Applying the Tung Oil Finish

Hands up all those who thought this blog had been left for dead! (Yep. Me, too.)

To pick up the story where we left off, the moment of truth has arrived and the first coat of tung oil is ready to go on. Thinking through the process, though, what do I do with a coated-all-over guitar body? I can't lay it down on anything without the marking the surface at the points of contact. The solution was to suspend the body above the work bench from a short, fat "neck". Any hoarder's shed will have all the bits and pieces necessary:

• 1 short length of framing pine (firewood pile) made to a big clearance fit in the neck pocket of the bass
• 1 length of angle iron (old bed frame)
• 1 eye bolt
• 1 threaded hook, washers and plastic-insert nut
• trestle stands

The application of the oil is very straightforward, which was one of its selling points. I used a clean strip of an old tee-shirt. Just pour a small amount onto the folded up cloth and then wipe onto the wood. The timber soaked up most of the oil that was applied. The colour change on the Bubinga was significant - to a much deeper red, and highlighted the change in grain direction. The result looked a lot like tiger stripes. Leaving the result to dry off, usually over night, it was rubbed back with a second cloth to remove any excess.

 From the photo above there a a couple of points to make comment on.

The first point is that tung oil rags should always be hung out to dry when application has finished. Rags have been know to self-combust when left scrunched up or in a damp pile. Prior to disposal, they are supposed to be washed first.

 The second point is, keep the tung oil can threads clean! The reason there is a juice bottle labelled "tung oil" and a tung oil can with piercings in the lid is because the can lid seized on with the remnant from pouring onto the rag.

The application process was repeated a total of fourteen times to get to the finished result. Both the Bubinga and the Swamp Ash behaved differently to the veneer samples in that no stray fibres in the surface lifted through the absorption of the oil, and so no sanding between coats was needed.

The neck received the same treatment, getting a similar number of coats of tung oil. The Wenge turning a beautiful chocolate brown. The hardest part of the whole exercise was waiting between coats to get the oil properly dry. Depending on the weather, which was tending to be come cold and damp, sometimes I left several days before rubbing back with the second cloth before applying the next coat.

The finished body is shown below. Pretty happy with how it turned out.

Sanding For The Best Result

Well, I've got a bit of catching up to do. It's been a while since the last post, but that's because I've been focused on getting the job done.

As discussed last time, the plan was a multi-stage sanding program, starting with 400-grit, and finishing with 2000.

Before starting, the work bench was cleared of anything that might scratch the wood inadvertently and a soft blanket laid on top.

Starting with the body, the sand paper was wrapped around a standard cork block when rubbing the flat surfaces on the front and back, and just paper in hand for all the curvy bits. The amount of dust generated at the beginning was a bit startling, but quickly became quite minimal as the grades increased, at the same time being very careful not to spend too long in one spot, creating an uneven surface.

The finer the grade of paper became, the direction of the rubbing became much less important, as there were no obvious score marks being created. Thankfully, the progress seemed to replicate the experience on the test panels. The surface became smoother and shinier, developing an almost polished appearance as the paper grade increased.

By the finish, at 2000-grit, a very satisfactory result had been achieved. The figure in the Bubinga laminate had started to "pop" and the chatoyance effect was obvious when changing the viewing angle. I did my best to make a video to show you, but it was way better in person than on screen. The best way to view the effect is to focus on one spot on the surface as the angle changes.

I had read somewhere that it is possible to really speed up the action of a neck by making the surface as smooth as possible. At my level of playing, there is absolutely no need for a super-fast neck, but I finished it to the same level as the body anyway. As a precaution, the fingerboard was masked with tape first, mainly to protect the ends of the frets from scoring from the coarser grades of paper.

With the sanding finished, it was time to embark on the most visually important, and time consuming, part of the build.

