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Cutting Taper In Face Of Parts

NickPretech

Plastic
Joined
Mar 10, 2022
Hey guys I have a Mazak QTN 350 MY II with a nexus control. I have been fighting this machine for awhile cutting taper in the face of my parts and in the faces of steps from one diameter to another. I have had mazak in the shop along with 2 other service companies and no one has figured out why it is cutting taper in the face of parts. They have tried to adjust the turret base and no luck on getting it to cut straight. Last guy in ended up telling me the X axis linear guides were bent. Guess its possible but i hear no disturbing sounds when x axis is in motion or in rapid. It use to cut outward and now that it has been messed with it is cutting inward. Head stock is fine. Over 10-12 inches I have around .0004-.0006 taper sometimes less. Does anyone have any experience dealing with this. I would appreciate anybodys input.
 

angelw

Diamond
Joined
Sep 10, 2010
Location
Victoria Australia
Hey guys I have a Mazak QTN 350 MY II with a nexus control. I have been fighting this machine for awhile cutting taper in the face of my parts and in the faces of steps from one diameter to another. I have had mazak in the shop along with 2 other service companies and no one has figured out why it is cutting taper in the face of parts. They have tried to adjust the turret base and no luck on getting it to cut straight. Last guy in ended up telling me the X axis linear guides were bent. Guess its possible but i hear no disturbing sounds when x axis is in motion or in rapid. It use to cut outward and now that it has been messed with it is cutting inward. Head stock is fine. Over 10-12 inches I have around .0004-.0006 taper sometimes less. Does anyone have any experience dealing with this. I would appreciate anybodys input.
Hello Nick,
Describe the method you used to test the taper on diameter over the 10-12 inch your referred to. Unless you used a very sharp pointed tool on a min diameter of 75mm aluminium, or other easily cut material, your 0.0004 - 0.0006 taper maybe misleading.

Regards,

Bill
 

ViktorS

Aluminum
Joined
Apr 26, 2021
Question: if you do a really light finish pass on the facing operation, say 0.1 mm, does the taper get smaller/disappear?

If it does, it's an indication that something is loose as there are less cutting forces to push the tool away (or into the material, if it's an 55 deg. diamond tool for example).

If the same taper is there, then it seems that the X axis rails are not square to Z. I have no idea how to correct it as I have never need to do that, but I assume that it involves loosening and shimming of the rails. Bent rails I would really doubt is the reason though.

This ofcourse requires the headstock to be aligned to Z. One way to get a rough idea about the alignment is to indicate on the face of the chuck with an indicator attached to the turret and running X up and down.

Mark a point on the chuck that you measure at with X as far up as the chuck diameter will allow. Then rotate the chuck 180 deg. and measure at the point again with X axis as far down as possible. Hard to explain but you get the idea. That way you get the X alignment in regard to spindle rotation axis, ie. the real Z.
 

NickPretech

Plastic
Joined
Mar 10, 2022
I was using a cnmg cutting across a piece of 1018. Material was 2.437 Dia. I then measured at both ends and adjusted.
 

NickPretech

Plastic
Joined
Mar 10, 2022
I will try this and I will try another holder. I have capto holders on it right now. I will go back to the original mazak holders and see if there is any difference as well.
 

Comatose

Titanium
Joined
Feb 25, 2005
Location
Akron, OH
If you grind the face of a piece (so you know it's flat) chuck it into the machine, sweep the face in the X direction with an indicator, rotate the spindle 180 degrees and sweep it again, what do you get?

Obviously, you'll never get it chucked exactly perfect, but that is okay. If your X axis is perpendicular to the spindle, then the difference should be the same (opposite direction) sweeping it in the 0 and 180 degree positions. So, if you gain .002 across the face at 0, you should lose .002 across the face at 180 degrees. If so, then your axes are aligned and you need to go chase something related to deflection. If not, then you know that something is misaligned.

