On Wednesday 26 September 2018 01:11:50 Chris Albertson wrote: > On Tue, Sep 25, 2018 at 1:04 AM andy pugh <bodge...@gmail.com> wrote: > > I can't help thinking that the way to determine the amount of > > correction needed is to actually machine a test bar and measure it. > > A laser beam is straighter than any bar. and is quicker and costs > less. What you do is place a camera in the tool holder and watch the > beam move as you move the carriage. You can measure at the > micrometer level typically 1/10th the pixel size. > > We live in a time when "nuts" level measurements is easy and cheap. > for example: I just bought a pair of BMP280 barometer chips on eBay > for $6. I have a live graph on my iMac showing the air pressure vs. > time. The chip is simple, just an I2C serial output. I can see the > plot on the screen move as I move the chip up and down. Clearly I see > that the air is thinner 10 inches above my desk then it is 2 inches > above my desk. It is a sensitive altimeter for $3. Upstairs I have > an oscillator that runs at 10.000000000000 Mhz and all 13 of those > zeros are significant. I have about $100 invested it that if you > count all the parts. > Thats all true. I can recall buying two custom made frequency srcs to replace the failing oven types in our old GE transmitter in the late 80's, paying $750 each, and building them into double-sided pcb boxes I soldered up, getting power to run them from the heater supply for the old crystals. They were far more accurate than the frequency monitors of the day made by Arnold Belar. It got to be a private joke of mine that when the Belar said it was off frequency, I sent it in for repair. TV transmitters were allowed +- 1 likohertz for the visual, and the aural was allowed that same 1 kilohertz but was 4.500000 hz above the visual. Those two srcs kept it well within the tolerance of a $6000 hp counter, and were probably never more than 10 hz off the rest of the life of that transmitter. Today that sort of accuracy can be had for under $100 for the pair. The trick is finding where to buy them.
But finding a camera chip big enough to shine these laser's on so that the laser stays on the imaging chip cannot be found in an integrated package that will plug into the 15 pin connector on a pi. The laser beams are 10x the size of the imaging chips even if they're perfectly aligned. To get something usable I may have to buy a lensless digital camera for around a 100 dollar bill, which of course has a usb-2 output, and controlling it to get the image data is something I'll have to invent. I've probably spent 20 hours online already looking for something I could use with a pi, or a rock64 since it also has the 15 pin camera connector. I can probably get, from digikey, an imager chip big enough (and low enough resolution, 1 megapixel is a great plenty) but to actually make the supporting circuitry to make a working camera out of it will take more than this old man has left in him. These $15-$25 cameras for the pi all have image chips less than 1/8" square, with as high as 8 megapixels. Some are even microscopic sized pin holes, no lens at all! Nevertheless, I've ordered some 3/8" brass tubing to put on the rear of the "cartridge" to extend a switchable, dimmable power supply out the other end of the spindle some 21" away, a cross polarizing adjustable from ND2 to ND400 filter, and another 12x24 sheet of half inch 6061 to make a new apron plate for the front of the carriage so I can re-arrange things a bit and move the z nut to the right by at least an inch, getting away from the forces from over compressing the left bellows when I'm right at the nose of the spindle. The plate I made was cut from the deck of an old Ampex VR-1200, and has quite a few holes I filled with permatex liquid metal and sanded flat and painted over, and a newly made one will only have holes where I put them. A bit less hacky looking I hope. And I'll clean up that DMT plate and remove the dings that are tipping the tailstock to the back of the bed by several thou when the tailstock is sitting on them. As it sits. I now have around 20 inches of +- a thou. There may be more dings in the edge of that front flat to address. Frankly, this lathe has been beat to hell in its 70 years and I, like a dummy, paid 4x what it was worth. But what's done is done, but I reserve the right to claim I was an idiot to buy it. ;-) The technology, Chris, has run off and left us behind. -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
