Avoid Breaking cutters by Caminstructor

[Shiva.aero]

There is an excellent video on the topic of Avoid breaking cutters by Caminstructor youtube channel and here is the link

Here in this videos, the author discussed about how the Feed per tooth increases,  when tool follows the curvilinear/curved tool path. After watching this video, I got the following doubt:

1. What should be "minimum toolpath radius" for 'Optirough toolpath' for the given cutter size to avoid overloading?

2. Dynamic toolpath is used for constant chip load by keeping engagement angle constant . If the chip load can be increased due to the difference in 'tool contact point feed rate' and 'tool center point/toolpath feed rate', then are we not loosing the advantage of maintaining the 'constant engagement angle' by 'increasing the tool contact point feed rate', because of the curvilinear/curved tool path generated by Dynamic toolpath?

Regarding the #1, I decided to derive the formula from the basics to understand it better and also by taking the same example shown in the video.

That is machining a 0.55" (13.97mm)  hole with 0.5"(12.7 mm) cutter with the toolpath radius of 0.05"(1.27mm) with 30 inches/minute feed rate (760 mm/min).

Now, even though the 'tool-contact / peripheral feed rate' different is 'toolpath' feed rate, the angular speed of both should be same. So,

Angular speed of tool-contact point = Angular speed of toolpath

since,  Angular speed = Linear speed / radius of curvature.                                 (Linear speed is the feed rate)

"feedrate-toolcontact-point" / (toolpath radius + tool radius) = "feedrate of toolpath" / toolpath radius

now, feedrate at toolcontact-point = ( (toolpath radius + tool radius) / toolpath radius) * feedrate of toolpath

                                                          = ((0.05"+0.5") / 0.05)* 30 inch/min     (used dia. since it is a ratio)

                                                          = 11 * 30 inch/min = 330 inch/min! (11 times more chip load!)

Now modified feedrate of toolpath = ( toolpath radius / (toolpath radius + tool radius) ) * required feed rate at the toolcontact point

                                                           = 0.09 * 30  inch/min = 2.7 inch/min 

Now the thing is that, even if we increase minimum toolpath radius equal to that of the cutter radius or even twice of it, there is a significant increase in the toolcontact point feed rate!. I attached an excel sheet to play with. This will make very difficult to machine the corners for difficult-to-cut materials even with dynamic toolpath. So after checking this, i got the question #2!

Please let me know if there is any mistake in the understanding or calculation.

 

Equivalent feedrates.xlsx

[MWearne]

On 12/31/2021 at 10:26 AM, Shiva.aero said:

2. Dynamic toolpath is used for constant chip load by keeping engagement angle constant

Constant chip load, no it doesn't. Constant engagement angle, yes. 

I'm not exactly sure why there is not an option to keep a constant chipload or maybe even MRR constant, I assume it is a patent infringement on someone elses toolpath as it seems like a no brainer to have this option in Dynamic. As is, we are over feeding on internal features and under feeding on external.

...I think there is mention in a posting somewhere here of handling this in the post processor. No idea how well it works as I've not tested it. 

Of course, not all will agree with me so I leave you this...   

[zero_divide]

IDK why they don't add Circular feed compensation to the dynamic toolpaths. Surfcam's true mill had it 15 years ago and by now all related patents must have expired.

[Shiva.aero]

18 hours ago, mwearne said:

Constant chip load, no it doesn't. Constant engagement angle, yes. 

I'm not exactly sure why there is not an option to keep a constant chipload or maybe even MRR constant, I assume it is a patent infringement on someone elses toolpath as it seems like a no brainer to have this option in Dynamic. As is, we are over feeding on internal features and under feeding on external.

...I think there is mention in a posting somewhere here of handling this in the post processor. No idea how well it works as I've not tested it. 

Of course, not all will agree with me so I leave you this...   

So the Dynamic toolpath maintains constant engagement angle in the corner, but it increases the chipload! What ultimate advantage we are getting from it?

As show in the excel, we need to have very high toolpath radius to avoid overfeeding the tool and when I give more toolpath radius for pocket milling, it almost look like a helical milling.

 

[Shiva.aero]

19 hours ago, mwearne said:

Constant chip load, no it doesn't. Constant engagement angle, yes. 

I'm not exactly sure why there is not an option to keep a constant chipload or maybe even MRR constant, I assume it is a patent infringement on someone elses toolpath as it seems like a no brainer to have this option in Dynamic. As is, we are over feeding on internal features and under feeding on external.

