Humble request for advise (or sympathy):
Just unboxed my new Jet 1014 and while checking it over,
noted that the alignment of the tips of the headstock and
tailstock centers is not perfect. The tailstock center is perhaps
..010 or .012 inch lower than the headstock center. This
is when the tailstock is moved right up close to the spindle.
I've read somewhere, probably on this newsgroup,
that when a tailstock center is tightened onto or into a
piece of wood, that the tailstock center has some tendency
to raise up. Depending of course on the bed's rigidity and
the tailstock stiffness as well.
My question, then, from anyone who might have encountered
about this type and amount of misalignment in a wood lathe,
should I worry?
Jiggling things around does not seem to alter this alignment
at all, and correcting this error would probably involve milling
a few thousandths off the headstock base. Something I'm not
very good at with my file and emery cloth!

Old Chief Lynn

Not to be too flippant about it, but just forget it. That isn't bad
for the Chiawanese these days. And honestly, you won't notice.

In a perfect world with perfect machinery, maybe. In all practical
use, I don't think it will be an issue because 1 / 100th of an inch
could just as well be in your Chiawanese revolving spur, your drive
spur, or it could be the way you have the tailstock set in the ways.

Also, think about that tiny amount spread out over the length of what
you are shaping. Doesn't amount to much.

And if it did bother you, what would you do to fix it? Just because
the drive spur point and the revolving spur point don't touch, what
would you adjust?

Then... it gets better. If you are thinking that you will always be
holding your piece in perfect coeccentricity while turning, thing
again. What happens when your revolving spur wears? And of course,
what happens when your drive spur wears and you need to sharpen the
blades a couple of times? Will you be maintaining machinist's
tolerances?

Nope.

As an easy field exercise to prove this, think of when you dismount a
piece of wood that you will be remounting on the spurs between
centers. You ALWAYS mark an index point so you can remount the same
way it came off, right? Think about it, if these things worked to
machinist's tolerances it wouldn't matter how the wood went on or came
off, no matter how many times as it would always line up the same.

I say spin up some wood and let the chips fly. Enjoy your new
machine.

Robert

Hi Chief, I agree with Robert that our lathes, hand held cutting
tools, the material being cut and the form of the turned objects don't
have and don't need the accuracy and precision of turning on a metal
lathe.

There are limits, of course as what we should reasonably expect of any
new machine. Why not ask technical advice of the dealer or the maker if
their quality control allows the tolerance this particular machine has?

If there is a mismatch at the headstock does this suggest a warped
unseasoned bed, poorly machined ways and/or stocks, or even flash or
grit between the bed and headstock? Loosen the headstock and check,
clean it, but I certainly would not attempt to machine it.

Will you enjoy your new machine and be satisfied over the life of your
lathe knowing it's imperfect to some degree? Does the mismatch vary
along the bed length? Is the mismatch amplified enough on long spindles
to matter? Is vertical displacement different from horizontal?

You might try different centers and see if the tail center makes a
circle and if so how big, instead of a dot on the tail end of blanks of
different lengths. I doubt that you could hold a tool on the rest with
enough precision to check for taper along the ways as machinists do.

In the end I guess it boils down to your personal feelings about a
slightly imperfect brand new expensive machine that you will be using
for some time. There are probably worse imperfections in your shop.
There sure are in mine.


Turn to Safety, Arch
Fortiter


http://community.webtv.net/almcc/MacsMusings

On Jun 9, 7:52 am, (Arch) wrote:

In the end I guess it boils down to your personal feelings about a
slightly imperfect brand new expensive machine that you will be using
for some time.

I would try turning on it, and see if I could turn the way I wanted to
using the machine. I have two Jet minis, and never checked them since
they do fine. Besides, it has been so long since they have seen new
drive spurs or centers I would have to buy one of those machined
gizmos to check it.

There are probably worse imperfections in your shop.
There sure are in mine.

I'm right there with you, Arch. In my case, your humble scribe is the
worst defect in the lot!

Robert

On Sun, 8 Jun 2008 23:03:45 -0700, "Lynn" wrote:

Humble request for advise (or sympathy):
Just unboxed my new Jet 1014 and while checking it over,
noted that the alignment of the tips of the headstock and
tailstock centers is not perfect. The tailstock center is perhaps
.010 or .012 inch lower than the headstock center. This
is when the tailstock is moved right up close to the spindle.
I've read somewhere, probably on this newsgroup,
that when a tailstock center is tightened onto or into a
piece of wood, that the tailstock center has some tendency
to raise up. Depending of course on the bed's rigidity and
the tailstock stiffness as well.
My question, then, from anyone who might have encountered
about this type and amount of misalignment in a wood lathe,
should I worry?
Jiggling things around does not seem to alter this alignment
at all, and correcting this error would probably involve milling
a few thousandths off the headstock base. Something I'm not
very good at with my file and emery cloth!

