This is a three-part discussion about the practice of stringed instrument inlay. Part I covers the principal materials and tools, Part II covers pearl cutting and layout techniques, and Part III covers inlaying technique. The usual disclaimers apply--I recommend specific brands only when either no other will work or I have no experience with others. As far as I know, no manufacturers mentioned here have ever heard of me. [ I. Materials and tools | II. Inlay patterns, layout, and pearl cutting | III--Routing and inlaying ]
Here is Part I, and the other parts will appear over the next few weeks as time permits. Your feedback is solicited and welcome. Feel free to download the text for personal use, but otherwise please do not crosspost, forward, or reproduce the text without permission.
I. Materials and tools
Any number of flat or flattenable materials can be inlaid into the surfaces of instruments, furniture, jewelry boxes, etc., but the most popular for stringed instruments has always been mother of pearl from pearl oysters and a similarly-derived material from abalone shells. Mother of pearl (nacre) is the material which composes the pearl oyster (_Pinctada_ species) shell, although normally the term refers only to the interior lining of the shell. All shelled molluscs possess a shell lining that resembles mother of pearl, but those of the pearl oyster and abalone are especially attractive and the shells are large enough to yield reasonably large flat pearl blanks. Oyster mother of pearl is usually white or gold, with red, blue, and green irridescence and often with swirl, "eyes," a curly pattern, or other figure that results from proximity to the hinge or from imperfections or worm borings in the outer shell. Pearl oysters are native to the warmer parts of the Pacific and Indian Oceans, from the Gulf of California to the Red Sea, and are "farmed" in Asia for the cultured pearl industry. I don't know if they are also used for food. I also don't know what, if any, percentage of the pearl oyster shells that are imported for inlay pearl originate in cultured oyster beds, but I hope it's large. Abalone (several _Haliotis_ species, of which red and green abalone are the most popular for inlay) is confined to coldwater parts of the Pacific Ocean, and doesn't occur in the Indian Ocean. Abalone for inlay originates completely from "wild" specimens harvested for their meat, which is considered an ultimate seafood delicacy. Some abalone is now being farmed, and perhaps in the future most of the commercial material for food and shell will originate from such sources. Other materials occasionally or commonly used for instrument inlay include bone, ivory, tortoise shell, silver, gold, brass, nickel silver, and various woods and plastics ("mother of toilet seat"). Each has its own peculiarities, but the process for cutting and inlaying all such materials is basically the same.
Several steps are entailed in converting an arched shell to flat pieces for inlay blanks. The first is to mark the shell (on the inside) to take best advantage of the figure and pattern, and to minimize the arch in any particular rough piece (the less arch, the larger and thicker the final blank). The resulting jigsaw puzzle is then bandsawn into arched individual pieces that are lined with mother of pearl on one side and with the shell exterior on the other. The rough exterior surface is then ground off to reveal the underlying mother of pearl. The resulting piece is anywhere from <1mm to 25mm thick (up to 1" for really thick shells at the lip), and it is still arched. Chuck Erikson, the man who taught me how to do inlay, had two large double-wheel enclosed grinders for flattening the blanks, and they did this job efficiently and well. I expect that other blank suppliers have similar equipment, because it is heavily tedious to flatten blanks against a normal grinding wheel, and the resulting product is very inconsistent. The amount of handwork that goes into planning, marking, bandsawing, and preliminary grinding renders the blanks rather expensive, especially for smaller, more difficult material, such as green abalone. Also, at least one pearl supplier that I know of has been so overexposed to the fine dust that results from grinding the shell that he has been seriously ill with silicosis, a potentially fatal lung disease--if you grind shell or cut lots of inlay, wear an OSHA-approved respirator. Even if you cut only a little inlay, wear at least a dust mask such as the fiber units sold in hardware stores, and it's a good idea to wear goggles too. The finished blanks are characteristically about 1.5-3mm thick. Some suppliers furnish two thicknesses--the thin one for inlaying flat surfaces, and the thick one for arched fingerboards. Blanks may be sold by the piece or by weight--thin blanks when sold by weight are usually more expensive because per unit weight more work is involved (there are more blanks).
