# Exploded a GTN3 holder



## Aukai (Mar 21, 2022)

4" diameter 316 SS, 135 rpm, I set the auto feed for the least amount of chatter(still some fine vibration) as the part was going the cut became silent, going well. Very quickly there was a big vibration, and before I could shut things down, the GTN3 holder snapped. I had previously parted with the same insert, I'm wondering if the bit should have been changed before attempting another 4" SS cut. My setup for parting is to indicate the blade with a dial indicator </= .0005 at least in and out deflection of the tool post. I use the auto feed to try, and stay ahead of the work hardening, and plenty of cutting oil. I also move the blade out of the holder, and hand spin the chuck to get to fresh metal. The piece of the of the insert that was imbedded in the cut was hard to remove, and it took awhile to get it out too.


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## mmcmdl (Mar 21, 2022)

CSS is your friend here .


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## 7milesup (Mar 21, 2022)

I am wondering if there is not enough of the insert holder (blade) in the tool holder thereby introducing chatter and/deflection.  Or did that insert tool holder break and that is what is left of it?


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## MrWhoopee (Mar 21, 2022)

That's a deep part-off in difficult material. I'm not sure I'd even try. Is your saw not working?


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## markba633csi (Mar 21, 2022)

Obviously he's a masochist and loves pain


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## Shootymacshootface (Mar 21, 2022)

I haven't had the balls to part with the auto feed yet.


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## Christianstark (Mar 21, 2022)

That blade looks too short to attempt such a cut. I know some of the blade broke, but seeing where the insert removal hole is gives me a good idea that the blade itself was not seated far enough in the holder to feel good about parting tough material.


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## mikey (Mar 21, 2022)

If the crash happened about 2/3 of the way in, I bet the SFM dropped too low at that point. Since you were on auto-feed, your feed exceeded the point at which the insert is able to cut so it crashed. Next time, take it out of auto-feed and feed manually as the cut approaches center OR increase your speed.


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## Aukai (Mar 21, 2022)

The blade is flipped in the holder, I guess I got fooled by the lack of noise, vibration, and the curls coming off nicely. I think that the tool bit into the work like Mikey suggested, It was approaching the half way point. The saw is not working, I need to get the electrician here to figure that out. Thank you all...


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## Parlo (Mar 22, 2022)

mikey said:


> If the crash happened about 2/3 of the way in, I bet the SFM dropped too low at that point. Since you were on auto-feed, your feed exceeded the point at which the insert is able to cut so it crashed. Next time, take it out of auto-feed and feed manually as the cut approaches center OR increase your speed.


The metal removal rate and therefore the load on the tool decreases as the diameter reduces when using a constant rpm and constant feed per rev. If the feed was excessive it would show at the beginning of the cut where the forces are greatest. I suspect the blade was too weak for the operation and a deeper blade and possibly wider would have been more suitable.


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## mikey (Mar 22, 2022)

Parlo said:


> The metal removal rate and therefore the load on the tool decreases as the diameter reduces when using a constant rpm and constant feed per rev. If the feed was excessive it would show at the beginning of the cut where the forces are greatest. I suspect the blade was too weak for the operation and a deeper blade and possibly wider would have been more suitable.



Look, given that his spindle speed was constant, the *cutting speed* at the point of cut was *continually reducing as the cut proceeds*. As he gets closer to the center, cutting pressure at the tip of the tool *increases*. Given that he was using auto-feed, that tool tip is being fed under increasing pressure but it is not cutting because the cutting speed is too low. A machining center controller would have increased spindle rpm to accommodate this but that wasn't possible here so the blade broke. 

This was about cutting conditions and had nothing to do with the blade.


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## Parlo (Mar 22, 2022)

mikey said:


> Look, given that his spindle speed was constant, the *cutting speed* at the point of cut was *continually reducing as the cut proceeds*. As he gets closer to the center, cutting pressure at the tip of the tool *increases*. Given that he was using auto-feed, that tool tip is being fed under increasing pressure but it is not cutting because the cutting speed is too low. A machining center controller would have increased spindle rpm to accommodate this but that wasn't possible here so the blade broke.
> 
> This was about cutting conditions and had nothing to do with the blade.


