New Drag Knife

[Cosmos275]

Rick, here are the specs (copied from site)
Features:

#19 heavy duty Exacto(TM) blade.
Two double sealed bearing rated for 310 static / 750 dynamic pounds radial load
Hardened steel 3/8" shank
Drag offset is 3.0mm
Max material thickness: 3.0mm
Min radius: 3.0mm
Length from collet: 72mm (2.84")
Kit comes with a pack of 5 blades and hex key

Vectric VCarve Pro and Aspire have a "Drag Knife" gadget that can do some cool things for calculating toolpaths. You can use it without that software, but I need to do some research on what the specifics are. Basically, with the spindle off, you can run a profile toolpath and observe where it starts and adjust the blade starting angle manually. When going for more than one profile, you have to be aware of the blade angle, which is what the vectric software does (very cool)

[markevans]

Any chance of a 1/4" shank?

[Cosmos275]

Yes. I went with 3/8" to be as stiff/robust as possible, but I think a 1/4" steel shank will do well also. If you order one, just put in the comments you want 1/4" shank. At some point, I'll set that up as an option.

[Cosmos275]

Here are some notes on programming the drag knife and some test photos

I was sent an image of a letter by a customer trying to get the drag knife going on small letters in thin vinyl. There had been some discussion of bearing drag, but I think the speed has more to do it at this point. The letter “E” was cut at 75IPM

I test cut a couple letters of the same size on a piece of paper (didn’t have any thin vinyl on hand).

You can see the letters “A” and “T” in the other two pictures. They came out pretty good for a 3mm offset tool. I do plan to come out with a 1.5mm offset tool soon (geared towards smaller work).

Programming notes:
The speed I ran was 12 IPM (1/6th the speed of the bad quality letter)
Cut depth was .13mm (.0051”)
Pivot depth was .12mm (.0047”)

I did some manual edits of the G code to remove the first pivot and the last pivot generated by Vectric’s Drag Knife Gadget. I noted the initial blade direction and set that manually before starting. With that, removing the first and last pivot eliminated some small damage the pivots do at the start and end.

So I think the main takeaway is for small details like letters, you must go slow. This allows the device time to pivot. Freeling up the bearing may help, but still, slower will give better results (if you already bought one, talk to me about making the bearings spin more free. New units will ship with this modification). The other takeaway is the Drag Knife Gadget in Vcarve is a good start, but isn’t perfect. It can be cleaned up doing some manual G code edits.

AT_sm.jpg

AT.jpg

75 ipm.jpg

[joe]

Very interesting tool. My complements!

Why is it called a Drag Knife Cutter? Most of us old hands know vinyl cutters are true drag knifes and the original tangential cutter like Gerger 4B moved in the same way at this one. When cutting thick materials like Sandblast Mask this is the way to go.

With concern about spring loaded: This is a novice question. OK here's a case, When cutting sandblast mask on a large rough cedar panel, you need some spring action in the blade. With this kind of work you wouldn't want to destroy the surface texture by surfacing.

When using SB mask it's sometimes best to make two or three passes. That's because the rubber can stiffen up when the temp drops. The reverse is so during the summer. All my masks,for this kind of work, was done with a Brad Point Roundover bit. I've posted on this topic several times. Today, on this forum, there are so few people sandblasting it's probably not worth considering.

[Cosmos275]

Some other concerns, as I see it, with a spring loaded design would be there's nothing preventing the blade from going deeper than planned. This could cause problems cornering or possibly just bogging down. For the most part, you can just cut into your spoilboard a little, so I'm not sure the added complexity it worth it.

[joe]

Cosmos 275. who ever that is,

You might be right about bogging down. When I'm cutting SB mask with a Brad Point bit I find it an advantage to go through the mask a little. Because you never know if the wood has a devit or two.

Sure like the tangential moves this knife makes but there is no dragging involved. It's under power at all times.

[Cosmos275]

Cosmos is my first name Life story located here: link

Ran some 1/16" rubber gasket material today. Easy. Tomorrow, I'd do some thick cardboard.

https://youtu.be/AEqYhbeKc6A

gasket_sm.JPG

[8Ball]

I'm looking for a diamond drag tool holder. Could this be modified to be a spring loaded diamond drag tool holder?
I would be very interested in one.

[Cosmos275]

This one is not spring loaded, just to be clear. I'm confused. I've seen diamond bits for engraving.. I'm not sure why you'd need to drag it.