DIY pressure sensor ? - Touch Off Plate ?

[deleteallusers]

Hello,

I have a DIY CNC machine running mach3.
I’m new to mach3 and to CNC machines; I’m trying to mill a PCB.
I’m using a 0.015 stub end mill 2 flute

I’m having depth problems, I always cut to deep or two shallow.
I need to cut Z-0.0075 down from Z0 (Z0 = the end mill just touching the top
of the material).

My problem is that I’m breaking my end mills because I can’t set them correctly
down on the material. (I level my work area via 4 screws at the corners)

Should I build and use a touch off plate ? I don’t know what to use.

I’ve heard about some kind of spring loaded depth guard that presses on the material each plunge. Is there a web link, How do I ?

I’m also thinking about adding a DIY vacuum modification.

QUESTION:

Is there anything I can build that will provide realtime feedback of the current depth
so the program can make sure it’s always at Z–0.0075 ?

What other DIY solutions can I use ? I don’t want to spend $$$ on ready made solutions.

What about a pressure sensor ? That way I could do somthing like this ...

if ( getEndMillPSI ( Spindle_POS ( Z ) ) >= dec_to_PSI ( 0.0020 ) )
{
set_drill_depth(Z-0.0075);
}else{

JOG ( Z, ( Spindle_POS ( Z ) - 0.0001 ) );
}



HOW can I build a DIY pressure sensor ? And/or How to solve the resolution
leveling presure depth problem for a newbe ?

Thanks,

[pastera]

The thickness of the base material in OCB is not well controlled and can vary almost the thickness of the copper.

The tool depth should be spring loaded and set by a foot that rides on the material close to the cutting tool (ideally surroundind it). This is how my PCB mill (T-Tech) works.

Aaron

[samco]

In a perfect world - yes. But you can get great results if your table is flat to the x/y axiss. Holding it down is also a problem I use a vacuum table. Others have had good luck with double sided carpet tape. If your using double sided circuit board - it gets tricky registering for line up of both sides. I use pins that line up 2 edges of the board. - when I flip the board I use the same two edges for alignment.

As for the touchoff.. I use a microswitch I found. It is has repeatablillty of around .0007" which is fine for me. I don't know how you would hook it into mach as I use emc2.

http://www.electronicsam.com/images/...ostart/top.JPG
http://www.electronicsam.com/images/...t/mounting.JPG

sam

Originally Posted by pastera The thickness of the base material in OCB is not well controlled and can vary almost the thickness of the copper. The tool depth should be spring loaded and set by a foot that rides on the material close to the cutting tool (ideally surroundind it). This is how my PCB mill (T-Tech) works. Aaron

[Zumba]

A pressure/contact sensor is good if you want automatic depth calibration. Problem is, more can go wrong with this approach and it's not the most accurate method.

Assuming that your table is perfectly flat relative to the Z-axis, the easiest way to verify cut height is to take a cut in some material (aluminum, wood, or plastic), and measure the height of the material using a depth micrometer. Then set the Z-axis height equal to whatever your depth mic reads. This is how I do it on a manual surface grinder to get .0001" accuracy.

If you find that your table isn't flat and needs adjustment, mount a dial indicator to your Z-axis and check at various points over the the entire table.

[deleteallusers]

Thanks, I've implelemted a touch off switch (I just used a modified estop
on a probe) & a vacuum table. My table is not level so I added 4 screws (one at each corner) so I can adjust it and lock it down as I zero my z-axis. I hope this all works.

I need to be succussfull very soon!

Thanks for all the advise, I really need it !