Deciding On The Finish

One of the reasons it took so long to decide what I was going to order, and how much the final project was going to cost, was in the finish of the body. For me, the project was as much focused on the wood used in construction and showing it off to best advantage, as it was about the sound of the instrument. The aim was a fabulous sounding, as well as fabulous looking bass guitar.

It would have been great to have the body finished in a urethane gloss that leaves the wood looking like it has been dipped in molten glass, but for Warmoth to do it would have added hundreds of dollars. For me to try it was asking for trouble. Also, I learned that the traditional guitar finishes of cellulose and urethane can be quite difficult to repair if (when) they get damaged. The research for the alternatives in high grade wood finishes then got underway

Almost immediately the subject of natural oils, such as tung oil and Danish oil, came up. The more information I uncovered, the more clear it became that tung oil was a very forgiving product to work with. That is, you are unlikely to make a total hash of the work piece with tung oil. That sounded like it was made for me. The other attraction is that tung oil is completely natural and non-toxic, as is it's solvent, terpene. In fact, the literature says that it is often used on products that come into contact with food, such as a fruit bowl, or kitchen bench tops.

The finish of tung oil is a natural satin. It is easily repaired, and blends well with the original application. A low sheen surface can be created using a finishing, or rubbing, oil over the top of the tung oil. Similarly, there is nothing to prevent using beeswax and buffing that up to a nice shine if that's the result you're looking for.

As in many projects, the end result is dependent on the preparation done before hand. In the case of a fine wood finish, the better the starting surface, the better the result at the end.

I selected for the body, a particular piece of Bubinga laminate for its beautiful, symmetrical figure and had every intention of making it the centre of attention. While I waited for the kit to be manufactured and shipped over to Australia from the U.S., I started practising on a piece of what I think is walnut veneer from an old bedhead. The existing stain and varnish finish was stripped off using a very coarse grit on a power sander. I then cut the piece into four sections so that I could compare results of different approaches to finishing. The power sander was put away and all the test panels were finished by hand.

400-Grit Sanded Finish

The first panel was worked up, grade by grade, to a 400-grit finish. The result was quite good, considering the state of the veneer before I started. The surface was smooth and the figure was starting to emerge very nicely. This was my baseline sample.

On the second sample, the sanding finished at 1200-grit paper. This was where it became clear how important a fine finish can be to the end result. Once you get up to about 800-grit, the figure in the wood really starts to pop out. By the time I finished the sample at 1200, the surface started to develop a polished sheen and the visual depth so desired in figured timber.

1200-Grit Sanded Finish

And this is when I learnt a new word - chatoyance. Chatoyancy in wood is the property whereby the finished surface reflects light differently depending on the angle from which it is viewed. This is a result of the wood fibres laying at different angles. Some will be parallel to the surface, while others will intersect the surface. Unfortunately, the photo can't really do justice to the appearance of the result. I was very happy with it.

At the time I was working on the panels I didn't have any 2000-grit paper, but that was the plan for the bass. With this kind of result for 1200-grit, it can only get better still working up to 2000, and with the application of the oils.


Tung Oil Over Sanding Sealer

An option I tested was tung oil over sanding sealer. This was to see if the sealer filled the pores and grain hollows to give a perfectly smooth finish.
The result of two coats of sealer before applying tung oil produced an OK finish in that it developed a shine fairly easily but it lost the touch of natural wood. It would have taken quite a few more coats to completely fill the grain, as well.

The key learning was by accident, literally. With the panel knocking around my work bench, before I tidied up properly, it acquired a couple of scratches and marks. These marks had chipped off the hard sealer, revealing the bare wood underneath. The damage would require sanding back the affected area, before re-sealing, sanding and re-finishing. I didn't try a repair as the experience confirmed that this was not going to be the best method for me.

        Tung Oil x 10               Finishing Oil Over Tung Oil

With the last panel, I started the multiple coats of tung oil. In the end there were ten coats of oil, with a light sand after a drying time.