With a constant RPM. The depth of cut - ie. feed per rev remains constant as the circumference decreases then the metal removal rate decreases. High metal removal imparts more pressure to the tool than a low removal rate. There are no references to minimum cutting speeds.


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## Janderso (Mar 22, 2022)

Shootymacshootface said:


> I haven't had the balls to part with the auto feed yet.


What lathe do you have?
If your set up is right and you have a rigid lathe, it’s a piece of cake.In my experience


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## Janderso (Mar 22, 2022)

mikey said:


> Look, given that his spindle speed was constant, the *cutting speed* at the point of cut was *continually reducing as the cut proceeds*. As he gets closer to the center, cutting pressure at the tip of the tool *increases*. Given that he was using auto-feed, that tool tip is being fed under increasing pressure but it is not cutting because the cutting speed is too low. A machining center controller would have increased spindle rpm to accommodate this but that wasn't possible here so the blade broke.
> 
> This was about cutting conditions and had nothing to do with the blade.


I’m sure you are right. Those type of cutters flex quite a bit so aren’t rigid. A 4” piece of SS is a lot to ask for that cutter imho.
Watching videos of machining centers with the ever changing spindle speeds is amazing.


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## Janderso (Mar 22, 2022)

Aukai said:


> 4" diameter 316 SS, 135 rpm, I set the auto feed for the least amount of chatter(still some fine vibration) as the part was going the cut became silent, going well. Very quickly there was a big vibration, and before I could shut things down, the GTN3 holder snapped. I had previously parted with the same insert, I'm wondering if the bit should have been changed before attempting another 4" SS cut. My setup for parting is to indicate the blade with a dial indicator </= .0005 at least in and out deflection of the tool post. I use the auto feed to try, and stay ahead of the work hardening, and plenty of cutting oil. I also move the blade out of the holder, and hand spin the chuck to get to fresh metal. The piece of the of the insert that was imbedded in the cut was hard to remove, and it took awhile to get it out too.


That’s a lot to ask of that cutter. I learned my lesson on the one that I broke. They are fine for lighter cuts in my experience.


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## Parlo (Mar 22, 2022)

Janderso said:


> I’m sure you are right. Those type of cutters flex quite a bit so aren’t rigid. A 4” piece of SS is a lot to ask for that cutter imho.
> Watching videos of machining centers with the ever changing spindle speeds is amazing.


Do you have any proof or references that tool loading increases as metal removal rate decreases.
I agree that the tool is not strong enough for the application.


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## mmcmdl (Mar 22, 2022)

Those Iscars like to cut and they will do just that . SFM is the issue . If not a CNC , the operator has to be aware of it adjust speeds and feeds . These cutoff tools aren't made to push or rub material off , they're made to cut . I've pushed some to , and past the limits with excellent results .


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## Parlo (Mar 22, 2022)

mmcmdl said:


> Those Iscars like to cut and they will do just that . SFM is the issue . If not a CNC , the operator has to be aware of it adjust speeds and feeds . These cutoff tools aren't made to push or rub material off , they're made to cut . I've pushed some to , and past the limits with excellent results .


Yes they need to be pushed hard like most carbide tools.
The problem with programming a CSS is that it will be running at max RPM as the part breaks off!! A capped RPM is used to lower surface speed from a set diameter. A tiny surface speed is unavoidable at small diameters but still cuts.
Speeding up on a manual lathe when getting smaller is ok, providing the trajectory of the part is considered.


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## MrWhoopee (Mar 22, 2022)

Something else to consider, which I have observed but have never seen mentioned, is the increased difficulty in getting cutting fluid down into the cut as the depth increases. This is peculiar to parting because of the narrow groove and the tendency for centrifugal force to throw the fluid out of the the groove. The absence of lubrication and cooling in the cut could result in heating and expansion of the material, causing binding. Flood coolant overcomes this problem, as would a squirt bottle.


