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Techbot
11-23-2009, 08:33 PM
Courtesy of saeman (http://audioheritage.org/vbulletin/member.php?u=1656) :

At the request of several forum members I'll start this thread to discuss the options I've tested to install grille cloth on the wood framework. Hopefully other members will chime in, not with their failures, but with additional techniques for success.

Since receiving my bundle of blue cloth from Zilch I have completed a pair of 4343 grilles and two complete sets of 4350 grilles. After the initial frustrations of trying to establish my process, I am now producing grilles that are EXACTLY as those done by JBL. My first grille took over an hour and required my wife's help. Knowing that JBL would not accept that kind of labor time I kept trying new ideas. My last grille took about 20 minutes to install the cloth, by myself. I'll consider that acceptable for now.

To get the most out of this thread I'll need to eventually include some pictures. When I do my next grille I'll get pics to show some of the details. For now babbling will have to do.

The first requirement is to choose the type of glue to use. First I tried hot melt glue. I bought a gun and enough glue sticks to do a bunch of grilles. What A Disaster - First problem is that it sets up way too fast. If you're trying to achieve a 1/2" to 3/4" glued border around the frame, there's no way to get an even coat of glue under the border cloth. Rolling the cloth down over the hot glue using a veneer roller was the only way to avoid lumps of glue under the cloth. In many places the glue bled thru the cloth and left an ugly appearance. I then tried wood glue, gorilla glue, construction adhesive and contact cement. Since I use wood glue for all of my veneer work I had high hopes. When veneering you let it dry and then reactivate it with heat. It requires that you coat both surfaces however and you cannot put a coat on the cloth, not knowing exactly where your glue line will be. Method failed !! Gorilla glue and construction adhesive dry too slow and nobody has enough hands to hold the cloth in place until it sets; so forget those options. Contact Cement turned out to be the choice.

With the frame face down I masked all around the frame leaving an exposed 3/4" border. Most original grilles appear to have a 1/2" border - your choice. After that I brush applied 2 coats of contact cement (not the cheap water based stuff, but the smelly kind that gives you a headache after a while). Let the glue fully dry to the touch. I had a few that sat for a whole day and had no problems. One coat will not be enough as there needs to be enough glue so that when heated, it penetrates into the cloth. 3 coats might be too much and it may bleed thru the cloth and foul your iron surface.

Until you get your technique down, cut the cloth with a full 2" border in excess of what you need to cover the frame. Lay the cloth down flat and center the grille frame on the cloth. Plug in your wife's clothes iron and get ready. Pick a corner, any corner, and pull the cloth up over the corner and over your glue border. Take the tip of the iron and press the cloth into the glue just 1" on either side of the exact corner. Go to the next closest corner and stretch the cloth laterally from your glued corner to your new corner (hope that makes sense). You need to get a feel of how much the cloth will stretch. Stretch it to 2/3 rds of it's limit and press the second corner into the glue the same as the first. Remember to keep the frame centered on the cloth while tacking down the 4 corners. Go to one of the farther corners and repeat the stretching and tacking process. Do the same for the 4th corner. If the frame is long, as my 4350's were, go to each side at the center and tack it down. Remember to stretch the cloth from the first side tack to the second before you do the second side tack.

This seems like a bunch of rambling but maybe with pics added later it will all make sense.

The goal is not to just cover the frame, but to achieve a perfect corner that is "wrapped" with no cuts or mitres. Properly stretching the cloth when tacking down the corners is the only way to ensure a good end result.

The frame is now sitting with the corners tacked down. Pick a corner and start an inch at a time, working away from the corner. Stretch the cloth over the glue and apply heat. Once you get 3-4 inches away from the corner in each direction, the job gets 10 times easier. If you stretch the cloth to it's limit it may put too much pressure on your glue and cause future problems. If you do not stretch enough the cloth will sag or blow in the breeze of a big woofer. For now I think stretching to 2/3 of it's limit is the way to go. If you don't take most of the stretch out at the corners you will have the cloth bunched up and have no place to get rid of it.

With the cloth tacked down around the entire perimeter, take a pair of scissors and trim off most of the excess. After that take a straight edge and utility knife and finish trim as "EVEN" as you can get with your 3/4" taped glue line. It's important to trim off all cloth that does not have glue under it. If you do not the exposed edge will fray and leave an untidy appearance. After the edge is finish trimmed take your iron and a veneer roller completely around the perimeter for a final set.

This procedure, if I haven't made it too complicated, has given me perfect results. I may edit this several times in case I have forgotten something or can make it easier to understand. Chime in with any questions.
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