This Week in Wood » Chisels

Purfling…what a funny word!

glennth — Fri, 14 Oct 2011 18:45:45 +0000

Purfling is a word that defines material between the binding and the top or back wood on a string instrument. Binding is a word that defines the outer most material surround the top and back wood on a string instrument. The purfling is decorative but the binding actually provides some function. First the binding provides protection for the end grain of the top and back woods and second (though I’ve not seem any testing that verifies this but it sounds right) the binding provides a hard border for the top wood (also called the sound board) for a string instrument which affects the tone waves.

On my 3rd guitar body (a full body, no cutaway), I decided to start with the purfling channel.

In a test board, I cut several channels adjusting the router bit’s depth of cut until the purfling was protruding just a smidge (and yes, it’s a technical term though I’ve also heard skosh). I then pick out a bearing which will provide the channel width to hold the purfling and the binding. In the picture above you can see that for the purfling, I have 3 layers (ebony, bloodwood, and a dark brown wood) The binding is a piece of maple bent to the shape of the guitar with a matching dark brown wood edge for the bottom of the binding. The purfling is so thin that it doesn’t need to be pre-bent.

I then use the tested set up to rout the purfling channel into the back and top of the guitar body. Remember in a previous post, I talked about the channel not being square (this is due to the router riding along the top and back and the top and back are arched ever so slightly). I use an adjustable square to test the squareness of the channel and a small chisel as a scraper to adjust the squareness of that channel.

After a lot of scraping, I finally get the fit to be perfect. After I finish both sides of this guitar body, I’ll work on the 4th guitar body (which is a cutaway model) then it will be time to repeat for the binding channel.

Post from: This Week in Wood (c)2009 Glenn Thompson. For Downloads, Pictures, and other great content go to This Week in Wood. See This Week in Wood Legal Information Page for specific usage rights.

Purfling…what a funny word!

Sharpening – Why oh why?

glennth — Sun, 09 Oct 2011 18:39:00 +0000

As I mentioned in my last post, I decided to refresh my blades throughout my shop. The hand plane blades took me 2 days and then sharpening the chisels took another day. All of that wasn’t really a problem. The real problem is why can’t I get into the rhythm of sharpening when I sense a blade needs sharpening. I even have a dedicated sharpening station.

I have been working on my guitar builds for the last 6-9 months and have often felt that I should be sharpening blades. Why didn’t I get the stones out and sharpening the micro bevel. Each blade might take 3 minutes if that to get a nice sharp edge. It’s not like I have to lap the back of the blades or the soles of the planes. They are flat and even mirror polished.

I think that this routine of sharpening frequently is the secret of keeping sharp blades in a shop.

I know I dread flattening the stones which I’ve always done at the end of a sharpening station but with a single blade, that probably wouldn’t be a problem. Maybe oil stones would be better for the frequent sharpener.

In any case, I will endeavor to get to my sharpening task more frequently.

Tongue and Groove for Doors

glennth — Wed, 21 Sep 2011 23:02:49 +0000

School is well under way for my 2 boys (Xander -12 and Mitchell -10). The beginning of the school year plays havoc with the entire families schedules and that of course means my shop time. I have gotten minutes in my shop since it began about 2 weeks ago. Today, I was able to resume a bit of work on the doors.

I’ve decided to go with a tongue and groove joint between the stiles and rails. You may have read a few posts ago when I was cutting the groove for the door panel and the tongues of the rails. In beginning this process I thought the most obvious tool would be my skewed rabbit plane and yes this is probably the main tool for the job but the thing that surprised me was that I would need a few others. I also used a rabbit block plane, a chisel and a side rabbit plane.

Working across the grain didn’t give the best cut but I was able to clean it up nicely with these other tools.

The result was a nice tight fit that I’m very happy with.

Now I have to cut the remaining rails and get the same fit. This job is much more satisfying than the groove.

Guitar 4 – Time for braces

glennth — Wed, 30 Mar 2011 03:44:42 +0000

It’s time for braces. In this case, it’s not about straightening teeth but about providing structure and tonal improvement to a guitar top.

