Fixing plastic Polk Speaker grills

Treker-1701

Recently I picked up a pair of Polk M7's at a local thrift shop for a little less than $30, and one of the speaker grills was broken. I decided to go ahead and fix the grill because other than that the speakers were in really good shape. IMHO, the repair turned out pretty well so I thought I would share how I went about it.

The first two pictures are of the grill before the repair, from both the front and the back. As you can see, there is a section of plastic missing from the top of the grill that needed to be replaced.

Treker-1701

Here are the first two pictures of the broken grill before the repair.

Treker-1701

I guess I need to preface this repair a bit. My other hobby is building radio control airplanes, so I had most of the tools and other things like 30 minute epoxy laying around left over from other projects. My repair came out pretty cheap because I didn't have to buy much.

The first thing I did was scrounge through one of my junk drawers to see what I had that might be appropriate to replace the missing plastic piece. I found some black ABS plastic that looked about right (the kind used to fill in dash openings in car stereo installations) and cut a piece about the same width and length of the missing piece. Try and use a piece about the same thickness as the missing plastic if you have it. If you don't have any plastic the appropriate color and size, you could substitute basswood from a hobby shop. Basswood is harder and stiffer than balsa, but it is not hard like maple so it is still easy to work with most hand tools. Unfortunately, if you use wood, you will probably want to paint it black before the final installation.

Next, I stopped by the local hobby store and bought a piece of solid round carbon fiber rod to act as a "bridge" to hold the new filler piece. The piece I bought was about 1/8" diameter, but I'm sure other sizes will work. I just wanted it to be stout enough not to flex easily, but thin enough to still cut easily. Plus, you will need some 30 minute epoxy for this project. I already had some, but if you don't, pick some up while you're at the hobby store.

Cut the carbon fiber rod to the correct length to bridge the gap and support the filler piece. CF rod will split and fray if you just try to cut it with a hack saw or something like that. To make a clean cut, wrap the cf rod with masking tape where you need to make the cut and roll it on a hard surface under a sharp X-Acto #11 blade until it is cut almost all the way through. Then it is just a matter of working the cf rod back and forth until it breaks at the cut you just made. Hint: a piece of 2 X 4 or plywood works well as a cutting surface.

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I next sanded the ABS plastic filler piece to give the epoxy a little more bite, and also drilled a line of small holes in a line under where the carbon fiber rod will rest. I used a small drill bit (1/16" diameter will do, but I used a little smaller) in a swivel head pin vice to drill the holes. (A swivel head pin vice is like a hand held finger drill.) Do not drill all the way through. You are just trying the give the epoxy a little extra surface area to grip on to.

Next, epoxy the cf rod to the plastic filler piece. If you end up using basswood, I would epoxy the cf rod to the wood before you paint it. That way the pores of the wood are a little more open and the epoxy will grip better. Set aside and let dry throughly. Even though the parts will be safe to handle after 30 minutes, they will not really be completely cured until after they have set overnight. Paint the filler piece as needed after the epoxy has dried, but do not paint the cf rod.

After the filler piece has dried, sand the edge that will go on the outside of the grill next to the cloth to a rounded edge. Try and match the rounded edge on the outside edge of the grill frame. I didn't sand mine enough at this step, but mine still ended up looking okay.

Treker-1701

Next I prepped the speaker grills. I sanded the surfaces where the epoxy will go, and drilled another set of small holes with the pin vise. Again, do not drill all the way through. You are just trying to give the epoxy a little more surface to bite on.

While I was prepping the grill, I noticed a couple of small cracks that I needed to take care of as well. I spread the cracks apart a bit and worked some epoxy into the gaps with the end of a toothpick. I set the grills aside to let the epoxy dry before the next step.

The grill cloth was in pretty good shape, so I decided I would try and preserve it. Since I was using epoxy, and there is always a risk of drips, I had to protect the grill cloth somehow. I went up to the kitchen and "borrowed" some of my wife's wax paper, and cut some small pieces to fit between the grill frame and the grill cloth during the final gluing process to follow.

I also made a couple of clamps out of wooden cloths pins. You can make these by taking the spring out of a regular wooden cloths pin and reversing it so it now has a long jaw and a short handle instead of the other way around as they were originally designed. This is another r/c airplane building tool that I just had laying around, but they are easy to make. I also wrapped one side of the jaw on each modified cloths pin with a small strip of wax paper so that the epoxy would not stick to it either.

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The final step is to epoxy the new filler piece into the broken grill frame. I mixed some 30 minute epoxy (I use a small yogurt cup and a wooden coffee stir stick) and carefully placed it onto the broken plastic grill frame. I then placed the cf rod on one side of the filler piece into the epoxy, and clamped in place with the modified cloths pin. I then placed the other side and clamped it. I then adjusted until it looked about right and set it aside laying face down on a flat surface to dry for a few hours. The pictures below show the final results.

Unless you are looking right at the grill frame, and know exactly what you are looking for, you cannot see this fix. It also went pretty quick, as I only spent about an hour or so on the whole job, not including waiting for the epoxy to dry of course.

I hope this helps someone that has a similar broken grill to repair.

If you have any questions about how I went about this repair, please feel free to ask.

Later,

Jay B.

Marty913

A very, very nice job Treker-1701. Also well-described and documented.

engtaz

Nice job.

Congrats,
engtaz

shadowofnight

Nice work...saved em from the garbage.

schwarcw

Nice job! The Monitor 7's are worth the effort. For $30 you have a nice set of speakers.

Treker-1701

Thanks for the comments guys. I really appreciate it.

I really am enjoying this set of Monitor 7's too. And they are all the sweeter since I got such a good deal on them.

Later,

Treker

george daniel

Outstanding work

honda cber

hey thanks for that, treker. looks great.
a

Minnie

Where can I get speaker grills? I have the speakers.