Old Chief Lynn

As the others have said, that's not enough variance to matter, unless it was a
metal lathe and you were making aerospace stuff..
Also, the alignment can appear different from different viewing heights and
angles.. It can make you crazy..lol
I put a piece of cardboard between centers and gently advance the tailstock
ram..
Then, you can "read" the holes.. If I can see only one place that the light
shines through, I'm happy..

Remember when checking.. Both centers must be firmly seated in clean Morse
tapers and the headstock and tailstock locked down..


mac

Please remove splinters before emailing

10 thou shim brass araldited to the underside of the sliding tailstock?A bit
Heath Robinson, but it would work. I would have thought first stop should be
a phone call to the supplier. Only if they refuse to do anything about it
would I try any home repairs.
"Lynn" wrote in message
...
Humble request for advise (or sympathy):
Just unboxed my new Jet 1014 and while checking it over,
noted that the alignment of the tips of the headstock and
tailstock centers is not perfect. The tailstock center is perhaps
.010 or .012 inch lower than the headstock center. This
is when the tailstock is moved right up close to the spindle.
I've read somewhere, probably on this newsgroup,
that when a tailstock center is tightened onto or into a
piece of wood, that the tailstock center has some tendency
to raise up. Depending of course on the bed's rigidity and
the tailstock stiffness as well.
My question, then, from anyone who might have encountered
about this type and amount of misalignment in a wood lathe,
should I worry?
Jiggling things around does not seem to alter this alignment
at all, and correcting this error would probably involve milling
a few thousandths off the headstock base. Something I'm not
very good at with my file and emery cloth!

Old Chief Lynn

"Lynn" wrote in message
...
Humble request for advise (or sympathy): Just unboxed my new Jet 1014
and while checking it over,
noted that the alignment of the tips of the headstock and
tailstock centers is not perfect. The tailstock center is perhaps
.010 or .012 inch lower than the headstock center. This
is when the tailstock is moved right up close to the spindle.



lynn - believe it or not, cast iron flexes - it is possible that the way the
lathe is bolted to the stand is flexing the ways - this is certainly an
issue with larger lathes (such as my 1200 pound metal lathe), so it could
certainly affect yours


** Posted from http://www.teranews.com **

On Mon, 9 Jun 2008 20:41:03 -0700, "William Noble" wrote:

lynn - believe it or not, cast iron flexes - it is possible that the way the
lathe is bolted to the stand is flexing the ways - this is certainly an
issue with larger lathes (such as my 1200 pound metal lathe), so it could
certainly affect yours


Good point, Bill..
There is also a bit of flex on all of my lathes when the tail stock spindle is
extended.. I sort of expect that and try to get as close as I can to the work
before extending the tail stock to apply pressure to the piece..


mac

Please remove splinters before emailing

Thanks to all for the wealth of experienced advice.
There are few groups that share so readily.

After reading those responses, and doing some actual thinking (!), I'll
probably
just ignore my alignment imperfection.
However, putting some thoughts together, I think that what actually
caused the
head and tail stock centers misalignment is worth considering.

How true, that iron is not perfectly rigid.

But if misalignment is apparent, and the axis of both the spindle and
tailstock
are exactly parallel, that would be one case. (a difference in the height
from the bed)
But suppose the misalignment was due to either the spindle or tailstock not
being
perfectly parallel to the bed. Were the headstock (spindle) not exactly
parallel to the
bed, then it seems like the further the tail is from the head, the worse the
problem
could be. Does that make sense?

I suppose that my Jet with a 14" bed, that won't be enough to worry
about.

Thanks again,
Old Chief Lynn

On Jun 10, 12:17 pm, "Lynn" wrote:

After reading those responses, and doing some actual thinking (!), I'll
probably
just ignore my alignment imperfection.

But then you put this really large *BUT* in there...

However, putting some thoughts together, I think that what actually
caused the
head and tail stock centers misalignment is worth considering.

But if misalignment is apparent, and the axis of both the spindle and
tailstock
are exactly parallel, that would be one case. (a difference in the height
from the bed)
But suppose the misalignment was due to either the spindle or tailstock not
being
perfectly parallel to the bed. Were the headstock (spindle) not exactly
parallel to the
bed, then it seems like the further the tail is from the head, the worse the
problem
could be. Does that make sense?

