Level Sanding and Buffing

I'm still chasing rogue sanding scratches and polish residue on this Claro Walnut/Port Orford OM body, but I'm calling it "done" for the time being. I'll return to it shortly with fresh eyes and renewed enthusiasm.

It's been some time since I last level sanded and buffed a guitar, and I've been reminded once again that a thorough approach to sanding through a sequence of ever-finer sandpaper grits is crucial to attaining the scratch-free finish that I'm looking for. I began levelling the finish with P600 grit wet-or-dry sandpaper, proceeding through P800, P1000, P1500 and P2000 papers, using soapy water as a lubricant, before buffing with Menzerna polishing compound on a buffing wheel. Having done so, I'm close to achieving the desired outcome, but there's considerable work remaining before sanding scratches are reduced to what I consider an acceptable level.

This guitar body is the first of five that I'll be sanding and buffing, and I'm aware that if I'm disciplined enough and pay sufficient attention to detail, I can minimise the level of frustration that I always deal with throughout this time-consuming process.

Cheers, Pete

Positioning the Bridge

There are several handy gauges and gadgets available that help the guitar builder determine the position of the bridge, but the method I've adopted works well enough that I haven't felt the need to try them out. To give credit where it's due, I believe I first saw the method I'm about to describe on Matt Mustapick's now defunct and sorely missed workshop blog.

On this particular Port Orford Cedar soundboard, the grain is incredibly fine and the centre join is extremely difficult to detect. I've lightly pencilled a line along the join to highlight it, then taped a sheet of graph paper to the soundboard with the centre grid line aligned with the pencil line. With the neck securely attached, I measure from the nut end of the fret board and mark the notional scale length on the graph paper - it's the longer of the three marks in the picture below.

I make a second mark a little under four millimetres further along the centreline to allow adequately for compensation, acknowledging that with wider saddles gaining favour among many builders these days - myself included - there's plenty of scope for fine-tuning of intonation once the guitar is strung up.

I measure the distance from the centre of  the saddle slot to the front of the bridge at its mid-point, then measure back from the compensated mark on the paper towards the nut by the same distance, placing a third mark on the graph paper to represent the front edge of the bridge. I extend this mark outwards in either direction.

The underside of the bridge has been sanded to conform to the dome of the soundboard, initally using a domed platform to which I've stuck some 120-grit sandpaper, and then, by way of fine tuning, by taping some 240-grit sandpaper to the soundboard itself then moving the bridge to and fro across the sandpaper until the white pen marks I covered the bridge underside with have been removed.

I insert a clamp through the soundhole, positioning a piece of MDF that conforms to the bridge plate outline inside the body and over the bridge plate as I do so. With the bridge clamped lightly in place over the graph paper, I wriggle it into position, using my third mark to align the bridge's front edge at its mid-point, and the grid lines that run perpendicular to the soundboard centreline to align the bridge's front corners. The clamp is tightened, and I drill through the first and sixth bridge pin holes so that the bridge can be accurately pinned in position when the time comes to permanently attach it to the soundboard. The MDF inside the body prevents chipping when the point of the drill bit exits the bridge plate.

Removing the bridge, I replace the graph paper with a thin, low-tack adhesive film known as frisket film. I give the film a light scuff with fine sandpaper so it's easier to mark. I pin the bridge into position through the first and sixth bridge pin holes, and lightly mark the bridge outline onto the frisket. I remove the bridge and, using a craft knife, carefully cut through the frisket around 3/16" inboard of the pencil line, being careful not to cut into the top wood. I can then peel off the frisket that sits outside the scored line. I've found that by leaving a generous margin between the edge of the remaining film and the actual bridge outline, it's much easier to level-sand and buff the finish in the area of the bridge perimeter, bearing in mind that the frisket film is removed only when the finish has been buffed and I'm ready to remove the remainder of the finish within the bridge outline prior to permanently gluing the bridge.

In the interests of a neatness, I'll leave around 1/16" of finish inboard of the bridge outline, and rout a ledge fractionally over 1/16" wide around the underside of the bridge perimeter to a depth equivalent to the target finish thickness. To do so, I clamp my laminate trimmer to a MDF platform that's been domed to replicate the curvature of my soundboard. To prepare the MDF, I laminated two 3mm layers of MDF in my go-bar deck using a 25' radius dish as a base, then drilled a hole in the centre large enough to accept my chosen router bit. As previously described, the underside of the bridge has been sanded to conform to the dome of the soundboard before I rout the ledge.

