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Flodstroem
03-27-2016, 01:17 PM
The back plate which holds the center pool piece in position is loose on one of my LE14H baskets. What to do for to get it back in original position again?
The clue here is to get the center pool piece back to exact position. The backplate has been out of position and I have tried to lift it of
I can manage that so its possible to get some shims in between the pool pieces for to get it centered in the top plate. Its a very strong magnet so
I had to be carefully and watch out because I dont want to put any fingers between the plate and magnet when trying to fit them together. :crying:

My question has anybody here done this before? Also what is the best type of glue for this type of job so the plate dont come loose again :blink:

Earl K
03-27-2016, 01:48 PM
For reference;

http://static.jbl.com/tl_files/themes/shop/skins/jblshop/02/stylesheet/series/about/m710066_JBL_TimeMachine__0019_1979_Large.jpg

PS; I don't know really the answer to your query / though you may need 2 different glues ( one > metal back-plate to ceramic magnet & then the second > metal to metal if the pole piece has also broken it's bonding to the back-plate ).

I do remember that RobH once fixed a broken 2435H ( quite a while back ) .



:)

Ah, here's Rob's 2435h repair thread called; How To Ruin Your Day (http://www.audioheritage.org/vbulletin/showthread.php?11490-How-to-ruin-your-day&highlight=) !

Flodstroem
03-28-2016, 06:17 AM
Thanks Earl K for your valuable answer and the links you posted here which I have read with great interest.
Im going to make a shim or a bushing for to have the two parts fit exactly in place when glued.
But first thing I have to do is to take them apart completely for cleaning and checking for other faults if any. The good thing
is that I dont think the center pole piece has come loos from the bottom plate only the bottom plate from the magnet.

I will post pictures later when the job is done, could be valuable to others that have to do a repair of this kind or for a consideration.........

Regarding your picture posted here and for your information I have painted it red where the pieces has come loos:

Earl K
03-29-2016, 03:07 PM
Hello again,

Here's another ( AudioKarma ) thread for you to read called Resetting a loose magnet (by RayW) . (http://www.audiokarma.org/forums/index.php?threads/resetting-a-loose-magnet-with-pictures.202963/)

It's worth the read !

:)

Flodstroem
03-29-2016, 04:40 PM
Thanks a lot again Earl K. Yea, it really was a good input regarding the issue and the pictures was worth more than thousand words :)

In my case there is a benefit though the speaker has no cone nor voice coil attached so my job will be a little bit easier I hope.
They also used the 30 min epoxy and that was good to get to know.
I have just ordered that 30 min epoxy. Im going to do the realigning and gluing of the magnet as soon as I receive it.

I dont know if I can find the PVC tube/pipe, it has to be approx 8-9" in diameter. I had to ask my local plumber................

Wagner
03-31-2016, 10:42 AM
Thanks a lot again Earl K. Yea, it really was a good input regarding the issue and the pictures was worth more than thousand words :)

In my case there is a benefit though the speaker has no cone nor voice coil attached so my job will be a little bit easier I hope.
They also used the 30 min epoxy and that was good to get to know.
I have just ordered that 30 min epoxy. Im going to do the realigning and gluing of the magnet as soon as I receive it.

I dont know if I can find the PVC tube/pipe, it has to be approx 8-9" in diameter. I had to ask my local plumber................
I used this in order to effect similar repairs on several Peerless drivers; Bob Smith also makes what is arguably the best over the counter 30 minute epoxy as well-I swear by his products. Any good hobby shop will carry both. I opted for the cyanoacrylate for better film thickness control:
http://ecx.images-amazon.com/images/I/41RUHJf9LML._SX342_.jpg

Wagner
03-31-2016, 10:52 AM
Thanks a lot again Earl K. Yea, it really was a good input regarding the issue and the pictures was worth more than thousand words :)

In my case there is a benefit though the speaker has no cone nor voice coil attached so my job will be a little bit easier I hope.
They also used the 30 min epoxy and that was good to get to know.
I have just ordered that 30 min epoxy. Im going to do the realigning and gluing of the magnet as soon as I receive it.

