Re: [Pcb2gcode-devel] PCB Board Expectations

[Filip D. <fil...@gm...>]

Hi, I also had problems with precision of commercial drills equipped
with rather massive spindles/chucks. Finally I solved this by building
a completely minimalistic spindle from a M4 brass screw:
http://fzu.cz/~dominecf/proj/fdcnc/img/mill_front.jpg

I use a common 0.8 mm HSS drill bit, sharpened manually to V-tip. With
a little skill in sharpening, it can produce not only an even 0.3-0.5
mm trace, but also drill the holes and cut out the finished board.

How is it attached to its place? The screw has a 0.8 mm hole precisely
machined in its axis. Additionally, at the bottom end, it was cut
twice by thin saw plate, as is visible here:
http://fzu.cz/~dominecf/proj/fdcnc/img/mill_frontbottom.jpg
The drill bit is clamped just by tightening the bottom two nuts
against each other. This creates a vertical strain in the brass, which
in practice manifests in pressing the four segments towards the axis
and clamping the drill bit.

The minimum rotating mass and little distance between the drill bit
and the bottom bearing result in quite good operation. There are other
problems, such as the need to resharpen and move the drill bit. Just a
tip.
Filip

2012/12/10, Patrick Birnzain <pbi...@us...>:
> On Sun, 9 Dec 2012 21:05:11 -0600
> "Ford Peterson" <fo...@hi...> wrote:
>> While the spindle on my CNC is light duty (a ball bearing dremel tool
>> running a 0.1mm 60 degree V bit).  I have a new spindle on order and may
>> not
>> see it for another week or so.  Adjusting the Z axis to obtain a cut
>> sufficient to remove copper, the narrowest insulation I can obtain with
>> this
>> 0.00397" V bit is about 0.030" using a micrometer.  Thinking this
>> through,
>> am I observing the run-out in the bearing at being roughly 0.026" ?
>> Inspecting the spindle I simply cannot believe there is that much play.
>> I
>> would certainly expect to visibly see 0.026" of play and I'm unable to
>> observe ANY play in the spindle at rest.  While I was expecting some play,
>> I
>> was not expecting this much.  Are my expectations unreasonable?