Inventables Community Forum

Does anyone have a working drag knife?

I’ve combed prior posts and run across a few different drag knife projects, but I haven’t seen a fully functional solution (did I miss one?). Has anyone come up with a functional drag knife for the x-carve? Or is there any commercial solutions available? I’d love to see some results, as well.

There’s a bit about them here: https://www.shapeoko.com/wiki/index.php/Spindle_Overview#Drag_Knives

and I published a design which could be either 3D printed or routed at: https://www.shapeoko.com/wiki/index.php/3D_printed_SO3_Drag_Knife

Expensive. Commercial.

I’ll have to take a look at this one.

Yeah, I’ve seen this one but it’s kind of outrageous in price. I’d rather take 20 shots at making my own than pay that, lol.

A drag knife is fairly trivial. It is the software that seems to be a sticking point. Offset compensation.

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Here is a guy that sells them not sure what you think is to much. https://www.etsy.com/shop/ADIYDad?ref=pr2018_faveshops

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How thick a material do you want to cut? Roland compatible blade holders are not expensive. There are 30, 45, and 60 degree blades available. Only the blade swivels (and the center of the ball bearings) so there is as close to zero mass as you can get.

The 30 degree blades are for fragile, thin materials. 45 degree blades are for most sign vinyl. 60 degree blades are for thicker materials like sandblast masking. None of these will cut through cardboard or leather.

https://www.averydennison.com/en/home/newsroom/avery-dennison-blog/Graphics-Solutions-Blog/how-to-choose-right-blade-for-plotter-and-film.html

Keep in mind that the thicker the material, the less severe the angle/curve can be cut without tearing the material. Especially with the 45 degree angle on CNC drag knife holders using utility knife blades.

That Etsy shop blade holder seems to be using a rubber band for pressure… yikes. My old Graphtec cutter uses a solenoid with PWM to alter the pressure.

If you don’t have drag knife offset compensation, none of this matters.

Steve, thanks for this information from Avery. I made that drag knife in the link above. I just ordered a Roland blade holder to do some testing. Up until now, I have been using the ratchet blades from a silhouette. Yes, it does use rubber bands for tension. They also have the added benefit of allowing height variations in the material (aka my plywood was warped). I was thinking of replacing it with a tension spring or latex to give a bit more pressure (I just add extra rubber bands if I need more). I originally built it so I could cut paint mask (Oramask 813 becuase I had it on hand) directly on the wood so I could make cornhole boards. Which I think it works great for. I am new to vinyl cutting but to me (feel free to connect me) it seems that offset compensation is like v-carving. Its how you get sharp corners but it works without it. I think this test is a food example of that. If you look closely you can see the radius on the letter.

This is the smallest thing I have done. This is right from Easel with no compensation.

Some of the projects I made with it.

I am not trying to compete with a large format cutter and I didn’t really like the 12" width limitations of home machines. So I designed and made this.

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If you only cut large shapes and use a blade with very little offset, like the Roland or Silhouette blades and holders, you can get away without drag knife compensation.

For smaller shapes and lettering, every curve will cut a little inside, every corner will be rounded, and the ends won’t quite meet.

If you use one of those huge knives that use a utility knife blade, drag knife compensation is absolutely required.

Makes perfect sense, I know vcarve as a option for compensation. Any other program suggestions?

I haven’t figured out how to use it yet, but GRBLGru has it.

https://youtu.be/8jHS2uZpfJg

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Inkscape seem to have it, but only outputs it in HPGL or DMPL. Look under Extensions, Export, Plot. It has Overcut so you don’t have those little bits still connected at the start/end, and knife offset correction. I have an old 36 inch wide plotter, Houston Instruments, that takes DMPL files.

Is it possible to convert either DMPL or HPGL to G-code? A quick search turns up a few. I hate having to add steps.

This one says it converts HPGL and a few other file types to G-code for free.

https://www.cnctoolsworld.com/application-all_to_g_code_converter_free-2.html

bCNC has a native drag knife plugin. I haven’t used it yet, but I plan to get some Roland blades and give it a try at some point. It can be found in the CAM tab. Here’s a screenshot.

There’s a also a reference in the wiki and a full thread of how it was developed here.

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I have a new Donek D4 that I wasn’t able to use I’d love to sell if you’re interested???

Hi ! Still available ?

Yes actually it is!

Sorry I didn’t see you responded til now. How much do you want for it ? Can you email me ?
noemoreno779(at)comcast(dot)net

Thanks !

Lmk. Thanks