Checking for Twist

sportfan said:
I chucked up a piece of aluminum that was 3.5" in diameter. I zero it in the chuck and took a light clean up cut across the face. Checked it with an indicator and it was zero. The cam lock chuck has .001" run out across the face and on the o.d.. I took the chuck off and checked the spindle. The big o.d. of the spindle ran out .0015", the tapered area o.d. ran out .001", the face of tapered area ran out .002" (I don't think the chuck touches this area when its on the spindle), and the bore of the spindle ran out .001" opposite of where the bore ran out .001. I'm going to check it some more before I try shimming it. One friend said the jaws could be the problem.
Click to expand...
A few questions...

How did you measure your facing cut? Did you measure front to back (across all 3.5"), or front to center?

Was the tailstock involved at all when cutting a taper? Was the headstock side or the tailstock side larger?
 
I used a magnetic base indicator on the carriage and cranked it across. I did cuts with and without the tailstock. I had a chance to work on this more today. I had a .900" od piece of aluminum sticking out of the chuck 5" unsupported. I took a cleanup cut and then a light .005" cut. I had a .0015" taper from one end to the other. The only thing I've done that might have improved the accuracy was I had the chuck off and then I reinstalled it. I think maybe there was a chip under the chuck that I missed cleaning out when I last had it off. Am I expecting more accuracy from this lathe than it is capable of?
 
sportfan, you are asking about how to level a lathe. There are literally tons of threads on lathe leveling on the net and this site. You can read to your heart's content but I'll give you some info to get you started:
  • Forget about the fact that you're using a 3 jaw chuck for all of this. All the turning done when leveling a lathe is a first operation so the chuck is inconsequential. A 3 jaw is fine and the runout of your spindle doesn't matter in the least.
  • There is a sequence of operations when leveling a lathe and not all of us agree on what that sequence should be. I won't argue this but having set up multiple lathes and having tried setups in every way we could find, I feel that the proper sequence should be 1) headstock alignment 2) leveling the lathe and 3) aligning the headstock ... in that order.
  • Taking facing cuts and measuring across the entire face is one way to align the headstock. The front side will be zero but the rear half will show you your deviation. I find this method works okay but there is a better way. Put a piece of 1 to 1.5" OD aluminum in the chuck with about 5-6" sticking out and unsupported on the tail end. Using a very sharp and properly ground HSS turning tool, take off 0.010" off the OD, then 0.003", then 0.001" all the way down the work piece and strive for a good finish. Now measure the OD at the far end, the middle and the chuck end; it should be precisely the same if the headstock is aligned with the ways. If the OD differs then you need to swivel the headstock until you can turn a rod without any difference in diameters. Look up how to adjust the headstock or call PM. Get this nailed down as precisely as you can (zero deviation) because it will impact on how level you can adjust your lathe in future tests.
  • Now that your headstock is aligned, level the lathe. You need a decent machinist's level that is calibrated. Mine is sensitive to 0/0002"/10". If you don't have a precision level then you can still level the lathe but it will take a lot more time. I suggest you forget using 1-2-3 blocks on the ways. Instead, remove the compound off your cross slide and clean the top of the cross slide well. Put whatever level you plan to use directly on the surface of the cross slide and aligned with the X-axis (pointing away from you). Use a square of some kind and align the level with the edge of the cross slide so the level is really straight. Once you get the level set up like this, do not touch it. Now, you are going to roughly level the lathe by adjusting the fore and aft leveling adjusters on the headstock end of the lathe and the front side leveling adjuster on the tailstock end. If you do not have these adjusters then you'll need to either fabricate them or use shims. Crank the cross slide to the headstock end of the lathe and level that end of the lathe with your adjusters and then lightly lock the lathe down. Now move the cross slide to the tailstock end of the lathe and level it with the front side leveler. Once that is done, lower the rear side leveler until it just touches down and provides support; it is not used to level the lathe. Go back and forth until the lathe is leveled. When that is done you can fine tune the level of the lathe to eliminate taper using the 2-collar test.
  • Look up the 2-collar test and make a bar as called for. It should be about 8-10" long and supported only on the chuck end. Again, a sharp HSS tool should be used for this and any other cutting tests. Take light cuts in the 0.001-0.002" range and adjust until all taper is eliminated.
  • Okay, now your headstock is aligned with the ways and you've adjusted all taper out of the lathe. NOW you can align your tailstock with either a shop-made test bar or a purchased one.
  • Done
None of this is hard but you do need to understand what you're doing and why you're doing it. Go do some more reading and then ask questions. The guys will give you all the help you need.

