Liutaio Mottola Stringed Instrument Design



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Dressing the Frets in a Fretted
Stringed Musical Instrument

After the frets are installed they have to be leveled, recrowned and have their ends rounded over. Then the frets are polished. These operations are collectively referred to here as fret dressing. This page contains instructions for dressing the frets on a new instrument, but the operations are the same for repair work as well. These operations can be performed using very basic tools, but there are a variety of special purpose tools that can help.

Fret dressing is done after the neck is attached to the body and after finish has been applied to the instrument, at least for acoustic instruments. On some electric guitars with bolt-on necks, the frets can be dressed at any time, with the neck on or off the instrument.

Initially appeared: May 23, 2009
Last updated: Sunday, June 01, 2014

Tools and Supplies for Fret Dressing

  • Single Edge Razor Blades
  • Masking Tape - 1/2" or 3/4" is fine.
  • Straight Edge - I like to have two, one that is long enough to cover all the frets at once, and one that can check from the first fret to the fret on the neck/body join at one time.
  • Trussrod Adjusting Wrench - Whatever you need to adjust the trussrod of the instrument. Not needed if the instrument doesn't have a trussrod.
  • Fret Leveler or 8" Mill File - The fret leveler tool is available from lutherie suppliers. I have one and use it for other purposes, but here I use an 8" single cut medium (second) mill file.
  • Fret Recrowning File - This is a special file for recrowning the frets. If you get one be sure to get the same size as your fret wire. You can use a triangular fret dressing needle file to do the crowning if you don't want to get another special purpose tool.
  • Fret Dressing File - This is a triangular needle file that has the edges between the file faces ground smooth so they don't mar the fingerboard. You can get one from luthier supply places, or you can grind off the edges of a regular triangular needle file on the belt sander.
  • Aluminum Oxide (Tan) Sandpaper, 220 and 320 grit - This is used for sanding the fingerboard and for final smoothing and polishing of the frets.
  • Silicon Carbide (Black) Wetordry Sandpaper, 400, 600 and 1000 grit - This is used for final smoothing and polishing of the frets.

Scraping and Sanding the Fingerboard

After finish is applied to the instrument the fret dressing process can be started. It is easier to do this work if the nut and bridge are not yet in position, so for new instruments I'll leave these off until after the fret dressing is done. Working on an instrument that has had finish applied is an exercise in caution. There is still work to do but it must be done so as not to mar the new finish. Before doing any work here, it is a very good idea to cover the top of the instrument around the fingerboard extension with cardboard and/or masking tape. Cover the headstock, too.

Before applying finish to the instrument I will always mask off the fingerboard and frets to keep finish off those areas. But invariably some finish leaks through, usually along the edge where a fret meets the fingerboard. I usually wet sand as part of rubbing out the finish, and this process also puts a certain amount of sanding slurry on the fingerboard. If the fingerboard is otherwise in good shape (i.e. sanded smooth, no dents or gouges, etc.) I will usually clean up the fingerboard now, and then apply masking tape to the wood between the frets to protect is from being marred by the fret dressing operations. But if the board is going to need serious sanding and scraping work anyway, I'll leave the masking tape off, do the fret dressing and then clean up the fingerboard after (and while) the fret dressing is done.

This fingerboard is in very good shape, but some lacquer got on it in a few places and there is some slurry from the wet sanding. You can see the lacquer around the ends of the first fret, and that white stuff around the second and third frets is the slurry from wet sanding the finish on the neck.

If you've got real big drips of lacquer it is best to take them off with a knife. These drips are small, so I'll use a scraper made from a single edge razor blade to clean up the fingerboard. Making the scraper is easy. You just run the edge of the blade across your scraper burnisher or the handle of your vise to turn the edge to one side, like this:

Since the edge is so thin and so unsupported a scraper like this won't last very long. When it stops working you can try turning the edge again, but I usually just throw it away and make a new one. I end up using about six or seven of these to do one fingerboard. If you are concerned about the sharp corners of the blade scratching the surface you are scraping you can round these over slightly by running the corners over a sanding block or sharpening stone.

