Hearing Aid Buffing - Seam
In the last two issues we have talked about how to safely open a
hearing aid, and then how to close the hearing aid using UV adhesive.
After closing, you will typically notice that the seam where the shell and
faceplate meet is a little rough, especially if you needed to do some
patching in the seam. This is excess adhesive and/or patch material that
seeped out of the seam when the shell was squeezed together, and has now
cured. The way to smooth out this material is a process called buffing.
And even though this is a beginner’s guide to buffing, we have a nice
time saving trick for even the most experience buffer at the end of this
Now, there are many reasons for buffing a hearing aid, but for this
issue we are going to look at the buffing technique for smoothing out the
seam after a hearing aid has been closed. We will discuss other techniques
in future issues.
You will need a lathe for the buffing process, such as the
Redwing Model 26A. The 26A is a very
durable two speed, two spindle lathe and is very popular in the hearing
aid industry. You will also need buffing wheels commonly referred to as
buffs, preferably 30 ply and 15 ply, and buffing compound. The ply for a
buffing wheel refers to how many layers of cloth a buffing wheel has, so
the more ply the thicker the wheel. Now for ease of use, the lathe should
be equipped with at least one tapered spindle. A tapered spindle is a cone
shaped attachment for the lathe that is threaded, and allows you to
quickly and easily attach buffing wheels by screwing them onto the tip of
the spindle. Because the spindles are treaded, they are made for either
the left side, or right side of the lathe. You will know if you install
one on the wrong side because the buffing wheel will come off the spindle
when you try and use it.
Now we are ready to buff that seam.
This is actually a two step process – the first being the
removal/smoothing of excess material, and second is polishing to give the
hearing aid a nice shine. First, attach a 30-ply buff to the tapered
spindle. Then, choose the slowest RPM setting on the lathe and turn the
lathe ON. We are now going to dress the buffing wheel using the buffing
compound. This is necessary because it is the compound that makes the buff
slightly abrasive, and allows you to gently remove the excess material.
Hold the compound firmly in your hands, and press an edge of it into the
wheel. You want to make sure you get plenty of compound into the buff.
Protect the aid from damage
Now, this is important. You have probably noticed the buffing compound
is a material that could easily migrate into delicate parts of the hearing
aid, such as the microphone and receiver ports. To protect the hearing
aid, insert a small piece of foam into the receiver and mic ports to
prevent any material from getting inside these areas during the buffing
Also important – put a battery in the hearing aid and turn the hearing
aid ON. This is a protective measure against static electricity, which is
created during the buffing process that could potentially damage internal
hearing aid components. The volume control does not need to be turned up,
the circuit just needs to be energized.
Let the buffing begin
OK, so we have the lathe ON, the buff is dressed, and the hearing aid
ports are protected – lets begin. Holding the hearing aid with two hands,
gently press the seam of the hearing aid against the buffing wheel,
working your way around the seam. It is helpful to rotate the hearing aid
as you work your way around the seam. Keep in mind, the harder you press
the hearing aid against the buff, the more material will be removed, so be
careful not to over-buff as you don’t want to distort the shape of the
aid. Inspect your work often, remember you are trying to take off excess
material, and smooth the finish at the same time. As you buff the hearing
aid, the compound on the buff will get used up, so redress the buff
occasionally. Keep in mind, the more compound on the buff, the more
abrasive it becomes. Also important is the speed of the lathe. The faster
the speed the more aggressive the buff, so keep it on the slowest speed
How come my aid looks dull?
Now that you have successfully buffed the hearing aid and smoothed out
the seam you may have noticed the finish of the aid looks dull. This is
from the compound and buffed debris that is now on the aid. It is time to
polish the hearing aid and bring back that luster it had when it was new!
Turn the lathe off and remove the 30-ply buff from the tapered spindle.
Install a clean 15-ply buff and turn the lathe ON. Do not use any buffing
compound on this buff. Press the hearing aid against the clean buff,
working around the seam as well as the whole hearing aid. This will remove
the old buffing compound and debris. Buff until the hearing aid is nice
and shiny. After you get some experience and are comfortable with this
process, you can try polishing with the lathe on high speed for an even
Now, carefully remove the protective foam from the mic and receiver
ports. The hearing aid is now ready to test.
What about buffing laser shells?
The new laser shells are made of nylon and are a littler trickier to
buff. Nylon material can be removed much easier than acrylic, so when
buffing just use a small amount of compound, keep the lathe speed low, and
only exert a slight amount of pressure.
For the more advanced
OK, now for that advanced tip I was mentioning earlier. You want to
save yourself some time when buffing? Take your 30-ply buff and drill out
the center hole to ˝" using a hand drill. Now you can insert this buff all
the way onto to tapered spindle, insert the 15-ply buff in the end of the
spindle, and use them both simultaneously. Pretty slick.
The Model 26A is capable of many buffing, grinding and polishing
procedures, and we will discuss some of these in our next issue.
About the Author
Chris Perkins is the owner of Lightning Enterprises, and facilitates
the Lightning Enterprises newsletter. He has worked in the hearing aid
industry since 1991 in hearing aid manufacturing and product development,
as well as equipment and process consulting.
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