Bracing a modern steel string guitar top has a couple of key elements. The main is called the x-brace and spans the bottom bought of the guitar (this is where the guitar is the biggest, if you think of a guitar body being roughly pear shape) and, like it’s name are 2 braces that form and X. In addition, there are tone bars that cross the bottom center and side tone bars that are close to the middle but on the side’s of the x-brace. The tone bars provide tonal changes to the top based on how they are shaped. Lastly, there are a couple of braces at the top which are perpendicular to the neck. You should be able to recognize each element from the photo below.

After the braces are glued, it’s important to shape them. As a beginner in guitar making, I’m taking the simplest approach. I make the tops rounded and then feather the ends of each brace down. For the x-braces and the top braces, I feather down to about 3mm thick. For the location where the tone braces meet the x-braces, they are also feathered down to about 3mm thick. For the edges of the tone bars (outer edges), they are feathered down to the surface of the top.

When it is all done and shaped, you should be able to loosely balance the top, through the sound hole, on one finger and tap around the top. The sound should have some resonance and sustain along with a greater or lesser base or treble quality to the tone. These qualities are adjusted by small amounts with the overall shaping of the braces.

Next steps include notching the kerfing inside the body to fit the x-braces and top brace and get a nice tight fit. I’ll be working on that next. One lesson I’ve learned though is to trim the top closer to the final size before glue up.

Guitar 2 – Shaping the Braces for the Top

glennth — Fri, 11 Mar 2011 06:08:00 +0000

Today, I began working on the shaping of the braces for Guitar 2.

I am far from an expert on bracing and it’s affect on the guitar’s structure and sound quality. At this point in my luthier or guitar making journey, I am following plans and instructions from people/sources that I believe I can trust. What will prove that trust in the end is the structure and sound quality of the resulting instruments.

First, one of the sources that I value () discuss the importance of testing the voicing of the guitar elements (mainly the top) as the steps progress. He was very careful in telling us that there isn’t a particular thing you are listening for but rather building up the voicing knowledge that certain things work and certain things don’t. I’ve listened after the top pieces are joined together, then again after thicknessing the top and after the braces are initially glued down. The plans first say that the braces are to be placed in very specific locations. After that, there are guidelines for shaping the braces to improve sound quality.

Above you can see the shaping of a few braces. Notice that the braces are tapered from their full height to various thicknesses based on locations and purpose. The top is also rounded. The braces above are called the side tone bars and they taper down to nothing before the location of the side wall of the guitar body and should allow the top to join to the sides very flat at this location. They also taper to the center where the main braces (also called X-braces due to their shape) are but there still remains some thickness and the contact is important.

Above, you can see all the braces shaped and sanded. I’ve listened to the top now and achieve a musical tone quality that might remind you of a very nice sounding wooden drum. The sound quality seems similar all over the top and the sound doesn’t fall off immediately giving a small sense of sustain. I can’t tell, at least to my inexperienced ear, whether the pitch and frequency of the tone is good but it seems pleasant to me.

My next step will be to join the top to the sides and back, thus enclosing the box of the body.

Braces shaped

glennth — Wed, 12 Jan 2011 20:17:29 +0000

Shaping these braces has been frustrating. I’ve had some splits that needed to be glued back and some gaps that needed to be filled. For the gaps, I feel that the next top I have some ideas on how to tackle them and get the joints tighter and not require filling. For the splitting, I think I was just be too aggressive with the chisel and coming at it from the wrong angle. When I shaped the repaired spots (2 of them), I was able to do it without any additional splitting.

In this shot, you can see the main and side tone bars which have been tapered down towards nothing at the perimeter. The main x-brace still has some meat to it (though I have to measure it to see if it is the correct thickness). The main x-braces must join with the side for the proper tonal quality in the body of the guitar.

More Bracing Work

glennth — Sun, 09 Jan 2011 05:53:35 +0000

After the X-braces that I talked in the previous post, I needed to work on the other braces and get them glued and clamped.

I’ve reviewed books and videos and have determined (especially for the x-brace) that some other shaping should be done before I glue it up to get even tighter joints. Also, I learned more about specifics with the large lower tone bars and the smaller side tone bars. Next guitar top will benefit from this knowledge. Doing so many guitars in a row really give benefit to each successive guitar.

