Magnet Shift Repair Solved...for me that is.

24

Comments

  • lawdogglawdogg Posts: 388
    edited May 2020
    I haven't paid much attention to them ... most are underneath the stickers. Can't be much help there.

    (If I can measure any that come in here on out I will do so)
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
  • xschopxschop Posts: 1,956
    After re-reading this thread and doing my phase plug project, I think a 1-piece cup design may work using the divet as a centering point.
    Both my magnets are 3.40" OD if you want to confirm that dimension on various MWs, then my design would work.
  • lawdogglawdogg Posts: 388
    edited May 2020
    xschop wrote: »
    3.40" OD if you want to confirm that dimension on various MWs, then my design would work.

    I measured the three MW6500 and two MW6502 magnets in the garage. All nominally 3.40" O.D. +/- 20 thou.

    The two MW6502 have annular stickers, exposing the centering hole. This hole measured 3/8" diameter on both. (The three MW6500 have a circular sticker, hiding any center hole, if it exists.)

    (I do very rarely get oddball magnets that are larger - I think really early MW6500. I had to make a second, larger PVC jig to re-center them.)
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
  • GardenstaterGardenstater Posts: 1,621
    edited May 2020
    I measured a few that I have that were easily accessible (made 2 measurements of magnets at right angles to each other)

    MW6500 1983 3.372, 3.384 (sticker covers entire pole piece, can feel a hole at center)
    MW6500 1983 3.402, 3.405 (same as above)

    MW6500 1979 3.318, 3.313 (sticker covers entire pole piece, something round protrudes at center)
    George / NJ

    Polk 7B main speakers, most mods comp. (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschopxschop Posts: 1,956
    Are the magnets' thicknesses all about 0.54" ?

    This is important because the positioning side screws will need to hit dead center on the backing plate and pole piece circumference.

    Thanks for you guy's help /info. I'll make a 2nd unit and send it out as loaner for the Polk community.
  • GardenstaterGardenstater Posts: 1,621
    MW6500 1983 0.538" to 0.546", avg. 0.542"
    MW6500 1983 0.538" to 0.541", avg. 0.540"

    MW6500 1979 ~0.55" (glue fillet makes caliper meas. impossible)
    George / NJ

    Polk 7B main speakers, most mods comp. (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschopxschop Posts: 1,956
    Again, searching the forum to no avail, I don't see mentioned where someone heated the magnet and pole-piece to separate the two without damaging magnet.

    After 1 hour submerged in acetone, the exposed layer of factory glue sloughs right off.
    After 24 hrs submerged, the two pieces still won't separate. Plan B is flame time.

    gscof8crwtf8.jpg
  • GardenstaterGardenstater Posts: 1,621
    edited May 2020
    Acetone in an ultrasonic cleaner? Mine is from harbor freight and it has a stainless steel basin which is about 5-3/4" wide x 9-1/2" long. The lid is made of plastic though and I don't know what the fumes would do to it so maybe you'd have to try it outside with the lid off.
    George / NJ

    Polk 7B main speakers, most mods comp. (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschopxschop Posts: 1,956
    The acetone won't permiate between the two, so high enough temp will need to be applied to break the glue compound, then pressed apart.

    I machined the centering spud already....

    0d7diasq3im2.jpg

  • GardenstaterGardenstater Posts: 1,621
    I was thinking the ultrasound might allow the acetone to penetrate. In my experience it does that but I don't know if it will be enough here.
    George / NJ

    Polk 7B main speakers, most mods comp. (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • I put mine in a vice.. I opened it up to hold the magnet and used a rag between the magnet and vice as not to cause any damage to the magnet and hit the pole piece with a dead blow hammer.. came apart with no damage.
  • xschopxschop Posts: 1,956
    I took the 2nd one apart and it is much closer to center. I'll still seperate it, so I can thru-tap the pole-piece....
    q7caklva9x83.jpg
  • xschopxschop Posts: 1,956
    edited May 2020
    I was hoping to score a drop-off of about 1ft of 3.5" ID x 4.5" OD aluminum tube this week. Anyone have some laying around?....
    :#
    I'll make 3ea and send you one and one out to the community as well.

    rcrobpgj30js.jpg

    q3642eqd9cxo.jpg

  • xschopxschop Posts: 1,956
    Had to post before I forget..