This scraper leaves a very fine finish. In general, a scraper will leave about as fine a finish as the abrasive grit used to sharpen the scraper. So for example, if you sharpen a scraper blade with 400 grit abrasive then that scraper when used will leave about a 400 grit finish. Razor blades are sharpened with very fine abrasives and then polished, so they leave a very fine finish when used as scrapers.

I'm using the scraper to scrape up the lacquer and other junk on the fingerboard. You can start right up against a fret and scrape right across to the next fret.

Be very careful when scraping down the edges of the fingerboard. There may be a little ridge of lacquer there and if so you'll want to scrape that down, but take care that you move the scraper inward, toward the center of the board on each stroke, to avoid chipping the finish off the edge. The finish is very delicate here and can chip off easily. If you do chip it off you'll have to fill the void with a lacquer drop fill or with thick cyanoacrylate glue. after you've scraped from one fret to the next, repeat the process starting from the fret you just scraped to, scraping toward the one you just came from. This scraping of the fingerboard between each pair of frets in both directions assures that you scrape the junk off the fingerboard right up to each side of each fret.

After the section between two frets is scraped, run the corner of the scraper across the board and right up against the fret to pull all the scrapings out. Do the entire fingerboard in this manner, scraping between each pair of frets in both directions and then cleaning out the inside corners with the edge of the scraper.

One reason I like to do this scraping at this point in the process is that while I am scraping I am also critically assessing the condition of the fingerboard. It may be easy to overlook bumps and dings in the board (especially if you have bad eyesight as I do) but when you are getting up close and personal with the razor blade scraper it is hard for such flaws to hide. If you do run into something that needs more serious work by all means do that work (sanding, scraping, hole filling) now. Another reason to do this fingerboard scraping now is that you tend to make marks on the frets with the scraper when you do this, and these marks will be taken off during the fret dressing process.

After the fingerboard is scraped it should be sanded. This is tedious work as you need to get right up to the frets. I make a little sanding block out of a short length of plastic binding material and wrap the sandpaper around that. The binding material has sharp edges so you can get right up to the fret, and it is somewhat flexible so you can bend it to conform to the camber of the fingerboard surface. I'll start with 320 grit and sometimes work up to 1000. You can sand to high grits and then buff the wood to make a really nice finish. But the problem with doing this is that this smooth surface shows all scratches made by the strings while playing and even from fingernails. If you just want to stop after 320 grit that works fine.

Now that the fingerboard is nicely scraped and sanded you don't want to mar it during the fret dressing process. The fingerboard between the frets is covered with masking tape before dressing the frets.

The tape is applied right up to the edge of each fret. You only want one layer of tape near the fret, so unless you have an assortment of thin rolls of masking tape you will have to cut thin strips of tape for this purpose. I stick one end of the tape down to the edge of the bench and then use a knife to slice the tape right down the middle.

For the upper frets I'll take two slices to get two really thin pieces.

If you haven't already done it you'll want to use masking tape and cardboard to protect the top of the headstock and the top of the body around the end of the fingerboard. Most of the processes involved in fret dressing make use of tools which can easily put big gouges in your nice finish, so it makes sense to spend a little time protecting those areas most likely to get dinged up. Better to be too cautious here than not cautious enough. Finish touch ups are not my favorite activity.

Fret Leveling Strategies: Cylindrical, Straight String Paths, Conical

It is desirable in some instruments for the action (height of the strings above the frets) to be very low. And it has been noted1 that for instruments with cylindrically cambered (radiused) fingerboards it is not possible for the outer strings to lie as close to the fingerboard surface as the inner strings do, due to the divergence of the strings as they approach the bridge. Although this is true, the actual distances involved are small2 - so small in fact that they are inconsequential for all practical purposes as will be discussed below.

To obtain low action some luthiers use what is called a compound radius fretboard. Fretboards of this type have their playing surface shaped like a section of a cone. But the work involved in making such a board is completely unnecessary, as optimally low action can be obtained by simply dressing the frets in a normal fashion. There are two reasons for this. The first is simply that the shape of the fingerboard surface is of no consequence when it comes to low action - it is the shape of the surface described by the fret tops that matters. The second reason is that the difference between an optimal fret top surface shape and a purely cylindrical shape is so small that you will generate the optimal shape automatically, as a consequence of normal fret dressing. Here's why.