After this glue dried, I started the shaping. It’s all chisel work which emphasized the forearm muscles which tire quickly. I’ve done almost half the shaping and will try and finish the rest tomorrow. I’ve put my initial effort on the tone bars and the x-braces.

Guitar 4 – Alignment looks good

glennth — Sat, 25 Dec 2010 00:25:20 +0000

Today, I took the back with the braces and joined it to the sides. I first had to finish shaping the braces and then create the slots in the kerfing for the braces. All this was exactly the same for guitars 2 and 3.

I spent a great deal of time during glue up getting the alignment of the center lines to match for the sides and back. The problem is that glue allows some slippage and the go-bars in the go-bar deck can cause some pressure that is not directly down when the go-bar is being bent into clamping position. It took a bit and some minor adjustments but I think I got it.

The important piece is that the center strip down the back should be exactly in the center of the edge joining the bottom edges of the sides. In this picture, you can see pretty good alignment.

Keeping Busy on 2 Guitars

glennth — Thu, 23 Dec 2010 22:47:23 +0000

Today, I got to unclamp the body of my 3rd guitar. The joint is very flush and I’m happy with that. I’m disappointed with my ability to align the back to the sides. This is where I’m supposed to take the center line of the back and line it up with the center line on the sides in the mold. On my 2nd guitar, I missed both ends. On the 3rd guitar (the one I just glued), I got the top to line up but not the bottom. It’s especially disappointing since the bottom is probably the most visiible element and really needs to be lined up. I will see if I can find my week technical points for the 4th body. I also cleaned up the glue squeeze out – there wasn’t much so I must be getting better at judging the right amount of glue to apply.

I also worked on the back to the 4th body. This involved more early shaping of the braces and glueing them in place. See previous post for specific steps.

You can see the back for the 4th body on the left and the 3rd body with it’s back attached and cleaned up on the right.

Guitar #3 gets Sides joined to Back

glennth — Thu, 23 Dec 2010 04:37:24 +0000

Today, I worked on attaching the sides and back together.

The first step is to shape the braces on the back. About 550mm from the edge of the guitar, the braces are pared down to about 2-4mm thickness. Once that is done, you determine where to cut the cross braces and the center brace so that you can fit it inside the sides. For the cross braces, there are 2 methods that can work. For Guitar #2, I cut away dado’s for the cross braces in the kerfing and the sides. For this guitar (#3), I cut the dado’s only in the kerfing. The difference is that once the sides and back are glued up, you can see the braces in technique #1 and you should get a smooth fit for technique #2. Once this is done, then you want to ensure the braces are to the edge of the sides (for technique #2) and the center brace goes from heel to heel block.

Once you have a good fit, it’s time to glue up the back to the sides. This MUST be done in the form so that the glueing process doesn’t distort the sides. It is also critical to keep the center lines on the side and form lined up to the center line on the back. This will affect the appearance of the guitar drastically. For the glue up, I’ve again used the go-bar system.

On this guitar, the next process will be to work on the top and get it glued on – closing up the guitar body. I do still have to work on guitar #4 though so that is likely to be my next task.

End Wedge

glennth — Thu, 16 Dec 2010 22:38:02 +0000

An end wedge or other end decoration is a technique used by guitar makers to place something attractive over the seem between the 2 sides. It is very difficult to get a tight joint between the 2 sides when glued up in the form. I expect that there are Luthier’s/Guitar Maker’s in the world that can and do get a tight joint and may choose to not use this technique because they like the purity of the wood they chose for the sides but I am far from having that kind of skill.

For the 3 guitar bodies I’m working on, I have chosen to use blood wood for the main opposing wood elements to the bodies sides and back which are maple. Blood wood gives a nice contrast with a bright color.

