May 12, 2008
Abrasive products and machines are essential to every facet of luthiery, from wood sanding to finish rubout. This two-part column will give you a rundown on the abrasives used in the JET Guitars shop, and valuable advice about using them. As you will see, all of the abrasive products are cycled through two or more “life stages” to get the most out of them before throwing them away. The basic tools used with them are a 48” x 6” belt sander, a 1/4 sheet electric random-orbit palm sander, a variety of sanding blocks and a 5” PSA air sander.
The belt sander is used for thickness sanding and rough shaping work. I use 60 and 100 grit aluminum oxide belts – I’m not too picky about the brand – with 150 and 180 grit for medium sanding. A Teflon platen is a good feature to reduce friction, and when it starts cupping, you can true it flat again or replace it. You might want to wrap the drums with friction tape – used on baseball bats – to eliminate the annoying drop-off from the platen. Another feature to look for is a quick-change lever. You will most likely need to adjust it so it works right, and maybe modify the arm to keep it out of the way. The most essential component of a machine like this is the quality of the bearings. Unfortunately it’s hard to know how good they are until years later when they start to squeal and wobble. Sanding belts can be recycled into metal work, or cut up for hand sanding after they start wearing out.
The electric palm sander, loaded with 180 and 220 grit AO, is for fine sanding of maple. I also use it to sand out the first stain wash on a figured top (for deep grain enhancement) and I work the tool pretty hard for that task. Using a lot of pressure goes against most recommendations for sanders like this, but hey, I’m a bad boy – and it works. You can deal with carved top re-curves by changing the stock pad with a thicker one that has rounder sides (see photo). Naturally, that is something you will never find for sale, so you will have to fabricate or modify one. Some luthiers like to use a disc sander on carved tops.
Selecting a random-orbit sander can be tricky, and you will go through more than one, but from my experience, here are the weak features to avoid when picking one out:
- Insufficient power
- Flimsy plastic internal support pylons that can break
- Wimpy paper fasteners that slip, break or are hard to use
- A sliding on/off switch, or one mounted on the sander’s handle
Always remember that the pad on this sander is not very firm. Fingerboards and headstock faces – especially with inlays – often require at least some precision hand sanding and a palm sander can distort their shape. Also, don’t use this tool on softer, plain-grained woods such as korina or alder as it leaves swirl marks that appear after staining. Instead, use a belt sander, and then hand sand with the grain using a block.
Used 180 and 220 grit quarter sheets get a second chance when it’s time to hand sand corners and roundover areas. Don’t throw them away yet! When they’re so beat up you think they can’t be good for anything else, keep a stack around for roughing clearcoats between spray coats.
In part two we’ll look at sanding blocks and air sanders.
Jeffrey Earle T.
Jeffrey Earle T. handbuilds JET Guitars in North Carolina, USA.