5 ms·

Take three somewhat flat stones to start out. Alternate rubbing the surfaces together in a random fashion. As you continue the high spots of the stones will be

Take three somewhat flat stones to start out. Alternate rubbing the surfaces together in a random fashion. As you continue the high spots of the stones will be ground down and the surfaces will become flatter and flatter. In the end you can get very precise flat surfaces. Two stones is not enough, you can then end up with two spherical surfaces. With three this isn't possible (imagine two of them are convex, when you rub them together they will grind eachother down and become less convex).

DougBTX 5y ago
With images: https://ericweinhoffer.com/blog/2017/7/30/the-whitworth-three-plates-method https://ericweinhoffer.com/blog/2017/7/30/the-whitworth-thre...
- was_a_dev 5y ago
  That is, one plate remains stationary while the other is lapped against it, and then the opposite is performed Is it a strict requirement that one plate remains stationary?
  - totalZero 5y ago
    In relative terms, one of the two plates remains stationary even if both are moving.
Akronymus 5y ago
Obligatory machine thinking: https://www.youtube.com/watch?v=gNRnrn5DE58 https://www.youtube.com/watch?v=gNRnrn5DE58 Altough, I disagree with the "random fashion". Alternating the pairs AB -> BC -> CA seems more logical to me.
- reportingsjr 5y ago
  It is necessary to grind in a random fashion (OP is talking about the method of grinding, not the order), or you will end up with imperfections. Lots of info about this if you look in to grinding mirrors for telescopes. Also, the order being random wouldn't effect the end result.
  - openandshut 5y ago
    If it's a machine doing the grinding, what is the source of randomness?
    - ruined 5y ago
      input
    - dylan604 5y ago
      function setPostion(float x=random(), float y=random()){}
      - datameta 5y ago
        I imagine the PRNG they use for this is a rather thorough implementation. Unless perhaps it is even necessary to used a cryptographic chip to generate true randomness.
        dylan604 5y ago
        pseudocode my man, pseudocode. ignite the imagination, and let the reader run wild. however, now my imagination is now running, and thinking about how overkill "true" random might be for this application. something "random" like an orbital sander would probably be enough. you're just trying to get away from side-to-side, left-circle, right-circle, up/down patterns. you're doing this to 3 different surfaces, so they would grind out any slight patterns which is the point. seems like a try crypto random would be as "effecient" as my roomba appears not to be.
        datameta 5y ago
        I suppose I went a bit overboard (no pun intended). 1 KB implementation should be more than enough for their precision. Maybe some code then, instead: https://www.dwitter.net/d/20446 https://www.dwitter.net/d/20446
  - platz 5y ago
- etrautmann 5y ago
  or a long-form textbook on the foundations of mechanical accuracy. Someone linked to this a year ago and I found it a fascinating deep dive: https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/Moore_Tools/Foundations_of_Mechanical_Accuracy.pdf https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/M...

DougBTX 5y ago

With images: https://ericweinhoffer.com/blog/2017/7/30/the-whitworth-three-plates-method https://ericweinhoffer.com/blog/2017/7/30/the-whitworth-thre...

was_a_dev 5y ago
That is, one plate remains stationary while the other is lapped against it, and then the opposite is performed Is it a strict requirement that one plate remains stationary?
- totalZero 5y ago
  In relative terms, one of the two plates remains stationary even if both are moving.

Akronymus 5y ago

Obligatory machine thinking: https://www.youtube.com/watch?v=gNRnrn5DE58 https://www.youtube.com/watch?v=gNRnrn5DE58 Altough, I disagree with the "random fashion". Alternating the pairs AB -> BC -> CA seems more logical to me.

reportingsjr 5y ago
It is necessary to grind in a random fashion (OP is talking about the method of grinding, not the order), or you will end up with imperfections. Lots of info about this if you look in to grinding mirrors for telescopes. Also, the order being random wouldn't effect the end result.
- openandshut 5y ago
  If it's a machine doing the grinding, what is the source of randomness?
  - ruined 5y ago
    input
  - dylan604 5y ago
    function setPostion(float x=random(), float y=random()){}
    - datameta 5y ago
      I imagine the PRNG they use for this is a rather thorough implementation. Unless perhaps it is even necessary to used a cryptographic chip to generate true randomness.
      - dylan604 5y ago
        pseudocode my man, pseudocode. ignite the imagination, and let the reader run wild. however, now my imagination is now running, and thinking about how overkill "true" random might be for this application. something "random" like an orbital sander would probably be enough. you're just trying to get away from side-to-side, left-circle, right-circle, up/down patterns. you're doing this to 3 different surfaces, so they would grind out any slight patterns which is the point. seems like a try crypto random would be as "effecient" as my roomba appears not to be.
        datameta 5y ago
        I suppose I went a bit overboard (no pun intended). 1 KB implementation should be more than enough for their precision. Maybe some code then, instead: https://www.dwitter.net/d/20446 https://www.dwitter.net/d/20446
- platz 5y ago
etrautmann 5y ago
or a long-form textbook on the foundations of mechanical accuracy. Someone linked to this a year ago and I found it a fascinating deep dive: https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/Moore_Tools/Foundations_of_Mechanical_Accuracy.pdf https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/M...