Is your Z axis aligned? If X and Z are both tapered, then the issue is your headstock. If Z is right and X isn't, then the issue is the X axis.
 

gregormarwick

Diamond
Joined
Feb 7, 2007
Location
Aberdeen, UK
Hello Nick,
Describe the method you used to test the taper on diameter over the 10-12 inch your referred to. Unless you used a very sharp pointed tool on a min diameter of 75mm aluminium, or other easily cut material, your 0.0004 - 0.0006 taper maybe misleading.

Regards,

Bill

I will try this and I will try another holder. I have capto holders on it right now. I will go back to the original mazak holders and see if there is any difference as well.

Best way to be sure is to mill a slot across the face in polar mode. That way rogue variables like tool centre height and surface speed are removed.

If the resultant surface is not flat, then the X axis is not perpendicular to the spindle.
 

NickPretech

Plastic
Joined
Mar 10, 2022
I did as instructed and took a .005 finish cut on the face. Ran my indicator across the face in the same direction as cut. From outside to 0 I'm get .003 taper inward. My indicator setup may not be the greatest but there is definitely something going on. Not sure how to post videos on here but I took one.
 

yardbird

Titanium
Joined
Jul 3, 2013
Location
Indiana
I face the bulk of material off facing in a downwards direction leaving maybe .001 then jump off the part then across the diameters skimming the faces with just a baby fuzz cut. Just saying

Brent
 

angelw

Diamond
Joined
Sep 10, 2010
Location
Victoria Australia
Best way to be sure is to mill a slot across the face in polar mode. That way rogue variables like tool centre height and surface speed are removed.

If the resultant surface is not flat, then the X axis is not perpendicular to the spindle.
Hello Gregor,
I assume you mean a radial slot. That being the case and you were to clock the slot after cutting via the X axis, the result will be zero. The spindle needs to be rotated 180 degrees and the slot clocked on the opposite side of centre line to see any error.

NickPretech said:
I was using a cnmg cutting across a piece of 1018. Material was 2.437 Dia. I then measured at both ends and adjusted.
Hello Nick,
The material and insert would be among the worst combination for checking the alignment of the spindle; you would be getting push away for sure.

I chuck a 300mm length of 75mm (min) OD aluminum bar and undercut the bar in two places so as to provide three journals circa 10mm long (long enough to easily measure with a micrometer). Only the end journals are required to determine the taper, but I throw the centre one in as a final check once the spindle has been trued up.

Either:
1. write and run a program to cut theoretically parallel for the length of the bar (rapid between the journals over the undercuts) and keep changing the X Offset and repeat the program after every adjustment to gauge progress.

or

2. write and run a program to cut a taper so as to result in the journals measuring the same diameter (parallel), then use a dial indicator traversed via the Z axis to see the misalignment of the spindle.

Number 2 allows check and adjust with only the one cut of the test bar. The narrow journals with undercuts between circumvents any tool wear in the exercise. I use a generic OD Threading Insert with practically no TNR. The combination of the material and small TNR nets practically no deflection of the test bar and a true indication of the alignment of the spindle.

Regards,

Bill
 

gregormarwick

Diamond
Joined
Feb 7, 2007
Location
Aberdeen, UK
Hello Gregor,
I assume you mean a radial slot. That being the case and you were to clock the slot after cutting via the X axis, the result will be zero. The spindle needs to be rotated 180 degrees and the slot clocked on the opposite side of centre line to see any error.

Hi Bill,

More or less yeah, specifically what I meant was; to cut a slot fully across the face in polar mode the tool will travel from the outside of the part to X zero, the spindle will rotate 180 degrees and the tool will feed back out again.

The result being two flat planes on the face of the part that are either at an acute or obtuse angle to one another (if the X axis is not perpendicular to the spindle) or perfectly parallel (if the X axis is parallel to the spindle)

Obviously this is no different in principle to a turned face, except that the process removes some difficult to control variables that might affect the result.
 








 
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