Topics

PC Turn 50 Headstock Alignment


mmcdade@...
 

Hi All,

 

I use a PC 50 lathe which turns a slight taper (wider by 0.0018" at 2" out from the headstock).  Is there a way to adjust the headstock?  I took the cover off and the prismatic shape of the front way is built into the headstock so that's not obviously adjustable short of scraping.  I tried shimming the far end of the bed like you would level to adjust twist in the bed of a conventional floor mounted horizontal engine lathe.  That didn't change anything and I suspect it just slightly deformed the sheet metal holding the bed.  Any ideas on this?  I admit that the error is pretty small but I sometimes make little optical mounts that slide together and they and I are happier when things are cylindrical.

 

Thanks,

 

Mark

 


David Rabenius
 

Mark:
  The reason why you have a taper is because the material is sticking out 2 inches. The material is springing away from the tool. As you get closer to the headstock the material doesn't deflect like at the 2.0 inch mark. You didn't mention the diameter of the material or the finished dia. of the part. Tool & billet deflection is common.
  These Lathes are very accurate and you also didn't mention if you have a center into the end of the part. You may need to spot drill and use either a live center or dead center held in the tailstock. Do you have a Live Center or dead Center?? This would help eliminate the taper you are experiencing.

Dave

On Saturday, June 6, 2020, 09:25:30 PM EDT, mmcdade@... <mmcdade@...> wrote:


Hi All,

 

I use a PC 50 lathe which turns a slight taper (wider by 0.0018" at 2" out from the headstock).  Is there a way to adjust the headstock?  I took the cover off and the prismatic shape of the front way is built into the headstock so that's not obviously adjustable short of scraping.  I tried shimming the far end of the bed like you would level to adjust twist in the bed of a conventional floor mounted horizontal engine lathe.  That didn't change anything and I suspect it just slightly deformed the sheet metal holding the bed.  Any ideas on this?  I admit that the error is pretty small but I sometimes make little optical mounts that slide together and they and I are happier when things are cylindrical.

 

Thanks,

 

Mark

 


rcflyer
 

There are many variables which can cause taper in a turned part. To test spindle runout, chuck drill rod or similar and indicate from the tool post.

On Sat, Jun 6, 2020 at 11:56 PM David Rabenius via groups.io <swedeson2002=yahoo.com@groups.io> wrote:
Mark:
  The reason why you have a taper is because the material is sticking out 2 inches. The material is springing away from the tool. As you get closer to the headstock the material doesn't deflect like at the 2.0 inch mark. You didn't mention the diameter of the material or the finished dia. of the part. Tool & billet deflection is common.
  These Lathes are very accurate and you also didn't mention if you have a center into the end of the part. You may need to spot drill and use either a live center or dead center held in the tailstock. Do you have a Live Center or dead Center?? This would help eliminate the taper you are experiencing.

Dave

On Saturday, June 6, 2020, 09:25:30 PM EDT, mmcdade@... <mmcdade@...> wrote:


Hi All,

 

I use a PC 50 lathe which turns a slight taper (wider by 0.0018" at 2" out from the headstock).  Is there a way to adjust the headstock?  I took the cover off and the prismatic shape of the front way is built into the headstock so that's not obviously adjustable short of scraping.  I tried shimming the far end of the bed like you would level to adjust twist in the bed of a conventional floor mounted horizontal engine lathe.  That didn't change anything and I suspect it just slightly deformed the sheet metal holding the bed.  Any ideas on this?  I admit that the error is pretty small but I sometimes make little optical mounts that slide together and they and I are happier when things are cylindrical.

