Forum member MW magnet repair tool set

Gardenstater

Kryten wrote: »

Hmm, as the plot thickens, novices are getting nervous............

I was nervous as all heck on the first one I separated. Less so on my 2nd. I wish I had a 3rd one that needed disassembly because I want to try the idea I had but didn't bother deploying; which is to insert two 3/8" dowels through the basket windows and use rubber bands to pull the cone and VC up so it is more out of harms way. I think that'll prevent (or greatly reduce) any possible damage during the smashing out of the pole piece process.

I will use this method during re-assembly for sure.

Kryten

One question I have is how to know if simply re-centering the magnet that shifted is enough when other issues may lurk which are discovered only by cutting the dust cap or disassembly. This thread has touched on the pole piece and the voice coil, and some Madonna looking phase plug

Gardenstater

I want to believe that my situation is extreme, where the voice coils are cocked and one of them is rubbing on the framepiece and the other one is almost rubbing or occasionally rubbing. The worse one (the first one I worked on), I was unable to center it perfectly so as not to get rubbing. I mean I *almost* had it but I knew something was wrong and the VC was out of round and/or was cocked and rubbing on the frame piece. I could center it on the pole piece visually and with shims and it *still* was rubbing.

I'm sure it can be done, but I wouldn't want to do the trial and error method of working blindly without removing the dust cap and I had made my mind up to do it that way, especially since I had also made up my mind to phase plug all my drivers, not because I have heard the results yet, but because I believe in the principal of it and most if not all high end drivers such as SEAS seem to use them and I trust Rob's ears.

I think in most cases if you can do the manual push test method without rubbing sound/feel AND you can play low frequency test tones at different Hz and volume without any problems you will be OK without disassembly of the driver and you can always do that at a later date if you are judicious with the adhesive and don't do something like a full circle fillet of JB-Weld. The Gorilla Max Strength Clear I used wasn't exactly a party to remove but it wasn't all that hard either.

xschop

That's extreme, from all the ones I've dismantled. None were that off axis or off-center.

xschop

xschop

The coil ohms out good, the coil edges are bent and can be straightened out. The hard part may be finding the correct compound to repair the 1" butyl tear in the surround, but you sleuths will have an answer.

The strangest thing about this driver is the 2-piece pole-piece. It's not loose in any way however.

xschop

These 6500s are indeed red-headed step childs of the classic MWs. These magnets match 6502 dimensions, so centering dowel works perfectly. The voice coil to base plate ID clearance is less than 6502s. This is probably reason why so many rub as the suspensions become worn and relax, there is very little error for that. That can be remedied even without having to remove a good voice coil. You'ld simply position coil all way forward of baseplate hole ID, carefully stuff a rag into frame to keep cone positioned that way, then use. A small 3 prong boring stone until you achieved @ .0.005" more VC clearance around perimeter.


My favorite tool to fix the jagged and out-of-round coil edges. This one was pretty bad, but it now clears baseplate ID on the stroke.



Since I found another issue with the spider either having set too long locked in forward position, or it's ANOTHER factory defect. I decided to practice rebuilding coil and take pics....

The Wuhan coils ohm out at 6.9-7.0 DCR
The ones I got are 32mm long and factory are 28mm long. No biggie as they both match where it matters at the coil winding length of 14mm....

xschop

Heres how you peel it out....
Cut through the factory slit with a sharp exacto knife. Then use a small set of needle nose pliers or diagonal cutters to scroll it out. It will break away from cone and spider glue area fairly easily.....

Gardenstater

My Silver Basket MW6500s are 7 mos. earlier production date than TonyM's and the centering dowel doesn't quite fit No biggie because I can always make one from a wood dowel or some PVC on my lathe.

Is the Wuhan coil made from a different awg of wire? Would be nice to get an Inductance comparison reading on the Wuhan vs Polk. Also, curious about I.D. and O.D. clearances.

Looking forward to the pictures. Do you have a picture of where the spider and the cone holes meet at the VC?

xschop

Base plate ID is 1.070".... That's the main problem with these MWs.




This is where you'd want to stuff the spider chamber/void because the basket frame thru hole is not much wider than the base plate hole...

xschop

Wuhan coil wire diameter matches factory diameter at 0.008"

xschop

I read here somewhere that the black bicycle tire repair adhesive works for fixing tears in the rubber surrounds. I had a a tube of butyl roof repair and tried it by lightly applying to inner curvature and outside surround. After overnight curing, it's bonded strong and supple...
I used the same paint that I used on cone area under dust cap for the old paper gasket that was peeling away. After drying, no more ugly paper peeling away...




Before I forget to post.....Also with dust cap removed, once base plate chucked-up on the lathe, I was able to get a 1\2" boring bar through the opening and fixed the factory defect. I opened the base plate ID up to what all other MWs I measured at....1.085 (+/- a thousandth)
This will prevent any future rubbing if the suspension gets more saggy....

xschop

If pole-pieces and baseplates came like this from factory, you could reset everything blind.... I just took off the stamped steel edge a couple thousandths.

