Loose back plate and pole piece

[Flodstroem]

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.

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

[Earl K]

For reference;



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 !

[Flodstroem]

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]

Hello again,

Here's another ( AudioKarma ) thread for you to read called Resetting a loose magnet (by RayW) .

It's worth the read !

[Flodstroem]

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]

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:

[Wagner]

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:

[Flodstroem]

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.

[Wagner]

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.

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]

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]

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!

Thomas

[Flodstroem]

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!

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 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

[Wagner]

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

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]

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]

NICE !




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 ) and that doesn't agree with the earlier L220A tech sheet.

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