For a typical guitar with a 10" radius fingerboard and cylindrically cambered fret tops, if the inner strings are at optimum low action the outer strings will be less than 0.005" higher above the fret tops. But the fact is a luthier would have to put some special effort into making an instrument with cylindrically cambered fret tops, by leveling the frets with a radiused sanding block. If you level the frets with a file as most folks do, you cannot help but file along the paths of the strings. And when you do this you automatically remove the small amount of material (less than 0.001") from the frets that causes the above-mentioned string height discrepancy. Optimum action is had when the tops of the frets along the string paths are made level with each other. Doing this requires no special effort. The technique for fret leveling described below is simple, does not require any special fingerboard surface shape, and will yield optimally low action.

Fret Leveling

The first thing to do is to adjust the trussrod, if the instrument has a trussrod. I use double acting trussrods which can bend the neck back when the adjuster is turned one way and can also bend the neck forward when the adjuster is turned in the other direction. For instruments using this type of trussrod you'll want to make the top surfaces of the frets from the first fret to the fret at the neck/body join as level as possible before doing any fret work. Place a straight edge on the frets along the fingerboard centerline and adjust the trussrod until you get the fret tops as level as possible. Here I'm using a carpenter's level, as it is long enough to check all the frets:

Click to enlarge

If you can rock the straight edge end to end then the neck is back bowed so loosen the adjusting nut. If you can't rock the straight edge then the fingerboard may be either straight or a little front bowed. You can check for the latter by sighting between the straight edge and the fret tops of the first fret to the one at the neck/body join from the side. Shine a strong light from the other side of the straight edge when doing this. If there is some space between the straight edge and the fret tops near the middle of the neck then tighten the trussrod adjusting nut until that space is eliminated.

Note that we are only interested in the frets up to the one at the neck/body join. The frets over the body should "drop off", that is, they should all be below the straight edge, assuming the fingerboard was properly planed. The drop off looks like this:

Click to enlarge

The reason the drop off is needed is that the neck will bend up a little under string tension, but the part of the fingerboard over the body will not bend up since it is (more or less) rigidly attached to the body. So we plane a little drop off onto the fingerboard end so that everything lines up nicely under string tension. I won't go into drop off in any more detail here since it is something we should have taken care of during an earlier construction stage. But it is a very good idea to check to be sure you have some drop off before going any further. If you just barely don't have any drop off it is possible to add some by filing the tops of the frets on the fingerboard extension (the part of the fingerboard over the body) more aggressively than for the rest of the frets. But if you don't have any drop off and the straight edge rests on the last fret and the first fret and you can't remedy this with trussrod adjustment, the frets on the extension will have to be removed and the fretboard planed down there.

It your instrument has a single acting trussrod (one which can only be tightened to back bow the neck) then it is a good idea to get things as straight as possible from the first fret to the fret at the neck/body join, then tighten the trussrod adjusting nut a bit more to get a bit of back bow. You'll file everything flat in the next step, but putting in a bit of back bow allows for some amount of correction of back bow if the neck develops this at some time in the future.

Here's a hint on trussrod adjustment if you are building a flattop guitar. The trussrod adjustment is often located so it can be accessed from inside the sound hole. If this is the configuration of your instrument you will notice that it is a major pain to get to the adjuster. I often find I have to use my off hand in a sort of back handed entry to get the wrench into the adjuster hole. If you wear a watch, take it off before working inside the sound hole. It is too easy to bung up the edges of the hole by accident if you have a watch on.

Before starting in on leveling the fret tops the instrument should be supported so that it won't move around while you work. The neck must be solidly supported in some way too. I use a rather large sandbag for this, but other folks use different kinds of supports. A guitar neck is quite flexible and the fret leveling operation is an attempt at a certain amount of precision. This precision can never be attained if the neck can readily flex under the file.