With this particular veneer, after each coat, the surface fibres soaked up the oil and stood up, giving a stubbly feel. The sanding was at 1200 to knock the stubble off. By the last coat, a lovely golden glow had developed in the veneer, which is largely missing in the photo, unfortunately

Finally, I divided the panel with masking tape and rubbed in the finishing oil to one side only, to give a side-by-side comparison. The photo doesn't really highlight the difference adequately, but a shine and depth to the finish started to build after a only a couple of coats. The decision was made to go with a finishing oil over a solid tung oil base.

Testing the proposed finishing method certainly inspired confidence that I would be able to do the job successfully myself. It also confirmed that this method would produce a lovely, natural result that highlighted the beauty of the wood.

Satisfied, I waited for my delivery from Warmoth.

Preparing for Minimum Noise (1) - Sealing the Cavities

One of the discussion points I came across was regarding proper earthing and eliminating sources of electrical noise. The prevailing opinion was that there is merit in electrically shielding the electronics from any sources of spurious noise. The two main options to achieve this are to finish the main control cavity with either copper impregnated paint or copper foil tape. To be really thorough, you can do the same for the pickup cavities. The paint may be effective, but again, the opinions I came across thought the paint to be somewhat unreliable. I have chosen to apply copper foil tape. If I have enough left over, then I will also attempt to line the pickup cavities.

The first step in the copper application process is to prepare the cavity for the best adhesion of the tape by sanding away the obvious lumps, bumps and machining marks. So this I did, using 400-grit sandpaper. I used this reasonably fine grade paper so I did not to remove too much material too quickly.

Sanding sealer came next because I thought it might be worthwhile. Sanding sealer prepares the raw timber for other clear liquid finishes, such as stains or varnishes. It is supposed to fill the wood grain to produce a smooth, even surface. The rationale was, that by filling the wood grain, it would provide the maximum possible surface area for the foil tape to stick to. I didn't want the sealer to influence the proposed tung oil finish for the rest of the wood, so I masked around all of the cavities before painting on the sealer.


The pictures show the cavities after I had painted on the sealer. There are a couple of points to note here, that may be of interest. The first being the colour change in the wood. Compare the cavities to the neck pocket or the main body, which weren't painted. This may be relevant if you are thinking of using a clear finish over sealer for your own project, but more discussion on this in a later post.

Also, from the lower photo, the relationship of the control holes to the cavity is clear. You can see how much space has been allowed for the body of the controls, as well as the small countersink next the hole for the orientation tab on the controls.

 Another modification I haven't mentioned before is the tiny bit of extra routing made for the switch. This allows the switch to be placed where I wanted it, but also for either a back-forward or up-down action. I'll make that decision after the wiring is finished, much later.

Repairing

Acknowledging that Warmoth can't cater to every minor variation in matching their products to others, I think in the instance of the bridge mounting holes they have made a mistake.

The Hipshot bridge I selected was on the list of standard patterns for which Warmoth will prepare the mounting, but when I did a trial fitting I found that the middle mounting screw hole was too large, the same size as the string holes.

There were a couple of different paths to a solution to this problem. The most obvious would be to just use a larger screw. That was too easy, and there was a risk of not matching the screw heads in design, size and colour to the bridge.


The most satisfactory fix, in my mind, was to install a wooden sleeve that would restore the hole to the correct size. The required sleeve measured 4.5 x 3 x 16mm. That is a wall thickness of 0.75mm! In wood! Not something that is readily available at the local hardware store or wood merchant.  I certainly don't have the equipment, or skill required to create something like this. Fortunately, my cousin Eric does! When I put my problem to him, he took up the challenge. Using a 25 mm round section I provided, he drilled the hole and turned it down to a fraction larger than the hole in the body. This provided a lovely snug fit.

 This is the result, glued in place and dressed back to the body surface. The hole is not perfectly centred, due to the difficulty of getting a small diameter twist drill to start truly into the end-grain, but the screw will definitely be able to get a bite into the wood all the way down the hole, not just at the very bottom, as before.

