[Baader Kevin]

One of our operators is having an issue with the consistency when he programs a taper.

This is the example he showed me - see picture

He programmed a .01mm taper and then measured every inch to show the inconsistencies.

If you notice in the picture from left to right the measurements are (in mm):

.095 .095 .092 .094 .098 .098 .100 .100 .103

The diameter gradually goes down and then goes too far before coming back up to be too large.

We have played with the x-axis backlash parameter BS15 and that didn't seem to do anything beneficial.

What do you guys make of this problem?

I will add that the spindle, turret, and tailstock have all been indicated to within .0005"

Its a QT-30 with a T-Plus control.

Thanks in advance and let me know if you need more info.

[underthetire]

My first question would be how does it cut a straight part with the same set up, maybe there is some twist in the bed. Next thing id check is servo error to see if its building up error then jumping to position. This would indicate something mechanical.

[Baader Kevin]

It cuts a straight part just fine. Thats how we checked and aligned the spindle and tailstock. How do I check the servo error?

[uperez]

Do you mean a taper of .01mm per inch? I'd check the level of the machine first before messing up with the spindle, turret and tailstock alignments.

[Baader Kevin]

.01mm on the entire piece. It started at .103mm and should have ended at .093mm. No, it does not have a Y-axis. I would think that if the machine had twist, we'd have issues doing a straight skim cut but we don't.

[uperez]

the problem is you can always cheat the straight cut by adjusting the tailstock in x direction to match the diameter on both ends. but if your machine is not leveled, your tool might be cutting off center on the tailstock end (error along y axis on the tailstock).

[deputydawg]

You might have better results by simply lowering the tailstock pressure. I've run parts that I thought couldn't possibly be flexing, but the middle was undersize. Lowering the tailstock pressure worked for me.

[MrMazak]

Considering the machine is probably not bolted down or level (unless you checked it recently) and not in a temperature controlled environment .01 mm over that distance is pretty good. The Mazak spec for a properly set up QT30 is .00039 inches per foot. Tailstock pressure could be an issue as previously posted. Try making a cut without the tailstock and see what you get. Don't forget you have a machine that is almost 20 years old and it could just be wearing out in the high travel areas around the chuck.