Donek drag knife

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Donek drag knife

Postby MJMStudio » Sun Sep 01, 2019 2:44 pm

Hey does anyone have experience with doing inlays with veneer?
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Re: Donek drag knife

Postby IslaWW » Sun Sep 01, 2019 2:53 pm

A drag knife may not be the best solution for tight fitting inlays as the knife tip, by design, is behind the cutting center, which slightly deviates from the cutting vector
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Re: Donek drag knife

Postby ger21 » Sun Sep 01, 2019 3:15 pm

Also, it can be difficult to cut veneer across the grain with a knife, as the grain will easily split. You'd want to use a paper backed or multi ply veneer.
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Re: Donek drag knife

Postby tomgardiner » Sun Sep 01, 2019 8:48 pm

I have had success cutting veneers for a few projects. I have cut some simple inlays of ebony. I first applied veneer tape to the face to guard against tearing along the grain. I did the cut in a single pass at 80 in/min. I stayed close to the control to be able to stop the cnc if the veneer lifted up. The pieces were about 1 1/2" x 1" leaf shapes. They only required a small amount of sanding off of incomplete cuts at the end to fit perfectly into the pocket.
I have also made straight cuts in laid up veneers to make chevron panels. The drag knife gives me a quick and sure straight seam for full length panels.
Coarse grained woods are more problematic. The knife tends to wobble slightly in it's path although I still achieved tight joints in a marquetry layup. I would recommend reinforcing oak with veneer tape at least inthe corners of all your cuts otherwise you can get sections torn off.
One challenge is how to keep the veneer flat on the table. The vacuum doesn't work well with thin flexible veneer. I tape down my veneer and worry like crazy thta the cut veneer will curl up and get shredded by the knife.
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Re: Donek drag knife

Postby MJMStudio » Sun Sep 01, 2019 11:46 pm

I have a good bit of experience these were done with a hobby knife, I am interested in doing same with the help of drag knife. I'm hoping to use a flat area clearance tool and the drag to outline the field...
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Re: Donek drag knife

Postby TReischl » Mon Sep 02, 2019 1:20 am

A low power laser works well too. I have a 2500mw el cheapo that will cut thru typical veneers fairly easily (.020-.030). Made a small vacuum table that works with the DC nicely.

Cutting veneers with a drag knife can be testy at times as others have mentioned. Another issue is that the knife can flip the small pieces around and they can end up in the wrong place at the wrong time. A vac table can be problematic if the holes are not real small.

I posted some examples a while back at:

http://forum.vectric.com/viewtopic.php?f=27&t=29430&p=212291&hilit=+marquetry#p212291

The pics are the very first attempt, since then I have improved it a lot.
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Re: Donek drag knife

Postby tomgardiner » Mon Sep 02, 2019 1:07 pm

Another thing to be aware of with the drag knife is that small changes in direction may be impossible due to the offset. I found that out when trying to make boxes from coroplast. The offset was larger than the tabs I was attempting to cut so the software ignored the turns. There are work arounds like breaking up the vectors.
With veneer your offset will be much less because of the thickness however it is something you will have to keep in mind.
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Re: Donek drag knife

Postby MJMStudio » Tue Sep 03, 2019 2:14 am

Thanks Tom
I thought I understood that the gadget put the dog ears and such to compensate, I saving up to upgrade to pro,
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Re: Donek drag knife

Postby tomgardiner » Tue Sep 03, 2019 12:06 pm

Yes the software will add a lift and swivel for sharp corners and at the beginning of every part. The problem arises for line segments shorter than the blade offset. Not much of a problem for veneer because the blade offset is a function of the thickness ofthe material being cut but became an issue with the thicker coroplast.
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Re: Donek drag knife

Postby IslaWW » Tue Sep 03, 2019 12:48 pm

All of the reasons above show why I have swapped to a tangential knife. Toolpaths on Vector using VCPro, blade rotation is an internal feature of WinCNC controller.

https://www.youtube.com/watch?v=X7SzwVDPtks
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Re: Donek drag knife

Postby mtylerfl » Tue Sep 03, 2019 3:52 pm

Love that knife, Gary! Looks like it does a great job!
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