Trailing knife addon

[macmanpb]

Is there a script or addon to prepare g-code for using with a trailing knife?

[jeff.walters]

what type of machine are you talking about? 

[macmanpb]

I am talking about normal cnc machine in gantry style.

You can find more information about the tool what i mean, here: http://donektools.com/

[jeff.walters]

I would have to say that right now no we don’t support a drag knife. I am curious how does the control handle indexing the spindle? Is it strictly a C axis callout?

[LibertyMachine]

As far as I know, most knives like that are often called "drag knives" or "tangential cutters". The spindle is in neutral, it does not rotate. The best example I could give would be to compare it to the front wheel on a shopping cart. The g-code would no longer be based on the centerline of the spindle, since you are basically dragging a blade around. Not sure of the method one would use to produce correct code

[macmanpb]

A c axis is not needed.

The tip of the blade trails behind the motion of the CNC.  The precision bearings in the tool allow it to freely rotate and act much like the castor on an office chair.

Sharp corners are achieved with what are referred to as corner actions within the CNC tool path.  These corner actions instruct the CNC to raise the blade such that the tip is just barely in contact with the material surface.  The machine then moves through a very small circle around the tip of the blade causing the blade to rotate, while the tip of the blade remains in the same location.  The machine then moves the blade back to the cutting depth and resumes cutting.

[jeff.walters]

I asked about the C only because in the video it looked like the tool was orientating with the tool up.

The corner action is the sort of thing that could be quite difficult to get the system to output. I’m sure there are times when you want one and when you don’t. That’s the kind of logic the system doesn’t have built in.

[macmanpb]

Before fusion360 i used "cambam" to create my CAM. I see, cambam has a script for those drag knifes.

I can use fusion to create my toolpath and then i will use cambam to add the script output to the g-code.

 

[daniel_lyall]

theres a small loop at the direction changes the knife moves up a small amount then goes around the loop what turns the knife to the correct angle for the next cut.

look at this vid it shows quite well how it works

https://www.youtube.com/watch?v=GnVx120Z_g0

[mike.spellman]

Within TruNEST (Magestic Systems) which was recently aquired by AUTODESK we have several work flows that support knife cutting. WIthin our solutions which are available today outside of fusion we fully support this aproach. We have filters that can automatically smooth the geometry to reduce the amount of up and down action required by knife cutting when cutting sharp angles or draging knife across sunden angular changes, The post processors also have the capability to automatically extend the begining or ending of a segment when cutting corners or corner looping based on angular changes. There are special cutting techniques to reduce the tearing of material (redirecting the direction of the knife) when cutting slivers for fabrics or composites. There is also support for other types of knives with C-axis, utlrasonic and pizza wheels, which for some geometries require a punching style of cutting for tight knotches, We are now working on bringing several processes and cutting domains into Fusion starting with Waterjet and many more to follow. 

---

@macmanpb wrote:

Before fusion360 i used "cambam" to create my CAM. I see, cambam has a script for those drag knifes.

I can use fusion to create my toolpath and then i will use cambam to add the script output to the g-code.

 

---

[sinklar]

Would some one on the Fusion 360 team give an estimated time on when we could expect to see the trailing knife option available?

It would be very nice to make my own gaskets for the servo motor project I am working on.

Tony

[jeff.walters]

Right now it’s not very high on the enhancement list so there isn’t a good estimate on when it will be added.

[gwcude]

Here is a YouTube video by John Grimsmo showing a drag knife and how it works on his machine.  He is cutting vinyl sticker material to use as mask for anodizing multi-color.

https://www.youtube.com/watch?v=3kL44yrf0Q8

[yoshimitsuspeed]

I am definitely interested in being able to use a drag knife on my machine as well.

[macmanpb]

This feature needs not a basic implementation into fusion, i think a script can do that.

The script should alter the toolpath so, that on each corner lower/higher than 90° the tool is lifted a little bit and added an arc to correct the tool position.

Then the tool dives in again and cut the next path section.