Absolutely NOT. Totally unfounded. This is a false trigonometric
argument. PERIOD.

This is not a compounding, cumulative error. This error could only be
of a multiplicative nature IF one end of the extrapolated triangle was
WAS set, and the other was NOT set.

You have nattered this math problem down to the point you are chewing
on the bones.

Let me try it this way:

Imagine yourself standing in front of your lathe with the headstock on
the left hand side. We are not looking at bowls, winged shapes,
warped and punky wood, offset turnings, etc. For purposes of
illustration, think of a round piece of hard maple spindle stock.

Say your headstock/tailstock (now known as hs/ts) is out of alignment
of a perfect center by 1/100 in one inch. That would mean that if
one side was perfectly stationary, then in two inches it would be
2/100 (I know, 1/50th). At 3 inches, 3/100ths, and so on and so on.
Then you get to 14 inches, which is the max working length between
centers on your lathe.

WITHOUT the end ts being secured (remember, working left to right) you
would have a cumulative effect of being 14/100ths ( a little more than
1/16th of an inch ) off center.

BUT BUT BUT.... your ts holds the piece in place, at near perfect
coeccentricity at the ts. In your case, the difference at the hs/ts
detail is about 1/100. This means that at the other side of the two
FIXED revolving axises of the lathe, it is still only 1/100.

Don't believe me on how little this matters?

Think about it this way. When you turn a spindle, you are moving your
piece into a concentric shape with every pass. So try this:

Make a temp gauge that is 1" in diameter (a one inch wrench will do
fine), or use a good set of calipers. Take a piece of wood about a
foot long or so, and secure it between centers. This long piece will
help you understand why the effect doesn't multiply.

Round this piece of wood carefully, until you get it a perfect one
inch diameter from hs to ts.

Wasn't that hard, right?

Where did the difference or cumulative error go? It went nowhere
because there isn't any!

(In case anyone is actually reading this... the error would show up on
the ends as the surfaces perpendicular to the error.)

The important thing to remember is that YOU will establish a round,
coeccentric shape every time you turn. By the nature of the lathe,
you are spinning the wood on an axis determined by you. You
establish a new line of coeccentricity.
The lathe spins the wood on that axis, and that is all there is. With
both sides of your line secured, there is simply no way for the error
to accumulate or compound.

Besides, since you are looking at this with your machinist's
micrometers and calipers, how do you secure your wood to the lathe?
Do you use a spur and tailstock revolving center? When you attach or
suspend your piece to the lathe, is your technique such that you can
gauge both sides (hs/ts) to less than 1/64 of an inch difference in
penetration to hold that piece perfectly.

I doubt it.

And once again, it doesn't matter if you did. The sides are the
bearing/holding points for a piece of spindle work. When you turn it
round, you have brought it into round, the level of perfection being
your limitations as a turner.

But while you are nattering this problem into tiny pieces, think about
this: NONE of this matters (even for a hypothetical argument) if you
get a piece of wood that had dried unevenly, has hard spots or voids,
is kind of green, it is reacts quickly to exposure to air, has a few
knots, is left on the lathe overnight, has hidden bug tunnels in it,
and on an on. All of those things will throw your piece out of round
by affecting the density of the wood in different areas of the piece.
THAT is what you watch for.

You are over thinking this. Go outside, put some wood in the lathe
and turn a spindle every way you can to see if you can get it to screw
up.
It won't happen.

Enjoy your lathe. These are nice machines. I have two, and do almost
all my turning on them and have for years. Don't ruin this for
yourself by dwelling on pointless details that in the end don't
matter.

Robert

After reading those responses, and doing some actual thinking (!),
I'll
probably
just ignore my alignment imperfection.

But then you put this really large *BUT* in there...

However, putting some thoughts together, I think that what actually
caused the
head and tail stock centers misalignment is worth considering.

But if misalignment is apparent, and the axis of both the spindle
and
tailstock
are exactly parallel, that would be one case. (a difference in the height
from the bed)
But suppose the misalignment was due to either the spindle or tailstock
not
being
perfectly parallel to the bed. Were the headstock (spindle) not exactly
parallel to the
bed, then it seems like the further the tail is from the head, the worse
the
problem
could be. Does that make sense?

Absolutely NOT. Totally unfounded. This is a false trigonometric
argument. PERIOD.

This is not a compounding, cumulative error. This error could only be
of a multiplicative nature IF one end of the extrapolated triangle was
WAS set, and the other was NOT set.