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## mmcmdl (Mar 22, 2022)

Some of my older Iscars had coolant passages directly to the insert which helped greatly . They almost need a separate flood or heavy drip line for optimal cutting which most hobby shops don't use . ( including myself these days ) . A squirt bottle filled with oil works good but it ties up your " emergency exit " hand .


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## mmcmdl (Mar 22, 2022)

Parlo said:


> Yes they need to be pushed hard like most carbide tools.
> The problem with programming a CSS is that it will be running at max RPM as the part breaks off!! A capped RPM is used to lower surface speed from a set diameter. A tiny surface speed is unavoidable at small diameters but still cuts.
> Speeding up on a manual lathe when getting smaller is ok, providing the trajectory of the part is considered.


Sure , a G96 CSS code along with a max RPM code is used to control this . FWIW , I wouldn't be parting this off totally . I would be leaving an inch or so for the saw to finish the part off . At 3-4-5000 rpm and cutting off , this would make for a pretty cool projectile flying thru the shop or your safety glass . I had a $5000 hunk of Berrilium do this once , not fun .


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## Parlo (Mar 22, 2022)

MrWhoopee said:


> Something else to consider, which I have observed but have never seen mentioned, is the increased difficulty in getting cutting fluid down into the cut as the depth increases. This is peculiar to parting because of the narrow groove and the tendency for centrifugal force to throw the fluid out of the the groove. The absence of lubrication and cooling in the cut could result in heating and expansion of the material, causing binding. Flood coolant overcomes this problem, as would a squirt bottle.


You're dead right. The original post stated that oil was used, this is definitely a job for plenty of *coolant*.


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## NC Rick (Mar 22, 2022)

I have some parting holders that look just like that. Fine, fine, fine and then…. That is a hell of a cut.  I have never parted 4”SS. 4” aluminum and one needs to be careful as the diameter reduces.  I prefer to saw off and face when I could.


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## mikey (Mar 22, 2022)

Parlo said:


> With a constant RPM. The depth of cut - ie. feed per rev remains constant as the circumference decreases then the metal removal rate decreases. High metal removal imparts more pressure to the tool than a low removal rate. There are no references to minimum cutting speeds.



Still stuck on metal removal rates and formulas, eh. What you seem to be saying here is that with a constant speed and a consistent feed then as the circumference at the point of cut decreases then so does the MMR. Then, since the MMR supposedly reduces under these conditions that this applies less pressure to the tool? 

*So how do we explain the crushed insert in the pic* at the start of this post? Seems to me that tool pressure increased here, no?


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## Aukai (Mar 22, 2022)

For what ever reason the bit buried into the material hard enough to snap the parting blade itself, and it made a big fuss trying to get the bit out. Parlo are you sure as the surface speed decreases, that the feed is the same taking a bigger bite didn't break things?


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## stupoty (Mar 22, 2022)

MrWhoopee said:


> Something else to consider, which I have observed but have never seen mentioned, is the increased difficulty in getting cutting fluid down into the cut as the depth increases. This is peculiar to parting because of the narrow groove and the tendency for centrifugal force to throw the fluid out of the the groove. The absence of lubrication and cooling in the cut could result in heating and expansion of the material, causing binding. Flood coolant overcomes this problem, as would a squirt bottle.



Yeah I always have this problem with parting , would like  flood coolant to help with this.

Stu


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## Parlo (Mar 22, 2022)

mikey said:


> Still stuck on metal removal rates and formulas, eh. What you seem to be saying here is that with a constant speed and a consistent feed then as the circumference at the point of cut decreases then so does the MMR. Then, since the MMR supposedly reduces under these conditions that this applies less pressure to the tool?
> 
> *So how do we explain the crushed insert in the pic* at the start of this post? Seems to me that tool pressure increased here, no?