I dont know if I can find the PVC tube/pipe, it has to be approx 8-9" in diameter. I had to ask my local plumber................
Simply for future reference:
I used this in order to effect similar repairs on several Peerless drivers, all were successful and still in service 5+ years later; Bob Smith also makes what is arguably the best over the counter 30 minute epoxy as well. Any good hobby shop will carry both (Amazon as well, but I don't know how that works for Norway and you'd have/need to inquire as for product freshness doing the mail order thing with any cyanoacrylate based products). Of secondary concern for 2-part epoxies as the shelf life is indefinite if you have a microwave oven.
I opted for the cyanoacrylate over the epoxy for better film thickness control:
http://www.neptuneaquatics.com/sites/default/files/imagecache/product_full/product_supplies_images/bob-smith-industries-bsi-cyanoacrylate-ic-gel-aquarium-frag-glue-20-gram-1.jpg

Flodstroem
04-01-2016, 02:13 PM
Thanks Wagner for your further information on the subject. I made a decision between the two types of glue, 2 component epoxy or cyanoacrylate based glue and my decision got to epoxy doe to long experience with epoxy. If heat treated you will get a firm, super thin joint of epoxy. After all is there a magnetic strength equal to the specified value there is no problem using epoxy. Also, I guess I will need the 30 min period for to adjust the center pole piece before the glue hardens. :blink:

Wagner
04-01-2016, 02:32 PM
Thanks Wagner for your further information on the subject. I made a decision between the two types of glue, 2 component epoxy or cyanoacrylate based glue and my decision got to epoxy doe to long experience with epoxy. If heat treated you will get a firm, super thin joint of epoxy. After all is there a magnetic strength equal to the specified value there is no problem using epoxy. Also, I guess I will need the 30 min period for to adjust the center pole piece before the glue hardens. :blink:
The name is mis-leading, that gel cyanoacrylate isn't quite as "instant" as "super glue"! :)

But with my shim and holding "systems" in place it didn't matter anyway (I used a controlled approach, like a little space station docking maneuver sort of a thing)
I wanted as instant a bond as possible in order to prevent anything from shifting after the fact; magnets this strong will and can do some strange things

Flodstroem
04-01-2016, 03:07 PM
Now I have made the fixture as per info from Earl K for to hold the bottom plate firmly in place when gluing it to the magnet.
I made the fixture from a 7" PVC pipe that I found on the local recycling facility? It was a hell of a job to cut off the short piece I needed for the project.
But it was much easier to turn it in my lathe. Next thing to make was the clamp for to hold the PVC pipe firmly on the magnet. Luckily I had those parts at home.....
I had to drill 6 holes for the screws and that was done with a 5 mm drill bit. those holes was then threaded with a treading tool, to M6 threads

The first three pictures was taken of the LE14 basket including the PVC fixture in the making.
Next two pictures was taken of the finished fixture. I was then able to take out the 4 shims from the magnetic gap without having the pole pieces come together :)

As you can see there is adjusting screws six of for controlling and adjust the bottom plate. When heating the magnet to approx 50-60 C for the hardening of the epoxy Im also going to use shims when magnet are glued just as a guarantee so the bottom plate should not move.

Wagner
04-01-2016, 03:16 PM
Now I have made the fixture as per info from Earl K for to hold the bottom plate firmly in place when gluing it to the magnet.
I made the fixture from a 7" PVC pipe that I found on the local recycling facility? It was a hell of a job to cut off the short piece I needed for the project.
But it was much easier to turn it in my lathe. Next thing to make was the clamp for to hold the PVC pipe firmly on the magnet. Luckily I had those parts at home.....
I had to drill 6 holes for the screws and that was done with a 5 mm drill bit. those holes was then threaded with a treading tool, to M6 threads

The first three pictures was taken of the LE14 basket including the PVC fixture in the making.
Next two pictures was taken of the finished fixture. I was then able to take out the 4 shims from the magnetic gap without having the pole pieces come together :)

As you can see there is adjusting screws six of for controlling and adjust the bottom plate. When heating the magnet to approx 50-60 C for the hardening of the epoxy Im also going to use shims when magnet are glued just as a guarantee so the bottom plate should not move.
Beautiful work.

I am a believer in NOT doing anything to accelerate a two part's cure UNLESS the adhesive manufacturer tells me to

I believe that @ 71 degrees F or above, the greatest cured strength is achieved by simply allowing the catalyst to do it's job as designed

I also do not use accelerators with cyanoacrylates either

"Natural" cure is the best cure

I am just sharing my opinion and own personal practices here, I really don't care what you do or how you do it just as long as you get the results you are after and save your nice driver-that is all that matters

So, good luck with the repair! :yes:

Thomas

Flodstroem
04-01-2016, 04:52 PM
Beautiful work.