You have nattered this math problem down to the point you are chewing
on the bones.

Let me try it this way:

Imagine yourself standing in front of your lathe with the headstock on
the left hand side. We are not looking at bowls, winged shapes,
warped and punky wood, offset turnings, etc. For purposes of
illustration, think of a round piece of hard maple spindle stock.

Say your headstock/tailstock (now known as hs/ts) is out of alignment
of a perfect center by 1/100 in one inch. That would mean that if
one side was perfectly stationary, then in two inches it would be
2/100 (I know, 1/50th). At 3 inches, 3/100ths, and so on and so on.
Then you get to 14 inches, which is the max working length between
centers on your lathe.

WITHOUT the end ts being secured (remember, working left to right) you
would have a cumulative effect of being 14/100ths ( a little more than
1/16th of an inch ) off center.

BUT BUT BUT.... your ts holds the piece in place, at near perfect
coeccentricity at the ts. In your case, the difference at the hs/ts
detail is about 1/100. This means that at the other side of the two
FIXED revolving axises of the lathe, it is still only 1/100.

Don't believe me on how little this matters?

Think about it this way. When you turn a spindle, you are moving your
piece into a concentric shape with every pass. So try this:

Make a temp gauge that is 1" in diameter (a one inch wrench will do
fine), or use a good set of calipers. Take a piece of wood about a
foot long or so, and secure it between centers. This long piece will
help you understand why the effect doesn't multiply.

Round this piece of wood carefully, until you get it a perfect one
inch diameter from hs to ts.

Wasn't that hard, right?

Where did the difference or cumulative error go? It went nowhere
because there isn't any!

(In case anyone is actually reading this... the error would show up on
the ends as the surfaces perpendicular to the error.)

The important thing to remember is that YOU will establish a round,
coeccentric shape every time you turn. By the nature of the lathe,
you are spinning the wood on an axis determined by you. You
establish a new line of coeccentricity.
The lathe spins the wood on that axis, and that is all there is. With
both sides of your line secured, there is simply no way for the error
to accumulate or compound.

Besides, since you are looking at this with your machinist's
micrometers and calipers, how do you secure your wood to the lathe?
Do you use a spur and tailstock revolving center? When you attach or
suspend your piece to the lathe, is your technique such that you can
gauge both sides (hs/ts) to less than 1/64 of an inch difference in
penetration to hold that piece perfectly.

I doubt it.

And once again, it doesn't matter if you did. The sides are the
bearing/holding points for a piece of spindle work. When you turn it
round, you have brought it into round, the level of perfection being
your limitations as a turner.

But while you are nattering this problem into tiny pieces, think about
this: NONE of this matters (even for a hypothetical argument) if you
get a piece of wood that had dried unevenly, has hard spots or voids,
is kind of green, it is reacts quickly to exposure to air, has a few
knots, is left on the lathe overnight, has hidden bug tunnels in it,
and on an on. All of those things will throw your piece out of round
by affecting the density of the wood in different areas of the piece.
THAT is what you watch for.

You are over thinking this. Go outside, put some wood in the lathe
and turn a spindle every way you can to see if you can get it to screw
up.
It won't happen.

Enjoy your lathe. These are nice machines. I have two, and do almost
all my turning on them and have for years. Don't ruin this for
yourself by dwelling on pointless details that in the end don't
matter.
Robert

Great, Robert! I intend to take your advise, "Don't ruin this for
yourself by dwelling on pointless details that in the end don't
matter.".

I do follow your explanations well, and I guess if the spur drive
is being used, there would be sufficient flexibility to take care of any
very small misalignment.

BUT (again), help me, if you are still reading, to understand what is
occurring
if a longish piece of stock is clamped solidly in the chuck (hs), and
turning slowly.
(ts end not yet secured) Now the stock is turning on an axis established by
the
spindle. Due to the slight misalignment problem, that stock's ts end axis
does
not point at the ts's center! If the ts's center is now cranked into the
stock, it appears
that something has to give. I imagine the ts's center would wallow in an
enlarged
center hole, or the stock would have to flex.

Old Chief Lynn (whose trig is but a stack of dusty, unused books)

Lynn wrote:
Were the headstock (spindle) not exactly
: parallel to the
: bed, then it seems like the further the tail is from the head, the worse the
: problem
: could be. Does that make sense?

I think it's the other way around. The further apart the two centers are,
the less the difference between (a) the line from one center parallel to
the bed, and (b) the line between the tips of the two centers.


And I don't think the lack of parallel you mention in your original note
matters.


