I think I've figured out a big piece of the mystery of what I
generically called chatter in the "Clausing 5914 Chatter ..." threads.

Tightening the lathe dovetails up helped a great deal, and is a good
idea in general, but didn't really solve the problem.

It came to me in the shower Wednesday morning - self-feeding would
explain just about everything seen, and that if one reverses something,
the sign of the mechanical feedback loop can be reversed. Now the
feedback is positive, yielding the vicious loop that causes visible
tilting, flake chips, and breakage. By contrast, negative feedback
causes stability.

The key experiment was to try face grooving a 2.125" diameter 6061
aluminum slug held in the 4-jaw chuck, and using the BXA-6 toolholder
with the huge overhang (~5" from cutting edge to toolpost center) but
with the tool bit held upsidedown and the lathe running in reverse.
Running backwards cases the self-feeding effect to change sign, becoming
a self-unloading effect as the toolpost tilts away from the workpiece,
reducing the bite of the tool bit.

Now I can peel very thin chips off the plate while face grooving,
although it is still necessary to use the back gear, and there was mucho
squealing. I did it dry, with too much overhang, and without properly
shaping the tool bit. But it worked anyway. The difference is
night-and-day.

So I now think it was the tendency to self-feed that caused all the
problems, even if the self-feeding effect wasn't so powerful as to cause
visible tilting of the toolpost. The squealing will go away with a
stiffer method of holding the tool bit, and perhaps a better-shaped bit.


This also applies to parting off, and specifically explains why using an
upsidedown blade coming towards the back of the workpiece, or coming
from the front with the lathe running backwards, works. (BXA-7R)

I never really believed the theory that better chip removal was why
upsidedown cutoff blades worked better, because I had problems even when
there were no chip wads to be found and the groove sidewalls were clean.
Actually, the galloping chatter tended to throw thick flake chips far
and wide, so they were everywhere but in the groove.

To summarize, there are two elements that are necessary for face
grooving, trepanning, and parting off on the Clausing 5914 lathe: Use
the back gear (for tortional rigidity), and use an upsidedown tool bit
(for stability).


As for use of a coaxial boring bar to hold a grooving/trepanning
toolbit, it turns out to be a common method. I found it mentioned in US
Patent 5,640,890 as prior art to be improved upon. The patentee is
trepanning stainless steel hydraulic hose fittings in production, and
needed a method that worked in a screw machine of some kind.


Joe Gwinn

Joseph Gwinn wrote:
I think I've figured out a big piece of the mystery of what I
generically called chatter in the "Clausing 5914 Chatter ..." threads.

Tightening the lathe dovetails up helped a great deal, and is a good
idea in general, but didn't really solve the problem.

It came to me in the shower Wednesday morning - self-feeding would
explain just about everything seen, and that if one reverses something,
the sign of the mechanical feedback loop can be reversed.
Yes, of course, you are dead right! But, proper serup of the
tool and how it relates to the toolpost, compound swivel, etc.
can make a big difference. You mentioned in an earlier post, I
think, that interference with the chuck jaws required you to
have so much overhang, so that points out that better work
holding would reduce the problem.

I had some real problems doing these types of operations on
Atlas/Craftsman lathes. The 5914 is a MUCH sturdier lathe with
a much heavier bed casting, so I'm surprised you were having
this sort of trouble. I finally traded up to a Sheldon R15-6,
which is an even heavier lathe, in the 3000 - 3500 Lb class.
You can stand on the bed with no measurable deflection (and I
have precision electronic levels that are REALLY sensitive).
It is amazing what a difference stiffness of the lathe makes.
Now, another comment is that you may have a poor "fit up"
between your carriage and bed. I totally rescraped my bed and
carriage to get the best fit between these surfaces. In my
case, due to the hardened bed, I had to grind it with Cratex
polishing wheels and then lap it smooth with bench stones.
(A carbide scraper blade wouldn't even SCRATCH the bed.)
I then used Moglice castable way liner to make the underside of
the carriage conform to the bed.

But, after all that work, I have no problem parting-off or with
other jobs where there is a bit of overhang. I haven't done
anything with quite as much overhang as you needed on this jb,
but my guess is there is somthing in your lathe that is "not
right" and allowing maybe the carriage to rock about some local
high points. Sometimes you can see this if you take the way
wipers off. You might be able to see the oil fillet between the
bed and carriage "pulse" a bit as force is applied to the
carriage. That is a dead giveaway that the carriage is rocking.