The tops of the frets can now be filed to level them off. There are lots of different tools that can be used for this but I use an 8" single cut medium (second) mill file, or the same special 6" fret beveling file used to file and bevel the fret ends during fret installation. Here's the mill file in use:

A shorter file makes it a little easier to blend one area into the next, but a longer file helps to keep things more level. The file is placed right down on the fret tops and then stroked back and forth, following the string lines. Don't press - let the weight of the file do the work. If you press down you are likely to bend the neck as you do, and this will reduce the accuracy of the filing operation. You should do the fingerboard extension area separately from the rest of the fingerboard, because the extension has the drop off and you don't want to eliminate that by filing away so all the frets are level. As you file you will notice that the fret tops get flat, and that some are lower and completely get missed by the file. You want to file so that the entire length of each fret ends up with a flat on the top. Some of these flats will be broader than others - don't worry about that. Just make sure each fret ends up with some amount of flat on top.

Click to enlarge

As you are filing you can feel frets that are higher than the others around them because you can rock the file over these high frets. The high ones will get filed down more than the ones around them of course. Be sure to cover the complete length of each fret, but do not let the file fall off the edge of the frets as this would file another bevel at the ends and we don't want that to happen since it decreases the usable length of fret top near the fret end, which makes it easier to push an outside string over the end of the fret, something a player never wants to do. As mentioned above, the filing is done in the two areas of the fingerboard separately. When you are done, the fret tops over the fingerboard extension should be level with each other, and the fret tops over the neck should be level with each other. You can check for level using a straight edge. Be sure to place the straight edge at each string path, and check to be sure you can't rock it over a high fret. Also attempt to sight under the straight edge, again placed at each string path, to be sure there are no low places. Any un-level places will need to be filed a bit more.

Another way to gauge your progress as you file is to watch the pattern of metal chips that are deposited on the masking tape over the fingerboard as you file. There will be even piles of these chips along each fret that the file has touched, but no chips will appear around frets (and areas of frets) that have not been touched. This is very easy to see, especially if you use light colored masking tape. Don't brush the chips off the fingerboard as you work! If you do they may find their way between the instrument and whatever it is resting on and scratch the finish on the back. When you are all done leveling the frets, thoroughly vacuum the chips off the fingerboard. Also vacuum up around the neck and neck support.

Recrowning

Now all the fret tops have flats filed onto them. Some of these flats may be pretty wide. The next step is to recrown the fret tops, that is, to file them so that the tops are again rounded, but retaining the leveling just performed. Recrowning is done with either a special fret recrowning file or with a small triangular profile needle file. It is very fast and easy to do with the recrowning file and so if you intend to make more than one instrument one of these files is a good thing to have. The edges are concave:

The one I have can recrown both large and medium fret wire. You place the appropriate sized edge on top of the fret and file back and forth to recrown the top.

As you file you'll notice the flat getting smaller. You want to stop filing when just the thinnest line of flat remains along the entire length of the fret. Better to err on the side of too much flat left rather than none at all. If there is no flat left on the fret you may very well have filed it down so it is now lower than the frets around it, which could make for playability problems. So stop when you get to a thin flat line on the fret top.

Click to enlarge

The fret tops look pretty messed up at this point in the process, but they are quickly and easily smoothed and polished in subsequent steps. Vacuum up the chips left by the recrowning before proceeding.

Dressing the Fret Ends

The next step is to round over the sharp edges at the ends of the frets, left there when the frets were beveled after they were inserted in the fingerboard. Note that traditionally, this operation is not performed on classical guitars - the fret ends are left sharp, the idea being that the player's left hand will never touch the edge of the fingerboard anyway. But a number of modern makers of classical guitars are doing a little fret end dressing. For this process I use a triangular fret dressing needle file. this is a standard triangular needle file with the sharp edges ground smooth so they don't scratch the fingerboard if they touch it. The process is very simple. You can file into the end of the fret or off the end of the fret. I am always worried about chipping finish off the edges of the fingerboard and so I try to file into the fret end whenever possible. That is not possible for the frets on the fingerboard extension of flattop guitars though, since the body of the instruments gets in the way there. The following sequence shows a fret end being dressed with two strokes, filing into the fret end.