But, now we need a person that can wrap this into a script 

[dongillett]

The company mentioned above for the drag knife has a script for adding the corners to g-code in the form of an excel file.

http://donektools.com/free-cnc-router-software/links-2/

Pick the file excel file that just works on g-code.

I was just looking at this because I was considering buying this drag knife but want to make sure I can generate g-code for it before getting it.

I was trying the script but am having some problems getting g-code generated in a supported form from my drawings and the script complained that my g-code wasn't supported.

First problem is what tool to use in a 2D contour operation.  I was just using a small end-mill to get a something going.  I really want g-code produced to cut right on the contour rather than offset by the bit size so need to figure out how to get just plane old g-code to follow a line rather than to mill.  Modeling as a milling operation has some bad side effects like avoiding small slots where the bit is too large.  I tried defining a really small bit but had problems with collisions I couldn't figure out.  Is there an option to produce g-code to just follow a line?  I can imagine something like engraving needs similar g-code where you really just have surface operations and ignore the tool width.  I've recently seen a dragging diamond tip engraver that looks interesting and it would need similar g-code but without the complexity of needing to add the loops.

Second... the script fails on g-code that has circular operations which my output from F360 appeared to have even though I only had straight lines in the drawing I used as a contour.  Perhaps this is lead in loops to plunge the bit?

This might take a bit more experimenting to figure out but I wanted to be make sure I could generate g-code for this before purchasing the above drag knife.

[dongillett]

I just got the script to add loops from donektools to work on F360 generated g-code.  I figured out that I should have been using a trace tool path in F360 rather than a contour toolpath and that got me g-code that looked reasonable without the bit size taken into consideration.  The center of the bit just follows the trace.  With the g-code output for that trace toolpath I was then able to run it through the excel file provided by donektools and add the loops to redirect the drag knife correctly on the corners.  I could then load it into Mach3 and see the corners as shown in the videos.  It did have a problem with one of my narrow openings but I think I can fix that with changing some settings for minimal thresholds that the script provides.

I imagine it would be possible to port this script into F360 if someone didn't want the external post-process.  I've written some F360 scripts but haven't looked at possibilities for scripting against generated tool paths and don't know what is script accessable on the CAM side.

[rwetzler]

I downloaded the script and run the macro on a very simple triangle sample file I created. I use a TinyG / Chilipeppr to run my machine. For some reason I can't get the macro to create the loops. It should create loops at each triangle tip, correct? I can see where the macro tweaks the gcode on few lines here an there but that's it.
There is this note on the macro page.. Note: This software assumes that you have defined your table surface as z-zero (which I did). It "will not work" if you have defined the surface of your as z-zero. At any rate if you can elborate a little more on how you accomplished getting the loops to work would be much appreciated. -- Thanks

[thburn]

Hi,

is there any progress visible for this issue?

I am also very interested in F360 supporting drag knifes / trailing knifes (of course including corner correction ;-))

[Anonymous]

Hi, I have been researching this matter quite a lot lately (not from a Fusion 360 standpoint) and here are my findings. First of all a drag knife and a tangential knife are two approaches of how to orient the blade along the travel path of the knife. In the case of a drag knife the center of rotation of the drag knife and the tip of the blade are offset so the drag created from the surface being cut aligns the blade (as others have mentioned, like the caster of a supermarket trolley or an office chair). A tangential knife on the other hand uses an extra axis to orient the blade. Usually the blade tip is centered with the rotation axis.

Both methods have their challenges. For the drag knife the corner movements are a must for it to work but in sharp corners imperfections are created and it is difficult to lift the drag knife and continue elsewhere. For the tangential knife either the g-code or the controller should control the rotation of the blade and in sharp corners lifts should be added to avoid damage of the material being cut. One other thing that I find challenging is the fact that the offset of the drag knife and the tangential knife changes depending on the cutting depth since the blade is angled and the deeper the blade is sunk the further the first point of contact goes. Attached is an illustration depicting this.

It would be great to have the option to input parameters such as tool type i.e. drag or tangential, cutting depth and minimum corner degrees for which to perform either corner movement or  lift respectively in order to get a g-code that compensates for the above mentioned.