Jon

On 2008-05-01, Jon Elson wrote:
Joseph Gwinn wrote:
I think I've figured out a big piece of the mystery of what I
generically called chatter in the "Clausing 5914 Chatter ..." threads.

Tightening the lathe dovetails up helped a great deal, and is a good
idea in general, but didn't really solve the problem.

It came to me in the shower Wednesday morning - self-feeding would
explain just about everything seen, and that if one reverses something,
the sign of the mechanical feedback loop can be reversed.

[ ... ]

I had some real problems doing these types of operations on
Atlas/Craftsman lathes. The 5914 is a MUCH sturdier lathe with
a much heavier bed casting, so I'm surprised you were having
this sort of trouble.
As am I. I've got the 5418 (similar bed profile, but manual
change belts), and have very little chatter.

I finally traded up to a Sheldon R15-6,
which is an even heavier lathe, in the 3000 - 3500 Lb class.
You can stand on the bed with no measurable deflection (and I
have precision electronic levels that are REALLY sensitive).
It is amazing what a difference stiffness of the lathe makes.
Now, another comment is that you may have a poor "fit up"
between your carriage and bed.

You know -- there is one other possibility which occurs to me.
I presume that your lathe, like mine, has the hollow level adjusting
screws in the feet of the bed through which pass the bolts to lock it
down to the stand. If you have something like the near side bolt loose
and the level adjusting screw a little clear of the stand, the bed would
wind up under torque, which could give you similar behavior.

Did you get a proper sensitive level and adjust the bed to
proper level at both headstock and tailstock end? (I did.) After that,
did you make sure that the hold-down bolts were tight (and didn't
disturb the leveling)? *This* may be where your flex is -- especially
since you have a longer bed than I do (I believe), and thus more total
flex possibility.

Get it chattering and feel each foot with the adjacent finger on
the stand so you can detect relative motion between them. If you find
any, you'll need to tighten the hold-down bolts, and probably re-level
the bed.

Good Luck,
DoN.

--
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 ---

In article ,
"DoN. Nichols" wrote:

On 2008-05-01, Jon Elson wrote:
Joseph Gwinn wrote:
I think I've figured out a big piece of the mystery of what I
generically called chatter in the "Clausing 5914 Chatter ..." threads.

Tightening the lathe dovetails up helped a great deal, and is a good
idea in general, but didn't really solve the problem.

It came to me in the shower Wednesday morning - self-feeding would
explain just about everything seen, and that if one reverses something,
the sign of the mechanical feedback loop can be reversed.

[ ... ]

I had some real problems doing these types of operations on
Atlas/Craftsman lathes. The 5914 is a MUCH sturdier lathe with
a much heavier bed casting, so I'm surprised you were having
this sort of trouble.

As am I. I've got the 5418 (similar bed profile, but manual
change belts), and have very little chatter.

I finally traded up to a Sheldon R15-6,
which is an even heavier lathe, in the 3000 - 3500 Lb class.
You can stand on the bed with no measurable deflection (and I
have precision electronic levels that are REALLY sensitive).
It is amazing what a difference stiffness of the lathe makes.
Now, another comment is that you may have a poor "fit up"
between your carriage and bed.

You know -- there is one other possibility which occurs to me.
I presume that your lathe, like mine, has the hollow level adjusting
screws in the feet of the bed through which pass the bolts to lock it
down to the stand. If you have something like the near side bolt loose
and the level adjusting screw a little clear of the stand, the bed would
wind up under torque, which could give you similar behavior.

Do you mean the bolts between cabinet and the floor, or that hold the
headstock to the bed? I assume you mean between headstock and bed.


Did you get a proper sensitive level and adjust the bed to
proper level at both headstock and tailstock end? (I did.)

I do have such a level (Starrett model 98-6), and did level the bed by
adjustment of the leveling feet between cabinet and floor.


After that,
did you make sure that the hold-down bolts were tight (and didn't
disturb the leveling)? *This* may be where your flex is -- especially
since you have a longer bed than I do (I believe), and thus more total
flex possibility.

Hmm. This I did not think of, or check. But I will.

I don't see why bed length would matter, given that while trepanning all
the action happens within a foot of the chuck face.


Get it chattering and feel each foot with the adjacent finger on
the stand so you can detect relative motion between them. If you find
any, you'll need to tighten the hold-down bolts, and probably re-level
the bed.

