Turning Roughing Pass Depth?

[Lonnie.Cady]

What is the idea behind reducing the last 2 passes when generating a rough turning tool path?

I now have 2 passes that don't break a chip vs one pass that does not break a chip.

[Laurens-3DTechDraw]

I'm pretty sure the idea is that you don't get a 0.05 mm cut in the end.

[Lonnie.Cady]

I kind of assumed that, but how is it better than just using a setting similar to milling like "use even step-downs" and just make all cuts the same?

One method would be to have an option to use even DOC with the option to choose to equalize by increasing the DOC or decreasing the DOC.

[Rob.Lockwood]

---

@lonniecady wrote:

I kind of assumed that, but how is it better than just using a setting similar to milling like "use even step-downs" and just make all cuts the same?

One method would be to have an option to use even DOC with the option to choose to equalize by increasing the DOC or decreasing the DOC.

---

I've had the thought several times that the 'maximum stepdown' logic is flawed, rather.. particularly when using even stepdowns, the logic should be 'maximum' and 'desired' stepdown parameters. In many cases, the maximum would simply be pulled from flute\insert length, but having both be user controlled is fairly important for reliable parametric-ness. It's often annoying to have to fudge my calculated number 'up' gradually until I find the balance i'm looking for, and there's always going to be a 'sweet spot', and that's the point that most users will want to hit.

P.S. I think 'even stepdowns' is currently broken in adaptive, but that's probably another thread..

[Lonnie.Cady]

I see what you are saying @Rob.Lockwood, but I don't think that would be a very good logic to use in turning.   Pulling the insert length is practically meaningless for turning.  A 80 deg diamond is going to have a shorter edge length than a 35 deg with the same IC yet be able to handle a larger DOC.

The way it is now there is no real way to tweak it to get nice even cuts.  Reducing the final 2 to prevent a light final pass results in 2 passes that will not break a chip in many roughing conditions.  I can keep increasing the DOC to the point of overloading the insert on the first passes to get the final passes deep enough to break a chip, or I could possible try to manually calculate the DOC so the system does not need to make any adjustments for the final passes.

I would think it would be some pretty simple math to have the software create equal cuts for the entire operation.  Then one could easily make a adjustment to the DOC and know what they are going to get.

I am sure there are improvements, but the turning software I use not is pretty much bullet proof in that area IMO.  I check a box to equalize cuts, then select a drop down choice of increase depth or decrease depth of passes to equalize the cuts.

[Rob.Lockwood]

Right, that's why I said in most cases, the default could pull the edge
length.. for turning, the tool itself should contain a max cut depth field,
since that often differs from the edge length)

[Lonnie.Cady]

I am saying pulling the edge length of a turning insert would be meaningless and should never default to that.  How much turning have you done that utilizes the full edge length of a turning insert.  I have a couple of times and it has never ended well.  

I could see having a DOC field in the tool library which would set the operation default, similar to feeds and speeds.

DNMG 3(2.5)1  edge lenght is .46"  (MFG recommend .015"-.07" DOC)

CNMG  3(2.5)1  edge lenght is .36"  (MFG recommend .030"-.120" DOC)

defaulting to the edge lenght would drive both tools deeper than MFG recommendations and also even a % reduction would end up with incorrect setting as the DNMG would always default to a greater DOC.

[Lonnie.Cady]

@Rob.Lockwood, 

I see what you are saying now.  I did not pause at the "..." when reading your response.  Makes better sense when I read if correctly.

Edge length for mill

max DOC for turning

[Lonnie.Cady]

Just to bring back the original topic, no matter how the desired stepdown field is populated it is not going to produce good results in turning roughing unless the algorithm/logic is changed.  I think I got a little side tracked about where to get the value and to me the real issue right now is that in turning you end up with 2 lighter passes at the end and it is not good IMO.

[Rob.Lockwood]

Right, first and foremost, at a minimum, some method of making the passes equal is necessary.. I just like to visit an issue once instead of over and over.

Adding the 'max DOC' field to the turning insert is a fairly wide ranging independent of this individual issue anyway, But it's lack really doesn't prevent anyone from doing work, so equal passes should see priority.

In turning, you really want to fall within a fairly narrow DOC range, and the more logic and automation we can get to keep it in that range the better. With that in mind, it would be excellent to store the minimum DOC to break a chip along with the maximum DOC. With those two values, the operations could pretty quickly set the best compromise of breaking a chip, evening passes, and maximizing material removal. Of course, there will always be situations where something has to be compromised (an operation with a total DOC just barely outside the inserts max DOC comes to mind, where dividing it in half might cause the DOC to fall below the 'chip break' DOC..

It's also an interesting concept, as the actual usable DOC must be derived from the tool orientation combined with the linear DOC along the edge.

Is the idea station working yet? should definitely get this in there, i'd vote it up as it drives me nuts to wind up with these un-optimized depth cuts.

[Lonnie.Cady]

I tried to post to the idea station since there are already 2 in there, but had access denied.

[Steinwerks]

Those two appear to be old and pulled from somewhere else on the Forum. Everyone's been denied (IE permissions are broken).

[Laurens-3DTechDraw]

---

@Steinwerks wrote:
Those two appear to be old and pulled from somewhere else on the Forum. Everyone's been denied (IE permissions are broken).

---

Actually working now.

[Steinwerks]

Yes, but not when I posted that 😉

[Anonymous]

I'm just posting to agree with the fact, that this designed technique is weird. I've noticed this recently myself, and often the last 2 passes are long unbroken stiff stringers. I'd rather have a finishing .010 or so deep single thin unbroken coil, than 2 long stiff .040 or so deep rigid spears tangling in my turret.

[Anonymous]

Dittos on the not right selection method here. What would also be nice is if we could have interrupted cuts that would break up those long stringers and be able to assign what we want for cut depths all the way down.

[Anonymous]

We've got no-drag now in InvHSM which is nice, but this "smart" roughing stepdown calculation really needs to go. Not sure where this idea came from but it is terrible. I'm trying to program some basic roughing step downs on a simple part, and the program mandates 3 un-even(chip stringer) step downs, where I only want 2 deep matching steps.

This is a really, REALLY, terrible function to make us do in turning.

[Laurens-3DTechDraw]

---

@Anonymous wrote:

We've got no-drag now in InvHSM which is nice, but this "smart" roughing stepdown calculation really needs to go. Not sure where this idea came from but it is terrible. I'm trying to program some basic roughing step downs on a simple part, and the program mandates 3 un-even(chip stringer) step downs, where I only want 2 deep matching steps.

This is a really, REALLY, terrible function to make us do in turning.

---

Guys,

(Saw this in Lonnie's example)

Are you using a finishing pass in these operations that really bother you?

I don't mean are you finishing with it, but is the finishing pass turned on?

[Anonymous]

Nope separate tool is used for finishing pass.

I spent tons of time trying everything in the program, to get even step downs but no luck, so I made even steps manually with a separate operation having a set minimum ID limit for each step down.

Turning 17-4 stainless it is a very fine line to get chips to break. These un-even steps set by the program are really making it hard to get a clean program I can let run for a few hours, without having to hover over non-stop so I can stop the machine every 5 minutes to pull stringers.

[Anonymous]

Here is the closest I can get without having to create each roughing pass manually.

Two .063" step downs would be ideal, and would rough the part in 2 passes to leave .004" for a finish pass. No matter what I set as the roughing step down, the program throws in that tiny little .002"(or more) pass for no reason.