It seems you don't see the correlation between MMR & tool pressure, so regretfully I will resist looking for simpler examples to explain this.

The tool pressure increased because it got hot + dull so the material work hardened, the tool could not cut and broke. The most brittle part is the insert, so chipping is certain.

No coolant leading to work hardening and premature tip wear.
No coolant on a dull tip that was worn on the first part - see above.
Excessive tool pressure on a dull tip.
Incorrect insert grade and geometry leading to premature wear.


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## ericc (Mar 22, 2022)

You can feel the cutting pressure go up.  There are potentially two things going on here.  First, the correct way to look at the cut is the feed per distance traveled.  Not the feed per rev, since this ignores the thickness of the chip being lifted.  Imagine unrolling the cut.  It is like a shaper whose downfeed is held constant, but the ram speed is getting slower and slower.  Eventually, the bit plows too deep and experiences excessive force.  The second thing going on is that any misalignment of the tool off center becomes more serious.  If the cutter is low, the tendency to roll over the top becomes worse as the stub gets thinner.  If the cutter is high, the clearance angle gets worse as the diameter decreases.  You can see this by just drawing a picture.

Once, an experienced machinist told me to just keep turning the cross-feed, and turn even harder if experiencing any trouble parting.  This works if one is having problems with chatter, but when the diameter gets small, pushing faster and harder doesn't help.  Yes, I admit it.  I followed the advice blindly (you know how certain those experienced machinists can be), and I got the expected bad results.  It reminds me of when I was criticizing an engineer's design.  It failed in the simulator, failed on the bench, and eventually failed in the field.  He grinned sheepishly and said, "that's just because you're an idiot", but at least that stupid thing never came up again.

Think through what you are doing!!!!


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## Parlo (Mar 22, 2022)

Aukai said:


> For what ever reason the bit buried into the material hard enough to snap the parting blade itself, and it made a big fuss trying to get the bit out. Parlo are you sure as the surface speed decreases, that the feed is the same taking a bigger bite didn't break things?


It takes the same thickness of chip at all diameters. It removes smaller and smaller amounts of material per revolution as the diameter decreases, lowering the tool pressure as it goes.


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## Aukai (Mar 22, 2022)

I think as you go to the center at the same advancing speed, the rotating speed slows down, and is making a deeper cut. That's how I'm thinking it's working.


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## mikey (Mar 22, 2022)

Parlo said:


> It seems you don't see the correlation between MMR & tool pressure, so regretfully I will resist looking for simpler examples to explain this.



Okay, I knew there had to be some engineer-type guy out there who could explain things better. How about this:

_*If the machine tool’s spindle speed remains constant as the parting tool moves to the center of the workpiece, the cutting speed will gradually decrease until it reaches zero at the center. A decrease in cutting speed is disadvantageous for the tool and can severely stress the cutting edge. As the edge approaches the center, pressure increases as the tool is fed at the decreasing cutting speed. In CNC lathes, the control increases the spindle speed as the tool moves toward the center to maintain the same cutting speed. Eventually, however, the machine cannot go any faster and the cutting speed decreases as the tool gets close to the center of the workpiece.*_

Simple enough for you?


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## Ken226 (Mar 22, 2022)

Complex things can rarely be  boiled down to simplicity.







On page 2.




			https://www.google.com/url?sa=t&source=web&rct=j&url=https://core.ac.uk/download/pdf/82734159.pdf&ved=2ahUKEwjbxYmDxtr2AhVkDzQIHfJNCQUQFnoECCYQAQ&usg=AOvVaw1rVN-nBW5NlMs07BihpZl3


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## Parlo (Mar 22, 2022)

Aukai said:


> I think as you go to the center at the same advancing speed, the rotating speed slows down, and is making a deeper cut. That's how I'm thinking it's working.