I am a believer in NOT doing anything to accelerate a two part's cure UNLESS the adhesive manufacturer tells me to

So, good luck with the repair! :yes:

Thomas

Thanks Thomas. Yes I know about that and I shall check what the manufacturer recommend for the epoxy ordered (havnt received it yet).
I nearly always use heat more or less when Im working with epoxy. I have used it for a long time by now, from gluing to casting with epoxy so Im used to it
Also, the higher temperature helps the glue/resin to float making the joint thinner and let the trapped air come out more easily. Thats my experience using epoxy glue so far.
Some information about applying heat to epoxy resin is to be found here:

Whilst some epoxy resin/ hardener combinations will cure at ambient temperature, many require heat, with temperatures up to 150 C being common, and up to 200 C for some specialist systems. Insufficient heat during cure will result in a network with incomplete polymerisation, and thus reduced mechanical, chemical and heat resistance. Cure temperature should typically attain the glass transition (https://en.wikipedia.org/wiki/Glass_transition) temperature (Tg) of the fully cured network in order to achieve maximum properties. Temperature is sometimes increased in a step-wise fashion to control the rate of curing and prevent excessive heat build-up from the exothermic reaction.
https://en.wikipedia.org/wiki/Epoxy

(https://en.wikipedia.org/wiki/Epoxy)

Wagner
04-01-2016, 05:25 PM
Thanks Thomas. Yes I know about that and I shall check what the manufacturer recommend for the epoxy ordered (havnt received it yet).
I nearly always use heat more or less when Im working with epoxy. I have used it for a long time by now, from gluing to casting with epoxy so Im used to it
Also, the higher temperature helps the glue/resin to float making the joint thinner and let the trapped air come out more easily. Thats my experience using epoxy glue so far.
Some information about applying heat to epoxy resin is to be found here:

https://en.wikipedia.org/wiki/Epoxy

(https://en.wikipedia.org/wiki/Epoxy)
As I "said":

I am a believer in NOT doing anything to accelerate a two part's cure UNLESS the adhesive manufacturer tells me to
As you are already well aware, there are MANY recipes for "epoxy", with as many differences in composition/ratios, not to mention efficacy and quality

And as I also mentioned, I use/treat both my resin and the hardener to a quick visit to the microwave no matter the brand/type/manufacturer; helps with the curing process, addresses/eliminates your viscosity concerns as well as "burns off" any H2O that may be present

I wasn't instructing you with any sort of "how to", only shared a brand/maker I know to be a good one

Thomas

mech986
04-02-2016, 03:32 AM
Would be great to also get Greg Timbers, Moro or Button to comment on the factory's or their design and engineering criteria for how the speaker parts are assembled. Of course, in their shop and factory, the magnets are not magnetized (or demagnetized) to facilitate ease of assembly, and the magnetized once everything is already glued/screwed into place. IIRC, GPA, and the late OCS could demag and remag, among others. That probably would make things a lot easier, but of course, requires two round trips. The RayW thread and what you've done here is the triumph of ingenious methods.

I would point out that using the metal strip shims may lead to a somewhat uneven gap which is inconsistent around the gap diameter. Obviously, if one had a cylindrical shim that was exactly the correct ID/OD, or a number of round pin like objects that were of the gap width, that would probably be more useful (blank drill bits, brass or piano wire rod or tubing??). OTOH, you work with what you have.

Earl K
04-02-2016, 06:48 AM
http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=70653&stc=1&d=1459548150

NICE ! :applaud:


http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=70651&stc=1&d=1459548071

I would like to add to the ( quite valid ) concerns ( over gap symmetry ) stated by mech986 .

Before you get to the gluing stage, I'd recommend spending some time creating/obtaining ( at least ) 8 aluminum shims of proper dimension to help you get ( & keep ) that voice-coil gap symmetrical during the glue-up stage of the back-plate .

So you know, the gap width of this woofer ( as well as many of the older/legacy woofers using 4" voice-coils ) is usually stated as .057" within literature meant for use by reconers. ( .057" is 1.45mm, after conversion )

Confusingly, the gap width was also stated as .053" ( for the le14h-1 ) in a couple of tech sheets ( ie; the 240Ti & 250Ti (http://manuals.harman.com/JBL/HOM/Technical%20Sheet/250Ti%20ts.pdf) ) and that doesn't agree with the earlier L220A tech sheet (http://manuals.harman.com/JBL/HOM/Technical%20Sheet/L220A%20ts.pdf).

Personally, I believe the .057" dimension to be correct ( but then I don't have a sample le14h-1 here to actually measure ).



:)

Wagner
04-02-2016, 11:01 AM
I have, over the years, collected quite the seemingly odd collection of hard plastic circles: old "new" plastic pill bottles of every size, the caps from large fluid containers (like laundry detergent/softeners etc) and anything else that might prove useful for restoring even, concentric gaps between two pieces of metal.

At times (they seldom work right off the shelf) with a little massaging, they have proven indispensable to making this sort of repair successful, especially with tweeters and smaller "mid" and "radio" speakers but have "saved the day" for larger transducers as well.