The first stroke begins with the file against one side of the fret end edge, right at the fingerboard top surface:

Click to enlarge

As the file is pushed it is also rotated toward the top of the fret, to file the edge off this half of the fret end. The file comes to rest here:

Click to enlarge

The process is repeated for the other side of the fret, with the file against this side of the fret end edge, right at the fingerboard top surface:

Click to enlarge

And the stroke ends again at the top of the fret end:

Click to enlarge

Notice I do not change the position of my hands on the file. This makes it faster to do all the frets. I also take two more light strokes, one from each side but just near the top of the fret. This evens up the shape of the cut along the entire fret end. The dressed fret end looks like this:

Click to enlarge

Do both ends of all the frets in similar fashion. This is an operation that is easy to overdo, so try to do it with a light and sure touch. You just want to get rid of the sharp edges, not do any heavy rounding. Again, you want to preserve as much length of the fret top as possible to lessen the likelihood that an outside string will get pushed over the end of a fret. Four light and consistent strokes are all that are required here. After all the fret ends are dressed it is easiest and most appropriate to check your work by feel. Running your fingers along the full length of the fingerboard at the edges will quickly detect any sharp edges that need a bit more work with the file.

Smoothing and Polishing the Frets

The frets tops and ends are smoothed by sanding. Since the sides of the fingerboard are not fully masked (there are gaps under each fret) a strip of masking tape is placed along each side of the fingerboard, just under the ends of the frets.

As you can see in the pictures above, the frets are pretty rough at this point, so they need to be sanded and polished. The file used to level the frets leaves deep marks, so fret sanding starts with 220 or 320 grit sandpaper. If the finer stuff will take off the file marks, use it, otherwise go for the coarser paper and work your way up. I take a quarter sheet, fold it in half, and then hold it in my hand so the thumb and little fingers hold the paper and the middle three fingers back it up. From the business side it looks like this:

And from the back, like this:

The frets are sanded along the length of the fingerboard with the fingers backing up the paper and serving as a compliant sanding block.

The reason you want some compliance (flexibility) here is that you want the paper to sort of fold over each fret as you go over it, so that not just the very tops of the frets get sanded. This removes the file marks and nicely rounds over the fret tops. The 220 grit paper should make quick work of the file marks. Keep an eye on the progress and don't sand any more than you have to. When the tops look good, tilt your hand and sand the fret ends.

You don't have to work too hard here, just a few passes will do it. After sanding in this manner with 220 or 320 grit, go to 400, then 600 and then 1000. Be sure to check your progress as you go. The frets should be fairly shiny after 1000 grit. Now polish them with a gray abrasive pad. You could do this with steel wool instead, but I don't keep it in the shop as steel wool dust causes problems with both waterborne finishes and with electric guitar pickups. The final step is to polish the frets with metal polish, polishing along the length of each fret.

When the fretwork is all done the masking tape on the fingerboard can be removed. First, remove the strips along the sides. Then remove the tape between the frets. When you do this pull the tape up from both sides of the fingerboard.

If you don't you risk pulling off the finish on the sides of the fingerboard - always a concern, and a potentially tough thing to repair depending on what you used to finish the instrument with. With all the tape off the fingerboard you can now give the fret ends another check to be sure there are no sharp endges. If there are, carefully file them. You may want to reapply masking tape as needed before doing this.

Now the fingerboard gets a coat of oil. First remove any remaining adhesive from the tape with naphtha, and then apply the oil.

You can buy "special" fingerboard oil from the lutherie supply places, but I just use furniture polishing oil. Apply the oil with a rag, let it sit for a few minutes and then wipe up the rest.

Fret dressing and final fingerboard work are now done. Some folks like to give the whole fingerboard a good buffing at this point to really make things shine.

References

1. Olsen, Tim "Cylinders Don't Make It"
American Lutherie #8 p. 49

2. F.A. Jaén "Not Only Cones Make It — and Cylinders Almost Do"
American Lutherie #101 p. 52