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Author Topic: 3d Probing on Granite slabs  (Read 5668 times)

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3d Probing on Granite slabs
« on: February 25, 2019, 02:34:48 AM »
Hello guys! I am Peter and I am stonemason and I use CNC mill for 90 percent of my jobs. I have read a lot of topics on the forum but none of them points me directly to solution of a problem:

My granite slabs are polished as glass and they are uneven on the surface. When I have to engrave a 100 or more letters on them I have to measure every two letters and make a separate toolpath in aspire or artcam. When i have a slab 1000mm on 2000mm and it has difference lets say 2mm from one side to the other and my letters are careved 2mm deep, I get no letters on the lower side and get bold (like offset) letters on the higher side of the slab. I can always  try to make the slab even, but since they are polished I cannot calibrate them with a tool, because I have re-polish them after the lettering. The other way I tried is to make the slabs even by putting something under the lower part, but this also did not worked, because most of the slabs are cut and polished like and arc. So they have a "belly in the center. So I get a slab that is Z=0 in the center of XY, and Z=-2 in one corner, Z=+1 in the other, Z=+2 in the third and Z=-3 in the fourth corner.

I found that my only solution is a some kind of material flatness detection software and hardware like mach3 plugin plus a laser scanning or touch probe digitizing.
Can somebody tell me what to buy to solve this problem, that I have been struggling for a long time. Thank you all in advance.
Re: 3d Probing on Granite slabs
« Reply #1 on: February 25, 2019, 02:52:05 AM »
Hi,
I make PCBs by isolating routing. The result is highly dependent on the PCB blank being dead flat  (within a few um)
OR use Autoleveller. It is a free software utility that probes the surface and subtly varies the Z axis depth of cut to maintain
constant cut depth.

You might be able to adapt Autoleveller to your needs.

http://www.autoleveller.co.uk/

Smurph, one of the developers of Mach4 has heralded the upcoming release of a Mach4 feature that does something similar.
A PM to Smurph or even an Email to NFS may net you enough details that would allow you to decide whether the new
Mach4 feature would suit your purpose.

Craig
My wife left with my best friend...
     and I miss him!
Re: 3d Probing on Granite slabs
« Reply #2 on: February 25, 2019, 03:05:08 AM »
Instead of probing the entire slab, would you be better off modifying your machine to have some sort of floating spindle.
Look into engraving using a nose cone.
Have a read of this. https://www.johnsonplastics.com/engravers-bible/nosecones
 
Re: 3d Probing on Granite slabs
« Reply #3 on: February 26, 2019, 12:46:12 AM »
Thank you guys for the advice. It means a lot to me that you spend your time to help me.
I found some producer for the nosecones. I will ask them if they can solve my problem. I am not sure if they can, because I engrave the slabs with pcd tools on few passes. Don't know if nosecone is suitable for engraving hard surface on passes.

About the auteleveller, today I will also ask the guys if they can help, actually this is where I started and still don't know which is the better solution.
I will post both of their responses, so this tread can be useful for other people.

I also thought about laser scanning. I am not sure if this is a way to deal with my problem. Maybe it is not since my slabs are polished and they will have mirror effect on the laser.
Re: 3d Probing on Granite slabs
« Reply #4 on: February 26, 2019, 01:37:31 AM »
Hi,
as I suggested ask Smurph about the upcoming contour feature in Mach4.

Have you tried to get a probe file from the Autoleveller software. I would recommend AoutlevellerAE, it produces
a probe file and THEN corrects the code.

Autoleveller software is open source, you can download it and see how it works.
My wife left with my best friend...
     and I miss him!
Re: 3d Probing on Granite slabs
« Reply #5 on: February 26, 2019, 02:25:27 AM »
Autolleveler is going to be the first thing that I will try these days. May I ask if somebody can recommend me a good touch probe? For now I have none experience with them.
Re: 3d Probing on Granite slabs
« Reply #6 on: February 26, 2019, 03:07:29 AM »
Hi,
with Autoleveller you present a Gcode job for the PCB. Autoleveller inspects the Gcode file to determine the
extents of the machined area and then proposes a Gcode file to probe the enclosed surface area in a rectangular
pattern. You might specify that you want probe points no more than 5mm apart so it will generate a Gcode file
that will drive a probe in that pattern and record the results.

I imagine if you present a Gcode file but instead of PCB tracks letters to be engraved then Autoleveller will
happily determine the extent of the letters to be machined and generate a probe file automatically.

I rather doubt you need an expensive probe. I would have thought a small button type switch with a stem on in that
you could mount in your spindle. If you glued a short extension onto the button and had the two wires from the
button terminals to your BoB that would be enough. Is precision beyond 0.1mm-0.2mm required?  Thus you could
make a probe for under $5.

If you use AutolvellerAE the data produced by all the probe points is put into a file which gives a colour rendering
of the surface. Thereafter Autoleveller will take your original engraving file and modify the Z cut depth to match the
surface contour. That modified or corrected file is the one you use to cut the letters.

Craig
My wife left with my best friend...
     and I miss him!
Re: 3d Probing on Granite slabs
« Reply #7 on: February 26, 2019, 07:37:23 AM »
Craig, the precision more than 0.1 mm-0.2 mm is not required. I will search the net or even in my country for a probe and star testing immediately. I am asking you for the a probe ideas, because, those I found in my country are some very expensive, around 1000 euro... And now you telling me 5 usd will do. So maybe I am searching for the wrong thing. I will search again and post what I found. Or maybe for fast result and delivery I should try ebay.co.uk. From there I will get the probe in a few days. Should I search for a "touch probe" or for "touch probe digitizer"?

Again thank you for helping me.
Re: 3d Probing on Granite slabs
« Reply #8 on: February 26, 2019, 11:28:07 AM »
Hi,
I wouldn't buy anything, I would make something simple and cheap. Prove the idea befoee
I spent anything.

Craog
My wife left with my best friend...
     and I miss him!

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Re: 3d Probing on Granite slabs
« Reply #9 on: February 26, 2019, 11:46:54 AM »
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