What I'm not quite sure of is which bolts you mean. On the 5914, the
headstock is bolted to the bed with four solid 3/8-16 hex socket cap
screws and two clamp bars, and the bed is bolted to the head pedestal
foot, which is in turn bolted to the cabinet, all with solid
non-adjustable bolts. The only hollow bolts I know of are in the
leveling feet between cabinet and floor, which doesn't seem relevant to
chatter (versus inability to turn a cylinder due to bed twist).

I looked the the 5418 manual. Now I understand. The designs of 5914
and 5418 are very different in this area. But there is no harm in
making sure that all those bolts are nice and tight, especially those
holding headstock to bed.

I suspect that on the 5914 they just machined the mating surfaces of
cast iron components close enough that adjustment wasn't needed, and
that the two pedestal feet isolated the bed and headstock sufficiently
from the sheet metal cabinet and chip pan that adjusters were not
needed. Unlike the 5418 manual, in the 5914 manual, there is no
procedure for adjusting how the cast iron stuff rests upon the sheet
metal stuff.

Joe Gwinn

On 2008-05-02, Joseph Gwinn wrote:
In article ,
"DoN. Nichols" wrote:

On 2008-05-01, Jon Elson wrote:
Joseph Gwinn wrote:
I think I've figured out a big piece of the mystery of what I
generically called chatter in the "Clausing 5914 Chatter ..." threads.

[ ... ]

I had some real problems doing these types of operations on
Atlas/Craftsman lathes. The 5914 is a MUCH sturdier lathe with
a much heavier bed casting, so I'm surprised you were having
this sort of trouble.

As am I. I've got the 5418 (similar bed profile, but manual
change belts), and have very little chatter.

[ ... ]

You know -- there is one other possibility which occurs to me.
I presume that your lathe, like mine, has the hollow level adjusting
screws in the feet of the bed through which pass the bolts to lock it
down to the stand. If you have something like the near side bolt loose
and the level adjusting screw a little clear of the stand, the bed would
wind up under torque, which could give you similar behavior.

Do you mean the bolts between cabinet and the floor, or that hold the
headstock to the bed? I assume you mean between headstock and bed.

I see that you figured out what I was talking about from
examining the manual for the 5418. Since I don't have the manual for
yours, I had not realized how different they were.

Did you get a proper sensitive level and adjust the bed to
proper level at both headstock and tailstock end? (I did.)

I do have such a level (Starrett model 98-6), and did level the bed by
adjustment of the leveling feet between cabinet and floor.

Hmm ... not nearly as sensitive. The 98-6 (and the rest of the
98 series) have a sensitivity of 0.005"/foot, while the No. 199 "Master
Precision Level" has a sensitivity 0f 0.0005"/foot -- ten times the
sensitivity. But, of course, the 98-6 gets you close enough if you then
do the "turn two rings on a single bar and measure them" operation
afterwards.


After that,
did you make sure that the hold-down bolts were tight (and didn't
disturb the leveling)? *This* may be where your flex is -- especially
since you have a longer bed than I do (I believe), and thus more total
flex possibility.

Hmm. This I did not think of, or check. But I will.

I don't see why bed length would matter, given that while trepanning all
the action happens within a foot of the chuck face.

O.K. As long as you are that close, it would not really matter.
Where it would matter is turning some distance from the headstock, or
running something like a 1" drill bit in the tailstock -- especially
with a long workpiece extension from the chuck.

Get it chattering and feel each foot with the adjacent finger on
the stand so you can detect relative motion between them. If you find
any, you'll need to tighten the hold-down bolts, and probably re-level
the bed.

What I'm not quite sure of is which bolts you mean. On the 5914, the
headstock is bolted to the bed with four solid 3/8-16 hex socket cap
screws and two clamp bars, and the bed is bolted to the head pedestal
foot, which is in turn bolted to the cabinet, all with solid
non-adjustable bolts. The only hollow bolts I know of are in the
leveling feet between cabinet and floor, which doesn't seem relevant to
chatter (versus inability to turn a cylinder due to bed twist).

O.K. Quite different. The 5418 is supposed to have the cabinet
bolted firmly to the floor (I don't), and the bed leveled relative to
the stand and chip tray.

I looked the the 5418 manual. Now I understand. The designs of 5914
and 5418 are very different in this area. But there is no harm in
making sure that all those bolts are nice and tight, especially those
holding headstock to bed.

