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Double sided board

Posted by papakel 
Double sided board
March 17, 2016 11:54AM
Hi all, I am a newby to this wonderful software and indead to electronics but now that I have got pcb-gcode working and running on my printer can someone tell me how I can line up the flip side of a double sided board so that all holes and tracks on the two sides line up. At the moment I simply zero all axes and set the full board slightly outside so that any actions are within the board holding the board stable by useing masking tape.
I should possibly say that I am not cutting the copper but just scribing tracks in permanent marker with a silver steel scriber to etch later.
Should I first cut the board to size or how is it done?
Re: Double sided board
March 24, 2016 11:21AM
Hi all, does anyone share this problem? I am trying to create a "Slum" board which is a small add on board for the sanguinololu printer controler to add a fifth stepper driver, I have successfully scribed one side of the board for etching but I am at a loss as to how I can turn the board over to scribe the second side so that the holes and tracks align with both sides. Can someone please suggest how it is done.
Re: Double sided board
March 24, 2016 11:57AM
papakel
See my response to you in this thread. "Re: Eagle 7.3.0 crashing"

Regards

Art
AKA Country Bubba
Re: Double sided board
June 11, 2016 02:40AM
Hi papakel,
I use a jig, or perhaps you could call it a spoil board with a pocket milled
into it.
If my project calls for a 100mm by 60mm board I cut a piece a few mm larger, say
110 by 70. Then I mount a piece of acrylic 10mm thick somewhat larger again. I cut
them up with a bandsaw 250 by 280mm and mount that on the table. I anticipate that
it will remain fixed throughout or otherwise have means of removing it from the table
and be able to refit it exactly where it was, alignment dowels or similar.
Using CAM software I then mill a pocket 110 by 70 about 1 mm deep. This helps
make the board dead level with respect to your spindle but more importantly gives
a straight edge which is exactly parallel to the x-axis, it was after all cut by it!

When I set the piece of board in it I ensure that the lowermost edge of the board
abuts this reference edge. All my boards have as reference 0,0 at the lower lefthand
corner when topside is viewed, usually the center of the mill outline. Using Eagle dimension
I measure the distance to the lower righthand corner, again the mill outline. In this example
lets say 98.4mm. Once you zero your machine just within the boundary of your piece of
board at the lower left I manually drill a small hole (I use 0.4mm endmills so I can slowly
plunge a hole) at 0,0 till just thru the board and then retract a bit. I then manually shift in
x to 98.4 ,0 and drill just thru the board and retract.

You can now run your top etch file per normal. To flip the board remove the piece and flip
it so the two drill holes you made are visable and along the lower reference edge of the
pocket. With any sort of luck the y axis need not change at all. All that remains is to manually
shift x to the righthand hole and zero the x axis. If the hole is reasonably small, 0.4 to 0.6mm
say, then it is quite easy with a magnifying glass to center the tool to the hole by eye to about
0.1mm. You can now run the bottom etch.

I try to move the piece of board just once, ie when flipping it. If I do so then the drill and etch
should line up indentically. I also use 'spot drilling' with the same 0.4mm endmill when I etch
so that small diameter drills don't walk off line. This has improved the accuracy of hole placement
greatly.

Craig
Re: Double sided board
June 11, 2016 06:53AM
Hi Craig,
Thanks for the above I will try to do the same method as it sounds very practical and simple
Re: Double sided board
June 11, 2016 04:14PM
Hi papakel,
I've read County Bubba's reply to your question at it too is eminently practical and easy.

His method is a variation of the same theme that I use. He calls for a 'fence' to which to butt
the board, one along the lower edge, the x axis and one along the y axis to the left when
top etching or to the right when bottom etching. The two work coordinates should differ
only in y the distance between the two fences.

When I was developing the method I use I did the same thing but it required that I manually
produce a blank piece of board to the exact dimensions of the pocket. So if I cut a board to
99.3mm by 61.2mm (I was trying to cut 100 by 60 but missed by a bit!) then milled the pocket
to 99.3 by 61.2 then my board was constrained in the pocket in x and y.

The problem I found was the required accuracy with which to cut the blank, it allways
varied by a few tenths or so making repeations of the same board tricky. I've found
the most accurate method of cutting a board to size with the best finish is to mill the
outline as the final operation. Provided there is one reasonably straight edge on the
blank to butt up against the lower reference edge of the pocket, Country Bubba's
x fence, the multiple boards are no trouble. In truth only one alignment hole at the
lower left (0,0) when top milling will when flipped end up at (0,y length) where
y length is the width of your board is required. I tend to place two holes at (0,0)
and (0,y length) so that I can flip and align to the topside if I stuff it up!

The same idea works if you are making a number of identical small boards out
of one larger blank. If your boards are all to be 25mm say then drill alignment
holes at (0,0), (0,28), (0,54), (0,84). Run the top etch at (0,0) for the first
board, manually advance to (0,28) and zero y and rerun the file for the
second board and so on.

Aligning by eye I can achieve 0.1mm or better which is adequate for trace sizes
of 0.4mm which I find to be a reliable practical lower limit.

Craig
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