Recommended Z Down Value For standard copper board

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BruteForce
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Joined: Sat Feb 20, 2016 8:13 pm

Recommended Z Down Value For standard copper board

Post by BruteForce » Sat Feb 20, 2016 8:29 pm

Hi,

I'm new for PCB milling, I bought Autoleveller to help in milling PCB's, I have a problem where I think the milling bit is going deeper than it should even after running Autoleveller on the .tap file produced by PCB-Gcode in Eagle or does not really etch the board, I tried many values for Z down settings in PCB-Gcode and could not reach to a solution , either it goes deeper or does not etch, referring to some documentation, the copper surface should be only about 0.035 Millimeter , but even when I set Z down to -0.13 it does not etch, it just leve some traces without reaching to the fiber, I wonder if I'm missing something in PCB-Gcode or in Autoleveller, is there a recommended settings for Z down in PCB-Gcode ? or what is wrong ?

Appreciate your help.

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Country_Bubba
Posts: 114
Joined: Wed Oct 02, 2013 3:07 pm
Location: LaGrange, GA USA

Re: Recommended Z Down Value For standard copper board

Post by Country_Bubba » Sat Feb 20, 2016 8:42 pm

How are you holding the board to your table? You might be getting some flexure when the cutter comes down and therefore is not cutting or if your solidly on the bottom when the cutter hits, it may go deeper than you want. If you have clamped it by the edges, can almost certainly guarantee the board will bow and move with cutting forces. (Don't ask how I know LOL) :roll:
Art
Country Bubba

BruteForce
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Joined: Sat Feb 20, 2016 8:13 pm

Re: Recommended Z Down Value For standard copper board

Post by BruteForce » Sun Feb 21, 2016 8:11 am

I'm attaching the board to a piece of MDF using bolts from the Edges,and clip the MDF to the table from the sides of the table. do you recommend different setup, also what should be the perfect Z down setting in general for etching.

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Country_Bubba
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Location: LaGrange, GA USA

Re: Recommended Z Down Value For standard copper board

Post by Country_Bubba » Sun Feb 21, 2016 1:30 pm

OK, that method will certainly allow flexing of the board. Probing places next to nothing for forces but cutting does. When I was first starting with probing, I tested the probe force by "wrinkling" up a piece of aluminum foil and probed it to see how much the foil would move. It didn't move at all!

To possibly improve your situation, I offer the following suggestions to try:
1. Mill the surface of your MDF to be sure it is flat. You want a solid backing for your board material.
2. In the past, I used double sided tape to hold the board down and it worked in a satisfactory manner, but the cleanup mess was a problem.
3. I then made up a vacuum chuck to suck the board down to a milled out pocket in a piece of derlin. This holds the board rigidly to the bottom of the pocket, but also registers the board accurately. The chuck is permanently located on the router so it is repeatable.
4. I follow the "Bit Calibration" routine as promoted by Poul-Henning Kamp at:
http://phk.freebsd.dk/CncPcb/calibrate.html
5. By following these procedures, I have been able to successfully etch boards with cuts as low as .0025" but generally work in the .005" range.

Hope this helps.
Art
Country Bubba

joeaverage
Posts: 26
Joined: Tue Aug 09, 2016 8:55 am

Re: Recommended Z Down Value For standard copper board

Post by joeaverage » Tue Aug 09, 2016 10:25 am

Hi Bruteforce,
I am a relative newbie too but Country Bubba's advice has helped me.
I had tried holding the board down at the corners with screws but they
induced to much flexing which AL can't cope with.
Over the weekend I used doublesided tape. I successfully etched a board at -0.05mm
(.002 inch) with standard, 0.035mm (.0014 inch) copper. It worked perfectly.

I then proceeded to solder on the Thin Shrink Outline chip I was using only to realise
when it was soldered on that I had put it on backwards an of course wrecked the
board trying to get it off !!! This hobby excercises my patience and sanity at times!

Cant fault AL though.

Craig

kostix
Posts: 1
Joined: Thu Aug 10, 2017 8:02 am

Re: Recommended Z Down Value For standard copper board

Post by kostix » Thu Aug 10, 2017 8:06 am

Hello! This is my first post here.

Just an idea to reduce board flexing when it is the case, you can put some kind of a shim below the board in the middle to provide rigid support and then fix it on the sides, then go on with the autoleveling.

Regards,
Konstantin

joeaverage
Posts: 26
Joined: Tue Aug 09, 2016 8:55 am

Re: Recommended Z Down Value For standard copper board

Post by joeaverage » Tue Aug 15, 2017 8:20 am

Hi Konstantin,
when I first started using Auotleveller I tried various ideas to stop the flexing of the board, none worked
very well. When I used double sided tape it went from being very 'hit and miss' to 'damn near perfect' every time.

In my previous post you saw that I used a 2thou cut on 1.3thou copper and ended up with a perfectly etched board.
If there had been anymore than 1/4thou flexure that would not have been the case. Your aim is NO FLEXURE WHATEVER!

A vacumn table is probably best but double sided tape is effective.

Craig

steveti
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Joined: Tue Mar 06, 2018 2:41 pm

Re: Recommended Z Down Value For standard copper board

Post by steveti » Fri Sep 28, 2018 4:16 pm

My experience is double sided cellotape (sorry advertising) and use of a can of label remover (Pro-Power Label Remover) to remove tape after etching, I tried clamps and always got flexure. This particular label remover is fast so about 60 seconds after applying tape can be all wiped off with kitchen towel.

For baseboard I use offcuts of white melamime shelving (about 15mm thick) bolted to a CNC XY table. This has safety feature as tool can bury itself without much harm if GCode goes awry.

The white shiny melamime surfce allows clean removal of tape for next PCB to be cut.

Steve

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