Kevin,
the issue with the prints stretching is a real one but as you say only
really critical when using a CNC drill
I use a CNC'd micro mill for most of my drilling now and quickly
discovered this.
The best mitigation I can suggest is to index near the centre of the
board, that way the errors are halved to each edge. It can make the
difference between being in the pad or outside it..
First off I always have a pad at the centre or near the centre of the
board...
Then I have an MDF board fixed with double sided tape to the mill table.
I hand drill two of the pcb holes by hand about 1/4 of the distance
from the side of the long edge of the board.
I then align the first board on the MDF and push a couple of broken
off drawing pins into the holes.. they then act as indexing pins for
subsequent boards.
To hold the boards to the MDF I use a couple of old drawing board
spring clips with the rounded edge cut off... They slide easily under
the MDF in the gap left by the thickness of the double sided tape. The
advantage of these clips is that they clamp firmly, are very low
profile and very very quick to change boards.
I generate the G-code for the drilling with the origin on the centre
pad of the board. I often measure between the two pads which are
furthest from each other on the actual resist layer on the boards and
add a correction factor so that the G-code is generated to be the
average size of the board... it has been up to 2% out on occasions.
I load up the G-code zero the drill in on the centre pad, set the
origin to the centre of the actual board.... and awayshe goes...
A bit of a performance but gives good repeatability..
I do runs of 50 or 100 boards without having to re-zero anything..
and I keep the mdf for the next run of that board.
One of the tasks i keep reminding myself to do is to wire up a decent
buzzer to the driver board and get mach3 to sound the buzzer when the
board is finished.... I tried getting mach to play a wav file but I
run the machine unattended and need the alert to be in the house, not
the workshop...
I must admit to still using and Iron, I haven't got around to using a
laminator but I reckon if it aint broke why fix it..
Chris (-=spiyda=-)
--- In Homebrew_PCBs@yahoogroups.com, "Kevin Morgan" <prizes@...> wrote:
>
> Hi Myc,
>
> LOL. This is not my first try. I just haven't been reporting the
> failures!
>
> Before the laser printer, I'd had some marginal success with
> photocopying onto the Staples paper at Kinko's, but it was a real
> pain, and the results were not that great. I had to do a lot of
> touchup, and then afterwards, I found that the image had been
> stretched, so I couldn't use my mill to drill the holes.
>
> I've also had very good success with isolation milling, using the
> cutters from Think and Tinker and my home built CNC, but I don't
> think that would work very well for the smaller SMD packages, so I've
> been wanting to find a way to get TT to work for me.
>
> Kevin
>
>
> --- In Homebrew_PCBs@yahoogroups.com, "mycroft2152" <mycroft2152@>
> wrote:
> >
> > Hi Kevin,
> >
> > Isn't it great when a plan comes together!
> >
> > You've found the right combination of printer, paper and laminator
> > right away. Usually it takews a lot of trial and error to acheive
> > your results.
> >
> > It sounds like the Techno LM 1910 is the same as the XEROX XRX 1910
> > laminator. It works great, doesn't it. It provides the right amount
> > of heat at the foil setting.
> >
> > TANSTAAFL!
> >
> > Myc
>