 

Thanks,

 

Mark

 


David Rabenius
 

To test spindle runout remove the chuck and using a Dial Indicator place the tip in the taper and gently turn by hand on the back of the spindle. Mount the indicator on the bed, its the most rigid part of the machine. This will give you the runout of the spindle, place the tip on the face and also check the face runout. these should be way under .001 runout
To test the runout of the chuck do as above. I am assuming that you have the precision 3 jaw chuck that has the square chuck key. The other cheaper chuck used a Jacobs drill key, I had one of these and it runout quite a bit. The precision 3 jaw I have now is less than .001 runout. The standard is usually measured at 1 inch from the chuck.
   If you have part taper then your tailstock may also be out of alignment. You can buy a ground steel Lathe mandrel that has a center on each end. I have one of these, bought years ago from ENCO, you must use a center in the spindle and one in the tailstock. Chucks do wear with use. The jaws can also have taper. Has the lathe been crashed? That could also be a problem. 
Sometimes gunk gets trapped under the tailstock, I would remove it and check the bottom for gunk. At that time I would also polish the bed. Are there any dings on the ways?, if so use a fine stone to remove them.
  My PCturn50 typically has less than .0005 on parts that are 6 inches long, I use a live center to support the part. If you have bench centers you can also use indicators to check the roundness of your parts, if you have roundness issues it will show.
  I worked at a precision shop where the 18 inch swing Mori-Seiki Manual lathe had bearing issues and ran out .002, the lathe had seen heavy use and was removed for rebuilding. 

Dave

On Sunday, June 7, 2020, 11:14:26 AM EDT, rcflyer <sclcl082@...> wrote:


There are many variables which can cause taper in a turned part. To test spindle runout, chuck drill rod or similar and indicate from the tool post.

On Sat, Jun 6, 2020 at 11:56 PM David Rabenius via groups.io <swedeson2002=yahoo.com@groups.io> wrote:
Mark:
  The reason why you have a taper is because the material is sticking out 2 inches. The material is springing away from the tool. As you get closer to the headstock the material doesn't deflect like at the 2.0 inch mark. You didn't mention the diameter of the material or the finished dia. of the part. Tool & billet deflection is common.
  These Lathes are very accurate and you also didn't mention if you have a center into the end of the part. You may need to spot drill and use either a live center or dead center held in the tailstock. Do you have a Live Center or dead Center?? This would help eliminate the taper you are experiencing.

Dave

On Saturday, June 6, 2020, 09:25:30 PM EDT, mmcdade@... <mmcdade@...> wrote:


Hi All,

 

I use a PC 50 lathe which turns a slight taper (wider by 0.0018" at 2" out from the headstock).  Is there a way to adjust the headstock?  I took the cover off and the prismatic shape of the front way is built into the headstock so that's not obviously adjustable short of scraping.  I tried shimming the far end of the bed like you would level to adjust twist in the bed of a conventional floor mounted horizontal engine lathe.  That didn't change anything and I suspect it just slightly deformed the sheet metal holding the bed.  Any ideas on this?  I admit that the error is pretty small but I sometimes make little optical mounts that slide together and they and I are happier when things are cylindrical.

 

Thanks,

 

Mark

 


lmcinroy
 

That error is pretty good , you could change the plastic strips on the saddle to see if it helps?
A new set of headstock bearings might improve things.
Before you do any of this , centre drill the end and use the tailstock to see if there is any improvement.

This would be considered pretty good on a manual lathe and at 2" out on a small Dia, say under 10mm this would be normal.
The Emco is well made but at 2" out and on small Diameters you are beyond the tolerance of the bearings

Regards Frank

On 7 Jun 2020 02:25, mmcdade@... wrote:

Hi All,

 

I use a PC 50 lathe which turns a slight taper (wider by 0.0018" at 2" out from the headstock).  Is there a way to adjust the headstock?  I took the cover off and the prismatic shape of the front way is built into the headstock so that's not obviously adjustable short of scraping.  I tried shimming the far end of the bed like you would level to adjust twist in the bed of a conventional floor mounted horizontal engine lathe.  That didn't change anything and I suspect it just slightly deformed the sheet metal holding the bed.  Any ideas on this?  I admit that the error is pretty small but I sometimes make little optical mounts that slide together and they and I are happier when things are cylindrical.

 

Thanks,

 

Mark