Rubber Cement on
Winslow,
In this post you suggested applying rubber cement to the underside of the backing plate:
http://www.bluesharmonica.com/chromatic_air#comment-6295
"First is to get some rubber cement and use it to coat the underside of the backing plate - the side that goes against the body of the harmonica."
How do you apply the rubber cement? Use the brush and paint it onto the backing plate? I want to make sure not to have it leak onto the front side of the backing plate and gum things up.
I will rubber cementing the backing plate onto an acrylic comb I ordered from Chris Reynolds.
Thanks,
Steve
There are two kinds of slide cage leakage: slide clearance and edge seams.
The slide cage (backing plate + u-channel) has a clearance that has to be slightly larger than the thickness of the slide, plus additional tolerance for the gunk that builds up on the slide - the less tolerance, the more frequently you need to remove and clean the slide to prevent it from locking up (not good if it happens onstage, and I've known this to happen).
You can reduce clearance leakage two ways: Thicken the slide or thin the sides of the u-channel.
You can thicken the slide by applying adhesive tape to one side and then cutting out all the holes; this is known as taping the side. You can also paint hard acrylic on the slide (such as clear nail polish). Taping an cutting is a lot of work but it assures a fairly uniform surface. Painting is easier but can make for an uneven surface (maybe spraying it on would work better; I haven't tried either one).
Thinning the sides of the U-channel is complicated by the locking tabs that interrupt the edges of the part. These interlock with notches in the backing plate to assure good alignment of the two parts. So you have to thin the long middle part between the tabs, and then the lengths from that tabs to the ends of the u-channel. Getting them all the same is a but tricky. One way to accomplish this is to lay the slide in the channel and then lay a piece of feeler gauge of other thin metal on top of it so that the two players of slide + feeler are thinner than the total height of the sides of the channel. Then scrape the edges of the channel - both edges at once - with a straight edge, using even pressure, until it catches on the feeler. Repeat for the ends.
Reducing leakage between the edges of the backing plate and U-channel can be accomplished by using a lo-wattage soldering iron - with a brand new tip that has not touched potentially toxic solder or flux - and melting a bead of beeswax into the cracks along the mouthpiece when fully assembled.
You could lay the backing plate face down on a piece of paper and paint it on. let it dry a little, then peel it off the paper.
You could also just hold the plate in one hand while you apply the cement to the other.
One nice thing about rubber cement is that you can easily rub it off the places you don't want it. So if you get some on the front, first place the plate on the front of the harmonica (cement side down) and apply mild pressure to fix it in place. Then just use your fingertip to rub off any cement that might have gotten on the front of the plate.