Agreed. Check the tailstock end too -- because that is what
would flex when the torque is transmitted from the spindle to the
carriage. It would wind up the bed (a little, at least).

BTW For parting there used to be a gooseneck parting tool. It went
in a lantern style toolpost, came out, turned up, formed an
Omega shaped arch, back down to where the parting tool is
actually clamped. The result is that excessive cutting forces
tends to move the tool away from the workpiece, thus eliminating
chatter. But your machine *should* be rigid enough to not need
this, especially with an Aloris style quick-change toolpost, and
the T-profile parting blades.

I suspect that on the 5914 they just machined the mating surfaces of
cast iron components close enough that adjustment wasn't needed, and
that the two pedestal feet isolated the bed and headstock sufficiently
from the sheet metal cabinet and chip pan that adjusters were not
needed.

Perhaps the bed feet were machined flat on the bottom, then
bolted to a thick flat plate (say 4" thick or so), machined flat on the
top, the bed mounted on this, and the ways finish-ground this way, so it
could get all the twist out of the bed by adjusting the cabinet feet.

Hmm ... another thing to check. While you have chatter, see
whether there is any relative motion between the headstock and the bed.
If it is not clamped down firmly enough, or if there are chips trapped
between the headstock and the bed, that could introduce enough give to
create problems.

Unlike the 5418 manual, in the 5914 manual, there is no
procedure for adjusting how the cast iron stuff rests upon the sheet
metal stuff.

O.K. This assumes that the sheet metal stuff is rigidly bolted
to the floor, I guess.

Good Luck,
DoN.

--
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 ---

In article ,
"DoN. Nichols" wrote:

On 2008-05-02, Joseph Gwinn wrote:
In article ,
"DoN. Nichols" wrote:

On 2008-05-01, Jon Elson wrote:
Joseph Gwinn wrote:
I think I've figured out a big piece of the mystery of what I
generically called chatter in the "Clausing 5914 Chatter ..." threads.

[ ... ]

I had some real problems doing these types of operations on
Atlas/Craftsman lathes. The 5914 is a MUCH sturdier lathe with
a much heavier bed casting, so I'm surprised you were having
this sort of trouble.

As am I. I've got the 5418 (similar bed profile, but manual
change belts), and have very little chatter.

[ ... ]

You know -- there is one other possibility which occurs to me.
I presume that your lathe, like mine, has the hollow level adjusting
screws in the feet of the bed through which pass the bolts to lock it
down to the stand. If you have something like the near side bolt loose
and the level adjusting screw a little clear of the stand, the bed would
wind up under torque, which could give you similar behavior.

Do you mean the bolts between cabinet and the floor, or that hold the
headstock to the bed? I assume you mean between headstock and bed.

I see that you figured out what I was talking about from
examining the manual for the 5418. Since I don't have the manual for
yours, I had not realized how different they were.

Ahh. Yes. It will take a while, but I may scan my manual, which does
not appear to be copyrighted.


Did you get a proper sensitive level and adjust the bed to
proper level at both headstock and tailstock end? (I did.)

I do have such a level (Starrett model 98-6), and did level the bed by
adjustment of the leveling feet between cabinet and floor.

Hmm ... not nearly as sensitive. The 98-6 (and the rest of the
98 series) have a sensitivity of 0.005"/foot, while the No. 199 "Master
Precision Level" has a sensitivity 0f 0.0005"/foot -- ten times the
sensitivity. But, of course, the 98-6 gets you close enough if you then
do the "turn two rings on a single bar and measure them" operation
afterwards.

I have not yet done the bar turning test, but intend to, once the more
immediate problems are at least understood if not resolved.

I probably should repeat the leveling exercise, as based on the other
kinds of ignorance-induced problems I've already found, it's likely that
the lathe was left unleveled and thus twisted for years, and may have
taken a set that needs to relax out.


After that,
did you make sure that the hold-down bolts were tight (and didn't
disturb the leveling)? *This* may be where your flex is -- especially
since you have a longer bed than I do (I believe), and thus more total
flex possibility.

Hmm. This I did not think of, or check. But I will.

I don't see why bed length would matter, given that while trepanning all
the action happens within a foot of the chuck face.

O.K. As long as you are that close, it would not really matter.
Where it would matter is turning some distance from the headstock, or
running something like a 1" drill bit in the tailstock -- especially
with a long workpiece extension from the chuck.