A good way is to imagine what is happening, consider a pointed the tool scribing a scroll on the face of the part as it feeds accross the face. The distance between the lines will remain constant. This distance is the feed per revolution. What happens as the diameter decreases is that the speed of the chip accross the top of the tool will decrease. The chip thickness ( feed per rev ) is unchanged throughout just less material is removed per revolution as the diameter decreases.


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## Ken226 (Mar 22, 2022)

Another source,  different material tested,  with similar results.  Also explained as the reason carbide inserts give better finishes and longer tool life at the appropriate speeds than they do at lower speeds.   Low speeds are better for sharp HSS tools. 






It's a long read, .pdf download.









						(PDF) Cutting Parameter Optimization when Machining Different Materials
					

PDF | Flank wear occurring on the cutting edge increases as machining time goes on. This results in an increase in the cutting force and the surface... | Find, read and cite all the research you need on ResearchGate




					www.researchgate.net
				





A quote from the article @mikey posted, which supports the information in both of the articles I posted:

"As the edge approaches the center, pressure increases as the tool is fed at the decreasing cutting speed."


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## Navy Chief (Mar 22, 2022)

Parlo said:


> It takes the same thickness of chip at all diameters. It removes smaller and smaller amounts of material per revolution as the diameter decreases, lowering the tool pressure as it goes.


As the tool moves to the center it is seeing slower and slower surface speeds for the same depth of cut, the tool cuts less and less efficiently and pressure required to complete the cut goes up. 

Sent from my Pixel 5 using Tapatalk


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## Aukai (Mar 22, 2022)

You seemed convinced, and I don't agree with your physics, so we'll have to just let it go


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## Parlo (Mar 22, 2022)

Ken226 said:


> Complex things can rarely be  boiled down to simplicity.
> 
> 
> 
> ...


This article has a constant metal removal rate & does not consider the ever reducing metal removal rate in parting off.


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## Winegrower (Mar 22, 2022)

Parlo said:


> The metal removal rate and therefore the load on the tool decreases as the diameter reduces when using a constant rpm and constant feed per rev. If the feed was excessive it would show at the beginning of the cut where the forces are greatest. I suspect the blade was too weak for the operation and a deeper blade and possibly wider would have been more suitable



Sincerely, this is about as far from my experience as possible.   Please, if you are uncertain about parting operations, read and believe Mikey’s approach, which he has shared widely for a long time…it works.


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## Parlo (Mar 22, 2022)

Aukai said:


> You seemed convinced, and I don't agree with your physics, so we'll have to just let it go


Can you please elaborate or demonstrate where or how the physics are flawed. No Googling .


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## Navy Chief (Mar 22, 2022)

Parlo said:


> This article has a constant metal removal rate & does not consider the ever reducing metal removal rate in parting off.


No, it shows that slower surface speeds produce higher cutting forces for an equal depth of cut. Which is exactly what happens as you part off a piece at a constant spindle speed, as the diameter decreases the cutting force will increase of the depth of cut remains the same. Sounds like exactly what happened to the parting tool in the original post. 

Sent from my Pixel 5 using Tapatalk


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## Ken226 (Mar 22, 2022)




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## Parlo (Mar 22, 2022)

Navy Chief said:


> No, it shows that slower surface speeds produce higher cutting forces for an equal depth of cut. Which is exactly what happens as you part off a piece at a constant spindle speed, as the diameter decreases the cutting force will increase of the depth of cut remains the same. Sounds like exactly what happened to the parting tool in the original post.
> 
> Sent from my Pixel 5 using Tapatalk


So you believe that metal removal rate has no effect on tool forces.  The graph shows that it does with the varying feedrates ( increased feedrate shows an increased tool load ).
The tool in the example broke " very quickly " which I read as near the outside diameter where the cutting speed was near ideal.


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## Navy Chief (Mar 22, 2022)

Parlo said:


> So you believe that metal removal rate has no effect on tool forces. The graph shows that it does with the varying feedrates ( increased feedrate shows an increased tool load ).
> The tool in the example broke " very quickly " which I read as near the outside diameter where the cutting speed was near ideal.



