Drag Knife for CNC [Pics+Video]

I decided to try to make a drag knife for my CNC. In architecture school, we were constantly making models out of museum board and chip board. I wish I had one of these back then!

I know that there are examples of utility drag knives on the 'Zone going back before 2003, but I didn't pay too much attention as the real trick is the G-code. The knife needs to be reoriented at each corner as well as a slight compensation on curves. Imagine taking a turn while pulling a trailer since the blade is trailing the center of the tool... There are also commercial drag knives available, but for almost $250 I decided to DIY one instead.

Fortunately, ten years later there is also now plenty of software out there that can do the compensation. I do not have this software yet, so I asked some of the other Platform owners to help me out with the g-code. David Hill came through with not only the gcode, but also the geometry for the tests!

Here is an image of the first prototype knife...

http://i175.photobucket.com/albums/w...a.jpg~original


What it looked like assembled...

http://i175.photobucket.com/albums/w...f.jpg~original


From this, I realized that the front part of the blade should be vertical to aide in the rudder effect... This meant that I should look at how to orient the blade for better results.

This concept came to me while I was milling another test out of acrylic....

http://i175.photobucket.com/albums/w...d.jpg~original

http://i175.photobucket.com/albums/w...5.jpg~original

Looks great, but I never tried it before I cut the most recent one out of aluminum. :)


Here is the assembly...

http://i175.photobucket.com/albums/w...b.jpg~original


Fully assembled, ready to test!

http://i175.photobucket.com/albums/w...9.jpg~original


So, does it work?

Guess you'll have to watch the video!

<iframe width="640" height="360" src="//www.youtube.com/embed/YqvgA1P5hWg" frameborder="0" allowfullscreen></iframe>

Happy Holiday Tinkering!

-Brian

Nice work!
I love it when one can take a thought to a concept to the real thing!

Great job!

Hey great work on the drag knife. Are you going to be selling them? Please let me know if you are.

very neat little tool!
would you be willing to share the dxf?

Wow! Another great design! Way to go! Would love to build one of these (once my cnc is built).

Looks Great, Nice Design.

Would you mind sharing the information from David Hill? What did he do for the came through with geometry tests!

Also Vetric Aspire now does drag knife integration for the G code side of things.

I made some modifications (just cuz I could, not because they were needed) of GrunBlau's drag knife and here is the result. This was my first time cutting aluminum, so I've still a lot to learn.

Attachment 230564

What S&F did you use with the onsrud 1/4 oflute? and the 1/8 2-flute?

What did you mean by "onion" when talking about the tabs?

looks a lot like the one from Donek Tools, they sale them if you want to buy something ready to use. I believe they also have related software for the dragknife.

Purchase A D1 Drag Knife - Donek ToolsDonek Tools

here is their youtube channel https://www.youtube.com/user/DonekTools/videos

They also have a crease add-on to make custom boxes.

Drag Knife
I have a problem using my CNC with the Aspire Program.
I have been watching all the tutorials and reading all the comments but my drag knife doesn't turn with the lines and get broken. I follow all the steps and the problem still be there.
How can I control the elevation of the drag knife in Z ,for change the lines, because in the Aspire program I couldn't find the Z's set up?
I will appriciated the help, and if somebody knows how fix it, please send me screen shoots, pictures or videos for how you set up the elevation of the drag knife in Z.
Thank you very much!
Maximiliano

I made one a year ago.

but I never got around to trying to make it work. I did not have a good way to write the g code for the drag knife itself.

So there it sits.

Quote:

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Originally Posted by WASNAPYRO77

Drag Knife
I have a problem using my CNC with the Aspire Program.
I have been watching all the tutorials and reading all the comments but my drag knife doesn't turn with the lines and get broken. I follow all the steps and the problem still be there.
How can I control the elevation of the drag knife in Z ,for change the lines, because in the Aspire program I couldn't find the Z's set up?
I will appriciated the help, and if somebody knows how fix it, please send me screen shoots, pictures or videos for how you set up the elevation of the drag knife in Z.
Thank you very much!
Maximiliano

---

There is a Dragknife Gadget for Aspire, check here: Vectric Gadgets

I see Tormach has a drag knife mill tool.

32440 - Spring-Loaded CNC Drag Knife

Pls dxf file for acrylic knife??

The Tormach drag knife is actually a WidgetWorks drag knife. Which can be purchased here as well:
Sign Vinyl Drag Knife Bit - Use Your CNC Machine to Cut Vinyl Stickers and Lettering, Paper, Cardboard, and Plastic - WidgetWorks Unlimited

I have one of these and while they are great for very thin materials, they will not work on thicker materials like cardboard.

I just did a writeup on my building of the Grunblau drag knife.
You can find it here:
Making a Grunblau Drag Knife — Kronos Robotics

Thank you for this write-up. Great job!

Hi,

Are you making the aluminum version of the drag knife? Interested in purchasing.

thanks
Jeff