Wednesday, April 19, 2017
CNC dust shoe
CNC creates a log of dust, and to make matter worse, the router I'm using blow air downwards to cool itself, this blows sawdust EVERWHERE. The dust was so bad, that I decide to make a dust collection solution before I do any more cutting. I do have a small shopvac that is dedicated for this machine, it's not a powerful one, but is relatively quiet and create a good suction. I want to tweak the dust shoe design before I decide if I want to upgrade the vacuum or not.
My initial attempt was to simply block the air from router exhaust and keep the vacuum hose as close to cutter as possible. It was meant to be a prototype, so I cut it up on a bandsaw and drilled out couple holes and made something worked reasonable well: it has two layers, base layer is attached to Z rail, it travels with the router, the opening for cutter is just big enough to let the collet nut turn freely and block most of the air from the router. The other bristle layer is attached to the base layer by magnets and 3 locating pin. I used some craft foam to make the skirt.
But there are obvious drawback to this design: the vacuum hose is not close to the cutter, but it's very close to the skirt, so it sucks skirt, and that blocks the air flow,
To solve this, I need to direct the air flow closer to the cutter, so I designed the V2 version, the main body is made from 2 layers of Acrylic, hollowed out to create a channel to direct air to the cutter. The bottom half also has a ring of skirt glued on to it. And the two part is attach by magnet and pin, this way I can take the lower half off to change bit. This design looks solid, but I'm a little worried it's too thick, so the shoe can get interfere with clamps.
Of cause I want to cut it out on the CNC, from what I read, cutting Acrylic can be tricky, the plastic melt easily, I really need to get the feed rate and rpm right. Since I have couple really small holes, I'm using a 1/8 bit, this doesn't help, because with smaller diameter bit, you need much higher RPM to match the same linear cutting speed, my router only go as high as 18000rpm.
I set the feed rate to be about 90ipm and DOC to about 0.05. It worked pretty well for pocket path, but doesn't work well enough for cut-out path, I have to pause couple times to clean out the chip. I think I need to reduce the DOC to 0.02 or even 0.01. Although the cut is not clean, I'm pretty happy with the design. The suction is now concentrated in the cutting area, and there's almost nothing left on the table. The only downside of the design is just as I expected, it's too thick, the skirt ring sometime rub against clamp. since I need to block the vent air from the router, I only really have about 1 inch to play with, without adding a lot more complicity, it's not easy to solve. I'm calling it good enough for now.
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