The tools necessary for cutting and inlaying pearl include good lighting, a jeweler's saw, a homemade cutting jig, a scribe (with a sharp metal point that is hard and stiff enough to scribe very hard wood), a few needle and small mill files, a Dremel Moto-tool (or similar high-speed drill) with a Dremel router base, various bits and appropriate collets for the Dremel, a jig or vise to hold the object to be inlayed, and a 2.5" x 5" or similar rubber sanding block. For lighting, use a Ledu or similar swing-arm lamp (some prefer fluorescents). The jeweler's saw resembles a coping saw with a very slender blade, and they and the blades are available from lutherie and lapidary suppliers. Blades are typically graded as "fine," "medium," and "coarse," but the actual thickness varies among suppliers, because dozens of thicknesses are available from the manufacturers. I use "medium" blades for most of my work because they are less subject to breakage than fine blades and less likely to bind and break the inlay sheet than coarse blades. Fine blades are usually recommended for scrollwork and other intricate inlays, but as your skill increases you will have less occasion to use them. Beginners should purchase at least 2-3 dozen blades. Many inlay artisans use a jeweler's saw with an adjustable throat to accomodate variations in supplied blade length. Such an adjustment feature also permits the use of broken blades, but in my experience this is a waste of time unless the blade was broken before it was ever used. The homemade cutting jig consists of a long piece of wood (preferably hardwood, such as maple or birch) about 12" x 3" x 3/4" with a narrow slot through the middle and a 1/2" or 3/4" hole at the end of the slot:
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The jig is C-clamped flat to a table so that the slot and hole extend beyond the edge, the pearl sheet is positioned over the hole, and the wood supports the sheet while the saw cuts downward. The scribe is used to inscribe the exact shape of the inlay into the wood that will be routed for the inlay. Many hardware stores sell utility scribes--the one I use consists of knurled steel shaft with a fairly fine hardened steel point that is removable with pliers--spare points are stored at the opposite end of the scribe, which is sealed with a hexagonal plastic cap. A small mill or needle file may be handy for removing the small spur that sometimes remains at the end of the blade path, but otherwise its use is rather limited. Do not rely on a file to clean up roughly-sawn inlay, as the pearl is quite hard and is not easily filed. Just holding an inlay for filing invites breakage.
The Dremel moto-tool, which is one of the most useful of all tools for general lutherie, is used to delineate and rout the inlay pockets in the wood. Economy on the Dremel is false: buy a variable speed, ball-bearing model, and if you can afford it, buy two. Three is not too many. Numerous bits, sanders, cutting wheels, buffers, etc. are available, but I have found that just 2-3 bits are necessary for inlay. These include a fine-pointed bit, a bit with a plain shaft that ends in a tiny cutting ball that is slightly larger in diameter than the shaft, and a fairly large (1/16" is good) router or downcut bit. The pointed bit is used in the tool freehand to cut down the edge of the inlay pocket, the ball-end bit is used on the tool in a router base to undercut the edge after the pocket is delineated deeply, and the router bit is used (also in the router base) to hog out waste wood in the middle of the pocket and to even up the pocket depth. All three bits are offered by Dremel, but I have found that their pointed bits and ball-end bits are generally too large for inlay work. I use dental bits that I obtained for free from my dentist--used bits are entirely sharp enough for inlay, and will remain sharp for a long time. Quite a variety of dental bits is available, from exceptionally finely-pointed carbide bits to tiny ball- and cone-shaped carbides and various straight and pointed diamond bits. One request to my dentist and a 30-day wait yielded a lifetime supply, even if I live a really long time. Ask your dentist to sterilize used bits, but if this isn't possible, soak them overnight in a "10%" chlorine bleach solution, made by adding one part of household chlorine bleach (which is 5.25% sodium hypochlorite, hence the quotes) to nine parts of water. Rinse away the bleach thoroughly with several water changes the next day. You will still need the router bit(s), and you will need one or more Dremel collets to match the dental bits. Dremel's router bits (as far as I know) are not carbide--they do produce some carbide-coated general cutting bits, but I have not been satisfied with way they cut ebony and especially rosewood. However, various lutherie suppliers stock very satisfactory carbide downcut and router bits with 1/8" shanks to fit the standard Dremel collet, and I happily use these for the rough work. Stewart-Macdonald and perhaps others (standard disclaimers) have various plexiglas router bases available for Dremels, but it is pretty easy to make your own from 1/8" Plexiglas or (as I recommend) 1/8" polycarbonate (Lexan). I don't use clear bases for inlay, but I do for some other lutherie operations. You can use a padded wood or metal-working vise to hold the object that you are inlaying (usually a fingerboard or peghead already attached to a neck), or you can build a jig to hold it on a tabletop--either way is fine. Purchase a standard rubber sanding block from the hardware store, along with lots of 80, 100-120, 220, 320, 400, and 600 grit open-coat and wet or dry sandpaper--a large mill file is handy also. Other tools you might need include a very small chisel for cleaning inlay pocket corners, various gravers if you intend to engrave the pearl, and other bits for the Dremel as the need arises.