The first step in creating the end wedge is to verify (because hopefully you’ve already determined the center line of the body) the center line at the end on the glued up sides. I then take a scrap of wood and cut it into the desired shape. For my case, I’ve decided to match the 2 backs I’ve already got. One back has a 7mm wide blood wood strip down the center while the other has a 12mm wide blood wood strip down the center. The above picture is body 4 (orchestra sized body with a cut away) and I’m using the narrower striped back. Once I have the actual wedge, I find it’s center and match it to the center of the sides and then mark the wedge location. I mark it with a knife and re-define the edge. Using a small router plane and a chisel, I then route the material out. It takes quite a lot of work on the sides of this routed out wedge shape to get crisp lines.

For my 2nd body, I actually didn’t devote enough time and had to come in and create a groove on the edges for a piece of ebony.

Once the fit is nice and tight it is time to glue it up. The cool thing about glueing up a wedge is that you don’t need to clamp it because it is self clamping. You push the wedge against the glue surface and then hammer the wedge into it’s matching wedge shaped groove. It get’s tighter as you hammer it. Always be careful to not over hammer because you can break out of the groove and damage the walls (yes, I speak from experience).

On the left, you can see body 3 (orchestra sized body with no cut away) which has the wider wedge matching the back that will be used with the wider stripe of blood wood and on the right is body 4 (orchestra sized body with a cut away) which has the narrower wedge matching the back with the narrower stripe of blood wood. In this picture, you can really get a good sense of the color and contrast.

Sides are done

glennth — Thu, 16 Dec 2010 05:08:38 +0000

The sides are done for both body 3 and body 4 guitars.

You can see body 3 which is the orchestra sized body with no cut away and body 4 which is also an orchestra sized body but with a cutaway.

The kerfing installed nicely and I did have more glue squeeze out (meaning I used too much) so clean up took a bit longer but in the end the sides on both bodies are nice and clean. I still need to do some sanding before I can totally close up the bodies.

As a quick aside, I’ve talked about radiusing the sides so I wanted to show a picture of this process.

You can see on the bench a radius disk. I am using the clamps to hold the disk from spinning or moving. The disk is round but the radius part is where the center of the round disk is hollowed out enough to match a certain radius. Imagine a circle that is perpendicular to the disk with a radius of 15 feet (used for the back of the sides – where the back will attach) or 30 feet (used for the top of the sides – where the top will attach). I got these disks from LMII but you could make them using a router and a jig.

To make the angle of the heel and neck block along with the kerfing attached to the sides match the radius of the appropriate disk, I rough in the size using a spokeshave, hand plane, or chisel until the gaps between the side and the disk are minimal. Then I move the sides (while in the form so I don’t get much distortion) back and forth until I get no gaps. I also have to measure the sides from time to time so that the side on the left is about the same thickness to the equivalent point on the side on the right.

I hope that clears up that process.

Back on Sides!

glennth — Fri, 22 Oct 2010 01:21:12 +0000

I had a crown done on Monday and surprisingly it made working on my guitar challenging. Today (Thursday) is the first day I’ve gotten back into my shop.

Today I had several small things to do and thought they would fill up my time.

First, I had to trim the ebony accents on the wedge and then fine sand the edges of the side where the top and back will be glued on. The ebony was really thin so trimming with a chisel was a piece of cake. Sanding was also short because the rough sanding had already been done.

Next I needed to finish the shaping of the braces on the back. I had already shaped the peaks or tops of the braces before glue up but now I needed to taper the braces down to where they meet the side. In my build of a guitar, I am thinning the ends down to about 2.5 mm thick with it going back into the brace over 40 mm. The shape of these braces can affect the tonal quality of the back. I am far from an expert on this but so that I can continue to learn about the shapes necessary to make a guitar, I continually tested the tone on the back as I shaped these braces. In the end, I felt I got a full bodied sound with some sustain (though it was not really an extensive sustain). The same testing will need to be done on the top and will even more critical to the resulting sound of the guitar.

I was done with my small projects and it seemed that I had plenty of time to attach the back. In doing this, I had to do a few things. First, I had to lay out the sides on the back so I could trim away the center brace where the neck block and heel block are in the sides. I then had to mark where the cross braces meet the sides and trim away a shallow dato so that the back joins the sides in a tight fashion.

In this shot where you see the back being glued down, you also get a real solid sense in my design idea where the end wedge meets the center strip on the back. I’m really pleased with how this looks.