By the way, if you cannot grind a good HSS tool then contact either @Z2V or @ttabbal for help. Both grind really good tools and have helped members before.
 
mikey said:
sportfan, you are asking about how to level a lathe. There are literally tons of threads on lathe leveling on the net and this site. You can read to your heart's content but I'll give you some info to get you started:
  • Forget about the fact that you're using a 3 jaw chuck for all of this. All the turning done when leveling a lathe is a first operation so the chuck is inconsequential. A 3 jaw is fine and the runout of your spindle doesn't matter in the least.
  • There is a sequence of operations when leveling a lathe and not all of us agree on what that sequence should be. I won't argue this but having set up multiple lathes and having tried setups in every way we could find, I feel that the proper sequence should be 1) headstock alignment 2) leveling the lathe and 3) aligning the headstock ... in that order.
  • Taking facing cuts and measuring across the entire face is one way to align the headstock. The front side will be zero but the rear half will show you your deviation. I find this method works okay but there is a better way. Put a piece of 1 to 1.5" OD aluminum in the chuck with about 5-6" sticking out and unsupported on the tail end. Using a very sharp and properly ground HSS turning tool, take off 0.010" off the OD, then 0.003", then 0.001" all the way down the work piece and strive for a good finish. Now measure the OD at the far end, the middle and the chuck end; it should be precisely the same if the headstock is aligned with the ways. If the OD differs then you need to swivel the headstock until you can turn a rod without any difference in diameters. Look up how to adjust the headstock or call PM. Get this nailed down as precisely as you can (zero deviation) because it will impact on how level you can adjust your lathe in future tests.
  • Now that your headstock is aligned, level the lathe. You need a decent machinist's level that is calibrated. Mine is sensitive to 0/0002"/10". If you don't have a precision level then you can still level the lathe but it will take a lot more time. I suggest you forget using 1-2-3 blocks on the ways. Instead, remove the compound off your cross slide and clean the top of the cross slide well. Put whatever level you plan to use directly on the surface of the cross slide and aligned with the X-axis (pointing away from you). Use a square of some kind and align the level with the edge of the cross slide so the level is really straight. Once you get the level set up like this, do not touch it. Now, you are going to roughly level the lathe by adjusting the fore and aft leveling adjusters on the headstock end of the lathe and the front side leveling adjuster on the tailstock end. If you do not have these adjusters then you'll need to either fabricate them or use shims. Crank the cross slide to the headstock end of the lathe and level that end of the lathe with your adjusters and then lightly lock the lathe down. Now move the cross slide to the tailstock end of the lathe and level it with the front side leveler. Once that is done, lower the rear side leveler until it just touches down and provides support; it is not used to level the lathe. Go back and forth until the lathe is leveled. When that is done you can fine tune the level of the lathe to eliminate taper using the 2-collar test.
  • Look up the 2-collar test and make a bar as called for. It should be about 8-10" long and supported only on the chuck end. Again, a sharp HSS tool should be used for this and any other cutting tests. Take light cuts in the 0.001-0.002" range and adjust until all taper is eliminated.
  • Okay, now your headstock is aligned with the ways and you've adjusted all taper out of the lathe. NOW you can align your tailstock with either a shop-made test bar or a purchased one.
  • Done
None of this is hard but you do need to understand what you're doing and why you're doing it. Go do some more reading and then ask questions. The guys will give you all the help you need.

By the way, if you cannot grind a good HSS tool then contact either @Z2V or @ttabbal for help. Both grind really good tools and have helped members before.
Click to expand...
Ok, thanks.
 
Thinking about a lathe moving when your hand presses on it...while I suspect there is a simpler explanation for this, I recall my old mechanical engineering professor saying one time "When you look really closely, the universe is made of jelly".
 
mikey said:
sportfan, you are asking about how to level a lathe. There are literally tons of threads on lathe leveling on the net and this site. You can read to your heart's content but I'll give you some info to get you started:
  • Forget about the fact that you're using a 3 jaw chuck for all of this. All the turning done when leveling a lathe is a first operation so the chuck is inconsequential. A 3 jaw is fine and the runout of your spindle doesn't matter in the least.
  • There is a sequence of operations when leveling a lathe and not all of us agree on what that sequence should be. I won't argue this but having set up multiple lathes and having tried setups in every way we could find, I feel that the proper sequence should be 1) headstock alignment 2) leveling the lathe and 3) aligning the headstock ... in that order.
  • Taking facing cuts and measuring across the entire face is one way to align the headstock. The front side will be zero but the rear half will show you your deviation. I find this method works okay but there is a better way. Put a piece of 1 to 1.5" OD aluminum in the chuck with about 5-6" sticking out and unsupported on the tail end. Using a very sharp and properly ground HSS turning tool, take off 0.010" off the OD, then 0.003", then 0.001" all the way down the work piece and strive for a good finish. Now measure the OD at the far end, the middle and the chuck end; it should be precisely the same if the headstock is aligned with the ways. If the OD differs then you need to swivel the headstock until you can turn a rod without any difference in diameters. Look up how to adjust the headstock or call PM. Get this nailed down as precisely as you can (zero deviation) because it will impact on how level you can adjust your lathe in future tests.
  • Now that your headstock is aligned, level the lathe. You need a decent machinist's level that is calibrated. Mine is sensitive to 0/0002"/10". If you don't have a precision level then you can still level the lathe but it will take a lot more time. I suggest you forget using 1-2-3 blocks on the ways. Instead, remove the compound off your cross slide and clean the top of the cross slide well. Put whatever level you plan to use directly on the surface of the cross slide and aligned with the X-axis (pointing away from you). Use a square of some kind and align the level with the edge of the cross slide so the level is really straight. Once you get the level set up like this, do not touch it. Now, you are going to roughly level the lathe by adjusting the fore and aft leveling adjusters on the headstock end of the lathe and the front side leveling adjuster on the tailstock end. If you do not have these adjusters then you'll need to either fabricate them or use shims. Crank the cross slide to the headstock end of the lathe and level that end of the lathe with your adjusters and then lightly lock the lathe down. Now move the cross slide to the tailstock end of the lathe and level it with the front side leveler. Once that is done, lower the rear side leveler until it just touches down and provides support; it is not used to level the lathe. Go back and forth until the lathe is leveled. When that is done you can fine tune the level of the lathe to eliminate taper using the 2-collar test.
  • Look up the 2-collar test and make a bar as called for. It should be about 8-10" long and supported only on the chuck end. Again, a sharp HSS tool should be used for this and any other cutting tests. Take light cuts in the 0.001-0.002" range and adjust until all taper is eliminated.
  • Okay, now your headstock is aligned with the ways and you've adjusted all taper out of the lathe. NOW you can align your tailstock with either a shop-made test bar or a purchased one.
  • Done
None of this is hard but you do need to understand what you're doing and why you're doing it. Go do some more reading and then ask questions. The guys will give you all the help you need.