Next: cutting pearl
This is the second of the three-part series on instrument inlay. I'm grateful for all of the positive feedback on Part I, and again I solicit and welcome your comments. Disclaimers and copyright rules are still in place.
II. Inlay patterns, layout, and pearl cutting
When last we met we spoke of tools and materials, and I left you staring at an array of scribes, jeweler's saws, thin blades, and noisy high speed drills. Now, you must choose an instrument or other object to be inlaid, purchase some inlay material, and either purchase or design a pattern to cut. For your first effort, I suggest that you stay with mother of pearl from the pearl oyster, and save abalone for a later endeavor. The reason is simply that abalone tends to be somewhat more brittle, and full of fragile natural laminations (the black lines that help to make it so attractive). If you insist on abalone for your first inlay job, use red rather than green abalone because red is less fragile (and less interesting) and generally comes in larger, more easily handled slabs--the shells are larger. I have seen pearl advertised in thicknesses that range from 0.02 to 0.06 inches. Use material that is 0.02--0.04" for flat surfaces, and thicker material for curved surfaces, such as arched guitar fingerboards. Thick slabs are also less likely to break as they are cut. Thick slabs do cause a higher rate of blade breakage, so be sure to have an ample stock of medium blades available. Pearl is sold by the piece or by unit weight, typically by the ounce. Many suppliers claim that one ounce is sufficient to cut a Gibson-style banjo neck, but I have found that it will cut all of the fingerboard pieces but not usually the peghead pieces (also, there are more thin than thick slabs to the ounce). Further, many peghead patterns require oversize blanks (e.g. Gibson Flying Eagle and Bella Voce), so if you have such special requirements be sure to discuss them with the supplier. Most suppliers do not "grade" mother of pearl (except to separate the "gold" pieces, which have a specialized market), because highly figured pieces are scarce enough so that the cost of sorting by hand would multiply the final cost of the pearl manyfold. The end-user should pick out the especially attractive slabs from any given batch and stash them away for the ultimate inlay job. In any case, use as plain and routine a selection of pearl as possible for your first cutting efforts.
The inlay design is dictated by the nature of your project, and for this, you must choose carefully. Please do not commit a fine instrument to your first inlay project, but don't use a clunker either. I think that the best instrumental candidates for practice material are instruments you have built yourself or instrument necks you have built or purchased. You might consider a medium- priced commercial instrument, one that is unlikely ever to be collectable, but you will have to strip and refinish the peghead, de-fret and refret the fingerboard, etc, none of which is simple and all of which increases the likelihood of failure. I really can't recommend altering even these instruments. Whatever you decide, please do not tamper with a collectable instrument--the value of your 1960's D-28 for example, will decline substantially if you alter its factory appointments, even if you do a first-rate job. Do it to a 1930's D-28 or a Loar and instrument connoisseurs will report you to the vintage police. Like many others, I started by inlaying a reproduction Gibson banjo neck, and this is one of the best ways to learn. Most of the 1920's and 1930's Mastertone patterns are relatively easily cut (especially the "Hearts and Flowers" pattern), and there are enough pieces in most of the patterns to give you lots of practice in layout, cutting, and inlaying. Banjos are generally very amenable to such decoration--in my opinion too much pearl on a guitar or mandolin is too much pearl, but banjos rarely have this problem. The various Gibson, Vega, Paramount, and other inlay patterns are available from suppliers, and for your first effort you should probably stick to one of those. Try to select a pattern in keeping with the instrument--a 1920's Gibson pattern looks pretty outlandish on a Vega long-neck. Still, the important thing is to get to work, so as long as you don't irrevocably festoon a venerable collector's piece with new inlay you should be fine. You could also just do a box, a cribbage board, or something similar.
If you are more adventurous and want to design your own pattern, by all means do so. Get ideas from extant patterns, Grecian urns and columns, $100 bills, TV test patterns, classic museum architecture, kitchen fixtures, chandelier displays, or deep within yourself, and draw them on a piece of translucent graph paper (I use Clearprint 100% rag, 10 squares to the inch, which is available from art suppliers--megabucks but worth it). I do script patterns (like my brand name) by writing with a medium-wide calligraphy pen until I have the pattern I like (and that fits within the space assigned--hence the translucent paper). Then I overlay a second sheet of translucent paper on the design and trace carefully around the edge of the script with a size-0 Kohinoor Rapidograph technical pen and India Ink (I use Pelikan)--any technical pen or even a "crowquill" with a fairly fine point and the right ink will work. Other patterns can be done in pencil, and then traced with the technical pen. If you design your first pattern, you will undoubtedly discover later as you are attempting to cut the pearl that not all designs can be cut. Try to remember as you design to keep straight lines straight, and curves as segments of a circle, rather than as ovals. Remember that you will not appreciate your design fully until it is embedded in the wood, after it is much too late to change it, so try to keep it simple and elegant, especially the first time out.
Lay out the pearl slabs on a table and examine each one to determine the best side, and remove the figured pieces and put them in the safe deposit box. Take your purchased or drawn pattern, make sure you have lots of accurate photocopies, and with scissors cut out the individual designs. I number each piece of the pattern so that all can be accounted for when the layout is complete. Glue (with Titebond or white glue) each paper pattern piece to a piece of pearl, and let the glue dry completely. Be sure to glue edges and corners adequately, because these are likely to lift during the subsequent cutting if not glued well. I have tried rubber cement and contact glue and both have failed to hold the design in place along thin areas and at corners. At least one of my correspondents designs patterns on the computer and prints them on laser printer adhesive labels, an approach definitely worth trying. Otherwise, use a very thin coat of Titebond or white glue (thin to avoid gumming up the saw blade), and after the glue has dried, it is time to cut the inlays (the use of Titebond or white glue is still optional--if you like some other glue, try it). Clamp your cutting jig to a table and set up the worklight. Install a blade in the jeweler's saw, and make certain that the teeth will cut on the downward stroke--the teeth should point toward the saw handle. Use the tensioning screw to tighten the blade so that it yields very little when plucked like a string. When you install the blade, be especially careful to avoid bending or twisting the ends, and make certain that the blade is as straight as possible. Put on your dust mask and goggles and fire up the CD player or the radio. There are peaceful but meticulous times ahead.
To cut inlay well requires only that you be able to follow a line with the jeweler's saw. This was easy to write, but if you are like most it will take many inlay-feet of cutting before you achieve the consistently smooth, graceful line that characterizes expert work. Patience is not a virtue when cutting inlay, patience IS cutting inlay. Many artisans like to cut along the outside edge of the line, which they endeavor to keep to the left of the blade as it lays on the jig. The left hand steadies, moves, advances, indexes, and turns the pearl slab over the hole in the jig and the right hand holds the saw handle beneath the jig, and saws up and down (remember, set the teeth so _down_ is the cutting stroke) and cuts the pattern. The saw should advance, turn or otherwise move very little (except up and down)--that's why the hole in the jig can be so small. Examine the pattern thoughtfully before you start to cut. Look for inherently weak areas, and plan the best route for the initial cut. Cut into the slab near the end of a point or corner--if you are cutting out a star, try to intersect the pattern at the apex of a point rather than somewhere along a side. When you hit a tight corner, back up the blade, cut a bit into the outside to widen the kerf, repeat if necessary, and use the widened kerf to turn the blade around the corner. Try to cut from weaker parts of the pattern into stronger sections, but frequently this will be impossible. Endeavor to cut long straight lines and curves without stopping, because a small bump or ridge often results where the cut is interrupted. Try to use the entire blade for each cutting stroke, except when you are approaching a stopping point, but even here keep you sawing movements as smooth as possible. To cut out "blind" interior sections, drill a hole into the blind pocket with a pointed bit in the Dremel high-speed drill, and then thread the saw blade through the hole and install it into the saw--this is tricky and a threaded blade is difficult to tighten, but you will improve with experience. Cut the blind sections first, and for that matter, if you have delicate sections that are not blind, try to cut them first as well. As your skill improves, your pace will quicken, but be careful not to cut too fast because the blade will heat up and break. The other principal reason blades break is that they bind in tight corners or from being forced to turn too tightly to follow a tight curve. Blades also break when the metal fatigues from use, or simply because they get dull. Again, be sure you have lots of blades on hand. Blades usually just break without causing problems, but I have had partially-cut inlays break when the blade broke. Once in a while a blade piece will fly when it breaks, hence the recommendation to wear goggles. Of course, you have been wearing a dust mask on your face (not on the top of your head) during the entire cutting process. The blade can also loosen somewhat during the cutting, which actually makes it easier to cut but it wanders aimlessly. Be alert for this and tighten as necessary. If this is a chronic problem, clean the blade attachment points or buy a better jeweler's saw frame. When the inlay is completely cut, carefully examine it for problems and then put it in the safe deposit box along with your figured pearl and family heirlooms.
