Taper tolerances on new CNC Lathes ?

I am having a little discussion with the company that sold me my newest CNC lathe ( 8" chuck , 500mm turning length) regarding the taper the machine turns.
After it was installed and leveled (by them )it turned 8my taper in 120mm. (3 tenths in 4,72").
I find the taper to be unacceptable due to a number of reasons, not least because the factory sheet had the taper at 1my in 120mm.
My question is: what are the factory tolerances for the various high-end lathe manufacturers when it comes to allowable taper ?

1my over 120 mm is fairly ballsy to claim lol.

8my over 120 seems ok to me. At least I would be happy about it haha.

I would never believe the claimed tolerance anyway.

120 mm you have to consider way to many variables into it anyway.

Sendt fra min EML-L29 med Tapatalk

Panza said:

I am having a little discussion with the company that sold me my newest CNC lathe ( 8" chuck , 500mm turning length) regarding the taper the machine turns.
After it was installed and leveled (by them )it turned 8my taper in 120mm. (3 tenths in 4,72").
I find the taper to be unacceptable due to a number of reasons, not least because the factory sheet had the taper at 1my in 120mm.
My question is: what are the factory tolerances for the various high-end lathe manufacturers when it comes to allowable taper ?

Click to expand...

what size stock was it and what type? was it supported via a tail stock? how deep was the cut?
Theres too many variables to take a guess. you need to be more specific.

"(3 tenths in 4,72")" .0003 in almost 5" isnt bad in some cases

It might be worth releveling the lathe, there's no guarantee that it's correct at the moment. As long as other parameters aren't compromised, a very small twist of the bed (if needed) to bring the accuracy in will be OK.

If the headstock alignment is off that's a different issue, lathe kinematics and geometry isn't as simple as it looks.

.0003" on dia, or per side?
What dia material? How is it supported/chucked? how much of that is material flex? I assume its bigger on the further end.

CNC machine builders try to hold .00005 in 12" so your new machine is bad. If the factory techs have been there and level/aligned the bed I agree wholeheartedly with Midland that they need to recheck it. There is usually a device that comes with new CNC lathes that is attached to the turret that you set a precision level (.0005" / 12" or better)on so you can tram or test the travel of the turret along the length of the bed, this spec should be the .00005" per 12" . Then see if the new machine techs has a test bar to insert in the spindle taper to check the headstock alignment. or do the two collar test. It should point toward the tool pressure side no more then .0001/12" to compensate for tool pressure. It should be the new machine dealers responsibility to fit it and not change the parameters to offset this error. Does your machine use a tail-stock?

The cut was a light cut (0,1mm DOC or so) in 3,5" Stressproof. Held in the chuck, since the sub was tested separately.
The taper I mentioned was total taper.
The tech came from the manufacturer. He did not use the plate to mount on the turret when leveling.

Thank you for the answer Mr.King. It it very helpful. The machine has a subspindle that can also be used as a tailstock.

Is it anchored down on a good thick slab?
Don't those Japan machines say something in the manual about how it needs it own 2' thick concrete pad or something like that?
Might help straighten her out and keep her that way.

Panza said:

......After it was installed and leveled (by them )it turned 8my taper in 120mm. (3 tenths in 4,72").......

Click to expand...

Unacceptable for a new machine from any reputable builder. When I was doing field service I would try for .0001 in 6" for a post crash repair/realignment. Of course, that was not always attainable based on the age and condition of the machine.

The test piece is best done by using a bar with the center ~4" of length undercut to a slightly smaller diameter. After relieving the center section, turn each ring then measure. This will remove some uncertainty about insert wear from the measurements.

SND said:

Is it anchored down on a good thick slab?
Don't those Japan machines say something in the manual about how it needs it own 2' thick concrete pad or something like that?
Might help straighten her out and keep her that way.

Click to expand...

It is not anchored down. I offered them to anchor it but they said it was not needed. The adjusting feet does not have locknuts either.

Thanks for the tip of turning down the middle of the testbar before doing the final cut Vancbiker !