5 ms·

2 um accuracy; tools so fine that tool change air flow will break them; amazing. I could use this for machining mmWave components.

colechristensen 7y ago
I've been acquiring tools to fix/measure/improve cheap CNC mill and 3d printer, the $100 dial gague I picked has 10 µm as its smallest increment, you can just barely see a 2µm variation. The force the measurement tool imparts on the part and its support structure is more than that. The next steps are either carelessly blinding myself trying to build a laser interferometer or spending a ridiculous amount of money on more precise gagues.
- new299 7y ago
  Sam’s lasers sells some refurbished HP laser interferometers on eBay (HP5517 head+the receivers). He has also worked with someone to supply open source software/counting electronics. My notes on the kit are here: http://41j.com/blog/2017/02/hp-interferometer-notes/ http://41j.com/blog/2017/02/hp-interferometer-notes/ You can often pick up the laser/receivers/optics quite cheap (few hundred USD). And then just use the software supplied by Sam. The Sam kit is tested which is nice (but it’s ~1000USD IIRC). Interferometers as used on high end CNCs often.
  - colechristensen 7y ago
    There is a cool effect where a laser reflecting back into itself will cause interference inside the laser diode and affect the power required to drive it in a measurable way and with it you can extract a surprising amount of information (distance, rotation, angle, speed, etc.) I was ... hasty ... with my first laser diode and burned it out in about 30 seconds. I like to tell myself the money wasted was spent on learning lessons. The second is coming in the mail. The upshot with this method is that it can be extremely low cost and give you access to write code that interfaces directly with physics instead of somebody else's device. The idea for hacking on these things comes from Ben Krasnow https://www.youtube.com/watch?v=MUdro-6u2Zg https://www.youtube.com/watch?v=MUdro-6u2Zg and several research papers.
    - jbay808 7y ago
      This is known as a self-mixing interferometer (as is explained in the video) https://en.m.wikipedia.org/wiki/Self-mixing_interferometry https://en.m.wikipedia.org/wiki/Self-mixing_interferometry
- YZF 7y ago
  The black matrix glass in an LCD is typically accurate to a few microns since it's made in a photolithography process. If you couple that with a microscope/camera (e.g. mounted where your tool usually goes) you can use that to calibrate your CNC mill across its work area with some machine vision software. This is probably going to be a lot cheaper and simpler than using interferometers and for any practical purpose should have better accuracy than what you can expect to ever get out of a regular CNC mill. I'm not sure if you can just buy those somewhere or you'd take a display apart or something along those lines...
  - madengr 7y ago
    Glass scales for DRO are relatively inexpensive. The Bridgeport EZ-Trak I bought at work uses them in the servo system. So getting static accuracy is probably not too difficult, but the dynamic accuracy is a whole different can of worms. I can’t remember who wrote the white paper, but it described “rounding a square”, and measuring how much tangential material was left over at the flats, as a test of dynamic accuracy.
    - jbay808 7y ago
      Even static accuracy is not so easy. The scales will measure the axis position. But when you move the table over to the other end of travel, the shifting weight tilts the knee, and now your cuts that were supposed to be parallel are not. None of the scales measure this rotation. Then, as the machine warms up, differential thermal expansion starts to twist things further...
  - colechristensen 7y ago
    My interests are more in general purpose tools for increasing accuracy, and perhaps using them to increase the accuracy of inaccurate tools through feedback systems. That is, throw out chasing perfection of rigidity, dimension, and flatness of a mill (etc.) Instead keep adding measurement and feedback until the precision of the machine parts doesn't matter. (or, continue to amuse myself and annoy my partner by making messes and spending my disposable income trying)
- d-sc 7y ago
  What is your goal with improving the cnc machine? I’ve used a capacitive distance sensor to measure vibrations in the micrometers and nanometers. At that scale things get unintuitive pretty quickly. I doubt your motors and linear tables will be able to keep up with much precision beyond what you can measure with a cheapish digital caliper.
  - colechristensen 7y ago
    Eh. When I'm following my own drives I tend to build something up from basics and improve it's ability to do X until it reaches a certain level of usefulness and I get bored and move on because my goal was building the thing not ever actually doing anything in particular with it. That section of the journey appeals to me. Ultra-precise laser range finders scratch a particular itch. I so often have found myself wanting one and being unable to find something suitable to buy. Let's say, 1mm to 50µm precision at 1cm to 10m distances, in that ballpark. What could I do with it? * Characterize and quantify improvements in machine precision, most of what I do seems to be wild shots in the dark without some better measurement tools. * Add feedback mechanisms to machines – work around imprecise parts and close the loop with cheap and super-precise measurement tools. * Lasers. The key features are programability and range+precision.
    - d-sc 7y ago
      Cool! Here’s a couple thoughts I have, forgive me if you already have these in mind. Feedback and Controls: I’ve found that feedback suddenly made a lot more sense and seemed less mysterious once I understood the math behind it. This is the textbook I used: Control System Engineering - Nise And these videos were particularly helpful: https://www.youtube.com/user/ControlLectures https://www.youtube.com/user/ControlLectures Regarding Precise Measurement: It’s hard, something that might not look moving to the naked eye might be vibrating back and forth several uM. I’ve heard that lasers are subject to error from the atmospheres but I’ve never used them myself. Good luck!
- Accujack 7y ago
  If you look, there's an excellent paper on an academic team that did a low cost construction project on a small mill for micromachining. They achieved very high accuracy with fairly ordinary components. Here's one link to the project: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=2ahUKEwivooDh3dLjAhUXLs0KHR7gD48QFjACegQIARAC&url=https%3A%2F%2Fpeer.asee.org%2Flow-cost-micromachining-development-and-application-for-engineering-and-technology-education.pdf&usg=AOvVaw3WvJzVKOiMUBBtQM3JRaYV https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&c...