As I said last time, do not rely on a file to smooth rough edges on your inlays. The pearl is quite hard and it is difficult to hold small, delicate inlays tightly enough to file without breaking. A small sanding wheel in a Dremel can be useful for some smoothing, but in general try to cut smooth lines with the jeweler's saw so that you don't have to try to improve the inlay after the cutting is finished. Also, do not attempt to inlay broken pieces, glued or not. Throw them away, save them for practice, whatever, but don't try to include them in a fine inlay job. If you proceed slowly and carefully, your skill will improve dramatically between the time you start and finish your first elaborate pattern, so much so that you will probably want to recut some pieces that are not on quality par with others. Rest assured that this skill will always improve, no matter how much experience you have, and you will become more critical of your own work as experience accumulates.
When you have cut all of the inlays, scrutinize them carefully-- compare and match paired patterns (such as opposite petals in the hearts and flowers pattern) so that the final product reflects care and attention to detail. Reject any inlays that are really clunky, but for a first attempt don't be too hard on yourself. However, the really meticulous (and irreversible) work is soon to begin. Don't commit substandard inlays to it, for once your patterns are inscribed in wood, it is difficult to change your plans.
Afterword: The above applies as well to other materials commonly used for inlay. These differ physically from pearl quite substantially, but none is especially difficult to cut. Wood veneer should preglued to a paper backing before it is cut. Bone for inlay should be at least .06" thick, which is somewhat thicker than most pearl slabs, because thinner bone is generally too translucent to make good, contrasting inlays. Sheet brass is fairly easy to cut, although somewhat harder on jeweler's blades than is pearl. The use of ivory is rightly controversial (although I'm not convinced that the lives of the oyster or the ebony tree are any less valuable than that of the elephant), but should you wish to inlay some old ivory, it cuts quite similarly to bone but is slightly less translucent. Old piano key tops are a common source of inlay ivory, but these tend to be quite fragile and are very translucent. Best to avoid ivory, but it is a lovely material.
Next: Routing and inlaying
This is Part III of the III-Part series on instrument inlay. Part I, a discussion of tools and materials, appeared in October, and Part II, an explanation of pearl-cutting technique, appeared at Thanksgiving. I will repost all three parts together in January.
As before, all standard disclaimers apply--to my knowledge, no company mentioned here has ever heard of me, and tools and materials are mentioned by brand name only when my experience indicates that few or no other alternatives exist, or I have insufficient experience with alternatives. Copyright rules remain in place: feel free to download the text for your own use, but please do not forward, crosspost, or otherwise distribute the text without permission.
Part III--Routing and inlaying
By now you should be finished cutting your chosen pearl pattern, and you are probably tired of repeated trips to the safe deposit box. Undoubtedly you have been staring at the Dremel Moto-Tool and the router base that you purchased after you read Part I and wondering what they do. Now you shall find out.
Go to your safe deposit box and retrieve your entire inlay set, and arrange it on the table in the proper orientation. With a pencil, label each inlay, and draw a small arrow that points toward the end of the peghead. The arrow is only necessary for those pieces that are part of a radially or bilaterally symmetrical arrangement with several identical pieces, such as petals of a flower. Once you have scribed and begun to cut the mortises, you must avoid confusion as to the precise location of each piece. From this point forward, you must not change your assigned positions--to do so will result in confusion, broken inlays, and problems during the final inlaying process. This is your last opportunity to recut any inlays that are not on quality par with the others, and to rearrange and rematch pieces to best advantage.
The next two steps are really the most critical in the entire inlay process. Up to now, if you broke an inlay or your pattern was uneven in quality, the problems were fixed easily by cutting new pieces. After you (temporarily) glue your inlays in place and scribe the patterns into wood, it will be tricky at best to replace any, so take special care not to break any or to change your mind about placement or replacement. Glue your inlays in place on the surface to be inlaid. In my experience, this is best done with DUCO cement, because this material can be dissolved away with acetone (Fire and toxic hazard! Use only in well-ventilated areas away from sparks and flames! Store safely!). "Spot" the glue lightly in several places on the bottom of the inlay, and press the pearl firmly in place on the surface. Script inlays (written text) are especially tricky and obviously fragile, and should be glued thoroughly on the bottom. Endeavor to clean up as much of the glue squeeze-out as possible while it is still soft. Double-check that all inlays are properly positioned (remember: guitars are inlaid on the 9th fret, banjos and mandolins on the 10th), and set the object aside for at least 24 hours. I used to use white glue instead of DUCO, but had problems removing the inlays--the only options are to pry up the inlays or soften the glue with water. The former can result too easily in broken inlays, and the latter tends to obscure the scribe lines, so I went to DUCO. Again, once your patterns are inscribed, it is highly desirable to use the same inlay that was inscribed, because it is impossible to cut another piece exactly like the original.