While using the 1" drill, the bed will most certainly wind up a bit. I
guess that what would resist permanent twist would be the leveling, with
the lathe resting on a concrete floor, as it now does.


Get it chattering and feel each foot with the adjacent finger on
the stand so you can detect relative motion between them. If you find
any, you'll need to tighten the hold-down bolts, and probably re-level
the bed.

What I'm not quite sure of is which bolts you mean. On the 5914, the
headstock is bolted to the bed with four solid 3/8-16 hex socket cap
screws and two clamp bars, and the bed is bolted to the head pedestal
foot, which is in turn bolted to the cabinet, all with solid
non-adjustable bolts. The only hollow bolts I know of are in the
leveling feet between cabinet and floor, which doesn't seem relevant to
chatter (versus inability to turn a cylinder due to bed twist).

O.K. Quite different. The 5418 is supposed to have the cabinet
bolted firmly to the floor (I don't), and the bed leveled relative to
the stand and chip tray.

The 5914 manual also speaks of bolting to the floor, but few people
actually do this I suspect.


I looked the the 5418 manual. Now I understand. The designs of 5914
and 5418 are very different in this area. But there is no harm in
making sure that all those bolts are nice and tight, especially those
holding headstock to bed.

Agreed. Check the tailstock end too -- because that is what
would flex when the torque is transmitted from the spindle to the
carriage. It would wind up the bed (a little, at least).

The tailstock now clamps pretty firmly to the bed. This is one of the
first things I cleaned and adjusted, mainly because it was easy and
could be done without the manual.


BTW For parting there used to be a gooseneck parting tool. It went
in a lantern style toolpost, came out, turned up, formed an
Omega shaped arch, back down to where the parting tool is
actually clamped. The result is that excessive cutting forces
tends to move the tool away from the workpiece, thus eliminating
chatter. But your machine *should* be rigid enough to not need
this, especially with an Aloris style quick-change toolpost, and
the T-profile parting blades.

I vaguely knew (from reading old books) that there was such a tool, and
that it involved a gooseneck, but I had the "picture" upsidedown in my
mind, and couldn't see how it would work. I just googled it, and found
a book from 1910 that explained the principle as applied to use in a
planer. They did understand the self-feeding effect, saying that the
gooseneck would eliminate gouging the work, but a sufficiently rigid
machine didn't need gooseneck tools.

http://books.google.com/books?id=Skd...lpg=RA8-PA36&d
q=gooseneck+tool+lathe&source=web&ots=edrQWKc6hu&s ig=QsKeq0Vn7zebOdjC5ydY
KtuqnkA&hl=en#PRA8-PA35,M1

It occurs to me that a negative rake cutting tool could be set up to
develop enough outward force to at least partially counteract the
tendency to self-feed. Perhaps this is why one commonly stated cause of
chattering is too-sharp tools. When one carefully blunts such a tool,
one puts a little bit of very negative rake right at the cutting edge.


I suspect that on the 5914 they just machined the mating surfaces of
cast iron components close enough that adjustment wasn't needed, and
that the two pedestal feet isolated the bed and headstock sufficiently
from the sheet metal cabinet and chip pan that adjusters were not
needed.

Perhaps the bed feet were machined flat on the bottom, then
bolted to a thick flat plate (say 4" thick or so), machined flat on the
top, the bed mounted on this, and the ways finish-ground this way, so it
could get all the twist out of the bed by adjusting the cabinet feet.

It's certainly a plausible approach, at least for the rough machining.
But the machining will release stresses, causing warping when the bed is
unbolted from the 4" slab. The bed ways are ground, so what may have
been done is that well-aged castings were rough machined and then
further aged and/or normalized, and then were finished on a surface
grinder. The exact procedure may have been a trade secret, as it was
exactly such recipes that were the secret sauce of lathe manufacture.


Hmm ... another thing to check. While you have chatter, see
whether there is any relative motion between the headstock and the bed.
If it is not clamped down firmly enough, or if there are chips trapped
between the headstock and the bed, that could introduce enough give to
create problems.

Hmm. Offhand, I don't see any safe way to do this, as my hand would
need to be very close to the spinning chuck, or to various gears and the
like.

I think I'll just torque all the clamp bolts, to see if any are loose.
I doubt that the headstock was ever unbolted, at least not by the people
who caused all the ignorance-induced problems. Taking the headstock off
would have frightened them, at least one fondly hopes that it would. In
any event, chips can only get in there is the headstock is unbolted.

