A Recone Guide

Very good write-up, with an incredible number of details covered.

I've run into a couple of snags over time, and I hope these comments help:

Step 2, Stripping.
I use a heat gun to soften up rubber based cements and then scrape while they are warm.  There's lots less solvents involved, so you retain more brain cells.  Also, the solvent/glue combo sometimes runs all over and makes your work look sloppy.  Also, I often use a rotary wire brush and/or rotary sanding disc for final cleanup of the spider and surround landing areas.

Step 4, Clean-out.
I put a shop vacuum hose on one side of the voice coil gap, and use compressed air to blow out the magnetic gap and magnet pot.  It works pretty well for getting fried varnish from the old voice coil out  Also, if there is rust in the interior of the magnet pot, chances of a successful recone are poor.  Rust may not be iron anymore, but it is still magnetic, and if/when it breaks loose, it will head straight for the gap.  When cleaning the gap with inside-out masking tape, if it comes out dirty, grab more tape and do it again.  Like he said, you get one chance to clean it out.

If the vent screen is old, a patch of polyester furnace filter material makes a nice replacement.  It's tough, and it breathes well.

Step 5, Dry Build.
Before I take the masking tape off of the voice coil gap, I put another layer of tape on top of the existing tape, and then take off both at once.  That way, any magnetic particles that were attracted and on top of the tape stay captive between the tapes.

Voice coil shims (this applies only to "loose parts" recone kits):
I make my own voice coil shims from machine shop type plastic shim stock.  In USA, "Artus" brand is popular and rather cheap.  I also make my voice coil shims "stepped".  The details in this example are specific for a JBL E140 with a WMA kit.  WMA kits (at least those I've bought) consist of all loose parts, except that the surround is glued to the cone.  With loose parts kits, you have to manually center/align the voice coil in all axes.  Magnetically centering the voice coil in the magnetic gap can be difficult.  To help,  I cut two pieces of Artus black (0.012") shim stock 155mm long, and about 40mm wide.  I cut two more strips 155mm long and exactly 16mm wide.  Again, this was for a JBL E140 with a WMA kit.  All dimensions, including shim stock thickness, vary with each speaker.  The math goes like this:  Take the distance from the top of the voice coil former to the midpoint of the voice coil windings.  The midpoint of the windings are the magnetic center of the voice coil.  Then take the thickness of the magnetic top plate and divide by two. This gives you the distance from the top of the plate to the magnetic center of the plate.  Subtracting half the thickness of the magnetic top plate from the voice coil former top-to-center length tells you how much voice coil former is exposed when the voice coil is magnetically centered in the gap.  I pre-curve a wide shim and a narrow shim, lay one on the other, line up two edges, and super-glue them together with the 16mm strip on the inside.  What you end up with is a pre-curved, "stepped" or "shouldered" shim.  When it (the set of two shims, actually) is installed, the 40mm section drops into the magnetic gap and radially centers the voice coil.  The 16mm wide section bottoms out on the inner magnetic top plate, and when the top of the voice coil former is flush with the top of the 16mm section that sticks up, the voice coil is magnetically centered.  It takes care of radial centering, axial centering, and makes it harder to accidentally cock (tilt) the voice coil during installation.  It also prevents you from losing shims into the magnet pot.  That's never happened to me...  Once the spider is glued to the voice coil, I usually remove the voice coil-spider assembly to put glue on the spider landing area, and reinstallation is easy because all you have to do is check that the top of the former is flush with the top of the shim set.  I also smear wax on the shim set so if any voice coil adhesive gets on the shims, they aren't stuck.  This type of shim is re-usable.  I put labels inside them to identify which ones they are.

Step 11, Electrical connections:
I have found the hard way that if your voice coil tinsel leads touch each other during assembly (like when they are glued in place, but not yet soldered to the terminals), when you move the cone, the voice coil will generate current which will try to circulate through the tinsel leads.  Since the tinsel leads are only in incidental contact, the intermittent current will make the speaker sound exactly like a voice coil rub, or as if you have foreign particles in the voice coil gap.  The first time this happens, you'll get this sick feeling as you move the cone and hear that sound.  Before you tear apart your new recone job, check to make sure the tinsel leads aren't touching.

Other:
It is difficult to remember that there is a magnet right there in the middle of the speaker, and one way to get educated is to place a screwdriver or some other tool nearby.  Also, when the job is done, consider buying a demagnetizer for your tools. 

For aesthetics, I cover the back of the magnet pot with several layers of masking tape.  This keeps debris out of the back of the magnet vent, and keeps the back of the magnet from getting scratched up while the driver sits face-up on the bench.  This can be a big issue if your customer is into appearances.  Putting a scrap of carpet on the bench helps, too.  Maybe this is just me, but it seems like when people don't know how to judge something on its technical merits, they tend to fall back on appearances, and then their perception is: poor appearance = bad recone.

I generally run finished drivers at Xmax somewhere near Fs for a while to see how well I performed.

Regards,
Rotorbar

Does anybody have recommendations for re-gluing a surround to the cone where the glue’s failed? I’d rather not have to pay for a recone, let alone ship a heavy ferrite driver somewhere to have it done for me if possible; plus it’s kind of a learning opportunity

toastyghost wrote: Does anybody have recommendations for re-gluing a surround to the cone where the glue’s failed? I’d rather not have to pay for a recone, let alone ship a heavy ferrite driver somewhere to have it done for me if possible; plus it’s kind of a learning opportunity

impact adhesive i reckon

toastyghost wrote: Thanks, any tips on application? Pallet knife perhaps?

a shim sized bit of card is easiest, to help you stop smearing glue everywhere you dont want it.

The nicest glue Ive used is the stuff JBL supply as an all-purpose speaker cement for both spider to basket, surround to basket and dustcap to cone. It is black, tacky but slippy, and flexible. It is also gap-filling (makes nice beads for the cap) and shiny if set in air.
It's made by the american company Moyen, part number RS3087.

Loctite in the UK make adhesives suitable for loudspeaker repair/manufacturer according to their web applications guide, however I'd love to know if they have a direct equivalent to the ubiquitous jbl stuff as its so nice to use.

I found this on you tube, it's a vid of "how to re-cone" from a U.S. company that makes kits. WELL worth the 10 mins to watch it.