The next step, the most critically important in the entire process, is to inscribe the inlay outline into the wood. Use the scribe that we discussed in Part I, and trace around the pattern as close to the edge of the pearl as possible (which should be flush with the edge), but avoid undercutting the pearl, and most of all avoid pushing on the inlay itself with the side of the scribe. At best you could dislodge the pearl (this only happens, according to Mr. Murphy, to complex inlays and then only after the outline is about 50% but less than 75% inscribed), and at worst you could break the inlay--again, this is a calamity if you have already inscribed much of the outline. If your scribe encounters a mound of glue, scribe carefully over it several times until it separates from the inlay, then scribe the wood. The wood grain will tend to divert the scribe point, so be aware of grain direction changes (relative to the inlay). Ebony is so hard that it is best inscribed by making repeated passes. Be slow, be cautious, be meticulous, be a perfectionist. This is your only chance to do this step correctly, and the quality of your final product depends on the scribed line (and your ability to follow it with the Dremel). I have tried to deepen the scribed lines later, after the inlay is removed, but with very limited success. Even though the pearl is not supposed to be a "fence," its presence offers a much better visual limit than does the scribed line alone. Inspect each scribed line carefully and make certain that all are complete and deeply inscribed. With a glass eyedropper, dribble some acetone carefully around each inlay, but just do one or two at a time.
*BE EXTREMELY CAREFUL NOT TO ALLOW ACETONE TO CONTACT FINISH OR PLASTIC BINDINGS, AS IT WILL CORRODE THEM. ALSO, REMEMBER THE FIRE HAZARD! A NEARLY EMPTY CAN OF ACETONE IS A POTENTIAL BOMB! THE FUMES ARE TOXIC!*
After the acetone has contacted the inlay for a few minutes, gentle side pressure will usually dislodge it. Allow very delicate inlays to soak up the acetone for at least 30 minutes, and then use the gentlest side pressure distributed over the entire inlay to dislodge it. It will be almost the ultimate in disheartening feelings to break it now, exceeded only by breaking it later. After each inlay is dislodged, take a moment to clean the residual glue from the inlay bottom and crevices, and renew the label and arrow (the acetone may tend to disperse the pencil marks, and it will dissolve away virtually any ink). Arrange the pieces carefully because you don't want to make any fitting mistakes attributable to picking up the wrong piece during the routing process.
Now comes the three-step routing process, the most difficult part of inlay technique to do really well. You must wear goggles and a dust mask, you must keep a steady hand, you must STOP if you can't see clearly where you are cutting, you must cut very slowly, and you must keep the faith in your scribed lines, even though many times they don't seem to be correct. The first step is to cut the inlay outline deeply with the pointed dental bit (again, the pointed bits offered by Dremel tend to be too large, but they ?1;2cwill work for many larger inlays, as long as there aren't tight corners).
Use the Dremel freehand, not in the router base, and cut downward and sideways with the point of the bit from the line into the wood. Hold the drill like a pencil and use the lowest speed, but vary this to suit the hardness of the wood and the part of the outline you cutting. This is actually the most difficult of the three steps, and it must be done slowly. BE SURE TO CUT INSIDE THE LINE!! Only experience will help you improve, but this step will establish how "close" your inlays are, that is, how much filler space results. Try to cut 2-3 millimeters down into the wood. If you can't see your scribed line clearly, stop and rearrange the workpiece until you can. I use two or three 25-pound bags of #7 lead shot (available from shotgun reloading suppliers) to pad and support a typical neck. These give great flexibility on repositioning and do not dent or nick the wood. Cut completely around the inside of each scribed line, and examine each very critically to make sure they are of uniform depth and that the corners and tight curves are cut vertically and cleanly. When you are satisfied go back over the workpiece visually once again. I have never failed to find spots that needed work, even after two or three examinations.
Next, chuck the router bit (not the ball-end bit) into the Dremel, and mount the Dremel in the router base. Leave enough bit exposed so that it will cut a mortise to about 95% of the thickness of your inlays. To check, use scrap wood and adjust the bit depth so that one of your inlays protrudes just slightly above the mortise. If you are doing large inlays in a curved surface (D-45 hexagons in a guitar, for example), your mortises will be curved as well unless you shim the bottom of the router base with tape so that it rides perpendicular to the peak of the fingerboard. For these inlays, set the depth to 95-98% of the pearl thickness. Straight router bits function best at very high speed, so use the highest speed setting. Use the router bit to remove as much of the inlay mortise wood as possible, but be careful not to encroach the edge, because this bit will cut really fast and do terrible, irreparable damage if it is not controlled very carefully. As before, if you can't see very clearly, STOP and rearrange the workpiece so that you can. Cut out all of the mortises and then examine them critically. Do not yet attempt to fit the inlays, because the mortises are not quite ready, and you may break an inlay if it binds in a mortise.
