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Cutting Readi-board foamboard with a CNC router

Zeron

Junior Member
#22
I use one of these to cut out all my planes. It works reasonable well once you learn to use it. Because foam board is not a consistent thickness; the corners of you cuts will not always be square. For outside corners this is easy to work around by extending the lines over cutting in a X pattern. Inside corners sometimes need some manual fixing afterwards.
 

nerdnic

nerdnic.com
Mentor
#23
I use one of these to cut out all my planes. It works reasonable well once you learn to use it. Because foam board is not a consistent thickness; the corners of you cuts will not always be square. For outside corners this is easy to work around by extending the lines over cutting in a X pattern. Inside corners sometimes need some manual fixing afterwards.
Hi there. I'd love to know more detail about your set up. Would you be able to provide more info as to what cnc machine you have and what cutting tool is used?
 

Zeron

Junior Member
#24
Hi there. I'd love to know more detail about your set up. Would you be able to provide more info as to what cnc machine you have and what cutting tool is used?
I have a 4'x8' ShopBot PRT and use the Donek D2 drag knife.

I built a small vacuum hold down box that connects to my shopvac and holds the foam in place and flat while it is being cut.

I also have a sharpie holder that I sometimes use to draw designs on the planes.
 

Balu

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#25
I'd love to see a video of it working on a sheet or at least some pictures :).

Routers like that are a little too big for my small appartment though. :-/
 

ringo42

Junior Member
#26
I have a 3 axis cnc machine. To use the drag knife I'm assuming I would need a 4th axis to rotate the blade, is that correct? Also I generate gcode from sketch up or dxf files, how do you generate the code so that it includes the 4th axis ?
 

Balu

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#27
Nope. The drag knife is built to rotate freely. The gcode has to incorporate that though. As far as I understand that the knife is put into the material so the tip barely goes in, then the router moves it into one direction so the knife turns around before being pushed into the material.

Youtube has a few videos on how drag knifes work.

Donek Tools sells a drag knife:


He also describes how to use it:


And here is one who built his own:


I've ordered the plans by "buying him a beer", but didn't get them yet. Which isn't too bad, because I don't even have a router yet :-D
 
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ringo42

Junior Member
#28
If you watch the videos he lifts the tool and rotates it and lowers it again. I'd like to see a video where it does not rotate in the air like that.
 

Balu

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#29
If you watch the videos he lifts the tool and rotates it and lowers it again. I'd like to see a video where it does not rotate in the air like that.
Hm. I wasn't able to see that effect. It's called "drag knife" for exactly the reason that it is dragged behind. Both versions have the lower part being held by ball bearings - no rotating mechanism with these.
 

Asuma

Junior Member
#30
What a great thread! My work place has a multicam MG series CNC thats at least 10 years old. Are blades like this compatible with such a machine? The operator of our machine at work says that the MG series cant be used with knife blades. But I've known him to be wrong about such things.
 

Asuma

Junior Member
#31
Oh also can anyone recommend a DIY hobby grade CNC kit that would be able to accommodate the 20"x30" size of the foam boards? I dont care how slow it would be. This would be for personal hobby use.
 

Balu

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#32
What a great thread! My work place has a multicam MG series CNC thats at least 10 years old. Are blades like this compatible with such a machine? The operator of our machine at work says that the MG series cant be used with knife blades. But I've known him to be wrong about such things.
Both blades are meant to be put into the standard router mount as far as I know. You just need to make sure the spindle doesn't spin ;).

Also the programming might need some changes because you have to put the knife just a fraction into the material, move the blade so it rotates in the right direction and then cut down.
 

nerdnic

nerdnic.com
Mentor
#33
Oh also can anyone recommend a DIY hobby grade CNC kit that would be able to accommodate the 20"x30" size of the foam boards? I dont care how slow it would be. This would be for personal hobby use.
Yeah this is what I want to know also. I want to get a CNC machine and use a drag knife to cut my DTFB planes.

Anyone have a suggestion?
 

Balu

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#34
For a few months now I'm thinking about building my own CNC, but I am a little afraid because of the mechanics and money involved. I like the options and builds I've seen from the openbuilds.com community / aluminium extrusion parts though and would probably go in that direction. The "Ox" seems to be one of the most popular builds over there.
 

srfnmnk

Senior Member
#35
I have access to a CNC machine and actually just got trained on the software and safety. I am still to cut my first piece of foam but I'm planning to do it as soon as possible (a week or so). I was going to experiment with bits and RPMs but would love any input anyone has. What is the right bit to use? Do you like to cut inside or outside the lines? Do you use the CNC to cut your internal lines and/or your score cuts? I was thinking about an 1/8 inch end mill with a high RPM but i'm all ears. Thoughts/ideas?


Thanks!
 

nerdnic

nerdnic.com
Mentor
#36
For a few months now I'm thinking about building my own CNC, but I am a little afraid because of the mechanics and money involved. I like the options and builds I've seen from the openbuilds.com community / aluminium extrusion parts though and would probably go in that direction. The "Ox" seems to be one of the most popular builds over there.
Thanks for this info, I'm gonna look into more info about the ox.
 

Zeron

Junior Member
#37
I have access to a CNC machine and actually just got trained on the software and safety. I am still to cut my first piece of foam but I'm planning to do it as soon as possible (a week or so). I was going to experiment with bits and RPMs but would love any input anyone has. What is the right bit to use? Do you like to cut inside or outside the lines? Do you use the CNC to cut your internal lines and/or your score cuts? I was thinking about an 1/8 inch end mill with a high RPM but i'm all ears. Thoughts/ideas?


Thanks!
An Endmill will not work to cut foam board. The paper will tear and the foam will melt on to the bit.
 
#38
i have a 6040 cnc for cutting both foam board and balsa / plywood

this is the machine i have
https://www.bilby3d.com.au/DispProd.asp?CatID=10&SubCatID=90&ProdID=cncRouter6040W1500

i got it in Australia but there are lots of places that sell this machine.

i use either a "corm cutter" bit https://www.bilby3d.com.au/DispProd.asp?CatID=10&SubCatID=103&ProdID=tlBitCorn3175x12

or a "Single Flute Endmill" https://www.bilby3d.com.au/DispProd.asp?CatID=10&SubCatID=103&ProdID=tlBitSFendmill3175x20

for cutting the foam board, both work very well.

also i use Rhino to draw and make the DXF files. http://www.rhino3d.com
import the design into vcarve Pro 6.0 for making the G-code http://www.vectric.com/products/vcarve-pro.htm

and use Mach3 to control the CNC router http://www.machsupport.com/software/mach3/

hope this helps
 
#40
An Endmill will not work to cut foam board. The paper will tear and the foam will melt on to the bit.
Well it worked for me. Just cut out two mini scouts and a mini speedster on a CNC at work.
I used a regular 4 flute 1/16 carbide endmill turning 3500 rpm at 10 ipm.
It fuzzed the paper on the top side, but a light block sanding with some 320 sandpaper before separating the pieces took most of it off.
I rigged up a crude vacuum chuck with a shop vac and some particle board strapped to the bed of the miller to hold the DTFB down.
I need to redo my set-up to get it flatter so I can cut all the way through consitantly but i'll post some pictures when I'm done.

I have a 40,000 rpm air spindle I want to try, so I can use these small diameter carbide bits I picked up a Harbor Freight.
http://www.harborfreight.com/micro-carbide-bit-set-20-pc-62379.html
 
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