I just had my apartment measured for carpet and the guy used a laser measuring device to measure the rooms. I was wondering if it’s possible to have a similar device mounted to the Z axis to set the zero off the surface of the stock.
John
This did cross my mind, but the precision would probably be quite poor compared to what can be done with electrical probing or the paper method, or require a sensing device that would cost an arm and a leg. I also considered various (cheap) proximity sensors, but again precision is the difficult part (including having a sensor that could accurately sense a wood or plastic or metal surface with equal accuracy/precision). It would be a fun experiment though, and I’m sure someone tried this already?
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One consideration in measurement is that one wants a device which is measuring in units 10 times finer than the measurement of the dimension you wish to actually measure.
For a belt drive Z-axis, that’s 1/40th of a mm further divided by 10, so 1/400th mm or 2.5 microns.
I suspect that some sort of sensor technology / positional encoding will be the next big development for inexpensive CNC — but it’s going to require a technological tour de force in terms of a breakthrough in measurement systems.
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but you would do this different, To find X/Y you do a height measurement straight down… so what you’re measuring is not 1/40th of a mm… but the height of the stock (say 1/8th" for thin stock) which is an order of magnitude simpler… and you basically just do an edge find (you can even find the center of the stock this way by finding all 4 edges)
and to find height, you do the same; on the side you have something that goes up and down at high precision mechanically, but you measure distance to the other side… if you go from high to low… when the distance suddenly goes way down, you found the top
I’m not an engineer…but rather than using an audio or physical probe of some sort, wouldn’t an optical sensor (edge sensing) make the most sense? If you put an optical target on the top of your surface you could likely use an optical focusing apparatus to determine “perfect focus” to a very high precision. I’m not sure if the handheld CNC uses the same technology, but it looks like it’s using something similar.
Arguably, as @GJM alluded to this is the province of machines such as the Shaper Origin — but isn’t it pretty much limited to X/Y positioning along a depth relative to the surface the machine rests on?
One thing which some folks have done for Z-axis positioning is to set it approximately, then to move the machine to a consistent point, jog until the endmill is just above that point, set Z-zero there, loosen it, let it drop, then secure it in place while resting on the desired Z-zero point.
Before the BitSetter came out I was contemplating making a fixture which could be slid into place at the front of the machine as part of an endmill change.
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Focusing systems are highly accurate. The distance between two points is easily discernible and, if known to be a precise value, can easily be used to calculate the specific distance of a known lens to the subject.
Juilen, I am with you the precision would need to very tight and reproducible. Has anyone quires NASA technical links as they likely have a very sophisticated laser distancing system to link the space station to an incoming transport ( rocket) with supplies. Also they must use range finders on their sampling devices, rover and chemistry of soil samples. Just thinking these boys have to be spot on; they may desire to share the technique and design. I’ll Inquire as I get the NASA technical magazine that offers their innovations to industry. Tom
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Just looking at the commercially available distance finders, most quote 1.5 or 2mm accuracy uncertainty, when considering the sub-$200 products. To be viable, I guess this sort of price range is what most users would consider ‘doable’
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Sensor company SICK make the OD Mini, 50-150mm range, 200um repeatability in distancing. Yours for the modest sum of £750 inc taxes… Gives a sense of scale to wants vs costs
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I retired several years back from a biomedical equipment company where one of the units I serviced was a robotic plate streaker for microbiology labs. It used pre-dispensed petri dishes in which the height of the media varied widely, and to compensate for this, it utilized a small ultrasonic sensor about the size of a Sharpie marker to regulate the Z-axis of the dispense mechanism. The accuracy of this device was such that we used Post-It note paper as a thickness gauge, much as I still do when zeroing the Z-axis on my Shapeoko. Not sure if this technology is available in hobbyist form, or what driver hardware might be available, but that was back in 2013.
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