-- Andy Barss

The issue here is the students have not gotten all the data, and the
data given is not fully defined.

Lets take a new out of the box lathe.

Lets let the bed season and settle while coming to temperature.

Then we level the lathe. Across and end to end. Jacking the feet as
needed to become true. [ in this process you might loosen the leg bolts
to allow movement. ]

Settle again and re-true. Beds gets stressed all the time if not proper.

Then and only then can we start looking at a center to center head to tail.

If not level in both x & y directions or if you didn't get it done completely:
If there is a bed warp or twist the tail center will float all around if
measured from a constant head stock or a line or standard off the lathe.

If a lathe is level - wood lathes normally need less, but if one does precision
work - work with precision tools and instruments.

If level then check center to center.

If the tail stock is offset 1" to one side or the other then tapers (massive
ones) can be cut. Normally the offset is much less as it in effect doubles.

So in-line is important - when working with projects like pool queues or
drum sticks or other thin spindle or bowl edge. You want to put in the
taper you want, not what the offset does.

Up and down offset means the lathe wasn't manufactured correctly.

With luck the tail stock is split and allows sheet shim stock (brass or Steel)
to be placed in order to lift up one or the other end. Or the headstock...

The lateral offset is by two setscrews on the tailstock.

I own bot Metal and Wood lathes and use both.

Martin

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


wrote:
On Jun 10, 12:17 pm, "Lynn" wrote:

After reading those responses, and doing some actual thinking (!), I'll
probably
just ignore my alignment imperfection.

But then you put this really large *BUT* in there...

However, putting some thoughts together, I think that what actually
caused the
head and tail stock centers misalignment is worth considering.

But if misalignment is apparent, and the axis of both the spindle and
tailstock
are exactly parallel, that would be one case. (a difference in the height
from the bed)
But suppose the misalignment was due to either the spindle or tailstock not
being
perfectly parallel to the bed. Were the headstock (spindle) not exactly
parallel to the
bed, then it seems like the further the tail is from the head, the worse the
problem
could be. Does that make sense?

Absolutely NOT. Totally unfounded. This is a false trigonometric
argument. PERIOD.

This is not a compounding, cumulative error. This error could only be
of a multiplicative nature IF one end of the extrapolated triangle was
WAS set, and the other was NOT set.

You have nattered this math problem down to the point you are chewing
on the bones.

Let me try it this way:

Imagine yourself standing in front of your lathe with the headstock on
the left hand side. We are not looking at bowls, winged shapes,
warped and punky wood, offset turnings, etc. For purposes of
illustration, think of a round piece of hard maple spindle stock.

Say your headstock/tailstock (now known as hs/ts) is out of alignment
of a perfect center by 1/100 in one inch. That would mean that if
one side was perfectly stationary, then in two inches it would be
2/100 (I know, 1/50th). At 3 inches, 3/100ths, and so on and so on.
Then you get to 14 inches, which is the max working length between
centers on your lathe.

WITHOUT the end ts being secured (remember, working left to right) you
would have a cumulative effect of being 14/100ths ( a little more than
1/16th of an inch ) off center.

BUT BUT BUT.... your ts holds the piece in place, at near perfect
coeccentricity at the ts. In your case, the difference at the hs/ts
detail is about 1/100. This means that at the other side of the two
FIXED revolving axises of the lathe, it is still only 1/100.

Don't believe me on how little this matters?

Think about it this way. When you turn a spindle, you are moving your
piece into a concentric shape with every pass. So try this:

Make a temp gauge that is 1" in diameter (a one inch wrench will do
fine), or use a good set of calipers. Take a piece of wood about a
foot long or so, and secure it between centers. This long piece will
help you understand why the effect doesn't multiply.

Round this piece of wood carefully, until you get it a perfect one
inch diameter from hs to ts.

Wasn't that hard, right?

Where did the difference or cumulative error go? It went nowhere
because there isn't any!

(In case anyone is actually reading this... the error would show up on
the ends as the surfaces perpendicular to the error.)

The important thing to remember is that YOU will establish a round,
coeccentric shape every time you turn. By the nature of the lathe,
you are spinning the wood on an axis determined by you. You
establish a new line of coeccentricity.
The lathe spins the wood on that axis, and that is all there is. With
both sides of your line secured, there is simply no way for the error
to accumulate or compound.

Besides, since you are looking at this with your machinist's
micrometers and calipers, how do you secure your wood to the lathe?
Do you use a spur and tailstock revolving center? When you attach or
suspend your piece to the lathe, is your technique such that you can
gauge both sides (hs/ts) to less than 1/64 of an inch difference in
penetration to hold that piece perfectly.

