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  • Originally posted by MattiJ View Post
    Do we fix the clumsy old bastard with metric or whithworth fasteners?
    Or just self-tapping sheet metal screws?
    Nah, I have a box of rusty nails we can use. We just nail the old fart back together. The fun will be in pulling the nails out with a claw hammer in a few weeks.
    Location: The Black Forest in Germany

    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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    • For those interested in the "PWM Vernier", here is the LTspice simulation and representative circuit:



      The LTspice ASCII file (with some modifications from above): http://enginuitysystems.com/pix/elec...WMvernier6.asc

      I repurposed an SCR drive circuit, designed to fire the gates of a dual SCR in antiparallel configuration. This uses the AC line power, or the voltage across the SCRs, as a phase reference so that the initial phase angle can be adjusted to fire at about 70 degrees from zero crossing for minimal DC offset into inductive loads. It can also be programmed for a specific ON time in cycles or seconds, optionally using a serial connection or Bluetooth. The modified PCB:



      The two common mode chokes are used as transformers to provide two isolated 12V drive power supplies for the two SCR gates, or in this case, MOSFET gates, using an IRS2453 self-oscillating Hi-Lo dual gate driver, at 100 kHz and two dual NMOS devices. They use SI8261 opto-emulated gate drivers, controlled by the PIC16F1778, which provides a 20 kHz PWM. The main 12VDC is supplied with a 12V 1A switching supply (about $3 from Banggood).

      The schematic (for the original SCR design):





      The PWM vernier design is much simpler. I might commit to a new PCB, after I do some more testing. I estimate the total parts cost will be under $30 for a 120/240 VAC unit rated for about 5-10 amps nominal. The same basic design could be used for several hundred amps using high power MOSFETs or possibly IGBTs.

      My use of the term "vernier" comes from the second definition as a device that facilitates fine adjustment, as applies to my experience designing circuit breaker test equipment which uses typically nine coarse taps, with a fine "vernier" adjustment between tap settings (with some overlap), to obtain any desired test current.

      Let me know if you are interested and have use for such a product, and I might be inspired to finish the design and offer it for purchase.
      http://pauleschoen.com/pix/PM08_P76_P54.png
      Paul , P S Technology, Inc. and MrTibbs
      USA Maryland 21030

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      • Originally posted by Alistair Hosie View Post
        my Fibula back one is hanging off from my front bone so I am all plastered up to my knee and will need a scan again to see if I need an operation tomorrow . Am I not unlucky or what heh heh heh so no chance to get into my shop anyways. Alistair
        Well now thats something to do on a day. Sorry to hear about it.. If you are lucky they will need to plate and screw it back together again. The lucky part? No cast. JR

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        • A neighbor gave me a low-miles but seriously filthy Husky pancake compressor - 2.5 SCFM at 90psi, so worth fixing (even though I have several compressors).
          It wouldn't output air, so after a scrub down I took it apart to find the regulator was made of pot metal and the adjuster screw was stripped.

          I came up with about 5 ways to fix it - the easiest being an insert. Not having an 8-1.25 female thread/'something I have a tap for' external thread threadsert, I took a 3/8-24 bolt (3/8-16 wouldn't work too well with 8mm) and drilled/tapped it for the 8mm thread. Drill and tap the housing for a high % 3/8-24 thread, a little red Locktite and a couple of stakes for good measure, grease the Adjuster threads and done - better than OEM!
          Kindergarten machining, of course, but a 30 min investment turned trash into a decent little compressor.
          Location: North Central Texas

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          • Originally posted by PStechPaul View Post
            Let me know if you are interested and have use for such a product, and I might be inspired to finish the design and offer it for purchase.
            Now I may just be speaking for myself here.....but I'm still not sure what it does, let alone whether I could use one! Does it act as an AC power supply with finely adjustable voltage based on a PWM input?

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            • Yes, it is essentially a lamp dimmer or variable voltage motor control that uses high frequency PWM instead of phase angle modulation (using TRIACs or SCRs). It will work equally well on raw DC as well as AC, as long as the voltage is within the range of the switching power supply (85-265 VAC or 120-375 VDC). Being based on a PIC, it offers additional features, such as:

              1. Remote control of output via serial connection or Bluetooth

              2. The ability to supply pulses of precise time duration.

              3. Adjustment of initial phase angle (when used on AC).

              4. Programmable soft start and turn-off.

              5. When supplied with DC, and a full H-bridge, the device can operate as a single phase VFD for induction motors or other devices.

              6. The basic design can be adapted to operate on voltages as low as 12V (AC or DC), and as high as 600V (AC or DC).

              7. With some simple added circuitry, it could be configured as a battery charger.

              8. It might work well as the control element for a spot welder, or perhaps even a stick welder.

              9. It could be used as a programmable bench power supply (DC or AC).

              10. It could be configured as an arbitrary waveform generator, within the parameters of what is possible using PWM.

              As usual, I may be getting carried away by fantasizing about various bells and whistles that might be added, and already I envision possibly adding more PWM channels to build a three phase VFD, but then I get caught in the loop of endless "feature creep" and stalled development that has led to my well-known habit of "never finishing anything".