I have a few small things to do and then I need to move on to the top. I need to scrape away any glue squeeze out and I need to sand the inside of the guitar. Then I need to create a creation certificate and glue it on the inside of the back (right under the sound hole). The top will be the next really interesting element and be a huge milestone.

Headstock Laminations

glennth — Thu, 16 Sep 2010 12:05:08 +0000

Part of making a guitar neck can be creating a certain look for the headstock (where the tuner machines are for tuning the guitar). For this guitar neck, I chose to go from the maple of the neck (which is a light colored wood) to a dark wood (ebony on one and mahagony on the other) then back to a light wood (maple or birch) and then to an element that I will put in at least one other spot on the guitar and that is a nice red Bloodwood. I think after I shape the headstock that it will give a really nice dynamic look.

Here are two shots of the current state. The first shows the 2 necks side by side with the truss rod slot cut out. Remember the headstock has not been shaped. I cut the basic channel for the truss rod with a router and then finished the groove on the headstock with chisels and then final cleanups and final thicknessing of the headstock with hand planes and scrapers. In this shot, I think you can see the interest that birdseye maple (front) gives over a simpler maple (rear).

The next shot is a closeup of the actual lamination so that you can see the effect that having those layers can give the headstock.

My next 2 steps including working on glueing up the end of the neck and then shaping the headstock and neck. After that, it’s onto the body.

Guitar Building

glennth — Mon, 31 May 2010 17:32:05 +0000

I mentioned in a past post that I was going to take a class in guitar building through my local Woodcraft store. The guitar kits they use are from US Guitar Kits. The kits are partially assembled. They have the sides bent and the back attached. They have the bracing attached (though in the 2 kits used in the class, they needed some re-glueing of the braces – minor). The sides and the back are a laminated wood (ours was a light colored outer veneer, the site says is Sapele). The top is solid spruce. The other parts look adequate but are probably not the highest quality. All in all a decent value for a $260 kit (price through the class at Woodcraft).

My hopes are to learn a few of the basics of luthier. With this kit, I get to learn about attaching tops (and bottoms though indirectly since the skills are similar); attaching the binding a purfling (which may give a hint at how to do the sound hold and other decorative elements on the back and heal side); working and shaping the braces; building a fret board including fret wires, nut; attaching the bridge; setup and tuning the guitar. With this class and kit, I DON”T expect to learn bending and shaping the sides; attaching the binding around the sound hole; shaping the neck; applying finish to the guitar.

In our class, the first step was to find the position of the top onto the assembled lower body. This required finding centers on the top and body. Once this is done, we can mark the positions of the braces and the rough outline of the body on the top. Next comes shaping/scaloping the bracing. The 4 points of the x-braces and the 2 points of the top brace will have an equivalent notch in the support/bent bracing the goes around the tops of the sides. The remaining points of the other braces get pared down to the top before they touch the sides. The scaloping of the the braces have hills and valleys and the kits come with a template to do these. In scaloping, I found it a little challenging with the grain changes. I believe that I got a pretty smooth result but it took quite a while (you can see some bad pictures at the bottom).

The next step was to rough cut the body using a band saw. I learned 2 things. First, I need to replace my band saw blade. Second, WOW! it is sure easy to cut softer woods. I eventually want to build a guitar using only hand tools (for this step, it might be a bow saw).

Next was cutting the matching notches for the x-brace and top brace points (6 in all). The teacher recommended a double sided skew chisel and this did make things easier than standard flat/single sided paring chisels. With a few attempts at dry fitting, I needed to make a few adjustments with the notches and the end points of the bracing.

Last for this class was glueing the top down. This required 25 or so clamps (see the picture for the style of clamps). It was important to focus on a few key points including the waist, the widest point on both top and bottom and both the heal and neck locations. One last point was using a straight board to clamp just above the sound hole (see picture). This ensures that the location above the sound hole will be flat so it can receive the fret board.

Overall, I learned a lot and had a lot of fun (good instructor).

Ultimately, I hope to build a guitar from the ground up (maybe not quite so far as harvesting my own wood) and doing it with only hand tools. There are suppliers of luthier grade parts that should make this a challenging but fund experience.