I doubt it.

And once again, it doesn't matter if you did. The sides are the
bearing/holding points for a piece of spindle work. When you turn it
round, you have brought it into round, the level of perfection being
your limitations as a turner.

But while you are nattering this problem into tiny pieces, think about
this: NONE of this matters (even for a hypothetical argument) if you
get a piece of wood that had dried unevenly, has hard spots or voids,
is kind of green, it is reacts quickly to exposure to air, has a few
knots, is left on the lathe overnight, has hidden bug tunnels in it,
and on an on. All of those things will throw your piece out of round
by affecting the density of the wood in different areas of the piece.
THAT is what you watch for.

You are over thinking this. Go outside, put some wood in the lathe
and turn a spindle every way you can to see if you can get it to screw
up.
It won't happen.

Enjoy your lathe. These are nice machines. I have two, and do almost
all my turning on them and have for years. Don't ruin this for
yourself by dwelling on pointless details that in the end don't
matter.

Robert



----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.pronews.com The #1 Newsgroup Service in the World! 100,000 Newsgroups
---= - Total Privacy via Encryption =---

Lynn got it also.

On tapers - you can find tail stock centers on a bar. A morse taper on
one side, A heavy bar on the other end with fixed center points at various
offsets. Prevents jacking with the tail stock.
Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


Lynn wrote:



After reading those responses, and doing some actual thinking
(!), I'll
probably
just ignore my alignment imperfection.

But then you put this really large *BUT* in there...

However, putting some thoughts together, I think that what actually
caused the
head and tail stock centers misalignment is worth considering.

But if misalignment is apparent, and the axis of both the
spindle and
tailstock
are exactly parallel, that would be one case. (a difference in the
height
from the bed)
But suppose the misalignment was due to either the spindle or
tailstock not
being
perfectly parallel to the bed. Were the headstock (spindle) not exactly
parallel to the
bed, then it seems like the further the tail is from the head, the
worse the
problem
could be. Does that make sense?

Absolutely NOT. Totally unfounded. This is a false trigonometric
argument. PERIOD.

This is not a compounding, cumulative error. This error could only be
of a multiplicative nature IF one end of the extrapolated triangle was
WAS set, and the other was NOT set.

You have nattered this math problem down to the point you are chewing
on the bones.

Let me try it this way:

Imagine yourself standing in front of your lathe with the headstock on
the left hand side. We are not looking at bowls, winged shapes,
warped and punky wood, offset turnings, etc. For purposes of
illustration, think of a round piece of hard maple spindle stock.

Say your headstock/tailstock (now known as hs/ts) is out of alignment
of a perfect center by 1/100 in one inch. That would mean that if
one side was perfectly stationary, then in two inches it would be
2/100 (I know, 1/50th). At 3 inches, 3/100ths, and so on and so on.
Then you get to 14 inches, which is the max working length between
centers on your lathe.

WITHOUT the end ts being secured (remember, working left to right) you
would have a cumulative effect of being 14/100ths ( a little more than
1/16th of an inch ) off center.

BUT BUT BUT.... your ts holds the piece in place, at near perfect
coeccentricity at the ts. In your case, the difference at the hs/ts
detail is about 1/100. This means that at the other side of the two
FIXED revolving axises of the lathe, it is still only 1/100.

Don't believe me on how little this matters?

Think about it this way. When you turn a spindle, you are moving your
piece into a concentric shape with every pass. So try this:

Make a temp gauge that is 1" in diameter (a one inch wrench will do
fine), or use a good set of calipers. Take a piece of wood about a
foot long or so, and secure it between centers. This long piece will
help you understand why the effect doesn't multiply.

Round this piece of wood carefully, until you get it a perfect one
inch diameter from hs to ts.

Wasn't that hard, right?

Where did the difference or cumulative error go? It went nowhere
because there isn't any!

(In case anyone is actually reading this... the error would show up on
the ends as the surfaces perpendicular to the error.)

The important thing to remember is that YOU will establish a round,
coeccentric shape every time you turn. By the nature of the lathe,
you are spinning the wood on an axis determined by you. You
establish a new line of coeccentricity.
The lathe spins the wood on that axis, and that is all there is. With
both sides of your line secured, there is simply no way for the error
to accumulate or compound.

Besides, since you are looking at this with your machinist's
micrometers and calipers, how do you secure your wood to the lathe?
Do you use a spur and tailstock revolving center? When you attach or
suspend your piece to the lathe, is your technique such that you can
gauge both sides (hs/ts) to less than 1/64 of an inch difference in
penetration to hold that piece perfectly.

