Rapidly Cycling DC Magnet For Metal Disintegrator

Discussion in 'The Projects Forum' started by PGB1, Jan 15, 2013.

  1. PGB1

    Thread Starter Member

    Jan 15, 2013
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    Hello Good People!

    I am new here & as a brief introduction, I'd like to say that I have been trying to learn electronics since the 1960's. For some God-sent reason, it is finally starting to sink in!

    Thanks to this forum's members & their posts, I have spend the last several days learning & learning about all manner of electronic functions & components. You folks are great teachers!

    General Idea Of This Post
    My question relates to an electric discharge machine for removing metal (in my case- broken taps). About 20 some years ago, I found the discarded half of a Rocklin "Electronic Router Metal Disintegrator" Model 9350A. I don't have the power source, just the electrode 'driver' end. (As-Found photo attached.) The people at Rocklin have not been able to find any information in their archives of the power unit. I certainly appreciate their efforts.

    Some Background Of The Device
    My studying leads me to conclude that typical home built EDM units use a solenoid to pull an electrode up. It is held up until a capacitor (in series with the coil) is saturated & the electrode holder falls. The capacitor then discharges into the grounded work piece, creating the spark. (Drawing attached)

    In this Rocklin unit, there is no solenoid. It has what I would call 'Half a transformer'. It seems to be an electromagnet. (Photo Attached)
    In this device, energizing the coil pushes the electrode holder down (into the work). It is kind of interesting. The E-Laminations are turned so the legs face up. The top lamination block is loose. Upon energizing the coil, the block is pulled into the E's arms, pushing a rod attached to the electrode holder down.
    (Drawing Attached)

    The Main Problem
    My problem is how to rapidly cycle the DC coil on & off. I suppose around 20 or 30 cycles per second is appropriate. Ideally, it will coincide with a capacitor being charged to create a spark. In a perfect world, the electrode will be positive for a cleaner cut. Not critical.
    After experimentation, 40 Volts DC would be the best to use for the coil, as it gives the longest stroke. At 20, although the stroke is shorter, the coil stays noticeably cooler, so that would be OK, too.

    Coil Notes
    The coil is marked "110-120" But, with AC it will cycle for only a few seconds then vibrate. (Saturation?) It also gets very hot very quickly. This is true for an voltage. It will not pull the lamination down until about 100 volts AC, regardless of gap adjustment.
    Coil Resistance = 143.44Ω

    With DC, I can adjust the gap of the top lamination to go as low as 20 volts.
    For Example- At 20 VDC, the arm can be set to move 1/128" & the coil draws .12 amps. At 40 VDC, it will move 1/32" & take .28 amps of current.
    On DC, the coil does not get hot. (Warm, but not hot)
    On the attached drawing, the notes about current draw & minimum voltage are wrong. Sorry about that.

    My Studying Lead Me To ...
    I have considered a Pulsed DC, something using a 555 timer, an oscillator circuit of some sort & a few methods.
    One idea was to wire a normally closed relay's coil in the manner of a 'normal' home EDM, as per the drawing. I would have the relay's contacts energize the Rocklin's coil. But, this does not coordinate a capacitor's charge for a spark. Also, it seems like cheating. (And, would it kill the relay by fast cycling for long periods?)

    Thank You
    I'd like to say Thank You for any suggestions about how to best configure a circuit to control this device. To be honest, my desire to have this unit operating is more for a learning experience than functionality. I do break taps (usually near the end of a project), so it should actually prove useful.

    Thanks again for ideas!
    Paul
     
  2. tracecom

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  3. spinnaker

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  4. shortbus

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    Edm is pulsed DC. Your Rocklin uses the DC to move the "electrode", it works like the old fashion door bell ringer or a tattoo machine.

    The Rocklinizer that tracecom linked to, is used in machine shops to add a slight amount of metal to a part that was machined undersize. It's electrode welds itself to the part and breaks off a little bit when it vibrates. The electrodes are a special pressed metal that allows this to happen.
     
  5. PGB1

    Thread Starter Member

    Jan 15, 2013
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    Thanks for taking the time to reply guys!

    I suppose a total re-think is in order.
    Rather than try to use the same low voltage DC power source for the spark & coil movement, relying on a capacitor to make the spark and operate the coil- Go for separate power supplies. THis way, I can have any "destruction" current I design for.

    Thanks to Shortbus' suggestion, I focused on pulsed DC.
    I did try adjusting the coil's gap & using sort-of pulsed DC. I put one diode in series with the coil. It moved the electrode up & down very well. Now I have to figure out how to make it work at a low enough voltage so the coil does not heat up. I think I can tweak the coil gap &/or spring to make it work at a good temperature.

    Since the unit's electrode is electrically insulated from the rest of it, I can most likely build a small spark power source from an old transformer, re-wound to suit. Perhaps from a junk microwave oven or HID light? Worth a try!

    Thanks Again for great help!
    Paul
     
  6. shortbus

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    Building a hobby size EDM is an ongoing project of mine. I ran EDM's at work for 13 years. The are several books and websites for hobby EDM.

    The best book (in my mind) is sold by Home Shop Machinist magazine - http://www.amazon.com/Build-EDM-Electrical-Discharge-Machining/dp/094165351X He goes into detail on how and why it works. And tells how to scale it to any level you want.