              Perhaps I will create a new thread on this project, as it seems to have considerable possibilities within the general umbrella of machining and associated electrical and electronic instrumentation and controls.
              Last edited by PStechPaul; 03-19-2019, 03:31 PM. Reason: Full H-bridge added
              http://pauleschoen.com/pix/PM08_P76_P54.png
              Paul , P S Technology, Inc. and MrTibbs
              USA Maryland 21030

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              • It also sounds like a very versatile IoT thing. Remote dimmer switch maybe. Granted that sounds like under-achieving for what it's capable of. A solution in search of many possible problems?

                Edited: to remove idiocy.

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                • I had a bit of time to spare so I took a look at my little Adept 2 power shaper and spent time refining my tool geometry.

                  It was well worth my time.

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                  • I think I will start a new thread. Meanwhile, I made a PDF document with the content from the three posts here. I may update it as I make progress toward a viable design. I also realized that the present design will not work directly as a VFD, because the output polarity is dependent upon that of the input. It will work on either positive or negative polarity. However, it would not be difficult to configure the four MOSFETs as a full H-bridge to obtain the ability to reverse the output and thus convert DC to AC. Here is the document:

                    http://enginuitysystems.com/pix/elec...ier_Design.pdf
                    http://pauleschoen.com/pix/PM08_P76_P54.png
                    Paul , P S Technology, Inc. and MrTibbs
                    USA Maryland 21030

                    Comment




                    • Polyethylene is ridiculously easy to work on, drilling is more like extruding

                      Location: Helsinki, Finland, Europe

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                      • Originally posted by MattiJ View Post


                        Polyethylene is ridiculously easy to work on, drilling is more like extruding


                        I've used my planers on aluminum with good results as well. They do need to be adjusted for a much less "bite".
                        Andy

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                        • Electric bike and cold spring night that froze everything to hard as concrete:


                          Havent had this much fun with bike for 30 years!
                          Location: Helsinki, Finland, Europe

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                          • I cleaned out my window wells and cleaned the windows, hadn't been done for ten years. Worst job there is.

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                            • I spent the week at my Mom's house, helping her get it ready to sell. She'd had a groundwater leak in the finished walk in basement. After a heavy rain the leak soaked the brand new carpet that had been installed after the burst hot water pipe soaked everything last summer. A sump pump and vapor barrier were installed by pros, but that entailed tearing out the 50 year old plywood backed paneling as well as the brand new "engineered wood" (fiber board) paneling from 4 walls in 3 rooms.

                              As usual, she could not find anyone who could commit to getting the job done in less than a month, possibly more. I could not see why I could not get it done in a couple days with my uncle's help, so I offered to make the 500 mile drive and do it over the weekend. I forgot that my stepdad had built that house and that nothing was consistent. It had neat features like a fake window in one wall that had a poster in it of a mountain side. The furring strips on that wall were 2x6 studs. It took 5 days.

                              To make a long story short, two senior citizens with failing memories end up being about as efficient as a single person. After measuring the first set of "furring studs" at 86-3/4 inches and cutting them 84 we got in the habit of both of us measuring, then going outside to cut the wood. Double checking each step worked fine, but really slowed us down. We found that the ceiling to floor distance sometimes varied as much as 1 inch in 8 feet. We had to map the whole thing out and custom fit each board.

                              Did I mention that we were told not to nail through the vapor barrier? Did I mention that the waterproofing guys installed a plastic channel along the base of the wall that was 5 inches high and 3 inches deep that needed protection? It's probably the only sump drainage line in the city protected by a custom fitted 2x6 enclosure.

                              By the end of the 5th day it really looks pretty good. Everything is straight and level, and the sump pump is doing as it should as the water slowly seeps through the seam that joins the wall to the slab.

                              Machining content; Del (my new step uncle) turns out to be a retired machine shop foreman. We swapped tales of machining as we worked. At one point we were cutting paneling using an 8 foot steel straightedge that was accurate to .001 over 8 feet. Del made it in his shop 40 years ago for my step dad. The only payment he wanted was that straightedge.
                              At the end of the project, there is a profound difference between spare parts and left over parts.

                              Location: SF East Bay.

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                              • Shop Layout using Fusion 360. My shop does not look like this, but I am trying to find out if it would be a realistic idea, the metal area put near the big garage port and given more space. A new wall put up and perhaps a sliding door that goes into the wall, or heavy plastic curtains between the areas.

                                All the models are roughly the correct size and footprint of machines I own. The black boxes are a shelf and compressor I didn't bother modelling. Workbenches on wheels are things I've planned to build in the future. Still need to fit in a jointer/planer there.





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