Face grooving problem

On CNC turning machine, with process parameters; feed=0.1mm/rev, depth of cut=5mm, cutting speed=220m/min.
material = mild steel

problem
chattering is noticed in face grooving with counter clock rotation of spindle , but there is no chattering during clock wise rotation of spindle with same tool and same parameters.

assuming tool is clamped rigidly.
how to tackle this problem??

How wide is your cutting edge and is there a programmed dwell or u going in and right out? Or even I reduced feed when u get close to depth of groove? I know my lathe just doesn't like groove tools over a certain width.. Can u reduce the width of your cutter and do multiple passes?

First thing I try with chatter is to decrease RPM while increasing the feed rate to maintain the same cycle time.

width of cutting edge =4mm, there is no dwell in program its just in and right out. feed reduction , increases cycle time.

moreover, cutting action is smooth in clockwise(left hand tool used) rotation of spindle but chattering in anticlockwise(same tool is put upside down)

Just do it the way it doesn't chatter. Sometimes there is no rhyme or reason for this stuff. The machining gods are fickle. If you've got it working don't worry how, just go with it.

djm77 said:

Just do it the way it doesn't chatter. Sometimes there is no rhyme or reason for this stuff. The machining gods are fickle. If you've got it working don't worry how, just go with it.

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i could have, but i want to know how direction of spindle affects the process ??? is it problem of spindle/bearing/belt/ motor /turret?? what exactly, i want to fix it. plz help in this regard.

I don’t know the machine or condition but I try to never use counter clockwise rotation for nothing but drilling and threading. By nature the clockwise rotation will transfer the load of the tool down on the bed. Counter clockwise rotation will want to lift the turret if there is any slop. I don’t know if that is your problem but I can’t come up with another since the only difference is the rotation.


Brent

yardbird said:

I don’t know the machine or condition but I try to never use counter clockwise rotation for nothing but drilling and threading. By nature the clockwise rotation will transfer the load of the tool down on the bed. Counter clockwise rotation will want to lift the turret if there is any slop. I don’t know if that is your problem but I can’t come up with another since the only difference is the rotation.


Brent

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This, been a problem in our shop for many years on many different kind of machines, no matter how rigid your setup/machine is, always try to choose tooling so you'll rotate towards bed/ways if possible. Also more forgiving when crashes occur.

david302 said:

width of cutting edge =4mm, there is no dwell in program its just in and right out. feed reduction , increases cycle time.

moreover, cutting action is smooth in clockwise(left hand tool used) rotation of spindle but chattering in anticlockwise(same tool is put upside down)

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If it is the same tool upside down is it on center. I'm trying to picture just turning tool upside down and can't picture it on center. Am I wacked and not picturing it correctly? You need left or right tools you can't just flip them?

J_M said:

This, been a problem in our shop for many years on many different kind of machines, no matter how rigid your setup/machine is, always try to choose tooling so you'll rotate towards bed/ways if possible. Also more forgiving when crashes occur.

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First statement; Why? Pretty sure, actually positive without question M3 is rotate clockwise and M4 is counter clockwise, and M3 rotates toward the door, while M4 rotates toward the way covers.

Second statement; how do you figure running that way is less catastrophic after a crash? Just curious about such unyeilding STATEMENTS, I thought people had preferences, and I am positive that MTB's have done much more research than I on the best way to run.

my plus or minus 2, Robert

FOXFIRE said:

If it is the same tool upside down is it on center. I'm trying to picture just turning tool upside down and can't picture it on center. Am I wacked and not picturing it correctly? You need left or right tools you can't just flip them?

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Well most turning tools really are not on true center regardless of M3 or M4, but with a normal turning tool turned upside down (M4) you can't get very close to the chuck, or take a very deep cut, or get a chip to come off. But with a face groovy if you have enough travel (which this guy does obviously) M3 or M4 would work.

@ the OP--is the groove tool the same width of the finish groove? Or are you leaving some material for finish? If your leaving some for finish then who cares if the rough chatters. If not feed off the finish floor about .01 when it's to depth, face grooves are a stressful operation, but like said before if one way works use it. Lathes are fickle funny creatures, but if I were to venture a guess it has more to do with set-up than M3 or M4.

Robert

FOXFIRE said:

If it is the same tool upside down is it on center. I'm trying to picture just turning tool upside down and can't picture it on center. Am I wacked and not picturing it correctly? You need left or right tools you can't just flip them?

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A lot of turret set up alow you to flip the clamp wedge and turn the tool over and still be on center. If you can see in the picture tool 7 & 11 are opposite from one another.