I doubt it.

And once again, it doesn't matter if you did. The sides are the
bearing/holding points for a piece of spindle work. When you turn it
round, you have brought it into round, the level of perfection being
your limitations as a turner.

But while you are nattering this problem into tiny pieces, think about
this: NONE of this matters (even for a hypothetical argument) if you
get a piece of wood that had dried unevenly, has hard spots or voids,
is kind of green, it is reacts quickly to exposure to air, has a few
knots, is left on the lathe overnight, has hidden bug tunnels in it,
and on an on. All of those things will throw your piece out of round
by affecting the density of the wood in different areas of the piece.
THAT is what you watch for.

You are over thinking this. Go outside, put some wood in the lathe
and turn a spindle every way you can to see if you can get it to screw
up.
It won't happen.

Enjoy your lathe. These are nice machines. I have two, and do almost
all my turning on them and have for years. Don't ruin this for
yourself by dwelling on pointless details that in the end don't
matter.
Robert

Great, Robert! I intend to take your advise, "Don't ruin this for
yourself by dwelling on pointless details that in the end don't
matter.".

I do follow your explanations well, and I guess if the spur drive
is being used, there would be sufficient flexibility to take care of any
very small misalignment.

BUT (again), help me, if you are still reading, to understand what is
occurring
if a longish piece of stock is clamped solidly in the chuck (hs), and
turning slowly.
(ts end not yet secured) Now the stock is turning on an axis established
by the
spindle. Due to the slight misalignment problem, that stock's ts end
axis does
not point at the ts's center! If the ts's center is now cranked into the
stock, it appears
that something has to give. I imagine the ts's center would wallow in an
enlarged
center hole, or the stock would have to flex.

Old Chief Lynn (whose trig is but a stack of dusty, unused books)






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On Jun 10, 4:22 pm, "Lynn" wrote:

BUT (again), help me, if you are still reading, to understand what is
occurring
if a longish piece of stock is clamped solidly in the chuck (hs), and
turning slowly.
(ts end not yet secured) Now the stock is turning on an axis established by
the
spindle. Due to the slight misalignment problem, that stock's ts end axis
does
not point at the ts's center! If the ts's center is now cranked into the
stock, it appears
that something has to give. I imagine the ts's center would wallow in an
enlarged
center hole, or the stock would have to flex.

OK, this is getting silly.

Worse, you have now completely changed the entire parameters of why
you were checking the tailstock. Are you going to use a CHUCK now,
which was not mentioned until this post?

If you are worried about your hs/ts lining up, that is one issue. I
am guess you didn't try the experiment I suggested, but just sat down
with another question and banged it off.

Now you slide in another problem/question altogether with your
mounting procedure into a chuck. REREAD my earlier post. I explained
that since BOTH SIDES ARE SECURED IN A SPINDLE (not specified, but
you know they centered with a pin) ---- BOTH sides ---- that it
won't matter. Think about it.

Now you are asking if a piece flopping around in a chuck will
accurately line up with a ts. You want to know if a piece that is
chucked up to reflect the ENTIRE amount of difference will line up
perfectly with the tailstock. Short answer: NO. The chuck will be on
center with the headstock, not necessarily the center of the ts. But
there are so many other factors when using a chuck that you can't
cover them all. Compression of a tenon, expansion in a dovetail,
different hardness of woods, and on and on.

And if this is a practical question of concern, make you check your
scroll chuck first before asking this question of yourself. Is it
also PERFECTLY perpendicular to a couple of thousands across its
face? Since it is now part of the equation now, take it to a
machinist that can measure its accuracy reflective of its relation to
the spindle, not to itself.

Regardless, if you are going to turn a spindle, you use both sides of
the lathe. If you are turning a shape that requires a chuck, it is
good technique to push the ts up to it until it registers well in
order to supply additional support. But once you are roughed to where
you are satisfied that you can refine the shape more to your liking,
you remove the tailstock and it is no longer a factor. You know are
using your lathe as a bowl lathe. They have no tailstock at all.

The whole point of the chuck is to not use the tailstock for certain
shapes. After you rough your piece of wood, then you remove your ts
so you can hollow a bowl, dish, platter, or anything else in those
genres. There is NO point to turning spindles with the chuck.

But, it is late. This is my last attempt, so let's be even more
absurd with this. Let's back all the way away from practicality and
good sense and focus hard in on the trig part again.

