Abrasive Personality, Pt. 2
A selection of sanding blocks used in the JET Guitars shop.
Plenty of sanding tasks in this business need
to be done by hand and making your own
specialized blocks can help. Most of the blocks
in the JET Guitars shop are made from scrap
korina or mahogany, both of which are easy to
shape on a 48” belt sander.
The photo shows some of the various sanding blocks used in our shop, starting with the
basic flat block (left). Moving to the right, the
radiused blocks are indispensable for neck and
fingerboard sanding. Most of these have fine
sandpaper glued onto them to help grip your
sanding sheet, although some use a leather
lining for fine sanding. A stick with a French
curve profile is useful for sanding chamfers.
A softer foam block for final scratch removal
tasks on fingerboards, rims or during clearcoat
rubout frequently comes in handy. Finally, the
Corian wedge (right) is used in corners during
rubout. Since this is a wet process, Corian is
better than wood because it won’t warp and
will retain a sharp edge.
In my shop, a lot of the sanding is done with
1/4” sheets and cut-up belts that have been
used on the machines. As far as brands go,
I have had good experiences with Canada’s
Carborundum brand and 3M. If you want a
really fast-cutting and long-lasting product, I
recommend 3M SandBlaster maroon 100 and
150 grit. When you get down to 220, using
aluminum oxide (AO) is perfectly acceptable,
although some prefer garnet for the final step.
That’s the overview for wood sanding. Wet
sanding of the final clearcoat prior to buffing –
rubout – is a completely different animal. A 5”
PSA air sander, running at around 50 psi, is my
tool of choice for larger surfaces. For smaller
surfaces like the headstock, I like to slow down
the sander. I get good results using Klingspor
silicon carbide discs (particularly PS11/12700T).
Plan on using one disc of each grit per guitar
and approximately three hours for this step.
Runs, edge build and drop fills should be leveled using a scraper or microscope slide before
you start sanding.
The basic technique is to soak the disc in
water, then sand at moderate speed. Start with
320 or 400 grit, and step through 600, 800,
and finally 1000. You will need to frequently
wipe off the residue and water, and inspect the
surface – look for pocks, scratches and swirls,
and go over them until they are gone. Being
thorough at this stage will pay off big because
flaws that are hard to see during rubout always
appear during buffing. In fact, I almost always
find some swirl or scratch during buffing that
needs a little more 1000 grit hand sanding.
A major risk during rubout is burning right
through to the wood, which will require you
to stop and repair the area. You may also see
lifting of the finish if water gets into the wood
near holes and cavities, although this may be
reversible if it’s not too severe. Learning how
to prepare and head off these problems is a
completely different process that begins even
before painting, and it is important to note
that nitrocellulose, urethane and polyester are
all chemically different coatings, each requiring
its own mindset and touch during rubout and
buffing. If you’re used to the heavy, hard, dry
character of polyester, you’ll need to lighten
up a lot and get used to more rolling and clogging of the abrasive disc as you switch to nitro,
Curved areas like the neck and rims need to be
rubbed out by hand – there is no way I would
trust a machine on them. You could use a soft
block, but I usually rely on my hands. In my
shop the used SC discs are recycled for fret
polishing or other metal work.
Jeffrey Earle T.
Jeffrey Earle T. handbuilds JET Guitars in North Carolina,