Drag Knife toolpaths

[mcphill]

I don't see a good way to create a Drag Knife toolpath in BobCAD. I can go in and add the lead in and out paths to lines myself, but for larger work this would be VERY cumbersome. I have put in a feature request to have this added by BobCAD, if you think it would be of use to you, please put in a feature request as well. BobCAM-CAM Software Issue Report, Feature Request | CAD/CAM | BobCAD-CAM

My understanding is that Aspire has added this functionality, would be nice to see it in BobCAD.

If you are currently doing Drag Knife work in BobCAD, please post your workflow so we can see how you accommodate it!

Does anyone know of an open source Drag Knife toolpath creation option? I have searched via Google and came up empty...

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[rfenn]

I haven't used a Drag knife but this has been posted about on the camheads forum. You have to use an Excel spreadsheet macro to post process the G-code. I'm a minority on the camheads forum since most use Vectric products so I don't think anyone has used Bobcad produced G-code. Based on the link below, looks like the Excel macro doesn't like arcs.

Add Corner Actions to your Tool Path | Donek ToolsDonek Tools

cutting posterboard [Archive] - CAMheads CNC Router Forum By: CAMaster CNC

[mcphill]

That is a workaround worth looking at, but could be embedded and improved as a native function in BobCAD. Just would need to be enough demand on them to get it worked on!

[rfenn]

If I was going to pick a feature to add, it would be to have a better preview of a cut item to show a customer. This is one thing that Vectric products do well. I do this for signs and I end up doing a lot of the work in Corel Draw just so I can show it (which is only 2D). I could make better use of Bobart for this, but a bit cumbersome if I'm not using Bobart in the first place for the sign. I picked Bobcad because it supported many types of machines - bought it before I had a CNC router. You can't do everything and also have a lower price. The drag knife is definitely a niche, so don't see that being added any time soon.

[mmoe]

What drag knife are you using?

I don't think there is a product that natively supports this. My guess is that the controller makes the needed motions when you have a commercial knife product (that actually rotates the knife in the head), but the Donek style drag knife requires code in the toolpath. Basically, you would have to have a way for the profile feature to recognize a change of angle between two geometries that exceeds a user defined amount, like greater than 30 degrees or something like that. Any intersection where that angle exceeds the definition, the toolpath would extend by the drag knife's offset, then it would rotate on an arc on a radius that is the same as the offset value as well. If you are good with your CAD system, this is easy to do and you can then just run a profile on the shape. Just add a circle with the offset radius to each corner where you feel it exceeds the minimum (probably eyeballing will work fine), the extend/trim lines to create the needed profile.

I'd like to see that feature built in as well, but honestly I don't think there are enough users to make it worth the development time. Plus, you have to be able to be specific about how the toolpath should work since they have likely never encountered such a device. The below drawing took about 5 minutes to modify in Viacad to be used as a dragknife toolpath, so it's just not a huge amount of effort on your part to produce what's needed. That's without any prior experience having done it, so I expect it would be half that amount of time if I did this regularly.

I didn't include a lead in/lead out, but I'd have to think of the best approach for that first. You'd also need to run a profile on the line sections at full cut depth, then run the corners as a profile at the pivot cut depth. It's not a simple operation for sure, but can be done efficiently for the limited amount of times you'd probably realistically use it.

As I think about it, if you're drawing has only lines, apart from the turns, you could use a text editor to insert a different Z value for G2/G3 lines and then back to cutting depth. If you have arcs in your drawing as part of the shape, you'd have to be more careful doing so, but it could still be done without a whole lot of time spent.

[ger21]

I don't think there is a product that natively supports this.

V Carve Pro and Aspire have a "Gadget" to create dragknife toolpaths. It's technically not a native part of the program, but you just select it from the menu, enter a few parameters, and the toolpaths are created automatically.

[mmoe]

V Carve Pro and Aspire have a "Gadget" to create dragknife toolpaths. It's technically not a native part of the program, but you just select it from the menu, enter a few parameters, and the toolpaths are created automatically.

Do you have to install that separately? I don't see it, but I probably don't have the latest release as well.

[ger21]

No, it's included in the install from my Aspire 4 DVD.

[eman5oh]

Sheet Cam is cheap and also has drag knife support for the Donek knifes too, I wish Bob would add this as well.

[aldepoalo]

There is no drag knife feature for BobCAD at this time. You could mod your post with a script and make it work.

You can use this link to request features you would like to see added to the software.

Software Issue Report & Feature Requests | CAD/CAM | BobCAD-CAM | BobCAD-CAM

[mcphill]

Al, as stated in the first post of this thread, I put that request in in January 2014... Guess it didn't make it to the "to do" list yet?

[SBC Cycle]

Is there a defined set of "rules" as to how a dragknife toolpath should be calculated? I remember discussing this in another forum with someone and it wasn't clear to me how accurate it would be without a servo controlling the "C" axis (the knife angle). The toolpath in the above picture is what I often see and is a slick way to go about it.

I agree it can probably be scripted. I saw a nice video where it is done post processor style with an excel spreadsheet to do the calculations. It looked like it was missing a routine to orient the knife for the first cut though. Maybe that is done manually. Either way, neat project. You guys should put your heads together and make it happen!

EDIT: lol, I see the link to the excel program was posted way back by rfenn. Everything needed is probably there but I don't understand what they mean by not using an arcs post processor. You'd have to look into that.

[artracing]

I started this thread back up because I have a application to use a Drag Knife. Its been 28 months since it appears a request to add this option.
Has anything been done?

Since this is a one off deal maybe there is a workaround ?

Rob