Re: Helical milling drill holes with endmill #pcbgcode #drill #helical


joeaverage
 

Hi,
as I have already posted any hole over 1.5mm diameter I use circular interpolation. Given that I use 1.5mm endmill for this purpose its fine to plunge and cut to full depth of the PCB at full speed (600mm/min) in one pass. That would fail with smaller diameter tools.

I do have, and use 0.8mm endmills, but have and use many 0.5mm endmills (Kyocera Tycom). I now seldom use them for PCB manufacture however I use them to bore holes in fractional sizes for which I do not have a drill. In particular drilling the hole to install a pointer on a meter shaft. If the shaft is 0.6mm in diameter (some Nissan tachometers for instance) then I need to bore
a hole 0.57mm to 0.58mm in order for the plastic of the pointer boss grip the shaft. For this purpose I would use 0.5mm endmill and a helical interpolated path.

Standard endmills are typically three times longer than their diameter. In the case of my 0.5mm endmills the flute length is 1.5mm. Thus drilling a 1.5mm PCB is about as much as it could handle without the flare of the tool fouling the top of the hole. I use Fusion and/or MachMill to generate the tool path for the helical milling. This is a toolpath for a 0.75mm hole 2.5mm deep:

(posted for Brass )
(Strategy: Equal )
(Rapid height: 2.0000  Clearance height: 1.0000 )
G98 G80 G17 G90 G54 G64 G91.1

G21 G90
(***New Tool Selected***)
(ToolNum: 21  Diameter: 0.5000  )
(Feed: 240.0000  SFM: 168.0000  Plunge: 120.0000  ChipLoad: 0.0050  )
M06 T21 (0.5mm EndMill)
G43 H21
M03 S24000
(***Cut Circle***)
(Inside)
(Xorign: 0.0000  Yorign: 0.0000  Dia: 0.7500 Dir: 01  )
(Ztop: 0.0000  Zdepth: -2.5000  Zstep: 0.8333 )
(will make  3.0000  cuts of:  0.8333 )
G00 Z2.0000
X0.1250 Y0.0000
Z1.0000
G01 Z0.0000 F120.00
G00
G03 Z-1.0000 I-0.1250
Z-2.0000 I-0.1250
X-0.1250 Y0.0000 Z-2.5000 I-0.1250
X0.1250 Y-0.0000 I0.1250 J-0.0000 F240.00
X-0.1250 Y0.0000 I-0.1250 J0.0000
X-0.0625 Y-0.0625 I0.0625 J-0.0000
G00 Z2.0000
M09
M05
M30 (end of file)

It helically interpolates down in two 1mm deep steps, followed by one 0.5mm deep helical path at a cut speed of 240mm/min. In harder materials, this was meant for brass, a less aggressive cutting strategy is required. 

This path was generated by MachMill, nothing special. I can choose to mill a pocket or as in this case just on the inside of the circle. With a diameter of 0.75mm there would be no divot and therefore a pocket is not required. I have found no appreciable difference in climb or conventional milling, either being selectable. The good thing is that it takes two, maybe three minutes to generate this path at my machine and the job takes less than thirty seconds. It takes longer to set the part in the work holding and touch off than it does to generate the path and do the job.

I have used this and many similar toolpaths in plastic, brass and aluminium, and would suggest that anyone wishing to experiment with helically interpolated toolpaths use it as a starting point.

Craig


From: pcbgcode@groups.io <pcbgcode@groups.io> on behalf of mariob_1960 via groups.io <mariob_1960@...>
Sent: Friday, 12 August 2022 7:00 am
To: pcbgcode@groups.io <pcbgcode@groups.io>
Subject: Re: [pcbgcode] Helical milling drill holes with endmill #pcbgcode #helical
 

[Edited Message Follows]

Hello people.
my opinion:
1- G2 and G3 can be used with R without problems (two 180° arcs) or I J mode (my Trochoidal 3d bCNC plugin uses R, without problem after years)
2- If the cut of the circle is to generate a cut of the material, I do not see it as essential to make a pocket
3-if pocketing, option a) by discrete jump to next circle (40% overlap?) or b) enlarge in spiral movement (it will always keep a lateral cut, in the other mode, each step to next circle is a slot ). I prefer spiral.
4- I think G3 generates a better finish (finish on the material on the left side of the cutter). Add option box CW - CCW?
5-Select descent step per lap (pitch). Flat final pass.
Perhaps this repeats other opinions: my English is terrible.
hugs, Mario

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