Acoustic guitar – Finishing

The finishing stage is more about applying ‘finish’ (varnish or other) rather than completing the instrument, though of course with each stage we mover ever closer to completion. 

The first stage of finishing is to sand every surface smooth, while sanding you have to be on the look out for any small gaps that may need filling. The sanding can take a long, long time and if you are in the wrong kind of mood can seem very boring! I found that I had to stop immediately I got bored or I would make mistakes. 

Inside the guitar you can see a balloon which is holding a piece of cardboard tightly against the inside of the sound-hole. This stops dust from the sanding process getting into the body of the instrument. 

During the sanding the sides are scraped to make sure they are really flat. I went a little overboard in this area and ended up with sides that were too thin in certain areas. Not much I can do about it now apart from try never to drop it.

There are lots of different options to choose from when varnishing an instrument. I chose to use a product called Tru Oil because it is easy to apply (wiped on with a rag) and it is not full of evil chemicals like some of the products available. I had to find something which I could leave to dry in a ventilated room in the house which would not poison the housemates. Tru Oil is not a true varnish and does not give a super high gloss finish as you can see above it gives a nice sheen which really enhances the natural appearance of the wood.

Before the top can be oiled the parts where the bridge and neck will be glued on have to be carefully masked off because the glue will not stick properly to an oiled surface.

I lost count of the total number of coats but it was in the region of 30 very thin coats over about 2 weeks.

Less coats are applied to the top because too much finish would dampen it’s ability to vibrate. Here I have unmasked the bridge and you can see the difference in colour between the natural wood and the Tru Oiled wood.

Above you can see a solid block of Ebony, it’s big enough for 2 small bridges. Below the big block is the nice pyramid bridge that came with the kit, I would have used it but I realised that because I had decided to made the neck narrower that it was on the plans that would mean that the strings would be closer together at the bridge. The bridge from the kit had pre-drilled string holes so I’d have to make my own.

After a day’s carving the bridge is looking pretty good. I have just routed the slot for the bridge saddle which will be made from bone.

I did not photograph the process of gluing on the bridge or fitting the neck because I was so nervous about getting them right I need to concentrate 100% on the job in hand. It took a long time to get the neck fitted properly, I won’t describe it in detail here as it’s a complicated process involving aligning the neck on all 3 axes by shaving small amounts of wood from certain surfaces of the neck joint. After getting a properly aligned and tight fit  I moved onto completing the other small tasks like cutting and fitting the bone nut and saddle to hold the strings and fitting the tuners etc…

After quite a lot of fine tuning the instrument was READY! 

See the finished guitar!

3 Comments to Acoustic guitar – Finishing

July 30, 2009

Great job ! Thanks for the info and for the ideas, your guitar is really beautiful…

September 17, 2009

Thanks to your site, I have been building my own StewMac kit. Interesting that you masked off your fret board and bridge gluing areas before finishing. Did you encounter any problems while hand-rubbing and sanding the finish and bumping into the masking tape?

Leafcutter John
October 4, 2009

No it worked really well, you hardly need to sand the top between coats. I sued the method found here Obviously don’t try and glue anything to an oil based finish! Good luck. John.

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