As I read it the cut was silent after some initial chatter and was going well with the auto feed engaged, this would imply that it was not right at the outside diameter. 

Sent from my Pixel 5 using Tapatalk


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## mikey (Mar 22, 2022)

Actually, if you read post #9, the cut was about halfway through when he began to have issues. This is right around the time that SFM is beginning to drop and tool pressure starts to increase. 

Parlo, please show us your formulas for MMR so we can all attempt to see where you're coming from.


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## Ken226 (Mar 22, 2022)

From the article Mikey posted.   Specifically, the article is talking about parting:

*"If the machine tool’s spindle speed remains constant *as the parting tool moves to the center of the workpiece, the cutting speed will gradually decrease until it reaches zero at the center. A decrease in cutting speed is disadvantageous for the tool and can severely stress the cutting edge. *As the edge approaches the center, pressure increases as the tool is fed at the decreasing cutting speed."*

Author​Scott Lewis
Scott Lewis is with Sandvik Coromant Co.



So,  if the spindle speed and the feedrate are constant,  then it stands to reason that the material removal rate and surface speed are reduced as well,  as the tool plunges deeper*.   *
    Yet still, it says that In that scenario, the pressure would increase  as the tool moves toward center.


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## Shootymacshootface (Mar 22, 2022)

Janderso said:


> What lathe do you have?
> If your set up is right and you have a rigid lathe, it’s a piece of cake.In my experience


Clausing 6329


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## Watchwatch (Mar 22, 2022)

How is this even an argument?

When you part by “hand”, you have to increase the feed rate in X the closer you get to the center of the part.

A player doesn’t need math or physics. The feel let’s you know. The sketchiest time of the operation is when you get closest to zero radially.


Sent from my iPhone using Tapatalk


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## Parlo (Mar 23, 2022)

mikey said:


> Actually, if you read post #9, the cut was about halfway through when he began to have issues. This is right around the time that SFM is beginning to drop and tool pressure starts to increase.
> 
> Parlo, please show us your formulas for MMR so we can all attempt to see where you're coming from.


Let's address the initial post. Parting 316 stainless steel without coolant breaks tools. Parting 316 stainless steel without coolant and with a dull insert previously used without coolant, always breaks tools. This is the overriding cause for the tool breakage in this example. I'm sure we can all compile a list of other minor contributing factors.

Let's consider the relationship between SFM and MMR.
I won't start scouring the internet for articles to reinforce my point, I will use the graph kindly posted by Ken226 in post #32.
The graph shows a gradual increase in tool pressure as the SFM drops. I get that.
The graph also shows a decrease in tool pressure as the feedrate or MMR reduces. Agreed?
The graph appears to indicate a larger decrease in tool pressure due to the lower MMR than the increase in tool pressure resulting from lower SFM.

I appreciate that the rates may not be linear and may reverse at tiny SFM but generally speaking the relationship remains the same. The graph refers to a constant MMR so does not account for facing and parting operations. It also does not take into account the increasing weakness of the ever decreasing diameter right near the centre which eventually won't have enough strength to impart a lot of pressure on the more rigid tool.

The question is:
If the tool pressure from both variables - MMR & SFM were averaged at various diameters and plotted on a graph, would the tool pressure rise or fall as the diameter decreased?
I believe it will fall until the diameter get's too small to be able to impart any significant pressure on the tool. This is just a considerd opinion, I believe the reduction in MMR has a greater effect on tool load than the reduction in SFM. I remember conducting lathe tool trials 40+ years ago with what I recall as a lathe tool dynamometer, I wish I had access to the facilities now to discover exactly what does happen when facing or parting off.


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## mikey (Mar 23, 2022)

Parlo said:


> Let's address the initial post. Parting 316 stainless steel without coolant breaks tools. Parting 316 stainless steel without coolant and with a dull insert previously used without coolant, always breaks tools. *This is the overriding cause for the tool breakage in this example*. I'm sure we can all compile a list of other minor contributing factors.



