trouble between centers


John Gallo
 

I have been getting some very smooth cuts with a Chinese insert tool when the work is held in a chuck or collet. When I try turning the same work between centers I get a very rough cut. I have a new live center(not the cheapest one I could find)and am using the same tool and speeds. The work is half inch mild steel rod. My lathe is a 9A and I have no idea what I am doing wrong. I hope this question falls in the scope of this forum. Thanks, John.



David Rysdam <david@...>
 

"johnnyblock1@yahoo.com [SOUTHBENDLATHE]"
<SOUTHBENDLATHE@yahoogroups.com> writes:
I have been getting some very smooth cuts with a Chinese insert tool
when the work is held in a chuck or collet. When I try turning the
same work between centers I get a very rough cut. I have a new live
center(not the cheapest one I could find)and am using the same tool
and speeds. The work is half inch mild steel rod. My lathe is a 9A and
I have no idea what I am doing wrong. I hope this question falls in
the scope of this forum. Thanks, John.
How are you driving the work when the end is held by the tailstock? If
it's held in a chuck, you may just be a tailstock alignment issue.


John Gallo
 

I am using a dog.


Robert H. Blodinger
 

You using a quick change tool post or the old style rocker?  How long is the work between centers? Are your inserts triangle carbide?  What speed are you running a bob

2


On Dec 9, 2015, at 5:16 PM, johnnyblock1@... [SOUTHBENDLATHE] <SOUTHBENDLATHE@...> wrote:

 

I am using a dog.


Tim Hennessy
 

having a similar problem at the moment trying to turn a 20.5" long length of pipe. i know my tailstock is aligned to the spindle to within half a thou, but i keep cutting a taper because the work heats up and binds the centers, so i cut slower, it cools off and is now loose, so by the time i get close to the spindle with a pass, the work is being pushed away almost 0.005" and rattles on the spindle center. short of buying a spring loaded center, my workaround right now is to stop the machine, leave the feed engaged, back off my cross slide and re-adjust the tailstock every couple of inches of cut, then bring the cross slide back to my number and turn it back on. using the follow-rest helped a bit, but means i have to flip the work over, set up the dog and follow-rest again just to finish off the last 3 inches of the part.

tim


John Gallo
 

I am using a quick change tool post with the triangular inserts. The work is 8 inches between centers. I tried both 800 and 1200 RPM with no noticeable difference between the two.


m. allan noah
 

Try a solid (dead) center in the tailstock instead of a revolving one.

allan

On Thu, Dec 10, 2015 at 4:18 PM, johnnyblock1@... [SOUTHBENDLATHE] <SOUTHBENDLATHE@...> wrote:
 

I am using a quick change tool post with the triangular inserts. The work is 8 inches between centers. I tried both 800 and 1200 RPM with no noticeable difference between the two.




--
"well, I stand up next to a mountain- and I chop it down with the edge of my hand"


oscar kern <kernbigo@...>
 

how much finish cut?



On Thursday, December 10, 2015 3:19 PM, "'m. allan noah' kitno455@... [SOUTHBENDLATHE]" wrote:


 
Try a solid (dead) center in the tailstock instead of a revolving one.

allan

On Thu, Dec 10, 2015 at 4:18 PM, johnnyblock1@... [SOUTHBENDLATHE] <SOUTHBENDLATHE@...> wrote:
 
I am using a quick change tool post with the triangular inserts. The work is 8 inches between centers. I tried both 800 and 1200 RPM with no noticeable difference between the two.



--
"well, I stand up next to a mountain- and I chop it down with the edge of my hand"



armne@sbcglobal.net <armne@...>
 

  Try a tool bit with less nose radius
Alec


From: "johnnyblock1@... [SOUTHBENDLATHE]" <SOUTHBENDLATHE@...>
To: SOUTHBENDLATHE@...
Sent: Thursday, December 10, 2015 1:18 PM
Subject: Re: [SOUTHBENDLATHE] trouble between centers

 
I am using a quick change tool post with the triangular inserts. The work is 8 inches between centers. I tried both 800 and 1200 RPM with no noticeable difference between the two.



Jim B. <btdtrf@...>
 

20.5” long!

Follower rest?

 

Jim B.