I have had good luck using hard plastic and nylon like materials due to the fact that they are perfectly round, non-magnetic and the fact that adhesives are reluctant to bond to them very well if at all (a bonus if any adhesive does somehow manage to creep too far) The height of this type of homemade solution helps too when the two pieces need to be brought togther in a controlled fashion (like the rectangular Peerless tweeters from long ago)

As a result, I have made and kept a number of these tools, almost to the point now of clutter. Problem is, with most of them, they are a one off, one time solution and most likely will never be used a second time, a mixed blessing of sorts.

Flodstroem
04-02-2016, 08:38 PM
Thanks guys for your inputs and concern about the magnet gap and the centering of the center pole

Im going to use som plastic tubes (from earlier JBL re-cone kits :D ) and brass shims for to center the pole piece exactly in the center of the top plate. But in the first step
the six screws will be used for to prevent the two poles to come together.
Also, I know that Alnico magnets eg a speaker magnet will be demagnetized if taken apart, but this is not the case with ferrite magnets.
I have the proper equipment (F.W.Bell) for to measure the magnetic field before and after doing the job. ;) So Im going to check this strictly.

I let you know when the job is done.........

Flodstroem
04-30-2016, 04:11 PM
Finally I received the epoxy. Yes, I used the epoxy only for the reason that it gave me the necessary time for adjusting the back plate for to have it exactly centered with shims before the glue was hardening.

I used raw force to get the two pieces to come loose. There was a lot of rust between the two pieces including som old glue. Locked like the "Elmers" glue or something like that. It was pretty easy to clean the magnet but fare from that concerning the back plate. luckily I have a lathe and that machine helped a lot. The lathes chuck couldnt grip around the back plate but I found a solution (see the pictures)
After cleaning (sanding) it become nearly as a new. I further cleaned it with compressed air etc...

Now the two parts was ready for gluing. After the glue had been applied I put the two pieces together. But before doing that I had made a tube of hard paper, only for to center the two pieces when they came together and that was the most scaring moment of all........ :eek:

After that and with no fingers in between......... :blink: I had to use the center screws mounted in the PVC-tube for to center the pole piece lifting out the paper tube and putting in hard (metal)shims for to lock the center piece exactly in place when the epoxy was hardening.

I used heat for the hardening period. One benefit among others for to use heat was to making the epoxy more liquid. When the heated epoxy became hot the excess epoxy came out doe to the force of the magnet.

I used my baking oven and I warmed it up to 70 Celsius /158 F. I left the basket w. the magnet in for approx an hour. After the "baking" it was finished and after some cooling period I then made som checking. I couldnt find any misalignment. If there was any maybe it was down to less than a thousand of an inch or so. I had the equipments for to check the magnetic force in the air gap and it proved to be in order and that also proved the benefit for the ceramic magnets robustness. I checked further with the old cone/voice coil assembly and it looked very good so far :)

In the pictures you could see what I had to struggle with.

Flodstroem
04-30-2016, 04:15 PM
More pictures

Earl K
04-30-2016, 04:29 PM
Lovely work there!

Congratulations !

:)

Flodstroem
04-30-2016, 04:53 PM
I dont know if I mention this earlier but I do have two LE14H-1 baskets. One with the magnet now fixed and the other that had a heavily rusty magnet.
How do you clean a rusty magnet? I had to think twice before I went on with this one. :blink:

I have had the other ones back plate in my lathe and that lead me to the decision for to choose the same procedure for the rusty magnet circuit.
It was a hell of a job but it went OK. When I was finished with the lathe I used an air gun for to get out most of the dust coming from the sanding.
Then there was a time boring job taking place: thoroughly cleaning of the air gap. If I may guess, I used approx 2-3 meter of that tape reel for to get all metal (iron) dust out from the air gap that the compressed air coldnt get out. I also used som solvents for to clean the air gap. Finally I made an inspection with a magnifier/loupe for to be 100% sure there was no iron particles left in the air gap. :)

The LE14H-1 baskets looked far from nice so I decided to sand them and then spray som mat black paint on the frames(outer rim). They became much nicer after painting them black. After that there was one job left that I had to do and that was the mounting of the cleaned magnet to the basket.
I used a glue that my brother had told me was very good for metal gluing, the name of it here in Norway is PL400 (by ilbruck)
The basket holds in place by 6 phillips? screws

And finally, now Im the owner of two excellent LE14H-1 baskets ready for new cone kits but I really had to look over my finances............... :crying:

boputnam
04-30-2016, 04:56 PM
Lovely work there!

Congratulations !

:)Yeah. This is a very impressive thread... :applaud: