I have a Smithy 1220 lathe/mill and was turning a 3/16" threaded coupler
down yesterday and I noticed that there is apparently a taper in it.
The end away from the chuck is about .006 wider than the end near the
chuck. There is no adjustment on the headstock as far as I can tell.
I'm going to call Smithy Tuesday but I was hoping some of you
knowledgible folks could come up with a solution. It's really wierd.
What I'm doing is turning the couplings down to be pressed/glued into
the center of a couple of cocobolo shift knobs I made for my Jeep. I
need to have them pretty much straight. thanks.

Jim

Most likely, you're dealing with part deflection. It bends away from the
cutter, making it larger the further from the chuck,

Very finely sharpenned and honed tooling helps a lot with this issue. if
you've got it, super high RPM and a light finishing cut help too.

Karl

Jim Chandler wrote:

I have a Smithy 1220 lathe/mill and was turning a 3/16" threaded coupler
down yesterday and I noticed that there is apparently a taper in it.
The end away from the chuck is about .006 wider than the end near the
chuck.

What was the l/d (length to diameter) ratio of the part your were machining?
Can you rig a test indicator to your carrage and indicate the side of chuck?
Might give you an idea if your headstock is mis aligned with ways.

Worn jaws can do it also. Wooped ways also.



Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller

Karl Townsend wrote:
Most likely, you're dealing with part deflection. It bends away from the
cutter, making it larger the further from the chuck,

Very finely sharpenned and honed tooling helps a lot with this issue. if
you've got it, super high RPM and a light finishing cut help too.

Karl



Thanks, Karl. I'll give that a try. I hadn't thought about deflection
because I thought everything was solid.

Jim

Wes wrote:

Jim Chandler wrote:


I have a Smithy 1220 lathe/mill and was turning a 3/16" threaded coupler
down yesterday and I noticed that there is apparently a taper in it.
The end away from the chuck is about .006 wider than the end near the
chuck.


What was the l/d (length to diameter) ratio of the part your were machining?
Can you rig a test indicator to your carrage and indicate the side of chuck?
Might give you an idea if your headstock is mis aligned with ways.

Worn jaws can do it also. Wooped ways also.



Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller

The diameter of the part started at about 1/2" and the length is about
2". I an turning it with a 3/16 grade 5 bolt run all the way through it
and am chucked (three jaw) on the bolt. I suspect Karl was correct and
I'm getting deflection that I hadn't considered. The machine is just
over a year old so I don't think that there is excessive wear in any of
the parts, especially since I've only used it a few times (not as many
as I'd like). Thanks for the reply. Every bit of information helps.

Jim

On Sun, 25 May 2008 02:44:56 +0000, Jim Chandler wrote:

Karl Townsend wrote:
Most likely, you're dealing with part deflection. It bends away from
the cutter, making it larger the further from the chuck,

Very finely sharpenned and honed tooling helps a lot with this issue.
if you've got it, super high RPM and a light finishing cut help too.

Karl



Thanks, Karl. I'll give that a try. I hadn't thought about deflection
because I thought everything was solid.

Jim

Zero deflection, eh.

It's amazing just how elusive 'zero' can be when you start looking hard
enough.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

On May 24, 10:48*pm, Jim Chandler wrote:
...
The diameter of the part started at about 1/2" and the length is about
2". *I an turning it with a 3/16 grade 5 bolt run all the way through it
and am chucked (three jaw) on the bolt.
Jim-

A 1/2" solid steel rod held in a collet could deflect that much from a
roughing cut. I'd chuck the 3/16" bolt in close, center-drill it, put
the part back on it and hold the far end steady with the tailstock.
You can use an indicator to check if the center hole runs true and see
if it shifts when you run the tailstock center in.

A Grade 5 bolt isn't any stiffer than an unmarked one.

Jim Wilkins

.006" is great compared to my lathe.
A few strokes with a file should take care of that.

On May 25, 8:46*am, Dan@ (Dan H) wrote:
*.006" is great compared to my lathe.
A few strokes with a file should take care of that.

This is not correct. A file is completely inappropriate for this
problem. The only reason anyone should use a file on a lathe is to
take an edge off (chamfer or radius) at a low RPM while paying a lot
of attention as to where the file, and his/her apendages are located.

I've never seen an application where a file yields a better result
than a correctly formed cutting tool, cutting under appropriate
conditions (RPM, feedrate, tool and workpiece overhang, cutting fluid,
etc). I'd be very impressed to see anyone file a taper out of a
workpiece faster than they can adjust their cutting parameters and
actually perform the operation correctly(!)

Not to mention using a file on a lathe is really dangerous (see pics
from thread several months ago - see if you can find the file among
the twisted flesh and blood).

As we've now found out, the length to diameter ratio on the OP's setup
is the cause of this issue. Karl's suggestion is right on the mark.