Now chuck the tiny ball-end bit into the Dremel (leave it in the router base) and set the bit depth so that the ball cuts flush with the bottom of the routed mortise. However, if with this setup the top of the ball is flush or within 1mm with/of the wood surface, the bit must be set deeper because otherwise it will greatly enlarge your mortises. You are going to undercut the edges of the mortises, and if the ball is too close to or at the surface it will overcut them too. Ideally, the ball diameter should exceed the shank diameter somewhat, and should never be smaller than the shank--the shank rubs against the wood "fence" (the edge that you established with the pointed bit) and thus keeps the ball from undercutting too deeply, but it must undercut a little or the inlay may bind when it is inserted. Use a low or medium-low speed and go around the edges of your mortises very slowly and carefully with the ball. Be very aware of the mortise limits, and do not exert any pressure against the wall of the mortise with the bit shank. Otherwise the spinning shank will tend to erode the wood and enlarge the mortise, and unfortunately you will be unable to see this because your scribed lines are gone. Tight corners and narrow curves may not admit the bit shank, and so these will be unreachable with the ball. Use the pointed bit freehand again to undercut these. When this job is complete, inspect each mortise carefully and recut any questionable spots. It is not unusual to spend hours with each large mortise (and sometimes with small ones as well)--be prepared to devote lots of time to a large inlay project.
Now remove the Dremel from the router base and chuck the pointed bit, and begin fitting the pearl inlays in their mortises. Once again examine each mortise for any rough edges or uneven lines, and smooth them carefully with the pointed bit. Gently press the inlay into place. If it won't go in easily, stop and find out why. Some inlays go a short distance and bind, and then yield to slightly greater pressure and slip in to full depth. This is undesirable-- remove the inlay, find out where it is binding, and smooth the edge. If you don't, even slight expansion of the wood during seasonal changes may crack the inlay. Tight spots are usually visible after the inlay is removed because the pearl leaves a white mark. Examine such spots carefully and decide how deeply to cut-- this is the place where all of your careful early work can be compromised by impatience, so use good judgement about enlarging the mortise. Remember that you followed the scribed line accurately (you did, didn't you?), so any binding has to be the result of little ridges and bumps on the mortise edge between the top of the ball-cut and the surface of the wood. Look carefully for these and smooth them a little, then try to fit the inlay again. I have modified a discarded dental "elevator" into a tiny chisel for cleaning out areas that will not admit even the tiniest of dental bits. I don't need it very often, but when I do nothing else seems to work. It is relatively rare for any inlay to fit perfectly on the first try, but it will become more common as your skill and experience accumulates. Now and again a delicate inlay (especially script) will become wedged in the mortise so that it is very difficult to remove. You must resist the temptation to 1) pry it out other than extremely gently; 2) leave it in place and attempt to pack filler around it. Work very carefully with toothpicks around the edges, and lift it out. It will come, but if you don't work carefully it will break. Then find out where it is binding and smooth the edge.
Once all of the inlays are fitted they can be glued into place, and any gaps between the pearl and the mortise edge filled at the same time. The process is simple: fill the mortise with a glue/filler, press the inlay into place, level it, allow the filler to set up, and file, scrape, and sand the inlay flush. The standard glue/filler has been epoxy with dust from the same type of wood mixed in for color and texture. This works well with ebony, but less so with rosewood--finely-divided rosewood dust mixed with epoxy is usually much darker and greener than solid rosewood. Some artisans use tinting colors, such as are used to tint house paint, with some success for rosewood, but I have yet to see a perfect match for rosewood with any coloring system. I just use rosewood dust and try to keep the mortises as close as possible.