...I think there is mention in a posting somewhere here of handling this in the post processor. No idea how well it works as I've not tested it. 

Of course, not all will agree with me so I leave you this...   

Plz check this link. It says "constant chip load"

https://www.mmsonline.com/articles/boost-metal-rates-with-constant-chip-load-machining

[cncappsjames]

10 hours ago, zero_divide said:

IDK why they don't add Circular feed compensation to the dynamic toolpaths. Surfcam's true mill had it 15 years ago and by now all related patents must have expired.

Negative. New patent issued in 2014.

https://www.tenlinks.com/news/celeritive-technologies-gets-2nd-us-patent-for-volumill/

 

https://patents.justia.com/patent/8880212

Quote

This application is a continuation of U.S. patent application Ser. No. 12/575,333, filed on Oct. 7, 2009, entitled “HIGH PERFORMANCE MILLING,” which claims the benefit of U.S. Provisional Application Ser. No. 61/103,515, filed on Oct. 7, 2008, entitled “HIGH PERFORMANCE MILLING.” This application also claims the benefit of U.S. Provisional Application Ser. No. 61/103,869, filed on Oct. 8, 2008, entitled “HIGH PERFORMANCE MILLING,” which is hereby incorporated herein in its entirety by reference.

[Shiva.aero]

22 minutes ago, cncappsjames said:

Negative. New patent issued in 2014.

https://www.tenlinks.com/news/celeritive-technologies-gets-2nd-us-patent-for-volumill/

 

https://patents.justia.com/patent/8880212

This old post explains it better

Is it possible that MC adjusts engagement angle instead of keeping it constant, to compensate for the increase in chip load due to Arc moves, instead of varying the feedrate?

[cncappsjames]

Engagement Angle (ex. 100% engagement = 180 Deg. Engagement Angle) is part of the Celerative Patent.

[Colin Gilchrist]

Check out this thread for some information on modifying your Chip Load "on-the-fly", by looking at the Arc Radius of the Tool, Path, and the "Linear Feed at Tool Center", versus "Linear Feed value at the Tool Periphery".

 

[zero_divide]

On 1/3/2022 at 9:49 AM, cncappsjames said:

Negative. New patent issued in 2014.

https://www.tenlinks.com/news/celeritive-technologies-gets-2nd-us-patent-for-volumill/

 

https://patents.justia.com/patent/8880212

Dang!

Didn't know they could/have done that.

There isn't really a lot of ways to mill the part. Everything including simple  parallel step-over must have a patent behind it then.

[Newbeeee™]

On 1/2/2022 at 6:46 PM, mwearne said:

Constant chip load, no it doesn't. Constant engagement angle, yes. 

I'm not exactly sure why there is not an option to keep a constant chipload or maybe even MRR constant, I assume it is a patent infringement on someone elses toolpath as it seems like a no brainer to have this option in Dynamic. As is, we are over feeding on internal features and under feeding on external.

 

Have they changed the algorithm in the last couple of releases then? Specifically if you just dynamic a square block?

Unless some manual jiggery pokery, first pass round was brutal on the corners....?

[Shiva.aero]

On 1/3/2022 at 11:30 PM, Colin Gilchrist said:

Check out this thread for some information on modifying your Chip Load "on-the-fly", by looking at the Arc Radius of the Tool, Path, and the "Linear Feed at Tool Center", versus "Linear Feed value at the Tool Periphery".

 

What if there are no G2 & G3 in the code? I mean approximating every Arc moves into linear moves. Will the overfeeding still occurs?

 

[Colin Gilchrist]

1 hour ago, Shiva.aero said:

What if there are no G2 & G3 in the code? I mean approximating every Arc moves into linear moves. Will the overfeeding still occurs?

 

Yes, because this particular code only applies to arcs.

If you are only outputting Linear Motion, then you should be using the High-speed Functionality on your particular machine to control the cutting performance. On a Fanuc, this is AICC, and it is sold in different packages.

The highest level (for Roughing) is 'G05 P10000'. (All integers, no decimal.)

You need to enable this "Outside or Inside" of Tool Length Compensation.

For example: 

Here is before the G43 line, and need to cancel it after the G49 command at the end of an operation. 

G05 P10000

G0 X0. Y0. S8000 M3

G43 H1 Z2.

.

.

.

G53 G49 Z0.

G05 P0