VBMT moving into holder?

[GG917]

Hi all !

Got an "interresting" problem happening yesterday. Parts were running fine, and then the OD was .25mm lower !

Roughing was not broken so no finishing tool digging due to too much stock left. Finisher also not broken...

I'm using a VBMT insert with .4mm nose radius for finishing, 200m/min in xc38 Steel (1035 Google says !), taking .5mm radial DOC at .15mm feed. It is a screw on holder, almost new (not crashed!).

Re-probed the tool after, tool offset moved quite significantly. My boss says it il the insert that moved in its seat because too much DOC? I used to take the same DOC in 316 SS at my old job, never had a problem but with the better held VNMG. He says .25mm DOC max for finishing. Tanks! I think its more the .2mm left on the faces of the shoulder that made it moved... I used to left only .1mm in SS...

What do you think guys?

Thanks!

 

[ManualEd]

For an insert to move that much in the pocket, it would have to be the wrong insert for the holder or wrong screw. With everything mounted properly, .020” movement in the pocket would bust the insert or mangle the screw.


.020” doc and .008” left on the face puts you close to .180” doc when you hit the programmed length up to a shoulder.
Depending on tool connection, it could be enough to pivot the tool in the pocket, cause it to cut deeper, or pull the shank out of the holder when it feeds out in X. Even .004” is more Z finish than I like on normal turning cycles.

 

[Ox]

I think that it could be a "wrong insert for the tool" situation actually.
It seems to me that there is a cpl of inserts that are almost identical, but one will not fill up the pocket properly.

I would suggest that you actually look up the toolholder part number in the OEM catalog and dbl check the insert designation requirement.


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Think Snow Eh!
Ox

 

[guythatbrews]

Yes double check the insert and holder match. 0.25 diameter change is tons. The shoulder position would have to move a lot as well. Maybe dirt in the pocket or screw not tight?

.2mm on the shoulder is way too much. If you feel you have to leave that much with the roughing tool, face all but .03mm off with the finish tool first, then finish turn. V style tools are pretty flexible.

 

[CarbideBob]

Was the insert indexed or replaced?
I only ask as that while very rare this is within the making tolerance for a VBMT tip height over pocket.
Agree that the above stated wrong insert/holder is much more suspect.
Holder and full insert number?
Bob

 

[Ox]

Bob, he said that it changed size while in production.


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Think Snow Eh!
Ox

 

[CarbideBob]

Bob, he said that it changed size while in production.


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Think Snow Eh!
Ox

That I thought so but brings about other questions.
A whole bunch of shit went wrong. Who has not been there?
So many here with lots of experience and chips made. Seen this? Talk.
I am no way qualified or understanding in this world of why it went wrong. So much is so confusing.
I guess I just add more poop just to try something.

 

[Ox]

I'm sure it was 2nd shift....
They grabbed the wrong box of inserts and set it there.
I'm sure of it.


With that said - it is best practice to come in and face off your shoulders down to, or near finish D, and then turn the D up to the shoulder.

If it is not the wrong insert for the holder, then I would start lookin' in the tool crib for a new holder b/c this one's shot.
(or it's an ICSAR holder, in which case it needs replaced anyhow....)
(OK, well maybe not a screw down one, but those gimmicky wedge lockers are TERRIBLE!)


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Think Snow Eh!
Ox

 

[gcodeguy]

We have CCMT and CPMT boring bars. I think I am the only person in the shop that looks to make sure the correct bar is being used for the insert.

I don't normally take that heavy of a cut for finishing, but have roughed (boring bar) a larger DOC with the same style insert.

Right insert for the holder, good pocket, good screw, so are you turning into a shoulder?

 

[GG917]

thanks for all your replies !

yes right holder for the insert, both sandvik. Holder is almost new, still black with no chip marks and no visible damage (you know the "new tool" look!). insert not new, it has been doing some parts but not showing excessive wear. No problem of other people tinkering with the setup, I am the only lathe guy in the shop ! The insert/holder combo has already done several parts during the week, it happened all of a sudden !