Aukai used cutting oil from the get go. Not sure if the insert was new but coolant was used throughout so no, I don't agree that this was the cause of tool breakage in this instance. *As I have stated multiple times, I believe it was due to the cutting conditions that developed as the cut was made*. It was not the blade. It was not the insert. I have parted 303, 304 and 316 on numerous occasions with a used GTN-3 insert without any issues. I have parted SS even more often with HSS and I know those blades were often not freshly sharpened and I had no issues parting with them, either. The difference between Aukai and me doing it was that I controlled the feed manually, that's all. No problems, no chatter, no crashes, no stalling. 

I will leave further discussion to you and others. I wouldn't want you to injure yourself trying to simplify things for me or have to scour the net for articles to reinforce your point. But I do congratulate you, Parlo, for being the single person to have made my Ignore list.


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## Parlo (Mar 23, 2022)

mikey said:


> Aukai used cutting oil from the get go. Not sure if the insert was new but coolant was used throughout so no, I don't agree that this was the cause of tool breakage in this instance. *As I have stated multiple times, I believe it was due to the cutting conditions that developed as the cut was made*. It was not the blade. It was not the insert. I have parted 303, 304 and 316 on numerous occasions with a used GTN-3 insert without any issues. I have parted SS even more often with HSS and I know those blades were often not freshly sharpened and I had no issues parting with them, either. The difference between Aukai and me doing it was that I controlled the feed manually, that's all. No problems, no chatter, no crashes, no stalling.
> 
> I will leave further discussion to you and others. I wouldn't want you to injure yourself trying to simplify things for me or have to scour the net for articles to reinforce your point. But I do congratulate you, Parlo, for being the single person to have made my Ignore list.




There is a significant difference between cutting oil and coolant, especially in this instance.

Cutting oil was manually applied, not flood coolant as I suggested.
The insert had cut one previous part without flood coolant. The cutting conditions did develop / deteriorate as the cut was made, due to the lack of coolant.
I expect any tool to still cut past half way at lower than 50% of the SFM.
You seem rather vexed if your opinion is challenged. A forum is for all to exchange views, not a competition.


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## jaek (Mar 23, 2022)

MRR = cutting speed x feed rate x depth of cut, right? 

Which of those change when facing or parting on a manual lathe with power feed?


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## Parlo (Mar 23, 2022)

jaek said:


> MRR = cutting speed x feed rate x depth of cut, right?
> 
> Which of those change when facing or parting on a manual lathe with power feed?


MRR refers to a volume per unit of time. Feed rate x depth of cut only gives an area. Turning a diameter on a lathe needs the area of the cross section x the feed rate to give the volume per rev. ( Like a stack of washers with each one the thickness of the feed per rev ). When facing, the cross section is continually reducing.
Hope this helps.


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## jwmelvin (Mar 23, 2022)

jaek said:


> MRR = cutting speed x feed rate x depth of cut, right?
> 
> Which of those change when facing or parting on a manual lathe with power feed?



Cutting speed, in this context, is RPM * circumference, and the circumference changes when facing or parting.


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## mikey (Mar 23, 2022)

Okay, one last time.



Parlo said:


> There is a significant difference between cutting oil and coolant, especially in this instance. Cutting oil was manually applied, not flood coolant as I suggested. The insert had cut one previous part without flood coolant. The cutting conditions did develop / deteriorate as the cut was made, due to the lack of coolant.


Okay, instead of some nebulous contentions about MMR that you were proposing before, now you seem to be stuck on the idea that coolant alone would have prevented any breakage issues that occurred. You have a tool that is being forced into a cut that it cannot make so it breaks. That is clear for all to see. I tried to explain it but you continued to insist that some force that I am too stupid to understand is responsible. Until today. Today, its not that force; its coolant, but only if its flooded. Really?



Parlo said:


> You seem rather vexed if your opinion is challenged. A forum is for all to exchange views, not a competition.


*Let me be crystal clear. I am "vexed" because of your veiled insults, Parlo*.