Regards,

Robin

Tim Wescott wrote:
On Sun, 25 May 2008 02:44:56 +0000, Jim Chandler wrote:


Karl Townsend wrote:

Most likely, you're dealing with part deflection. It bends away from
the cutter, making it larger the further from the chuck,

Very finely sharpenned and honed tooling helps a lot with this issue.
if you've got it, super high RPM and a light finishing cut help too.

Karl




Thanks, Karl. I'll give that a try. I hadn't thought about deflection
because I thought everything was solid.

Jim


Zero deflection, eh.

It's amazing just how elusive 'zero' can be when you start looking hard
enough.



That's what happens when you're not a real machinist and are judging
things by feel. It is amazing how weak things really are. The first
time I tried turning this thing I had a 3/16" bolt threaded all the way
through it with a nut on the end cinched down tight. I chucked it up
and started turning. About the third pass, I got a little overly
enthusiastic I guess, and took too big of a cut. The bit dug in and the
bolt bent nicely right behind the nut. I was amazed. you don't think
of those things. At least I don't.

Jim

Jim Wilkins wrote:

On May 24, 10:48 pm, Jim Chandler wrote:
...

The diameter of the part started at about 1/2" and the length is about
2". I an turning it with a 3/16 grade 5 bolt run all the way through it
and am chucked (three jaw) on the bolt.
Jim-


A 1/2" solid steel rod held in a collet could deflect that much from a
roughing cut. I'd chuck the 3/16" bolt in close, center-drill it, put
the part back on it and hold the far end steady with the tailstock.
You can use an indicator to check if the center hole runs true and see
if it shifts when you run the tailstock center in.

A Grade 5 bolt isn't any stiffer than an unmarked one.

Jim Wilkins


That's true, now that I think of it. The grade only signifies tension
strength. DUH! Using the tail stock is not a bad idea either. Thanks,
Jon.

Jim

On May 25, 1:56*pm, Jim Chandler wrote:
Jim Wilkins wrote:
...
Jim Wilkins

That's true, now that I think of it. *The grade only signifies tension
strength. *DUH! *Using the tail stock is not a bad idea either. *Thanks,
Jon.

Jim

Glad to help, Joe.

Jim Chandler wrote:

That's true, now that I think of it. The grade only signifies tension
strength. DUH! Using the tail stock is not a bad idea either. Thanks,
Jon.


Just the other day I had to remind an engineer that heat treating won't make
a shaft stiffer. I think he was a bit suprised having a tool box pusher
mention Young's modulus.

4:1 is tail stock territory though there are things like a follow rest. I've
never used one but I could see them being handy.

Wes

Jim Wilkins wrote:
On May 25, 1:56 pm, Jim Chandler wrote:

Jim Wilkins wrote:
...

Jim Wilkins

That's true, now that I think of it. The grade only signifies tension
strength. DUH! Using the tail stock is not a bad idea either. Thanks,
Jon.

Jim


Glad to help, Joe.



DAMN! I guess old age is catching up and I can no longer read well! :-)

Jim

Wes wrote:

Jim Chandler wrote:


That's true, now that I think of it. The grade only signifies tension
strength. DUH! Using the tail stock is not a bad idea either. Thanks,
Jon.



Just the other day I had to remind an engineer that heat treating won't make
a shaft stiffer. I think he was a bit suprised having a tool box pusher
mention Young's modulus.

4:1 is tail stock territory though there are things like a follow rest. I've
never used one but I could see them being handy.

Wes


Well, I don't know about THAT now. MY shaft always gets stiffer when it
is warmed up! :-)

Jim

"Wes" wrote in message
...
Jim Chandler wrote:

That's true, now that I think of it. The grade only signifies tension
strength. DUH! Using the tail stock is not a bad idea either. Thanks,
Jon.


Just the other day I had to remind an engineer that heat treating won't
make
a shaft stiffer. I think he was a bit suprised having a tool box pusher
mention Young's modulus.

4:1 is tail stock territory though there are things like a follow rest.
I've
never used one but I could see them being handy.

Wes

ya know, Wes - there are two types of engineers (actually this probably
applies to any group of folks) - those who think they know more than eveyone
else and are out to prove it, and those who end up actually knowing what
everyone else knows because they listen and ask questions - I haven't worked
production line stuff for decades, but I found that the Techs and even the
assembly folks could generally teach me something if I would just shut up
and listen to them - and at least in my experience, everyone I asked for
help was willing to help - maybe it had to do with the asking and listening
parts.


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

On May 26, 1:19*am, "William Noble" wrote:
ya know, Wes - there are two types of engineers (actually this probably
applies to any group of folks) - those who think they know more than eveyone
else and are out to prove it, and those who end up actually knowing what
everyone else knows because they listen and ask questions - I haven't worked
production line stuff for decades, but I found that the Techs and even the
assembly folks could generally teach me something if I would just shut up
and listen to them - and at least in my experience, everyone I asked for
help was willing to help - maybe it had to do with the asking and listening
parts.

I listen to the people who do the work, but have learned to separate
their observations of what happens, which is valuable, from their
interpretation of why it happens which is often incorrect if they
don't know the science behind it.

Jim Wilkins