By the way, if you cannot grind a good HSS tool then contact either @Z2V or @ttabbal for help. Both grind really good tools and have helped members before.
Click to expand...
In Para. 3, if you align the headstock by turning a bar, any twist in the ways will be also be compensated for in the headstock alignment. I made that mistake when I originally aligned my lathe. I had a .004" taper over 6" which I removed by adjusting theheadstock.It didn't turn a taper but now, I cut a cone when I faced a part which was equivalent to .004" over a 6" face..

By using a facing cut to check and align the headstock, the carriage is close to the headstock and it doesn't move so the effect of twist is largely eliminated. I aligned my lathe by checking the face first and when I could cut a flat face, I then went to leveling and then to turning a bar and shimming the tailstock end as required to correct any taper.
 
RJSakowski said:
In Para. 3, if you align the headstock by turning a bar, any twist in the ways will be also be compensated for in the headstock alignment. I made that mistake when I originally aligned my lathe. I had a .004" taper over 6" which I removed by adjusting theheadstock.It didn't turn a taper but now, I cut a cone when I faced a part which was equivalent to .004" over a 6" face..

By using a facing cut to check and align the headstock, the carriage is close to the headstock and it doesn't move so the effect of twist is largely eliminated. I aligned my lathe by checking the face first and when I could cut a flat face, I then went to leveling and then to turning a bar and shimming the tailstock end as required to correct any taper.
Click to expand...
When I made a face cut check, it was good. When I made the last od cut check I got the .0015" runout/ taper unsupported by the tailstock.
 
RJSakowski said:
In Para. 3, if you align the headstock by turning a bar, any twist in the ways will be also be compensated for in the headstock alignment. I made that mistake when I originally aligned my lathe. I had a .004" taper over 6" which I removed by adjusting theheadstock.It didn't turn a taper but now, I cut a cone when I faced a part which was equivalent to .004" over a 6" face..

By using a facing cut to check and align the headstock, the carriage is close to the headstock and it doesn't move so the effect of twist is largely eliminated. I aligned my lathe by checking the face first and when I could cut a flat face, I then went to leveling and then to turning a bar and shimming the tailstock end as required to correct any taper.
Click to expand...

I've been aligning headstocks this way for decades and feel it is the best and fastest way to get the job done. Once the headstock is aligned with the ways, leveling the lathe removes any twist from the bed. You have to start somewhere and some guys feel leveling the lathe first, then aligning the HS should come second. Some guys feel facing cuts work better. Go with what works for you. My lathe has zero deviation when making test cuts for HS alignment and has zero deviation on a 10" 2-collar test bar so my methods work for me.
 
This is my preferred method of set up.

1. Level the bed ways. Like mikey does, I prefer to put my level on the cross slide and run the carriage left to right. I'm not as worried about the ways themselves as I am the tool bit. The cross slide itself is an indicator of the level changes of the tool. It's also wild to see the changes in that level as the carriage moves down the ways. If you have a big change in the middle of the ways left to right but is level on both ends you will know and may have to split the difference to get a better average.

2. Align the headstock. You can use a commercial bar that runs in the spindle taper or cut a bar in the chuck. I just cut one. Two collar bar. After getting headstock aligned with the bed ways, try cutting a face. If it cuts a dish then your cross slide isn't square with the bed ways. Decision time. If the dish is small, say .002 over a 6 inch face it might be worth just leaving it. If your normal facing is an inch or two the dish will be very small. If you do large facing jobs and this will be a problem then you will need to do some work. First align the headstock to take out the dish. Then you will have to put a twist in the bed to get it to not cut a taper.

3. Align the tailstock. I use a test bar from Edge Technology. Run it between centers and adjust tailstock. Quick and simple.
 
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