colechristensen 7y ago

I've been acquiring tools to fix/measure/improve cheap CNC mill and 3d printer, the $100 dial gague I picked has 10 µm as its smallest increment, you can just barely see a 2µm variation. The force the measurement tool imparts on the part and its support structure is more than that. The next steps are either carelessly blinding myself trying to build a laser interferometer or spending a ridiculous amount of money on more precise gagues.

new299 7y ago
Sam’s lasers sells some refurbished HP laser interferometers on eBay (HP5517 head+the receivers). He has also worked with someone to supply open source software/counting electronics. My notes on the kit are here: http://41j.com/blog/2017/02/hp-interferometer-notes/ http://41j.com/blog/2017/02/hp-interferometer-notes/ You can often pick up the laser/receivers/optics quite cheap (few hundred USD). And then just use the software supplied by Sam. The Sam kit is tested which is nice (but it’s ~1000USD IIRC). Interferometers as used on high end CNCs often.
- colechristensen 7y ago
  There is a cool effect where a laser reflecting back into itself will cause interference inside the laser diode and affect the power required to drive it in a measurable way and with it you can extract a surprising amount of information (distance, rotation, angle, speed, etc.) I was ... hasty ... with my first laser diode and burned it out in about 30 seconds. I like to tell myself the money wasted was spent on learning lessons. The second is coming in the mail. The upshot with this method is that it can be extremely low cost and give you access to write code that interfaces directly with physics instead of somebody else's device. The idea for hacking on these things comes from Ben Krasnow https://www.youtube.com/watch?v=MUdro-6u2Zg https://www.youtube.com/watch?v=MUdro-6u2Zg and several research papers.
  - jbay808 7y ago
    This is known as a self-mixing interferometer (as is explained in the video) https://en.m.wikipedia.org/wiki/Self-mixing_interferometry https://en.m.wikipedia.org/wiki/Self-mixing_interferometry
YZF 7y ago
The black matrix glass in an LCD is typically accurate to a few microns since it's made in a photolithography process. If you couple that with a microscope/camera (e.g. mounted where your tool usually goes) you can use that to calibrate your CNC mill across its work area with some machine vision software. This is probably going to be a lot cheaper and simpler than using interferometers and for any practical purpose should have better accuracy than what you can expect to ever get out of a regular CNC mill. I'm not sure if you can just buy those somewhere or you'd take a display apart or something along those lines...
- madengr 7y ago
  Glass scales for DRO are relatively inexpensive. The Bridgeport EZ-Trak I bought at work uses them in the servo system. So getting static accuracy is probably not too difficult, but the dynamic accuracy is a whole different can of worms. I can’t remember who wrote the white paper, but it described “rounding a square”, and measuring how much tangential material was left over at the flats, as a test of dynamic accuracy.
  - jbay808 7y ago
    Even static accuracy is not so easy. The scales will measure the axis position. But when you move the table over to the other end of travel, the shifting weight tilts the knee, and now your cuts that were supposed to be parallel are not. None of the scales measure this rotation. Then, as the machine warms up, differential thermal expansion starts to twist things further...
- colechristensen 7y ago
  My interests are more in general purpose tools for increasing accuracy, and perhaps using them to increase the accuracy of inaccurate tools through feedback systems. That is, throw out chasing perfection of rigidity, dimension, and flatness of a mill (etc.) Instead keep adding measurement and feedback until the precision of the machine parts doesn't matter. (or, continue to amuse myself and annoy my partner by making messes and spending my disposable income trying)
d-sc 7y ago
What is your goal with improving the cnc machine? I’ve used a capacitive distance sensor to measure vibrations in the micrometers and nanometers. At that scale things get unintuitive pretty quickly. I doubt your motors and linear tables will be able to keep up with much precision beyond what you can measure with a cheapish digital caliper.
- colechristensen 7y ago
  Eh. When I'm following my own drives I tend to build something up from basics and improve it's ability to do X until it reaches a certain level of usefulness and I get bored and move on because my goal was building the thing not ever actually doing anything in particular with it. That section of the journey appeals to me. Ultra-precise laser range finders scratch a particular itch. I so often have found myself wanting one and being unable to find something suitable to buy. Let's say, 1mm to 50µm precision at 1cm to 10m distances, in that ballpark. What could I do with it? * Characterize and quantify improvements in machine precision, most of what I do seems to be wild shots in the dark without some better measurement tools. * Add feedback mechanisms to machines – work around imprecise parts and close the loop with cheap and super-precise measurement tools. * Lasers. The key features are programability and range+precision.
  - d-sc 7y ago
    Cool! Here’s a couple thoughts I have, forgive me if you already have these in mind. Feedback and Controls: I’ve found that feedback suddenly made a lot more sense and seemed less mysterious once I understood the math behind it. This is the textbook I used: Control System Engineering - Nise And these videos were particularly helpful: https://www.youtube.com/user/ControlLectures https://www.youtube.com/user/ControlLectures Regarding Precise Measurement: It’s hard, something that might not look moving to the naked eye might be vibrating back and forth several uM. I’ve heard that lasers are subject to error from the atmospheres but I’ve never used them myself. Good luck!
Accujack 7y ago
If you look, there's an excellent paper on an academic team that did a low cost construction project on a small mill for micromachining. They achieved very high accuracy with fairly ordinary components. Here's one link to the project: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=2ahUKEwivooDh3dLjAhUXLs0KHR7gD48QFjACegQIARAC&url=https%3A%2F%2Fpeer.asee.org%2Flow-cost-micromachining-development-and-application-for-engineering-and-technology-education.pdf&usg=AOvVaw3WvJzVKOiMUBBtQM3JRaYV https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&c...