mon, 13 Dec 2010 07:12:28 GMT, "Harold & Susan Vordos"
wrote:

[ ... ]

2) The reason for soft jaws is ease of machining to fit the part?

Correct, but there are more reasons that just that. For one, if you are
running volumes of parts, they offer the ability to remove and replace parts
on a continuing basis without losing registration with tooling. They are
also capable of holding concentricity and parallelism to a half thou, or
less.

Would steel jaws not do the same?

Yes -- if you can machine them. One-piece jaws are often
hardened and ground to finish dimensions, so you can't turn them to
achieve the accuracy you need. But two-piece jaws often have the top
jaws a mild steel (actually probably more often than aluminum for the
bigger ones).

For that matter -- that is also how the master jaws for
two-piece jaws are made -- hardened and ground, so the wear is
concentrated on the replaceable jaw parts.

[ ... ]

4) Should one be able to get pie jaws that will hold larger OD than
the regular external jaws in a 3-jaw chuck? The current 4" 3-jaw chuck
is just too small to hold the 4.5" piece on the outside (hence the
4-jaw use).

The big problem you'd have with soft jaws is that small chucks normally do
not have what I call master jaws---those two piece jaws that make it all
possible. If you do have them, you can design a soft jaw that will hold
the maximum swing of your machine---all without trouble. That's the beauty
of soft jaws. They can be built to conform to your needs, so long as they
don't exceed the capacity of the machine on which they're used. A good
example is a set I made to turn some 4" aluminum tubing. Fairly heavy wall
at about 1/2", but the pieces were more than a foot long. Made 8" long
jaws, installed a stiffener to prevent the ends from springing and ran the
job with no issues.

My Taig 3-jaw has two-component jaws. I have turned the aluminum ones
to suit a similar job on a much smaller scale. I do not think I have
seen 4" 3-jaw scroll chucks with two-component jaws at the usual
vendors. I have not looked elsewhere.

Have you seen the pie jaw blanks for the Taig? I just posted
pointers to a web site which offers them.

The question is whether you could adapt the Taig 3-jaw to your
larger machine. (Or whether you could put a riser block in the Taig and
use the 3-jaw with the pie jaws for your workpiece size.

Good Luck,
DoN.

--
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wrote in message
...
snip-

A thought occurred to me:
Say one wants to turn something close to the swing of the 9x20
(actually 8.75") - say 8" disk. If I get pie jaws that just clear the
bed (8.5") would a rim of only 1/4" be enough to hold such a piece?
Just thinking ahead to the next project...

Michael Koblic,
Campbell River, BC

That's more than enough material to hold a piece, even if the jaws are made
of aluminum. Key to success is not having an overly long piece, which can
be levered from the chuck, or to take excessive cuts, which may do the same
thing. Also, there's nothing preventing you from running a live center
with a plate on the item being held. That keeps it from pulling out of the
chuck under adverse conditions. You'd put the center drilled plate against
the part, then start the machine. Back off the live center ever so
slightly, so the plate can find natural center as the part rotates.
Assuming you have machined a proper pocket for the part to be turned, it
holds the part securely against the back of the pocket. Only enough torque
on the handle of the chuck needed to drive the part, with no fear of the
part coming out.

If the part must be faced, you'd have to use good judgment as to how hard to
tighten the chuck. It's all just a matter of having a little experience.
You get a feel for these things pretty quickly.

If you do explore soft jaws, make sure you understand how they should be
applied. If you don't follow the simple rules, they don't work worth a
damn. No better than hard jaws in most cases.

Harold

wrote in message
...
On Mon, 13 Dec 2010 07:12:28 GMT, "Harold & Susan Vordos"
wrote:
snip-

Correct, but there are more reasons that just that. For one, if you are
running volumes of parts, they offer the ability to remove and replace
parts
on a continuing basis without losing registration with tooling. They are
also capable of holding concentricity and parallelism to a half thou, or
less.

Would steel jaws not do the same?

I trust you mean steel jaws that can be machined, not the factory hard jaws.

Yes, they can do the same, and may well be made of steel. Some of my soft
jaws are. Because you preload the jaws before they're machined, and
because you machine an identical profile in reverse, the parts are nested
such that they are oriented properly. No worry about perpendicularity, and
rarely a concern of more than a half thou eccentricity. They can be even
closer, depending on several conditions. The point is, even a rather
worthless universal three jaw can yield surprising precision when soft jaws
are applied.

If you're interested in reading a document I prepared years ago, pertaining
to the use of soft jaws, please ask and I'll provide a link. Not promoting
myself here, just trying to share what I learned in my years of using soft
jaws.

Harold

wrote in message
...
snip-

Roger Shoaf suggested something essentially identical. I can see the
benefit of doing the ID first even using pre-fabricated blanks as I
do. I am still confused as to the benefit of a mandrel vs. 3-jaw
chuck.