 

From: SOUTHBENDLATHE@... [mailto:SOUTHBENDLATHE@...]
Sent: Thursday, December 10, 2015 2:05 PM
To: SOUTHBENDLATHE@...
Subject: [SOUTHBENDLATHE] Re: trouble between centers

 

 

having a similar problem at the moment trying to turn a 20.5" long length of pipe. i know my tailstock is aligned to the spindle to within half a thou, but i keep cutting a taper because the work heats up and binds the centers, so i cut slower, it cools off and is now loose, so by the time i get close to the spindle with a pass, the work is being pushed away almost 0.005" and rattles on the spindle center. short of buying a spring loaded center, my workaround right now is to stop the machine, leave the feed engaged, back off my cross slide and re-adjust the tailstock every couple of inches of cut, then bring the cross slide back to my number and turn it back on. using the follow-rest helped a bit, but means i have to flip the work over, set up the dog and follow-rest again just to finish off the last 3 inches of the part.

tim




John Gallo
 

I tried a dead center and got the same bad results. My finish cut was about.005.


m. allan noah
 

Half inch mild steel, 20+ inches long? Try a follower rest.

allan

On Thu, Dec 10, 2015 at 6:22 PM, johnnyblock1@... [SOUTHBENDLATHE] <SOUTHBENDLATHE@...> wrote:
 

I tried a dead center and got the same bad results. My finish cut was about.005.




--
"well, I stand up next to a mountain- and I chop it down with the edge of my hand"


Gregg Eshelman
 

On 12/10/2015 12:04 PM, timh2870@yahoo.com [SOUTHBENDLATHE] wrote:


having a similar problem at the moment trying to turn a 20.5" long
length of pipe. i know my tailstock is aligned to the spindle to within
half a thou, but i keep cutting a taper because the work heats up and
binds the centers, so i cut slower, it cools off and is now loose, so by
the time i get close to the spindle with a pass, the work is being
pushed away almost 0.005" and rattles on the spindle center. short of
buying a spring loaded center, my workaround right now is to stop the
machine, leave the feed engaged, back off my cross slide and re-adjust
the tailstock every couple of inches of cut, then bring the cross slide
back to my number and turn it back on. using the follow-rest helped a
bit, but means i have to flip the work over, set up the dog and
follow-rest again just to finish off the last 3 inches of the part.
So you need to set it up with a flood cooling system. Deep chip tray with a sump, filter, pump etc.

Could also be the wrong cutting angle and/or wrong cutting tool type for the material.

What kind of pipe are you cutting?


Mark R. Jonkman
 

Carbide tends to give a much better finish when combining high speeds and heavy cuts which is what it was designed for. On my heavy 10 I tend toward high speed steel inserts 75% of the time unless I know the work piece is fairly hard and or its above 2" diameter. I assume you swapped cutting edges on your carbide bit to make sure you have a fresh edge? If you have a 3/8" high speed steel tool bit kicking around I'd grind it into a good shape with reliefs for holding in the quick change tool post and give it a shot.  You don't mention whether you are hearing chatter as its cutting vs a course tearing/thready type finish. You also don't mention feed rates - assuming you've tried slower feed rates and faster feed rates. Did you brush on any cutting oil to help things?

For the other guy turning the 20" between centers and complaining about heat build up. Other than using cutting oil, if you have a air compressor and a regulator, try turning the air pressure down to about 20-40 psi (maybe even less) and keep an air stream hitting the tool bit. That might keep your heat down in a pinch. I have a Cool Mist that i mount on whatever machine I'm using when I have to keep the heat down. Obviously it uses cutting fluid and air but there are others on the market I think that strictly use air (Chilly bits??? or something like that). Worth a shot and might get you by as a poor man's temporary cooling system.

Sincerely
Mark R. Jonkman


From: "johnnyblock1@... [SOUTHBENDLATHE]"
To: "southbendlathe" Sent: Thursday, December 10, 2015 4:18:15 PM
Subject: Re: [SOUTHBENDLATHE] trouble between centers

 

I am using a quick change tool post with the triangular inserts. The work is 8 inches between centers. I tried both 800 and 1200 RPM with no noticeable difference between the two.



John Gallo
 

Thanks for all the advice. The thing that I don't understand is that I get a great finish with the work in a chuck at the headstock, and a lousy finish with the work between centers with a dog, and all other conditions exactly the same.


Jim
 

Is the lathe dog held firmly where the tang enters the face plate? If the dog can rotate - even a small amount - that might explain what you are experiencing.

