Forum member MW magnet repair tool set

Gardenstater

@Kryten this is ready for you now. You're up bud! Just PM me your address

I took 50 thou off of it to ensure clearance to Dynamat and there is now a PVC insert that is removable but will help people with smaller magnets/pole pieces like in my MW6500s, in the pole piece removal process/smashing.

Kryten

PM Sent (with a bit of trepidation). This and other threads will be referenced!

Gardenstater

@Kryten How ya making out with that?

Kryten

Thanks for the nudge! The email the system sent reminded me I haven't logged in here in ages and I immediately remembered I haven't even opened the box with the jig yet. I do feel badly as there are others who could use this. Things seem to be calming down with the elderly in-laws and their health issues so hopefully in the next few weeks. It really shouldn't take long to center and powergrab (or is Epoxy now the standard?) 4 or 5 drivers.

pitdogg2

Slacker!

xschop

That's slacktastic.

Kryten

Yes, Thank you both so very much. I deserve the accolades (and epitaphs).

MrGeology

Thanks for the tip on my other thread @xschop .

Please put me on the list for the centering jig.

plastic_avatar

Alrighty.

Hey @Kryten! You done with the deed?

@MrGeology and I have needs!

[unintentional rhyme]

I can't see a the name Kryten, or Crichton, or variation thereof, without hearing D'Argo screaming 'CRICHTON!!!' on Farscape... in my head, of course.

xschop

MW-6509 factory base plate ID is 1.140"
(Large VC gap compared to all others)
DCR is 8.5 ohm. All other pole-piece and magnet dimensions same as other MWs.

It has the same thin-weave spider as a 6510 or 6511 and same suspension give as well using alloy spud weight as reference.

xschop

Thanks to Lawdogg's donation, I got this experiment done over the break and had some warm weather to do it... (and rescued a 6509 to boot)...

I took a baseline weight of a 3.25 gallons of water (used a gallon measurement container)and a Home Depot bucket to break the factory magnet and pole-piece away from the baseplate at dead-center pull.

I took three subsequent measurements of breakaway points by using a graduated cylinder to get three accurate volumes of 3gal-5oz, 3 gal-6oz, and 3gal-6 oz again.

Weighed bucket and water and got 27.4 lBs
3 times....



Placed a blanket under bucket for a soft landing each time so not to loose any water....

















When I can get ahold of this size ferrite ring magnet, I will also break-point measure it accordingly, as this size matches all the factory ones I've measured dimensionally...

https://www.guysmagnets.com/ferrite-magnets-c13/guys-magnets-86-mm-x-32-mm-x-14-mm-c5-ferrite-ring

Gardenstater

Very cool, you did it! And no ferrites were harmed in the making of this film?

xschop

I can't edit anymore, but 3rd pic was initial test to get gallon baseline and magnet splashed water out of bucket when no blanket was placed...

By the way, the factory Polk internal wiring is pretty strong lol, never snapped.

Zero magnet fatalities with this method I am happy to report.🙂

Gardenstater

I can visibly see how much more gap there is between the VC O.D. and the framepiece I.D. than my old 6500s. It would be interesting to see what the breakaway pull strength is of the old 6500 magnets, by comparison. They may have gone to edge wound voice coils (greater Bl) at some point after the 6500s, to try to compensate for the increased gap. Hard to measure mine with magnetic stainless steel calipers. I wish I had my non-magnetic ones I had at an old place of employment. This is what mine measure approx.:

O.D. = 3.320" (84.3mm)
I.D. = 1.272" (32.3mm)
Ht. = 0.543" (13.8mm)

Gardenstater

This one is about 1/8" too thin and only 7lb pull vs the 27lb you measured (what up wid dat?). Grade C5.

https://www.magnetshop.com/ceramic-ferrite-ring-magnets-p-104.html

Grades of Ceramic Magnets. Y30 most popular grade (apparently C5 on the old nomenclature of C1 - C8)

https://www.first4magnets.com/us/tech-centre-i1093/information-articles-i1401/ceramic-magnet-information-i1422/grades-of-ceramic-magnets-i1433

xschop

How do they arrive at their pull force? Axially/radially?

Gardenstater

xschop wrote: »

How do they arrive at their pull force? Axially/radially?

In the direction that it is magnetized.

Lots of info. here. They measure at various air gaps and then try to extrapolate to zero gap, but they also measure at zero gap I think.

https://www.magnetshop.com/magnet-design-guide

https://www.magnetshop.com/resources/magnet-testing.html

xschop

This one is stateside and would be the correct thickness and same overall volume/size...

https://appliedmagnets.com/ceramic-c8-magnets-90mm-od-x-36-mm-id-x-15-mm/

Gardenstater

xschop wrote: »

This one is stateside and would be the correct thickness and same overall volume/size...

https://appliedmagnets.com/ceramic-c8-magnets-90mm-od-x-36-mm-id-x-15-mm/

I like that it is C8 grade which should (?) be a higher flux strength. I wouldn't be surprised if that is the grade they used. Those are quite a bit bigger than my magnets but yours are larger than mine?

xschop

This one is
3.344 OD
1.282 ID
.555 thick

In my search, I've found other suppliers saying the pull is determined from a perpendicular position to a clean flat steel piece.

Gardenstater

xschop wrote: »

This one is
3.344 OD
1.282 ID
.555 thick

In my search, I've found other suppliers saying the pull is determined from a perpendicular position to a clean flat steel piece.

There was somewhere I'm pretty sure I remember reading 1/2" thick plate. This is more vague about it:

"5.1 A test plate made of 1018 cold rolled steel, ASTM A794 (current edition), with a surface area large enough for the magnet-working surface to make 100% contact. A surface roughness of 63 micro inches, and a flatness or 0.001 " over the contact surface is required. Plate thickness must be such as to absorb all lines of magnetic flux emanating from the magnet, i.e., remains unsaturated."

^From the link I posted previously which has the nitty gritty of testing in it:

https://www.magnetshop.com/resources/magnet-testing.html

PS: I wonder if the breakaway force would be greater in a plate that isn't thick enough, due to the magnetic flux being saturated. Not sure. If so that could explain your high reading.

xschop

I suspect that once a ceramic/ferrite magnet with these vintage Polk driver dimensions are found, then only can we confirm by replicating my simple experiment due to the particular constants. Basically glue the magnet to pole-piece and I drilled 1/8" hole thru center with a locknut and washer holding insulated wire....

So maybe get a C5 and C8 to test and compare?

xschop

Alright, I spun another one of these off in the lathe and tapped.

2 New rules...1) If you need to borrow the jig and dowel, send $60 deposit, Ill ship to you and when you are done, you get deposit from next Polkie.

2) 50 posts required

Got 8 new non-mag stainless setscrews that will go with it too....

Gardenstater

If any forum members live near:

Manassas, VA 20112

Maybe a polite visit could recover the MIA jig including PVC insert?

xschop

Bump for @MrGeology

Tony M

Did that last jig go missing from that last user?

xschop

It grew legs, as they say.

bcwsrt

Anyone try an @Kryten yet?

He might get an email notification that way.

That is the last person to have it, right?

If not, I apologize.

xschop

Would be ideal to have 2 of the kits floating around here.

Gardenstater

Back in April March he said he had some problems and was sorry and would be sending it on in a week or two. Since then silence.