I am not a big fan of the screw down VBMT holder, I used the one with the small 11-sized insert with a screw don holder in my old shop and they were terrible. Moved to the bigger 16-sized VBMT insert and the clamp holder, never had a problem. .4 DOC (radial) and 0.1 left on the faces of shoulders in 316, no problem with a 0.4mm radius insert.

Here in my new shop with the 16-sized insert and screw-down holder I though the insert was well held but it seems I was wrong. 0.5mm DOC and 0.2mm on the faces may be a bit too much? The 0.2mm left in Z seemed too much but recommended by my boss Actually I do no pull in X to finish the faces, I finish turn the diameter up to the shoulder, pull in X 1mm and then finish turn my face in -X direction. But I suspect a combination of insert wear and too much stock left in Z made it moved when contacting the shoulder face?

I'll try with 0.25mm left in X (radial) and 0.1mm on the faces, I am a bit worried that leaving less than that on the faces the finish will not be good. I have always been told to take more than the insert corner radius in DOC (so the 0.5mm DOC for the 0.4mm insert).

 

[guythatbrews]

I don't comply with the TNR depth of cut rule for finish passes.

I routinely make .01" diametral and .001 face stock finish passes in 316ss. If you leave .004" face stock and turn to your finish face length or close to the extra force can cause tool flexure and an undercut on the diameter at the shoulder.

I leave .005/.010 face stock for finishing and face all but .001 of that off with the finish tool. Then finish turn the profile so the face is turned from inside to outside. Face has less chance of getting damaged by chips finished facing in to out.

Pick a chip breaker for small DOC.

I usually have thread relief to cut so that is why the V style tool. If not for that I'd use a C.

 

[Ox]

For external apps I use VCGR (Top Notch) profile toys.
Those will pull back into the holder so tight that they can need tonked out a bit at times.
They don't move!

The screw downs are for internal use only.


------------------

Think Snow Eh!
Ox

 

[GG917]

I don't comply with the TNR depth of cut rule for finish passes.

I routinely make .01" diametral and .001 face stock finish passes in 316ss. If you leave .004" face stock and turn to your finish face length or close to the extra force can cause tool flexure and an undercut on the diameter at the shoulder.

I leave .005/.010 face stock for finishing and face all but .001 of that off with the finish tool. Then finish turn the profile so the face is turned from inside to outside. Face has less chance of getting damaged by chips finished facing in to out.

Pick a chip breaker for small DOC.

I usually have thread relief to cut so that is why the V style tool. If not for that I'd use a C.

Will try that tomorrow once back to work. The deflection/undercut makes sense with too much stock left on the faces. I'll check if the faces still have a good finish with less stock left.

For external apps I use VCGR (Top Notch) profile toys.
Those will pull back into the holder so tight that they can need tonked out a bit at times.
They don't move!

The screw downs are for internal use only.


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Think Snow Eh!
Ox

Never had a problem at my old job with clamp and pin/screw MVJN holder at my old job. I only have screw down holder at my new job and got to do with what I got...

 

[GG917]

quick update: re-started this morning with the same tool, but changed to 0 .25mm left in X (radial) and 0.1 in Z. The insert moved again, I could see that the faces were not clean. Changed to a SECO DNMG finishing tool (clamped insert), no problem then. I could see some area on the face were there was some chip marks, so I programmed my finishing pass to finish at 0.1mm of the shoulder and finish the faces in -X direction. Perfect parts since then !

 

[gcodeguy]

I always face X-. When I started, the owner's son finish faced X+. Finish normally looks much better facing from outside. Second I never finish turn into a shoulder with any depth of cut without first facing it with the finish turning (boring) tool and leaving .001 on the shoulder's face for when the finish tool makes its pass.