Let's say your hs/ts is out of alignment (for heaven's sake... just
one direction of the point of concentric perfection) 1/4 of an inch
over an inch. That means in 12 inches, it will be out 3 inches! If
you mark your piece of wood accurately and place a dimple to
accurately seat the point of both the pins on each side of the hs/ts,
you will see that at a 3" difference, the one side or the other, or
both, will not SEAT properly on the wood. You will see 3" difference
in a foot, I assure you.

And yes, if you start it up and turn it, it will wallow out both
sides.

On the other hand, why do you think the ts does not have teeth on its
revolving center? IT IS MADE to take up the tiny bit (in your case
about 1/100 th of an inch) that your piece will be off. And this is
also why it is good practice to adjust the revolving center until it
seats against the face of the center. You don't put the point only in
unless you have a rounded piece and you are finishing up your turning,
or it is so lightweight and fragile you are worried about breaking
your piece. Riding on a good bearing, the tailstock will compensate
easily for that little bit and much more that your alignment *might*
be off.

And you are fretting over a piece of wood that would be the most
perfect piece in the world to achieve machinist's tolerances. I have
never seen or turned that piece of wood, and I have turned several
cords of the stuff. You will be farther out of alignment after your
turn your piece for a while than you will ever believe until you start
checking it as you go.

And actually, you still don't know what your actual "problem" is or if
you even have one. All you did was push the centers together and
measure. You still don't know if it is and actual alignment problem,
or your center or spur, or if each or out a little to combine (say
5/1000ths each side) to have this difference. That's right, each side
could be out .005 of an inch to get what you are seeing. For
reference, this is just a little thicker than a dollar bill.

I will try to be plain. Your little hundreth doesn't amount to an ant
pile of crap. Your 1/100th won't show up ever when you turn spindles,
which is the only reason you check hs/ts alignment. It isn't
necessary when you chuck or faceplate turn.

Your second hypothesis is not a valid test for the lathe as it is not
proper use of the accessories. When you use the ts with your chuck,
it will be to hold an unruly piece until it becomes manageable with
some rounding. You don't use a chuck to turn between centers as that
is not its purpose. If you are turning a 5 pound piece of wood that
you have chucked with the intentions of making a bowl, platter, plate,
or anything else like that, you won't notice your 1/100th anywhere, I
promise.

Since you will probably take this down another rabbit trail, you can
exchange "chuck" for faceplate and all principles of geometry and
motion will apply equally as well.

I do hope you make it to the shop one day and try out your machine.
AND WHEN YOU ARE HAPPY WITH IT, I hope you let us know as well.

Done.

Robert

I don't have enough sense not to add to such an exciting thread. So
for my two net friends: For Robert, I take your point and retract my
previous confusing post mixing offset turning on an axis parallel to the
bed with an angled axis. For the old Chief, re your humble request for
optional sympathy, you have mine.

Anyway, you're gonna love that little lathe. but you probably shouldn't
begin by making eccentric turnings. (there I go again)


Turn to Safety, Arch
Fortiter


http://community.webtv.net/almcc/MacsMusings

Thanks, Robert,
You have been more than generous in explaining the
difference between impractical thinking (mine) and
doing.
I've gradually progressed (over the past 70 years) from
dad's Sears Dunlap lathe, with tools I ground from old
files, to my homemade, then a Grizzly (best of all, so far),
and now this little Jet.
.........Caution, Robert, another "rabbit trail": .......... My concern
with alignment probably grew from tinkering with my shop's
little "pre-war" Dunlap metal turning lathe. In the late 1940's
I "horsetraded" it from a fussy machinist who spent many
hours trying to make it perfect......... but failed. I never mastered
it, but learned to appreciate those who could perform miracles
with greasy machinery.
Cheers, Robert, and thanks for taking the time to send
me back to the shop.

Old Chief Lynn

On Jun 11, 10:53 am, "Lynn" wrote:

Cheers, Robert, and thanks for taking the time to send
me back to the shop.

Anytime. The last post may have sounded a bit cranky, but not
intended that way.

It is difficult to try to explain something in writing that would take
a few minutes in person. I am glad I could help.

Now.... remember this... when the next guy comes along and you can
help, you're up!

;^)

Robert

On Jun 11, 10:26 am, (Arch) wrote:
I don't have enough sense not to add to such an exciting thread. So
for my two net friends: For Robert, I take your point and retract my
previous confusing post mixing offset turning on an axis parallel to the
bed with an angled axis. For the old Chief, re your humble request for
optional sympathy, you have mine.

You do make me laugh, good sir. When I read your post I was laughing
out loud.

Still snickering, too...

Robert