On 12/11/2015 07:30 AM, johnnyblock1@... [SOUTHBENDLATHE] wrote:
 

Thanks for all the advice. The thing that I don't understand is that I get a great finish with the work in a chuck at the headstock, and a lousy finish with the work between centers with a dog, and all other conditions exactly the same.



ww_big_al
 

I’m not very experience at machining but I will give you my thoughts.

We know that all factors of turning are the same except for the way the part is mounted.

                Same tool bit

                Same piece of stock

                Same feeds & Speeds

                Same cutting oil (if used)

                Same live/dead center in the tail stock

 

Making some assumptions, by lousy finish you mean a rough surface. Also you are not getting any chatter.

The only difference is the part is either turned using a chuck (3 jaw) or Dog. When the part is in a chuck, it is firmly clamped. When held between centers the part is squeezed and turned by a dog that “floats” with rotation. I don’t understand why that would make a difference but I would start looking there.

 

Try putting in a dead center clamped in the chuck. True up the point then see if you get a better finish.

Do the same with a dead center mounted directly in the spindle.

Check your live center in the tail stock. If you have a different one try it.

You may also try a dead center in the tail stock.

 

Do each of these one at a time and you will be able to hone into what your problem is.

 

Good luck to you.

 

 

From: SOUTHBENDLATHE@... [mailto:SOUTHBENDLATHE@...]
Sent: Friday, December 11, 2015 7:31 AM
To: SOUTHBENDLATHE@...
Subject: Re: [SOUTHBENDLATHE] trouble between centers

 

 

Thanks for all the advice. The thing that I don't understand is that I get a great finish with the work in a chuck at the headstock, and a lousy finish with the work between centers with a dog, and all other conditions exactly the same.


Rick Rick
 

 

, but i keep cutting a taper because the work heats up and binds the centers,

 

800 RPM is still too fast as you are still building heat.

I would slow way down to reduce the heat.

Another solution might be to use mist of flood coolant.

Rick in WA State


oscar kern <kernbigo@...>
 

put never size on the center problem solved



On Friday, December 11, 2015 10:28 AM, "'Rick' crvtfan@... [SOUTHBENDLATHE]" wrote:


 
 
, but i keep cutting a taper because the work heats up and binds the centers,
 
800 RPM is still too fast as you are still building heat.
I would slow way down to reduce the heat.
Another solution might be to use mist of flood coolant.
Rick in WA State



Nelson Collar
 

John 
If I might throw in my two cents. Try a high speed steel, grind and hone to as sharp as a razor blade and put a slight radius on the tip. See how that works. HSS will cut at low speeds where most inserts will not. 
Nelson Collar 



From: "mark.jonkman@... [SOUTHBENDLATHE]"
To: southbendlathe
Sent: Friday, December 11, 2015 7:21 AM
Subject: Re: [SOUTHBENDLATHE] trouble between centers

 
Carbide tends to give a much better finish when combining high speeds and heavy cuts which is what it was designed for. On my heavy 10 I tend toward high speed steel inserts 75% of the time unless I know the work piece is fairly hard and or its above 2" diameter. I assume you swapped cutting edges on your carbide bit to make sure you have a fresh edge? If you have a 3/8" high speed steel tool bit kicking around I'd grind it into a good shape with reliefs for holding in the quick change tool post and give it a shot.  You don't mention whether you are hearing chatter as its cutting vs a course tearing/thready type finish. You also don't mention feed rates - assuming you've tried slower feed rates and faster feed rates. Did you brush on any cutting oil to help things?

For the other guy turning the 20" between centers and complaining about heat build up. Other than using cutting oil, if you have a air compressor and a regulator, try turning the air pressure down to about 20-40 psi (maybe even less) and keep an air stream hitting the tool bit. That might keep your heat down in a pinch. I have a Cool Mist that i mount on whatever machine I'm using when I have to keep the heat down. Obviously it uses cutting fluid and air but there are others on the market I think that strictly use air (Chilly bits??? or something like that). Worth a shot and might get you by as a poor man's temporary cooling system.

Sincerely
Mark R. Jonkman




From: "johnnyblock1@... [SOUTHBENDLATHE]" To: "southbendlathe"
Sent: Thursday, December 10, 2015 4:18:15 PM
Subject: Re: [SOUTHBENDLATHE] trouble between centers

 
I am using a quick change tool post with the triangular inserts. The work is 8 inches between centers. I tried both 800 and 1200 RPM with no noticeable difference between the two.