I’ve been prototyping product stickers and need an intricate shape with cutouts — and I have a CNC. Since my Pick and Place machine is temporarily not being used I thought… hmmm.
So, I purchased a $16 vinyl cutter blade, 3D printed a holder for the PnP, and built a vacuum box to hold down the sheets. Here’s how.
The vacuum box is not necessary but sure is easier than taping stuff down.
How it Works
The overhead camera in the Pick and Place first finds a fiducial (dot) on the paper. The blade is then moved a fixed amount to be over the bottom left of the image.
Then a standard CNC cut is made. I use VCarve Pro with curves imported from the 3d modeling program that creates the box. It’s a simple profile cut. I make two consecutive cuts — one at mid-height and one at full height — otherwise the material is usually not cut at the start spot (since the knife start orientation is random). This is fed as gcode to the 3d printer controller running the PNP. Full height is set so the base of the holder is flush with the paper surface during the cut.
It’s easy to cut anything up to an 8.5x11 sheet and it’s repeatable to perhaps .005" using the visual tracking. In my case I make a first cut, laminate plastic onto the sheet and then make a second cut — so repeatability is a necessity.
The Vinyl Cutter Blade and Holder
It’s hard to tell from the picture but each individual ‘blade’ is spring-loaded into the holder and rotates to follow as it gets dragged through the material — much like the wheels of a shopping cart.
I picked a blade at random and inserted it. You want very little blade to come out — the trick is to cut the top layer of a two layer sheet without cutting through the second layer. In practice I put a sheet of standard white paper down first and since the paper is porous it works great to hold the ‘vinyl’ and to protect the vacuum box surface.
The Pnp Blade Carrier
It took three tries to get this right. Since the vacuum box is never going to be perfectly flat it helps to spring-load the blade holder. So this works by having a front and back plate screwed together allowing 1.5mm of up/down movement and with a spring at the end. See here.
The spring was scavenged from a AAA battery end. I cut half of it off so it would fit the space. The spring pushes down on the knurled knob.
The Vacuum Box
This is a great add-on. It holds the paper flat and it doesn’t let the paper move while it’s being cut. Since all the holes are blocked off when the paper is down you don’t need much CFM to get a good hold. It’s hard to move the paper when the vacuum is on.
The first version of this used HDPE (high density polyethylene) and acrylic. The HDPE is very smooth and has little air resistance but it was hard to get it to lay flat. I finally gave up and used MDF and acrylic.
The idea is to have consistent runs to the air holes to roughly equalize suction at all the holes. Two 6mm (1/4") tubes to provide the vacuum.
This box is three layers. There’s a top layer of cork/rubber (1/8"). Then .6" of MDF cut by a CNC router as shown. Finally there’s a .1" acrylic cover that is epoxied to the MDF.
The box has 64 1/8" holes for vacuum and 9 5mm holes to screw it to the framing.