removing trace isolation swarf #mill #development

John Ferguson
 

I suppose swarf isn't the best word, but I'm curious about how you guys get rid of the chips which lodge in cuts.  I've been chasing them out with a needle, buy it's tedious.

I've got 90 psi air in the shop. Maybe I should try that.

I've got my production system running very smoothly. Design In Eagle, generate Gcode in pcpcode, sometimes include autocad millwork with gcode generated in SheetCAM, set up work piece, set height on cutter and go.

I make all of my boards from 2.5x4.0 workpieces. I made an aluminum fixture with a depression which fist these workpieces and has a lid which locates 4 holes one in each corner.  I drill the holes and then screw the board down to an HDPE fixture bolted to the table on my 6040 router.  The HDPE has 4 holes which take 6-32 nylon socket head caps screws.  I face off the surface the board sits on every 4th or 5th board to maintain level. 

I adjust the bit height by rolling a piece of .250 drill rod back and forth until the bit just clears and then dropping it one click on the servo so it doesn't quite clear.  I have vertical "home" set at Z=1.000 on the machine so I have to raise the spindle .750 before I start.  I suppose I could lower the home to .250 and eliminate the "raise" but having it at one inch gives me enough time to catch some kinds of screw-ups.

I've been delighted with this bit. I buy them from Precise Bits and they seem to last pretty well. 

EM3E8-0100-15V 0.0100in. (0.254mm) tip dia., 3-flute 15° tapered stub trace-isolation bit, 0.020 in. DOC, 1.42 in. (36mm) OAL 2 $16.95 $33.90

The size of the bur on the edge of cuts seems to increase as they wear out, but only downside of this seems to be more dressing of the finished board. I use 400 grit paper and final clean up with 800 crocus cloth.

I've been tinning the finished boards with MG Chemical 421.  I'm a bit mystified why I get better tinning if i rough up the board with 400 grit before plating it.  I wash board with acetone before tinning.

After I've soldered everything (all through hole - no smds yet), I go over the board with a loupe and remove any shorts with braid and clean out any suspicious cuts with a needle.

and they always work, at least the ones I haven't messed up the circuits on.

If you read this and see anything stupid, let me know.  Also I'm still like a better way to get rid of chips.

regards,

John ferguson  delray beach

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