Method for probing acrylic sheet

[airnocker]

I saw a post here for probing non-conductive material like plastic and I want to learn more as I do acrylic engraving and so far lived with acrylics uneven surface height issue akin to copper clad boards.

This post mentioned using .02mm aluminum foil and water tension to make the foil hug the surface of the plastic.

Has anyone had success using this method? Are there better methods?

Thanks

[CitizenOfDreams]

Foil and water would probably work, although sounds messy.

As for me, a couple years ago I made myself a small probe which I am still very happy with. You can see it here on CNC Zone forum: https://www.cnczone.com/forums/calibrat ... roach.html

[airnocker]

Foil and water would probably work, although sounds messy.

As for me, a couple years ago I made myself a small probe which I am still very happy with. You can see it here on CNC Zone forum: https://www.cnczone.com/forums/calibrat ... roach.html

Thanks C.O.D., I looked at your post, very creative and inventive. I like it. Could you share more design details (to me, the flat of the needle as it raises would seem to have to rise far more than a few thousandths or tens-of-thousandths to occlude the photo sensor. What specifically is the new photo interrupter sensor you are using from Ebay?

[CitizenOfDreams]

The needle has about 0.5mm free movement before it activates the photo interrupter. The less free movement, the better, but it does not affect accuracy in any way.

My first probe used HOA0971 interrupter which I found in a local store by accident. It has all the pulse forming circuitry already built in.

My second probe uses cheap HY870P interrupter that only has an LED and a photo transistor. It would work on its own, but adding a 7414 chip should (in theory) improve repeatability.

[airnocker]

The needle has about 0.5mm free movement before it activates the photo interrupter. The less free movement, the better, but it does not affect accuracy in any way.

My first probe used HOA0971 interrupter which I found in a local store by accident. It has all the pulse forming circuitry already built in.

My second probe uses cheap HY870P interrupter that only has an LED and a photo transistor. It would work on its own, but adding a 7414 chip should (in theory) improve repeatability.

Thanks, for the interrupter specs. So .5mm of free movement translates to .0196" before probe triggering. Once you've probed a mesh area and saved XYZ values to CSV file, do you take this free movement into account when calculating Z height adjustments for the g-code file?

[airnocker]

The needle has about 0.5mm free movement before it activates the photo interrupter. The less free movement, the better, but it does not affect accuracy in any way.

My first probe used HOA0971 interrupter which I found in a local store by accident. It has all the pulse forming circuitry already built in.

My second probe uses cheap HY870P interrupter that only has an LED and a photo transistor. It would work on its own, but adding a 7414 chip should (in theory) improve repeatability.

Thanks, for the interrupter specs. So .5mm of free movement translates to .0196" before probe triggering. Once you've probed a mesh area and saved XYZ values to CSV file, do you take this free movement into account when calculating Z height adjustments for the g-code file?

Nevermind, after thinking about it, the trigger height is relative to the zero height reference.

[CitizenOfDreams]

That is correct, the trigger point is your zero height. What happens to the needle before that point is irrelevant.