Brent

litlerob1 said:

if I were to venture a guess it has more to do with set-up than M3 or M4.

Robert

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Unless im missing something the only difference in the set-up is the M3 & M4 other than flipping the tool holder the way i am understanding things. Im not saying that is the problem just the only difference mentioned.


Brent

Depths of cuts, feed rates, speed are all factors. Rigidity of tool and holder are critical also. I have always noted with face grooving the tool must have adequate clearance on the sides and behind the cutting surface. If you take some dykem and coat the tool and then take your cut you can see where the tool / insert if rubbing and grind a little here and there to gain the right geometry.

Spinit said:

Depths of cuts, feed rates, speed are all factors. Rigidity of tool and holder are critical also. ....

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How can these be a problem when the only change is flipping the tool and rotation direction?
None of these are different upside down.
Bob

yardbird said:

Unless im missing something the only difference in the set-up is the M3 & M4 other than flipping the tool holder the way i am understanding things. Im not saying that is the problem just the only difference mentioned.


Brent

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There are plenty of factors that change, coolant, angle, infeed, toolstation? what is z zero? approach, acceleration, surrounding toolstations, gravity, bolt tightness, I don't know but there are variables.

Robert

litlerob1 said:

There are plenty of factors that change, coolant, angle, infeed, toolstation? what is z zero? approach, acceleration, surrounding toolstations, gravity, bolt tightness, I don't know but there are variables.

Robert

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Did you see Bobs reply to spinit before posting this? I don't see all that changing. The only thing I could come up with from reading the OP was clockwise rotation transferring the load of the tool down to the bed making it more rigid maybe not allowing it to chatter. Apparently we care a lot more than the OP.


Brent

litlerob1 said:

Well most turning tools really are not on true center regardless of M3 or M4, but with a normal turning tool turned upside down (M4) you can't get very close to the chuck, or take a very deep cut, or get a chip to come off

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What are you talking about?

When running M4, you buy opposite handed tooling.

And running M4 makes a giant difference. You are compressing everything down into several tons of iron... WITH gravity.
The way everything in the machine normally sits.

Running M3 ,you are trying to pull a few hundreds pounds of iron up against the ways, and the ways have a lot smaller contact area on
the bottom.

So we can run M3, go against gravity, and have no weight or rigidity advantage, maybe a few hundred pounds at most...

Or we go M4, Gravity is going with us, larger area of contact on the ways and we are then leaning on many tons of iron...

Bet your ass it makes a difference.

Bob in my defence, I'm pretty sure they were talking about using a conventional tool and turning upside down, and I wasn't arguing for or against said method, just that MORE is going to change than simply the direction of pressure. Feel free to kick my ass if I am wrong.

Robert

litlerob1 said:

Second statement; how do you figure running that way is less catastrophic after a crash? Just curious about such unyeilding STATEMENTS, I thought people had preferences, and I am positive that MTB's have done much more research than I on the best way to run.

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Hi Robert,
As far as damage to the Chuck, Tools, Tool Holders, Turret etc., there is no difference. However, and I'm sure Phil, aka machtool, a machine builder of some note here in Australia, will agree with me on this, that a machine having Box or V slide ways often sustain damage to the keeper plates, and or the mating surfaces of the keeper plates as the result of a severe crash, when the spindle rotation is such that its trying to lift the turret and carriage. This same magnitude of crash where the cutting forces are directed downwards towards the top surfaces of the slides is generally soaked up without damaging the slides.

I've seen quite a few machines I've been called to repair, with keeper plates having pieces from the area around the retaining bolts broken away completely, and if not completely broken, more often than not, cracked in these same areas. On machines that don't have the keeper plates surfaced with turcite, you will often see an imprint of the end of the keeper plate in its mating surface on the underside of the slide-way.

With regards to the MTB's doing what's best, it's more a case that machines have evolved around tooling rather than tooling made to suite machine design. Without question, a lathe having the cutting tools at the back of the machine would be better equipped with Left Hand cutting tools so that the cutting force is being directed downwards onto the top surfaces of the slide-ways; this is the basic load bearing design of just about all lathes. Overwhelmingly, right hand drills are more readily available than left hand, and from a production point of view, its better to not have to keep changing spindle direction to accommodate Left Hand turning tools, when the drills available were Right Hand.

With machines having Linear Bearing Slides, the difference in terms of damage sustained would be marginal, but still leaning towards downward forces having the least effect.

Regards,

Bill