Gardenstater

I appear to have found the perfect shim material for the 6500s. This is about 0.0065" thick and is from those plastic labels you get when you buy a plant. They go in firmly but they go in, if you round the ends first and the material has good flexibility. I had all different thicknesses and some stuff was a brittle plastic but this is soft. I knew I would find something in my own house if I kept looking I cut them to 3/4" width.

Gardenstater

I'm thinking that, if I phase plug these, all things considered, I will use a 1/2" long #8-32 threaded stud to secure them to the pole piece. Since I can probably chuck the pole piece up in my 4 jaw chuck on my Taig Micro Lathe it should be easy enough to bore and tap both pieces. That way if I ever have to disassemble this one again because the dreaded VC rubbing comes back because of the tight clearances and aging suspension, I will be able to remove the phase plugs by just unscrewing them.

xschop

Just clearance the base plate ID by .014" and be done. I bet they'll be sagging worse that George Soros' eye sockets after a few hours playback.

Gardenstater

*If* I can chuck the whole speaker in my Micro (lol) Lathe with the riser blocks, I *might* be able to bore out the hole in the base plate. I'll save that maneuver for when or if I need to, and at the same time as replacing the VC with a Wuhan one. I don't want to give up yet on resurrecting these and restoring them to the tolerances that they *should have* left the factory with. If I do have to do that, at least I'll be able to insert the acoustically absorbing foam washer a la Vandersteen patent.

xschop

Little insider knowledge.. On small bore IDs like these 1", you can use a Dremel drum sander with light pressure in circular motion to take out a few thosandths at a time. I did this to a steel pole piece tool a awhile back at the house. Was very accurate allowing friction drum and light pressure to control the cutting rate and accuracy.

xschop

If you can, take off another 0.050" from basket/frame interface for thicker Dyna mat clearance...

Gardenstater

I could chuck it and spin it, but I don't think I can face to 4.9" O.D., even with a left hand turning tool. I'll check it out.

xschop

I meant take 50 thou just off bottom.

I'm making the brass 6500 mag removal insert sleeves today...





I made mine 0.950" long since I took .050" off jig bottom. The one for the kit I left 1.150 for easy finger removal...

xschop

This is not completely necessary for resetting mag, but I made a 3/4" hardened stainless dowel punch for when I want to separate a non-shifted mag (but not concentric from factory)when phase plugging.
I machined a sharp divet to bite the softer pole piece to prevent it vectoring sideways and damaging voice coil ID...

Gardenstater

I like that idea. I was going to use a disc of double sided carpet tape between the oak dowel and the pole piece but I chickened out on that idea and just went with a piece of shelf liner from the $1 $1.25 Store.

Gardenstater

Another thing I almost did is I *almost* attached the oak dowel (shortened to a few inches to the end of my slide hammer (somehow) and I figured I could level the jig and plumb the slide hammer and tap it out that way. Chickened out on that one too.

Gardenstater

2 MW6500 Voice Coil Alignment Fixtures completed. Very tight clearances on these early drivers. This would've come in real handy way back when I had a cracked spider, in order to make sure everything was centered and perfectly perpendicular during the glue up process. But I didn't know then what I know now. Going to let both of these drivers sit on these fixtures for some weeks to see if they re-align over time. If that doesn't work will break the surround to basket bond and re-glue it while on the fixtures. One of these could be available as a loaner to members with 100 posts or more when I'm finished with it. Feel free to PM me.

Tony M

That looks like a well-designed Jig for its purpose.

I hope it works.

xschop

Sweet. Do you think you could heat the spider/cone/coil connection and let cool to speed process?

Gardenstater

xschop wrote: »

Sweet. Do you think you could heat the spider/cone/coil connection and let cool to speed process?

That's a darn good idea. As soon as I read it I moved them both and they are now sitting on the radiator cover for one of my radiators that gets pretty warm (steam). The hot and cold cycles should help here. A blow dryer on low might not be a bad idea though, also. I was thinking that, after the weeks long chiropractor session, maybe a thin bead of Aleenes at the joints in question might help to keep things where they are relocated to.

Gardenstater

Still cooking/aging but I removed the fixture from one and when I re-inserted.....carefully because only 0.001" clearance , the perpendicularity seemed perfect. True test will be to see if they stay both centered and perpendicular, when the shims are also removed.

Gardenstater

Well so far not successful. Removal of shims resulted in VC almost rubbing. Not sufficient to put back in service for sure. Looks like more drastic torquing of the VC will be necessary for these *braces* and heat cycling method to be successful.

I did some calcs. and measurements this morn. after coffee kicked in (of course) and it turns out that with the MW6500 you can have max. angle misalignment of 3.118 deg which would of course completely freeze up the VC but that is how much corrective *torquing* I can do with this fixture without removing the framepiece and with no VC shims. So that would mean 0.080" shims between 2 of the brass standoffs and the framepiece. I think that's what I will try next.