My pearl inlay mentor experimented during the 1960's with various epoxy brands (five-minute epoxies were unavailable at the time, so he worked with overnight-cure material) to find those that set up hard (without a tacky surface) and that crept minimally--epoxies are technically fluids even when set, and tend to flow just like water, except much slower. Really creepy epoxies soon leave gaps and pits in the fill space, and a superior inlay job can end up looking very inferior. My mentor selected Wilhold epoxy (standard disclaimers, remember?), and I followed his advice with good results. Unfortunately, lately I have been unable to find the correct material--a long-setting yellowish two-part adhesive. I know that many are using five-minute epoxy, and I guess this is all right except that one must mix several batches in the course of an inlay job, and many of these preparations never lose a slight tack. I think the best material is the light-colored long-set material, and recommend that you find and use it if at all possible. Whatever epoxy you use, be sure to mix dead-equal quantities of resin and catalyst, as a mixture of unequal quantities (particularly an excess of resin) tends to creep. I make up the mixture, stir carefully to ensure uniformity, and mix with just enough wood dust to yield a fluid mixture of the correct color. In my experience, the best dust is produced by filing wood with a metal file, as other dust may be too coarse or may be mixed with "impurities" (sandpaper abrasives, etc).
If you are using long-set epoxy, you can fill all of the inlay mortises to about 3/4 depth with the epoxy filler. If you are using five-minute material, only fill one or two large mortises at a time. I emphasize this--if your epoxy sets up before you embed the inlay, you will have to re-rout the mortise. After the requisite number of mortises is filled, press each inlay into place, and level it by rocking gently with a couple of toothpicks or thin dowels. Another advantage of long-set epoxy is that there is time to self-level prior to embedding the inlay. Embed all of the inlays and double-check each to make certain that they are seated to full depth and that filler has oozed all around. Be especially careful that none are tilted. In the past I have applied heat from a high-intensity reading lamp to each inlay-filler to increase fluidity and allow bubbles to escape, but this practice is now discouraged because it has been shown that most epoxies liberate toxic gases such as phosgene when heated. This practice also accelerates the cure, so that long-set epoxy when heated may harden in just a few minutes. In any case, allow the epoxy to harden completely before proceeding.
The final steps are to clean up the excess filler and level the inlays with the surrounding wood. I use a cabinet scraper (sorry I forgot to mention this in Part I), a double-cut mill file (ditto), and a hard rubber sanding block with various grits from 80 (pretty coarse) through 600 (pretty fine). Start with the (dull) scraper and shave away the epoxy from around and on top of the inlay. Be very careful in this and the following steps not to gouge or otherwise damage the surrounding wood. Continue to shave until most of the epoxy is gone. A coarse file can take the process a step further and begin to level the inlays with the wood, but again please be careful not to dig into the wood. Finally, use the sanding block alternately with the scraper on each inlay (avoid the surrounding wood, because it is much softer than the inlay and will erode at a much higher rate--this will result in high and low spots). Change to 120 grit after the inlays are completely leveled and flush with the wood, and sand carefully to remove the 80-grit scratches. I emphasize--use a sanding block, or at least use cork- backed sandpaper... ...do not use your fingers as a sanding pad for this or any other operation in lutherie. If large bubble holes show up in the filler, take an extra day to fill them and to cure the new epoxy, then level with the sanding block and scraper. After the 80-grit scratches are gone, move on in turn through 220, 320, 400, and 600 grits (all used dry). Sand the entire fingerboard with all of the grits from 220 and finer. By the time you get to 600, the inlays should be free of visible scratches and they should look pretty good against the dark wood. You should be beaming with pride....
Carefully clean out the fret slots with an X-Acto knife and #11 blades, and with a vacuum cleaner hose before you attempt to install frets.
I don't oil fingerboards, other than to allow skin oils to put the characteristic patina in the board with time and playing. I have found that a final vigorous polish with a cloth diaper or dish towel does at least as nice a job as oil on the board and inlays, and doesn't add any chemicals to the wood, so I recommend that over any oil, plant-derived or not. If your pattern involves engraving, now is the time--this is beyond the scope of this discussion, as it is one of those processes that is technically easy but takes vast experience to even begin to master. Buy some gravers, draw some lines on the inlays, follow the lines with the graver(s), use jeweler's wax or the epoxy-ebony dust mixture to darken the lines. Just keep doing that until you're good at it.
Dot inlays: Purchase the correct dots, purchase a matching (preferably brad-point) drill bit, purchase a drill press. Do not attempt this with a hand drill. Drill the holes to nearly full depth, press each dot into place, put a drop of cyanoacrylate glue (Crazy-Glue or similar) around the edge of the inlay, let it set up, sand off the glue and polish as above. And while on the subject, some of the old Gibson Mastertone patterns use small dots in floral array--buy these, don't try to cut them with the jeweler's saw.
I'd be interested in hearing what others are using for inlay filler these days, as the good epoxies are ever scarcer. Your input on or off the newsgroup is most welcome. Again, my thanks for the positive feedback from earlier parts, and I hope you have found this segment worthwhile as well. If interest abounds, I'll write about other lutherie operations as the time and my experience allows.