Don't even try to put me in a position where I seem to be the inflexible authoritarian. Not only is that totally inaccurate, it makes you out to be the poor wronged martyr and absolves you of having any part of this - I'm not having it. If anything, we are here because of you. I have been a member of HM almost since the day it was created and my record of exchanging views is there for all to see. 

So is yours.


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## Jim F (Mar 23, 2022)

Parlo said:


> MRR refers to a volume per unit of time. Feed rate x depth of cut only gives an area. Turning a diameter on a lathe needs the area of the cross section x the feed rate to give the volume per rev. ( Like a stack of washers with each one the thickness of the feed per rev ). *When facing, the cross section is continually reducing.*
> Hope this helps.


Same as parting.............


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## jaek (Mar 24, 2022)

Parlo said:


> MRR refers to a volume per unit of time. Feed rate x depth of cut only gives an area. Turning a diameter on a lathe needs the area of the cross section x the feed rate to give the volume per rev. ( Like a stack of washers with each one the thickness of the feed per rev ). When facing, the cross section is continually reducing.
> Hope this helps.



If we have an area and we need volume per time, don't we need to multiply by a speed (distance per time) instead of a cross section (area)?


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## Parlo (Mar 24, 2022)

Jim F said:


> Same as parting.............


Yes, facing and parting are the same when referring to varying stock removal rates.


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## Parlo (Mar 24, 2022)

jaek said:


> If we have an area and we need volume per time, don't we need to multiply by a speed (distance per time) instead of a cross section (area)?


Yes, my comment #52 split the speed into its two components - distance and time. I used the distance to multiply the area to give the volume. The distance i.e. the circumference, reduces as the cut proceeds towards the centre and therefore the volume decreases.


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## Parlo (Mar 24, 2022)

mikey said:


> Okay, one last time.
> 
> 
> Okay, instead of some nebulous contentions about MMR that you were proposing before, now you seem to be stuck on the idea that coolant alone would have prevented any breakage issues that occurred. You have a tool that is being forced into a cut that it cannot make so it breaks. That is clear for all to see. I tried to explain it but you continued to insist that some force that I am too stupid to understand is responsible. Until today. Today, its not that force; its coolant, but only if its flooded. Really?
> ...



My post #22 first mentioned plenty of coolant and again in post #27.
My post #44 states that lack of coolant was a large factor, *not* " coolant alone would have prevented any breakage issues ".
I think I have been fairly consistent on this.

I innocently added that other varying forces are applied to a tool that also affect its loading and never denied the existence of the surface speed forces. This seemed to unleash some anger and references were posted that I debunked as they did not consider varying loads. Thats when the nasty comments started...

I fully outlined my findings in post #48, I hope someone finds them interesting.
The link to research posted by Ken226 in post #32 - here - https://core.ac.uk/download/pdf/82734159.pdf shows on page 4 (160) section 4 item 2 confirms in its conclusions that MMR has a greater significance in tool load than surface speed.


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## Parlo (Mar 31, 2022)

Ken226 said:


> From the article Mikey posted.   Specifically, the article is talking about parting:
> 
> *"If the machine tool’s spindle speed remains constant *as the parting tool moves to the center of the workpiece, the cutting speed will gradually decrease until it reaches zero at the center. A decrease in cutting speed is disadvantageous for the tool and can severely stress the cutting edge. *As the edge approaches the center, pressure increases as the tool is fed at the decreasing cutting speed."*
> 
> ...


He was only referring to cutting speed.


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## Parlo (Mar 31, 2022)

ericc said:


> It is like a shaper whose downfeed is held constant, but the ram speed is getting slower and slower.  Eventually, the bit plows too deep and experiences excessive force.
> 
> 
> Think through what you are doing!!!!


A shaper and lathe both have their feeds mechanically linked to the spindle speed or stroke rate. So any speed decrease has a proportional feed decrease.


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## Firstram (Mar 31, 2022)




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