Drag Knife - Cuchilla de corte para CNC (papel, vinilo, etc.)

by onasiis Sep 9, 2016
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Onasiis, I don't understand why you need to put the ball bearings, doesn't the spindle spin freely anyways? I would just make a support for the knife and bolt it on a shaft directly.

Hi!, Yes, you are right!, but depending of the brand, age, use, etc, of the spindle or the milling machine, the direct movement may be hardener than with the adapter. Another point may be the inertial movement when cutting on angles. It is not the same to cut a little angle that cut a circle. If the machine has to cut sharp angles, for sure it will be more difficult with the direct adapter, and it has to perform slower movements to get good results.

Anyway, if you have a good milling machine, with good ball bearings, it should work pretty well.

Hi, with what controls the movement of the blade?

Hi ! Over here you have the explanation about how it works, and another more info:

Basically, you do not need any electronics, motors, etc to control the blade. The only thing you need to let the blade perform the right movements is create the appropiate GCODE. The CNC machine will move and the blade will follow that movement.

To generate these GCODE you may use some computer programs, like SheetCAM, Vectric Aspire, or use this script

The original forum where you can find information about the script:


Thanks you so much

Built one here in the US. Used .25 inch shaft and pressed into the upper bearing holder. The passage for the shaft needs to be longer so the shaft has a chance to straighten out while it is pressed in. It was leaning slightly to one side. Screws were a standard size but don't remember what they were. The offset is pretty large for the swivel shaft. I have not run it yet but I think it may flex when cutting anything thicker than vinyl. Could you add a swivel shaft with a smaller offset? Would really help with corners. I use Solidworks. If you could post those files it would be nice to customize your knife. Thanks for the upload!!!!!!

saludos, tengo un router con entrada para vastago 1/8 o sea 6.35 mm, que modificaciones deberia hacerle a tu modelo para hacerlo efectivo, que router usais tu, mil gracias, excelente pieza maestro

Uso la Makita 3709, que es para vástago de 6mm.

Si tu router admite fresa de 6mm no tendrás que hacer modificaciones.
Por el contrario si te vieses forzado a usar fresas de 6,35mm, podrías imprimir un vástago que fuese por un extremo de 6.35mm y por el otro de 6mm, insertando la parte de 6mm en la herramienta para cuchilla, y la parte de 6.35mm en tu router.
De todas fornas, te recomiendo que uses metal para ponerlo como vástago, en lugar de plástico.

, es un gran diseño, espero poder realizarlo pronto, mil gracias por los consejos

I printed this without issue but have a question. What is the tip offset? Need that to plug into my drag knife software to calculate how to position the tip around corners. Sorry if you posted the info, I may have missed it.


Hi, sorry for the delay. I just updated the info.
You usually have to use between 3mm and 4mm as a tip offset.

You posted a "I Made one". If you have tested it, please, tell us what tip offset you used. There are a few types of blades and depending what one you use, the configuration is different as you know.

I used .175 in (4.45mm) as the offset and the CamBam Drag Knife plugin to generate the gcode. The blade I used was a standard box knife blade with the 2 notches in the top edge of the blade and a 45 degree angle on the top edge of each end. This was close but I didn't have enough time to play with offset to see what it really should be.

It worked well except for the shaft that goes thru the bearings will flex if you try to cut more than about 1/64 - 1/32 inch in each pass. I used two passes to go thru poster board. I am going to reprint the part with the shaft in a stiffer material to see if that helps with the rigidity. If that doesn't work, I will print it with the shaft hollow and insert a bolt or aluminum rod in the middle of the shaft.

Thank you very much atwooddon for give us more info about your "I made one".
I will appreciate more feedback with the new modifications you are thinking to do.