Fettling

Warmoth's business is making guitar and bass kits, virtually any way you can imagine them. Having said that, it must be still necessary to impose limitations based around industry, or generally understood standards. And this is where I faced my first, unexpected hurdle.

The pickup routing option was selected from the list of standard offerings, being a Jazz style for the neck and a Musicman lugless for the bridge, in the "sweet spot" position. It turns out that either the Delano Musicman case has a slightly smaller than standard corner radius, or the corner radius in the routing is oversize. The result being that although the pocket is OK for width and height, the bridge pickup wouldn't drop into the routing. A fitting job was about to begin.

 I didn't get out the router, or even the 80-grit sandpaper. Following the established methodology for the project thus far, excruciatingly slow but steady was the way forward. I found a plastic ball point pen with a close-enough radius, and wrapped it in 400-grit wet & dry sandpaper. The next hour or so was spent wearing away the corners until the pickup fitted the pocket. In the back of my mind is the plan to line the pickup cavities with copper tape, so there needs to be at least a tiny bit of clearance to allow for the foil.


Another job done. It wasn't in the plan but I feel that progress has been made.

Finally, The Holes Are Drilled!

I'm guessing I've broken the first rule of blogging by failing to post regularly. I got off to a flying start with a bit of preparation in the bank, but I knew from the start that there would be interruptions, delays and sometimes limited opportunities for consistent updating. After all, should I be spending my spare time working on the bass, or just writing about it? Nevertheless, just because there hasn't been a post recently, it doesn't have to follow that no progress has been made.

So where we left off was working out how to mark the positions for preamp control holes. There were a few false starts, but they all contributed to the result at the end. The aim was to align the controls in an arc that matched the curve of the lower bout. The first attempt of copying the arc was to trace out the profile onto plywood and then cut out this shape. The difficulty here was to get that profile translated correctly onto the internal cavity template so that it was parallel to the body outline. By marking the cavity width on the plywood I could position reasonably accurately and mark the curve on the template. The control knobs were put in place on the arc line and positioned to be equal distance apart. The result didn't look too bad, but when I checked by measuring the distance from the edge to the centre of the knobs, as in the picture, there was quite a variation from one to the other. Therefore, the arc could not be parallel with the body. And once I thought about it, that had to be right. If you think of concentric circles, the inner circle has to have a smaller radius. By copying the body arc, I did not get a smaller radius. I'm glad I measured twice!

In the end I used the arc as a guide and then measured with the small square and ruler the perpendicular distance from the outer profile to the centre of the knob. I marked a circle around the knobs and then marked the centre of the circle for the pilot hole.

Having the centre holes now marked on the template, and the template captive in the cavity, I drilled pilot holes of 1/16" diameter. Finally, I was committed, with no turning back. The 7 mm holes were next.

Another aspect of my paranoia regarding the holes was achieving a clean cut at the knob surface. I learned from my research that the Forstner bit is recommended to give a nice, clean cut. You can see from my test on a veneered panel the difference between the brand new Forstner bit and a not so new regular twist bit. To be honest, I expected more tearing on breakout of the twist drill. From this result, the surface would clean up OK with a light sanding. I think the key here is to have the workpiece very securely clamped over a sacrificial piece of wood, so that you do not drill out into fresh air. 

Finally, four holes drilled. Just one more, for the switch, to go.

Working out the best place for the switch was the next issue. In the end I decided to position it in line with the rear-most knob, mainly so that it didn't get in the way. In theory, it should lie midway between the knob and the bridge. The final result is shown below.

 

 Now the hard part is over. Getting to this point took, literally, weeks of agonising, measuring, checking and procrastinating. The holes are where they are. They can't be moved or corrected in any way, but to my eye, they look acceptable, and close to what I had in mind.

From here it should be full steam ahead!