    Then there are Ben Fleming's books and web site. "Build a pulse EDM machine" and "EDM how-to book".

    Web group - tech.groups.yahoo.com/group/EDMHomeBuilders


    Lots of info on the web now about EDM. Good luck with your Rocklin machine. :)
     
    Last edited: Jan 16, 2013
  7. PGB1

    Thread Starter Member

    Jan 15, 2013
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    Thank you for the links, Shortbus.

    I think an investment in one or more of the publications is a wise beginning.

    I may as well make this a Full-On fun project & do it correctly. (Especially since in the last day or two I've thought of many uses for the device beyond removing broken taps.)

    I toured the user group you referenced. It is amazingly full of great ideas & detailed information.
    Thanks Again for your help!
    Paul
     
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  8. oldgoaly

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    Apr 6, 2014
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    As usual I'm a year late and a bunch of dollars short!
    Did you get your machine to work? I'm a owner of a Rocklinizer and have been looking at adapting it to zap broken taps. tt
     
  9. MaxHeadRoom

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    Simple tap disintegrators are usually much simpler than EDM, no pulsating DC, just very low voltage, high current ac and a AC solenoid is used as a vibrator to oscillate the electrode against the work.
    This is the way most of the leading disintegrators work.
    Max.
     
  10. #12

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    This thread is a year old and the Original Poster has not been back for a year.
     
  11. PGB1

    Thread Starter Member

    Jan 15, 2013
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    Hi All!
    I'm the original poster & I have, indeed, been back to this user group quite frequently in the past year. I simply did not have anything new & exciting to add to this thread.

    Thanks for asking Oldgoaly, but I have not yet gotten the unit up and running. I have done some experimenting around, but life sent complications which took me away from my Fun Project Shelf.

    The odd part of this unit is that the power pushes the electrode down to the work. On the others I've seen, power lifts the electrode away from the work, so the circuitry would be easier to build.

    For my 'backwards' unit, the latest idea I have is to use a normally closed relay which can act quickly and repeatedly. Maybe a 555 timer circuit would do the same thing? I'll (try to) attach a quick sketch of my rough ideas to this reply.

    I have not worked out details for a power source. The coil on the Rocklin is 120 volts AC. I prefer to send DC at a lower voltage to the electrode. For an electrode, I'm thinking about a piece of tungsten such as those used for TIG welding.

    Hopefully you will get yours up and running. (Me, too!) Of course, when I make a breakthrough, I'll post again here.

    Have Fun Building and Enjoy Today!
    Paul
     
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  12. MaxHeadRoom

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    Jul 18, 2013
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    The ElectroArc types I have worked on the head is vibrated by a 50/60hz operated solenoid armature.
    In your case, maybe the head could drop down to the work by gravity, which then closes a N.O. contact which then returns the head up and opens the contact and the process repeats as a normal vibrator function, or something along this line.
    As I mentioned, it is not considered necessary to use DC on a dis-integrator as you are usually not concerned about fine erosion.
    The principle used on the Electroarc is similar to a SMAW welder when you tap the rod to start the arc, but the voltage is much lower so welding cannot take place in this instance, just the 'splash'.
    But also they use a hollow copper material electrode with a recirculating to pump fluid through the hollow copper to flush and cool the work.
    Max.
     
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  13. oldgoaly

    New Member

    Apr 6, 2014
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    Thanks for the reply!
    here is the Rocklin circuit from the patent info it might give you an idea.
    View attachment 2.pdf
     
  14. oldgoaly

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    Apr 6, 2014
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    another more simple version of a different model

    schematic02.jpg
     
  15. shortbus

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    @oldgoaly, would you be oldgoaly from MetalMeet.com?
     
  16. oldgoaly

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    Apr 6, 2014
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    yes sir! your Cary right? I thought you might be the same SB. The Rocklinizer search found this thread. I have read other threads for other repairs and replacement ideas. Most of the old stuff I work on it's rare to find anything on the net. I hope all is well with you and your family! Take care! tt (I haven't been on mm in a year or two)
     
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  17. shortbus

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    So if I understand right, you want to adapt the Rocklinizer into a tap burner. I have used both the Rocklin and EDM over the years at work. The Rocklin uses AC and is basically a 'welder', it uses a spring to break the electrode off when the AC crosses zero volts. The tap buster and EDM use DC on the electrode and pulse it on and off. And they need a liquid to wash away the 'chips' of metal made from the sparks from the electrode. I think I have a old magazine article or two on simple tap buster circuits, can look for them if you want them.

    The quality of the work the guys on MM are doing just keeps getting better and better. Hope everything has been good with you and yours too.
     
  18. oldgoaly

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    Apr 6, 2014
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  19. shortbus

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    Good find!. Before I retired I tried to make it to HGR every couple of months. Good people to buy from. Never be afraid to offer them less than asking price, they are pretty flexible on price.

    Know what you mean about the body! Would love to keep the knowledge and get a new body. Take care, tt
     
  20. PGB1

    Thread Starter Member

    Jan 15, 2013
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    Thank You for the drawings, OldGoaly. Very helpful, indeed!
    Paul
     
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