As always, I'm open to suggestions and I welcome any comments.

Cheers
Pete

The Modified OM

With the messy job of constructing a new bending form and outside mold finally out of the way, I've been able to make some progress on this guitar over the past week.

The walnut sides bent willingly, as they always do, and I was pleased to see that they conformed closely to the new mold, with the exception of some minor spring-back on one of the lower bouts. The spring-back was a useful reminder that it's advisable to subject the sides of any wood species to a couple of heating and cooling cycles before removing them from the bending form. I have to try hard to resist my innate impatience, and on this occasion I was a little premature in taking the second side out of the side bender, hopeful that such a compliant wood wouldn't require a second cycle. A quick touch-up on the electric bending iron soon had the side sitting obediently in the mold.

With the head block, tail block and kerfed linings glued to the sides, I'm better able to assess the new body shape. Needless to say, I'm greatly relieved that it matches my expectations, and that the time-consuming and incredibly dusty task of making yet another bending form and outside mold has been averted.

Noting the recent emergence of guitars referred to as "modified dreadnoughts", and lacking a more imaginative idea, it seems reasonable to dub my new guitar model the "modified OM"! 

Cheers

Pete

Soundboard Braces

The soundboard braces have been shaped to a 25 foot radius and attached to the top, again using hot hide glue. I look forward now to profiling and carving them to their final dimensions, my goal being a light and lively soundboard. This is surely the most tactile and intuitive stage of the entire building process, when machinery and power tools lay temporarily silent, and finger planes, chisels and sandpaper take over.

A useful pointer to where I'm at on my quest to build a high quality instrument is that the soundboard bracing on each new guitar still seems to be lighter than that of the last. In many respects, I'm sure it's a good thing that my evolution as a guitar builder has been such a gradual process, with small incremental improvements marking what has been a long journey. Where soundboard bracing is concerned, I acknowledge that a bolder individual willing to take risks would equal my progress after far fewer guitars, but I'm happy nevertheless to plod along at my own cautious pace, learning as I go, improving my skills and gaining satisfaction from the improvements I see and hear after each guitar is completed.

With my weekends still dominated by household chores, my resolve to chip away at this guitar in spare moments through the week is certainly yielding results, as evidenced by my latest posts. Lurking in the background, however, is the need to construct bending forms and an outside mold to accommodate the modified body shape I've recently devised. Unfortunately, at some point soon, this necessity will act as a barrier to further progress and I'll be unable to avoid the task any longer! 

Cheers

Pete

A Guitar Back is Born.

A half hour here, an hour there, and before you know it, a guitar back has materialised. I've been making a concerted effort to make progress on this guitar after work throughout the week, when I would typically be less than productive where guitar building is concerned.

The back halves were joined with Titebond as usual, but I thought I'd attempt to use hot hide glue wherever else I can on this instrument. Apart from its great strength and resistance to creep, I enjoy the fact that it's so easy to clean up once the parts are joined and clamped. After allowing a short time for the squeeze-out to gel, most of it can be easily removed with a chisel-shaped scrap of spruce. A sponge dipped in the hot water from my glue pot, wrung almost dry, removes the remainder of the glue pretty effectively.

Attaching braces to the soundboard would seem to be a realistic goal for the week ahead. We'll see whether Murphy's Law allows me to achieve it!

Cheers

Pete

New Design, New Guitar

While the task of spraying my Walnut/Redwood OM remains on the "to do" list, I've managed to sneak in a little progress on a new guitar, this time combining a Port Orford Cedar soundboard with the sister set of Claro Walnut back and sides.

I fell in love with the venerable Martin OM when I first saw one many years ago, and as much as I still admire its timeless design and elegant curves, I feel ready to leave it behind me and develop a more contemporary body profile I can call my own.

I build guitars with the fingerstyle guitarist in mind and, taking note of player preferences commonly espoused by players in that style, I've nipped in the waist slightly, reduced the width of the upper bout and rounded the shoulders, the end result of which - I hope - is a comfortable and aesthetically pleasing body shape. The price I pay is the additional work involved in constructing molds and bending forms to accommodate this new design, so it's sobering to reflect on the fact that until the first body is assembled, I won't know for sure that the dimensions will appear balanced and attractive. Building molds isn't exactly my idea of fun, so I certainly hope I don't have to repeat the exercise! 

Cheers

Pete