Tangential knife using 4th stepper

I am looking to future uses for the OF CNC, and considering plans to build a tangential cutter for cardboard and Coroplast sheet material. I read somewhere in the forum where the controller does not yet support a 4th rotary axis, but would it allow control of a stepper motor for a tangential cutter? I believe there would be a few Gcode hurdles to overcome, but there has been work done in other forums on both the hardware and software side that demonstrates it is possible.

Any insights are appreciated,


I guess it is all about just how far down a rabbit hole you want to go. They don’t support the 4th axis; they do support on and off commands from the breakout.

Do you need to control the speed in real-time?

The knife would need to be raised using z axis, the 4th stepper would need to be controlled with gcode to follow the cutting path as it moves along x and y axis. Thank you for your input - my world is filled with rabbit holes, some I’ve even been down and returned from.


That comment sounds familiar

Okay I understand now and no, a separate one Chanel controller would not work. Going to need 1f to support a 4th or a whole different controller.

From what I understand, and it is limited, I need control of a ‘C’ axis - one that rotates a stepper motor perpendicular to the x/y plane - like the z axis but not linear motion. The tangential blade would follow a vector direction created by the x/y G code. The BuildBotics and OF controller have the driver and plug connection I believe, so it seems if there is any limitation it comes down to the software. I was looking at the UCCNC software - looks like a great UI and has I believe the control I need - but that is a different CAM software than the one the OF already has installed.

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Something I’d try before going tooooo deep into the tangential and trying to drive C and all would be a simple Razor knife drag knife.
Vcarve fully supports toolpathing for this and it works well for most use cases.

Thank you for that. I have seen some great 3D printed versions that I will most likely build, as well as the classic ‘Donek Tools’ knives. I was also thinking this was the place to start, for a variety of good reasons, and then see where future needs take me. Thank you for commenting.

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I would highly suggest the Donek Tool knives…
I have a Donek Drag knife (large model), and use it on my 5’x10’ cnc router table, It works perfectly. I use it for foam boat carpets 0.25-0.375 thick
As for programming the knife, there is an add-on app. for Fusion 360 available.
I’m not a big fan of Fusion, but it does work ok for programming the knife movements.
Note: you might want to verify the height of the knife assembly VS the available Z on the 1F.
Also, installing the knife is like a regular tool-change, no wiring involved.

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Thank you for the information. I have been using F 360 since purchasing my 3D printer, and have spent a fair bit of time learning what I need, so am happy to continue to use it for the drag knife. I found a great tutorial video on the Autodesk app store that details the set up of the add-on you mentioned. From the OF spec page it looks like the z axis has a bit over 5" of travel from router bottom to base mounting surface. I would need to buy the Donek D4, but I have not yet found anywhere that gives its dimensions to make sure it will fit with the OF - I assume it was made to work with most CNCs. Was this the caution you were referring to in your post?

Here is a pic for reference, somehow I remembered it being larger…
This is the Donek D2, and on my OF the Z slider rack is on the lowest position. So it should fit, if raised. Just make sure that when the knife pivots that the blade doesn’t hit the lower/rear portion of the rack.

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That is extremely helpful - thank you for taking the time to set up and send the picture. I imagine the dimensions of the D4 are the same given only the shaft diameter is different.

On the Donek site, there is a chart
Stack Height OA (over-all length) for reference.
btw i’m in Mtl. s-shore

Thank you. I have been all over that site and did not find a chart. When time permits, would you mind explaining where it is found?

Oops, my mistake,
I just realized that I was on the ToolsToday site. Sorry about that!!

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No problem - and thank you. Donek should add this table to their site!

Thank you again for the information you provided earlier. Just to confirm, and noting your comment on F360, could you confirm that the drag knife app for F360 works well. I plan to experiment with it when I get my machine in a few months, but wanted to check in again to see if it works, and if you have found any limitations or issues with it in your application. I plan to either buy a Donek, or make one, in the time I have to wait. The video tutorials I have found explain the settings well, but no one is using a OF CNC. I plan to use it for cardboard. I am also considering the purchase of a Vectric product, which I have seen has a ‘gadget’ that also seems to work well from the videos I have seen.