Drag Knife Pluggin

[ApexAutomotive]

So i am currently trying to create a drag knife for my cnc plasma cutter
I am using sheetcam and machine 3 with a lonestar cutting solutions spitfire 4x8
I purchaced the drag knife plug for sheet cam and designed my attatchment for the plasma cutter
As you can see in the video it is just a prototype with alot of play but it also seems like the drag knife is not possitioning itself correctly and it should be rotating to the direction of cut I currently have a 0.19 in offset for the blade because that was the default value in sheetcam so i designed the attatchment around that but i have a feeling the blade not rotating correctly could have something to do the with offset
I am also having an issue with sheetcam as it is producing m03(torch on) commands when trying to post process with the drag knife attachment and machine 3 stops the program when it realizes that the torch did not fire
I tried to set the tool number greater than 100 in an attempt to make it think it was a scribe tool so it did not include the m03 command but no luck it also includes

And help or information is greatly appreciated thank you

https://www.dropbox.com/scl/fi/2lagcx6p ... te9d4&dl=0

https://www.dropbox.com/scl/fi/fkqyph88 ... vvxvf&dl=0

https://www.dropbox.com/scl/fi/2aev5gaq ... w97ln&dl=0

https://www.dropbox.com/scl/fi/kuzhsjel ... 96dig&dl=0

Sorry for the ugly dropbox
links it wouldnt let me attatch the files directly

[Les Newell]

I see a number of issues.
None of the plasma posts are set up for drag knife. You need to use a milling/routing post.
The 'Offset amount' in your cut operation is to adjust the overall size of your part. Normally I'd recommend setting it to 0 unless you are doing something like inlay work where you want to tweak the dimensions slightly to get a good fit.
Drag knives struggle to cut small shapes like you are trying to cut. For testing I'd recommend going for much bigger shapes until you have the settings dialed in.
Is your knife exactly in line with the pivot point? Any slight twist will pull the blade out of line. Think of a shopping cart caster. The point of the blade needs to follow exactly behind the pivot.

[ApexAutomotive]

Hey Les, thank you for the response, and I apologize for the delayed response from me.

I'm wondering how I can create a post for my machine that would work with my plasma table. I'm pretty new to CNC, being only 17, so I appreciate your help.

I'm not exactly sure if I understand what you mean by the offset amount. I thought it was the measurement from the center of the "spindle" or just the bearing axis, in this case, to the tip of the razor blade, but it seems more like an inside/outside cut with kerf? I'm not sure if I understand, so I just wanted to clarify. Thank you.

As for the blade position, it's a 3D printed attachment, so it's entirely possible that it's not perfectly centered, as you mentioned, but I do have the center of the blade being in the middle of the attachment in my design.

I'm also now wondering what the difference is between a tangential knife and a drag knife. Do I actually need a spindle/fourth axis to rotate the blade at the correct angle, or can I have it "freewheel" as I am doing now?

Again, thank you. I really appreciate it.

[Les Newell]

I'm wondering how I can create a post for my machine that would work with my plasma table. I'm pretty new to CNC, being only 17, so I appreciate your help.

What CNC controller does your machine use?

I'm not exactly sure if I understand what you mean by the offset amount. I thought it was the measurement from the center of the "spindle" or just the bearing axis, in this case, to the tip of the razor blade, but it seems more like an inside/outside cut with kerf? I'm not sure if I understand, so I just wanted to clarify. Thank you.

The offset in your tool definition is the distance from the center line of the spindle to the tip of the knife.
The offset in your drag knife operation offsets the outline in or out.

I'm also now wondering what the difference is between a tangential knife and a drag knife. Do I actually need a spindle/fourth axis to rotate the blade at the correct angle, or can I have it "freewheel" as I am doing now?

Tangential uses a motor to point the knife in the direction of travel. This gives the best results but it is more complicated and expensive to set up. The tip of the blade is in line with the center line of the spindle.
Your setup with a pivot is drag knife. It relies on the tip of the knife trailing behind the center line of the spindle. It is a lot more finicky to set up.

[ApexAutomotive]

I use Mach3 for my controller

Thank you for the clarification I understand what you mean now about the offsets

I plan on cutting out foam flooring sickers for my boat so it doesnt have to be perfect

If i cant get it to work i added a pen plotter to the plasma cutter using the scribe tool so i will just have to manually cut it out
Again thank you I really appreciate it

[Les Newell]

For the knife use the 'Mach3' post processor.