The headstock is located on the bed ways by careful fitting of headstock
bottom to ways, plus a pair of steel dowel pins to prevent sliding.


Unlike the 5418 manual, in the 5914 manual, there is no
procedure for adjusting how the cast iron stuff rests upon the sheet
metal stuff.

O.K. This assumes that the sheet metal stuff is rigidly bolted
to the floor, I guess.

That would make sense. In the 5914, these adjustments have moved to the
cabinet-floor feet.

Joe Gwinn

In article ,
Jon Elson wrote:

Joseph Gwinn wrote:
I think I've figured out a big piece of the mystery of what I
generically called chatter in the "Clausing 5914 Chatter ..." threads.

Tightening the lathe dovetails up helped a great deal, and is a good
idea in general, but didn't really solve the problem.

It came to me in the shower Wednesday morning - self-feeding would
explain just about everything seen, and that if one reverses something,
the sign of the mechanical feedback loop can be reversed.

Yes, of course, you are dead right! But, proper setup of the
tool and how it relates to the toolpost, compound swivel, etc.
can make a big difference. You mentioned in an earlier post, I
think, that interference with the chuck jaws required you to
have so much overhang, so that points out that better work
holding would reduce the problem.

I knew the setup wasn't what it should be, but was limited by the
available toolholders, which were either too short or far too long. The
hope is that the coaxial boring bar will solve this problem.


I had some real problems doing these types of operations on
Atlas/Craftsman lathes. The 5914 is a MUCH sturdier lathe with
a much heavier bed casting, so I'm surprised you were having
this sort of trouble.

So am I, and it has lead to a real research program. I certainly did
not expect that parting off would involve so much drama.


I finally traded up to a Sheldon R15-6,
which is an even heavier lathe, in the 3000 - 3500 Lb class.
You can stand on the bed with no measurable deflection (and I
have precision electronic levels that are REALLY sensitive).
It is amazing what a difference stiffness of the lathe makes.

This is about three times what the 5914 weighs. If one assumes that
this is accomplished by tripling the thickness of everything, the
stiffness will increase by the cube of three, or a factor of 27, so I'm
not surprised the a few hundred pounds on the bed has little effect.

What are the dimensions of your Sheldon? One reason I didn't go that
heavy was space limitations, and the difficulty of getting such a heavy
machine into my basement.


Now, another comment is that you may have a poor "fit up"
between your carriage and bed. I totally rescraped my bed and
carriage to get the best fit between these surfaces. In my
case, due to the hardened bed, I had to grind it with Cratex
polishing wheels and then lap it smooth with bench stones.
(A carbide scraper blade wouldn't even SCRATCH the bed.)
I then used Moglice castable way liner to make the underside of
the carriage conform to the bed.

There is some bed wear which prevents the hold-down plates from being
too tight on the underside of the bed way, but the slop is about 0.001".
I did take one 0.002" shim out from under both hold-down plates, which
both had visible wear.

One reason that self-feeding is less of a problem when the tool moves
perpendicular to the spindle axis than when the tool motion is parallel
to the axis may be that the carriage is narrower along the way than
across the way, by a factor of about two.

The ways were hardened and ground, but not scraped. But I doubt that I
will ever have the time or energy to re-scrape them.


But, after all that work, I have no problem parting-off or with
other jobs where there is a bit of overhang. I haven't done
anything with quite as much overhang as you needed on this job,
but my guess is there is somthing in your lathe that is "not
right" and allowing maybe the carriage to rock about some local
high points. Sometimes you can see this if you take the way
wipers off. You might be able to see the oil fillet between the
bed and carriage "pulse" a bit as force is applied to the
carriage. That is a dead giveaway that the carriage is rocking.

I think that it does rock slightly, as I can feel slight movement if I
put a finger spanning the gap between carriage and way. But the skin is
very sensitive to motion in such setups, and this is probably the
~0.001" slop I already know of. The problem is that this was observed
while the lathe was shaking with chatter, and everything was bouncing,
and it wasn't clear what was cause and what was effect.

A dial indicator between carriage and way and an iron bar in the boring
bar holder (to apply force while the lathe is stopped) may be useful
here, though.

More generally, I've been finding and fixing many problems, few of which
were huge, but they do add up.