It's pretty simple. Any time you can avoid using a mandrel, you're likely
better off. That would be especially true when attemting to turn what is,
essentially, a large, thin washer. Chatter is an ongoing problem, as is
driving the part without slippage. By preparing the OD of the part first,
easily accomplished by pressing the part against a plug, using a plate with
a live center. Once the OD is machined, the part can then be chucked in
soft jaws and faced, bored and reversed with no issues. Best of all,
chucking the OD pretty much eliminates chatter, especially if the part nests
on a proper cavity. Soft jaws solve all the problems of holding large
diameter thin pieces.

Harold

On Tue, 14 Dec 2010 09:48:57 GMT, "Harold & Susan Vordos"
wrote:


wrote in message
.. .
On Mon, 13 Dec 2010 07:12:28 GMT, "Harold & Susan Vordos"
wrote:
snip-

Correct, but there are more reasons that just that. For one, if you are
running volumes of parts, they offer the ability to remove and replace
parts
on a continuing basis without losing registration with tooling. They are
also capable of holding concentricity and parallelism to a half thou, or
less.

Would steel jaws not do the same?

I trust you mean steel jaws that can be machined, not the factory hard jaws.

Yes.

Yes, they can do the same, and may well be made of steel. Some of my soft
jaws are. Because you preload the jaws before they're machined, and
because you machine an identical profile in reverse, the parts are nested
such that they are oriented properly. No worry about perpendicularity, and
rarely a concern of more than a half thou eccentricity. They can be even
closer, depending on several conditions. The point is, even a rather
worthless universal three jaw can yield surprising precision when soft jaws
are applied.

If you're interested in reading a document I prepared years ago, pertaining
to the use of soft jaws, please ask and I'll provide a link. Not promoting
myself here, just trying to share what I learned in my years of using soft
jaws.

I am very much interested.

Michael Koblic,
Campbell River, BC

On Tue, 14 Dec 2010 09:42:19 GMT, "Harold & Susan Vordos"
wrote:


wrote in message
.. .
snip-

A thought occurred to me:
Say one wants to turn something close to the swing of the 9x20
(actually 8.75") - say 8" disk. If I get pie jaws that just clear the
bed (8.5") would a rim of only 1/4" be enough to hold such a piece?
Just thinking ahead to the next project...

Michael Koblic,
Campbell River, BC

That's more than enough material to hold a piece, even if the jaws are made
of aluminum. Key to success is not having an overly long piece, which can
be levered from the chuck, or to take excessive cuts, which may do the same
thing. Also, there's nothing preventing you from running a live center
with a plate on the item being held. That keeps it from pulling out of the
chuck under adverse conditions. You'd put the center drilled plate against
the part, then start the machine. Back off the live center ever so
slightly, so the plate can find natural center as the part rotates.
Assuming you have machined a proper pocket for the part to be turned, it
holds the part securely against the back of the pocket. Only enough torque
on the handle of the chuck needed to drive the part, with no fear of the
part coming out.

It's boring and ID on such piece that had me worried.

[...]

Michael Koblic,
Campbell River, BC

On Tue, 14 Dec 2010 09:55:04 GMT, "Harold & Susan Vordos"
wrote:


wrote in message
.. .
snip-

Roger Shoaf suggested something essentially identical. I can see the
benefit of doing the ID first even using pre-fabricated blanks as I
do. I am still confused as to the benefit of a mandrel vs. 3-jaw
chuck.

It's pretty simple. Any time you can avoid using a mandrel, you're likely
better off. That would be especially true when attemting to turn what is,
essentially, a large, thin washer. Chatter is an ongoing problem,

You said it! The piece I described certainly does that. I have got rid
of the chatter by putting a spacer behind it.


driving the part without slippage. By preparing the OD of the part first,
easily accomplished by pressing the part against a plug, using a plate with
a live center. Once the OD is machined, the part can then be chucked in
soft jaws and faced, bored and reversed with no issues. Best of all,
chucking the OD pretty much eliminates chatter, especially if the part nests
on a proper cavity. Soft jaws solve all the problems of holding large
diameter thin pieces.

I see your point, too. OTOH you gotta love the diversity of opinions
on this group :-)

Michael Koblic,
Campbell River, BC

wrote in message
...
On Tue, 14 Dec 2010 09:48:57 GMT, "Harold & Susan Vordos"
wrote:
snip-

If you're interested in reading a document I prepared years ago,
pertaining
to the use of soft jaws, please ask and I'll provide a link. Not
promoting
myself here, just trying to share what I learned in my years of using soft
jaws.

I am very much interested.

Michael Koblic,
Campbell River, BC

Here's the link.
http://www.chaski.org/homemachinist/...hp?f=44&t=4266

There's a few pictures included, which you may not be able to view unless
you're a registered reader. We used to allow open registration, but Marty
changed board policy a few years ago to deter spamming.

Should you attempt to register, do provide the reasons you'd like access to
the board. Marty approves all registrations.

Good luck! I think you'll find the thread very enlightening.

Harold