    Base plate ID.... 1.085"
    Voice coil ID..... 1.010
    Voice coil OD..... 1.060
    Pole piece OD....0.995"

    This all calculates to only 0.010" air gap on either side of VC and and confirms why a 0.020" thick plastic shim half the circumference of VC, inserted between VC and pole-piece will re-center the pole-piece, if you remove the dust cover to accomplish the task.
  • xschopxschop Posts: 1,956
    Is everyone's base plate O.D.'s 3.10 (+/- 0.005")?



  • The 2 in have measured 3.096. So yes your correct
    Mw6511
    Mw6510
  • GardenstaterGardenstater Posts: 1,621
    edited May 2020
    MW6500 1983 3.097 3.099
    MW6500 1979 3.105 3.107
    George / NJ

    Polk 7B main speakers, most mods comp. (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschopxschop Posts: 1,956
    I'll share my design now since I can't get to this project just yet. Look it over, share some input. I've got two large dia. 5" billets and am waiting to procure 4" diameter billets for the secondary jig that is 3-purpose. It sets the magnet to pole-piece 1st when gluing, then sets the Main base-plate positioning set screws on the Main unit. If your Base plate OD is 3.10" (+/- 0.005) then it will probably center on first hit (all depends on Base plate ID to OD concentricity due to the stamped steel. Final adjustment is done on top screws. I ordered Non-Magnetic Stainless 1/4-20 x 1.5" lengths that are CUPPED to allow Base plate self-centering/clearance as the magnet snaps and avoids voice coil damage. Dog-points would probably catch the base-plate OD and go off-kilter.
    Thirdly, I can set 0.996' phase plugs with 3M sticky tape.




  • xschopxschop Posts: 1,956
    edited May 2020
    Sorry fellas, ever since "downgrading" to Windows 10, I've experienced the Blue Screen o' death, failure to start, loss of data/files, and now .png hostage by way of one-drive.

    What's most ridiculous is the non-MD "philanthropist" that wants to manipulate mRNA code to fix the world, when he can't even keep his computer code from crashing.
  • xschopxschop Posts: 1,956
    Let's try this again...

    jxyqxs6j6cno.png
  • GardenstaterGardenstater Posts: 1,621
    Looks good and you put a lot of thought into it. I like it! Aluminum billet material so as to be non-magnetic?
    George / NJ

    Polk 7B main speakers, most mods comp. (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschopxschop Posts: 1,956
    Yes, and the magnet/pole-piece after gluing is held in main jig by base plate set screws.
  • GardenstaterGardenstater Posts: 1,621
    Yep I got that, and the base plate set screws of the main jig are set to initial depth on the 3.11 dia. of the first jig, which is also used for gluing up the magnet/pole piece while maintaining concentricity. Then the adhesive is applied to the base plate and the main jig with the magnet/pole piece secured in it by the set screws bearing on the pole piece is lowered onto the speaker's base plate so that the pole piece is approximately in the center of the voice coil and the exact center is then found by playing with the set screws bearing down upon the pole piece by counting turns or measuring the position of the set screws with a depth gauge.
    George / NJ

    Polk 7B main speakers, most mods comp. (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • Yes xschop!! Looks great. Nice design
  • lawdogglawdogg Posts: 388
    I admit I can't really visualize how this works from your drawings.
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
  • xschopxschop Posts: 1,956
    edited May 2020
    The 2nd piece is not absolutely necessary, it just makes quick work of setting the base plate set-screws or the top screws if you wanted once the magnet/pole-piece is inserted into main jig. You can use decent calipers and calculate all 4 base plate screws using the main jig body as reference.

    Still you need to hit dead center the pole-piece and magnet beforehand.


    Post edited by xschop on
  • lawdogglawdogg Posts: 388
    Ok so the horizontal holes are for set screws? Trying to visualize how it works
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
  • xschopxschop Posts: 1,956
    lawdogg wrote: »
    Ok so the horizontal holes are for set screws? Trying to visualize how it works

    Yes, the inner lip at 1.00 from bottom sets perfectly level on top of magnet aligning all screws automatically.
  • xschopxschop Posts: 1,956
    Fits my MW6502s like a glove. Setting up tapping operation....

    vdzlkdbhynlr.jpg

    s5q9vinp7b7f.jpg

    ilxawnk3yx3t.jpg


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