Joe Gwinn

Joseph Gwinn wrote:

This is about three times what the 5914 weighs. If one assumes that
this is accomplished by tripling the thickness of everything, the
stiffness will increase by the cube of three, or a factor of 27, so I'm
not surprised the a few hundred pounds on the bed has little effect.

Yes, this was a move up from a 12" Atlas/Craftsman. Wow, what a
difference! The cross slide is beefier than the carriage ways
on the Atlas, and the carriage spans 25" along the bed.
What are the dimensions of your Sheldon? One reason I didn't go that
heavy was space limitations, and the difficulty of getting such a heavy
machine into my basement.

It is about 80" long, and I had to take off the nice door over
the back end of the headstock, as there's a bench right there.
The bed itself is 6 feet, exactly, giving a conservative 42"
between centers. I'm sure I could turn a 48" long part with no
trouble.

One of the reasons I bought this house was the grade-level door
to the back yard from the basement. I had to take a couple
handles off the lathe to slide it through the door. The biggest
problem is the soft terrain and the immense weight of fork lift
trucks.

See http://jelinux.pico-systems.com/sheldon.html
for the story and some pictures of the lathe.



Now, another comment is that you may have a poor "fit up"
between your carriage and bed. I totally rescraped my bed and
carriage to get the best fit between these surfaces. In my
case, due to the hardened bed, I had to grind it with Cratex
polishing wheels and then lap it smooth with bench stones.
(A carbide scraper blade wouldn't even SCRATCH the bed.)
I then used Moglice castable way liner to make the underside of
the carriage conform to the bed.


There is some bed wear which prevents the hold-down plates from being
too tight on the underside of the bed way, but the slop is about 0.001".
I did take one 0.002" shim out from under both hold-down plates, which
both had visible wear.

Depending on the shape of this wear, it may allow rocking of the
carriage on the convex curvature of the bed. This is "bad"!
It allows external forces to easily move the cutting point.
The larger the lathe, and the more distance between bed and
spindle centerline, the more this rocking is magnified.
One reason that self-feeding is less of a problem when the tool moves
perpendicular to the spindle axis than when the tool motion is parallel
to the axis may be that the carriage is narrower along the way than
across the way, by a factor of about two.

The ways were hardened and ground, but not scraped. But I doubt that I
will ever have the time or energy to re-scrape them.

Well, you can't scrape them, I suspect. Hardenable beds are not
grey or white cast iron, and when hardened, even without flame
spraying, they get immensely hard. I have developed a system
for "hand scraping" hardened beds, using a die grinder and the
muslin-bonded Cratex polishing wheels. If hand scraping is
slow, this "hand polishing" is even slower! It took me 14
months to do my Sheldon bed, but that involved several detours
down wrong paths.

I think that it does rock slightly, as I can feel slight movement if I
put a finger spanning the gap between carriage and way. But the skin is
very sensitive to motion in such setups, and this is probably the
~0.001" slop I already know of. The problem is that this was observed
while the lathe was shaking with chatter, and everything was bouncing,
and it wasn't clear what was cause and what was effect.

A dial indicator between carriage and way and an iron bar in the boring
bar holder (to apply force while the lathe is stopped) may be useful
here, though.

More generally, I've been finding and fixing many problems, few of which
were huge, but they do add up.
I think it really doesn't take much rocking to set up the
vibrations, then the natural resonant frequency of the machine
and workpiece take over. I have noticed with the Atlas machines
that the setup of tool overhang has a large effect on this.

Jon

In article ,
Jon Elson wrote:

Joseph Gwinn wrote:

This is about three times what the 5914 weighs. If one assumes that
this is accomplished by tripling the thickness of everything, the
stiffness will increase by the cube of three, or a factor of 27, so I'm
not surprised the a few hundred pounds on the bed has little effect.

Yes, this was a move up from a 12" Atlas/Craftsman. Wow, what a
difference! The cross slide is beefier than the carriage ways
on the Atlas, and the carriage spans 25" along the bed.

What are the dimensions of your Sheldon? One reason I didn't go that
heavy was space limitations, and the difficulty of getting such a heavy
machine into my basement.

It is about 80" long, and I had to take off the nice door over
the back end of the headstock, as there's a bench right there.
The bed itself is 6 feet, exactly, giving a conservative 42"
between centers. I'm sure I could turn a 48" long part with no
trouble.

Uff. A bit too large for my basement. But it sure would be nice.


One of the reasons I bought this house was the grade-level door
to the back yard from the basement. I had to take a couple
handles off the lathe to slide it through the door. The biggest
problem is the soft terrain and the immense weight of fork lift
trucks.

