New CNC Drag Knife, and a very large Cast Iron Part

by: Andrew Grevstad

New Product:  CNC Drag Knife

We’ve added this CNC Drag Knife to the webstore.  We knew it could cut sign vinyl – that’s cool enough, on its own – but also wanted to see what else you might be able to do with it. So we came up with a few application notes for how to use it with the help of our friend Scott at SDM Fabricating, including:

  • Sign Vinyl  (you can buy some here, don’t forget the application tape!)
  • Gaskets
  • Copper Traces
  • Metal Shims

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You can download our application notes here.  I also know that you can cut paper for sandblast masks, etc., as well.  Does anybody have any other ideas?  Let us know.


Choo! Choo!

This monster part is a smoke box for a 1/8 scale Union Pacific Challenger Locomotive.  4th Axis work was programmed with SprutCAM.  The fixturing looks very well engineered, to say the least.  Thanks to Tormach PCNC 1100 owner Steve Gnas for the video.


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I believe this is the the full-scale edition:

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Rating: 9.0/10 (9 votes cast)
New CNC Drag Knife, and a very large Cast Iron Part, 9.0 out of 10 based on 9 ratings
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Andrew Grevstad


With over ten years of professional experience in advanced manufacturing systems, digital design tools, and applied software, Andy Grevstad has worked in product development and technical support for Tormach since 2008. Grevstad has received engineering degrees from Michigan Technological University and the University of Wisconsin-Madison. He is a regular contributor to Digital Machinist magazine and also blogs weekly about CNC milling and related topics on the Tormach blog, Milling Around.

11 Responses to “New CNC Drag Knife, and a very large Cast Iron Part”

  1. R.DesJardin says:

    The cutter is a great idea.
    Hey it’s great to see all the different projects guys do. I give this 10 stars but clicked too soon on the above star scale, my apologies.

  2. Andy G. Andy G. says:

    I think so too. I’m going to make some sweet custom tool box stickers with it when I get a chance. Not exactly our idea, though. These knives are made by Widgetworks, and we are a reseller.

    I think the gasket idea is very cool- hadn’t seen that done before.

  3. Cairns says:

    I recently built a drag knife for my Tormach using the cutter from a Cricut machine. However mine wasn’t spring loaded. Using a cutting mat under it seemed to help quite a bit but a spring is definitely the way to go.

    A tip: when defining your tool path it helps to overlap the start and end points of your cut, otherwise you’ve got to hand cut the tab that remains.

  4. Andy G. Andy G. says:

    Somebody here had a cricut (Heather, I think – she’s our web person) and that’s what got us talking about this.

    Yes, that’s absolutely true – you need to be intelligent about lead-ins and lead-outs. We have some additional programming tips in the Tech Document for the product:

    I hadn’t noticed your blog before – very cool.

  5. harley573 says:

    Yeah, so where’s the video of that 4th axis part being cut?

  6. Andy G. Andy G. says:

    I’ll see if they exist…

  7. harley573 says:

    I just got my 4th axis all set up, so it’d be neat to see. Of course, it wouldn’t hurt my feelings if Tormach posted more 4th axis videos as well!

  8. brucec12 says:

    How thick was the shim Brass?? I have been using photo-etch for cutting out shapes in 0.010″ Brass sheet. This would be great for some of the less intricate pieces and would be alot more convienient!

  9. Andy G. Andy G. says:

    Brass was .030″ thick. Check out Page 8 of this document for application notes with the Brass shim stock.

    Definitely agree this is going to be less work then photo etching.

  10. Scott_M says:

    The brass shim stock was .002″. The programed Z depth was .030″ with the spring pressure adjusted very high. Also to get clean cuts 2 passes were used. I think .010″ may be a bit beyond the capabilities of the drag knife. Possibly with a heavier spring it would work.


  11. Andy G. Andy G. says:

    Whoops. Scott is right. I’m going to change the application note sheet so this information is included.