See http://jelinux.pico-systems.com/sheldon.html
for the story and some pictures of the lathe.

I didn't have near the drama. It was in the middle of the Winter, so I
hired a rigger, and he had the equipment to handle a 1200# lathe like a
toy. They would not have had much more trouble with 3500#, so the issue
is where to put it.


Now, another comment is that you may have a poor "fit up"
between your carriage and bed. I totally rescraped my bed and
carriage to get the best fit between these surfaces. In my
case, due to the hardened bed, I had to grind it with Cratex
polishing wheels and then lap it smooth with bench stones.
(A carbide scraper blade wouldn't even SCRATCH the bed.)
I then used Moglice castable way liner to make the underside of
the carriage conform to the bed.


There is some bed wear which prevents the hold-down plates from being
too tight on the underside of the bed way, but the slop is about 0.001".
I did take one 0.002" shim out from under both hold-down plates, which
both had visible wear.

Depending on the shape of this wear, it may allow rocking of the
carriage on the convex curvature of the bed. This is "bad"!
It allows external forces to easily move the cutting point.
The larger the lathe, and the more distance between bed and
spindle centerline, the more this rocking is magnified.

One reason that self-feeding is less of a problem when the tool moves
perpendicular to the spindle axis than when the tool motion is parallel
to the axis may be that the carriage is narrower along the way than
across the way, by a factor of about two.

I don't think I'm having much rocking. And, it turns out that the
carriage is more of less square, not a 2:1 rectangle.


The ways were hardened and ground, but not scraped. But I doubt that I
will ever have the time or energy to re-scrape them.

Well, you can't scrape them, I suspect. Hardenable beds are not
grey or white cast iron, and when hardened, even without flame
spraying, they get immensely hard. I have developed a system
for "hand scraping" hardened beds, using a die grinder and the
muslin-bonded Cratex polishing wheels. If hand scraping is
slow, this "hand polishing" is even slower! It took me 14
months to do my Sheldon bed, but that involved several detours
down wrong paths.

The ways are flame hardened, according to the nameplate on the lathe.
This means that grinding is the only way. One can do this by hand,
using coarse diamond grit embedded in a piece of aluminum as the tool.
It won't be fast, but it will work. Diamond dust cuts hard steel quite
well.

I wonder if the dovetails are also hardened. Most of the wear is in the
gibs, so one assumes that they are softer that the dovetail material.


I think that it does rock slightly, as I can feel slight movement if I
put a finger spanning the gap between carriage and way. But the skin is
very sensitive to motion in such setups, and this is probably the
~0.001" slop I already know of. The problem is that this was observed
while the lathe was shaking with chatter, and everything was bouncing,
and it wasn't clear what was cause and what was effect.

A dial indicator between carriage and way and an iron bar in the boring
bar holder (to apply force while the lathe is stopped) may be useful
here, though.

More generally, I've been finding and fixing many problems, few of which
were huge, but they do add up.

I think it really doesn't take much rocking to set up the
vibrations, then the natural resonant frequency of the machine
and workpiece take over. I have noticed with the Atlas machines
that the setup of tool overhang has a large effect on this.

Yes. But the first thing to do is to fix the gibs, as described in
another thread.

Joe Gwinn

On 2008-05-04, Joseph Gwinn wrote:
In article ,
Jon Elson wrote:

Joseph Gwinn wrote:

[ ... ]

One reason that self-feeding is less of a problem when the tool moves
perpendicular to the spindle axis than when the tool motion is parallel
to the axis may be that the carriage is narrower along the way than
across the way, by a factor of about two.

I don't think I'm having much rocking. And, it turns out that the
carriage is more of less square, not a 2:1 rectangle.

Yes -- the Clausing carriages have wide wings.

[ ... ]

The ways are flame hardened, according to the nameplate on the lathe.
This means that grinding is the only way. One can do this by hand,
using coarse diamond grit embedded in a piece of aluminum as the tool.
It won't be fast, but it will work. Diamond dust cuts hard steel quite
well.

I wonder if the dovetails are also hardened. Most of the wear is in the
gibs, so one assumes that they are softer that the dovetail material.

Actually -- the wear is normally on the harder of two mating
surfaces. This is because harder objects (grit, etc) embed in the
softer surface and cut the harder. This is how a lap works.

Enjoy,
DoN.

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