Proper set-up is essential to get the optimum tone from a resonator guitar. The interaction between soundwell, cone, spider bridge and saddle are very important. Use a fresh set of strings when setting up the instrument. You may want to consider one of the many replacement cones that are currently available, if the existing cone is damaged. The following set-up procedures will improve the tone and playability.
Fitting a Dobro-style cone
After disassembling the instrument, inspect the soundwell for any delaminations may need to be re-glued. Check the top ledge of the soundwell (where the cone rests) for lacquer drips or glue residue that may keep the cone from seating. These can be removed with a scraper blade, chisel, or even a single-edge razor blade, leaving a smooth, flat surface for the cone. The cone should make good contact with the soundwell around the whole circumference.
To fit the cone, place it in the well (thread the spider tension screw into the cone-it makes a good handle during the fitting process) and using your finger, lightly tap around the outer bead while applying light pressure in the center of the cone.
There will be a difference in the sound of the tap where the cone is firmly seated compared to where there are gaps. Rotate the cone until you find the position with the best contact. Make a small mark on the edge of the cone, pointing toward the tailpiece for reference. If the lip of the cone is deformed, it can be bent or smoothed out for better contact.
NOTE: Never glue, tack, or in any way attach the cone to the soundwell. Proper installation allows the cone to "float" on the soundwell. Attaching the cone to the soundwell will severely degrade the tone and response of the instrument.
Truing the spider
The legs of the spider bridge must contact the surface of the cone with equal pressure. Place the spider on a flat surface, such as the table of a drill press or table saw, and tap the tips of the legs. Ideally the spider will only contact the surface at the tips of the spider's legs. If the spider rocks back and forth or the ends of the legs do not touch the surface, they will need to be gently bent into place.
To adjust the spider, place a thin wooden shim (1/16" to 3/32") under the high leg (at the intersection of the leg and the outer ring), hold the center of the spider down, and tap the tip of the leg lightly with a small mallet. Check your progress frequently. The spider bridge is made of cast aluminum, which may break if excessive force is used. When the legs of the spider are uniform, level the tips by moving the spider back and forth over a sheet of 320-grit sandpaper on a flat surface. Be sure the surface is flat.
The saddle for a spider bridge is typically made of thin, quartersawn maple (endgrain is parallel to the strings), although some builders prefer maple with an ebony cap, similar to a banjo bridge. The thickness will vary depending on the slot in the spider bridge. The saddle should be a snug press fit but not so tight that wood is shaved from the saddle as it is pressed into the spider.
Standard string spacing at the saddle for resonator guitars is 2-1/4". Dividing that spacing by 5 gives a string-to-string spacing of .450". Measure .225" from the center of the tension screw to get the spacing for the two middle strings. Space the remaining strings .450" from these. Mark the locations of the string slots and proceed to the next step.
Loading the cone
Attach the spider bridge to the cone and tighten the tension screw a half-turn after it makes contact. Tighten or loosen to produce the best tone when set-up is completed. The saddle should be as high as possible to "load the cone" for maximum volume. Trim the saddle so the strings touch the bottom of the coverplate when there is no tension on the strings. Once tuned to pitch, the saddle will pull down to the proper height. Some coverplates have a lip on the underside of the armrest around the access hole for the adjustment screw. This will prevent the saddle from touching the underside for set-up. It can be peened or flattened with a hammer and ball bearing slightly larger than the hole. The saddle height for proper cone loading will vary for different instruments.
When the strings are installed, the coverplate can be moved temporarily (with strings loose) while small adjustments are made to the saddle height. Expect much trimming and testing here, but the results will be worth it. When the saddle is at its proper height, each slot should be just deep enough so that half the diameter of the string rests in the slot. Take measurements of the completed saddle to make a spare one.
For slide instruments, string height at the nut is typically 3/8" from the fretboard. If the height is too low the steel will hit the fingerboard during hammer-ons. A nut that is too tall will make the action stiff. The string spacing at the nut will depend on the width of the neck and the preference of the player. If the instrument is to be played fretted, the nut will be shaped and slotted the same as a typical acoustic guitar.
Make sure the string slots are not too deep. Typically half of a wound string's diameter protrudes from the slot, while the plain strings' slots are the same depth as each string's diameter. On slide guitars, the tops of the strings should all be the same height above the fretboard, so the bar will not hang up when moving across the strings.
For fretted instruments, the string height will be determined by the string gauge, and by player preference. Typically, the bottom of the string will be .005"-.020" above the first fret. Plain strings will be closer than wound strings. We offer our #4596 Extension Nut, which allows a fretted guitar to be quickly converted for slide playing. Simply loosen the strings, slide the Extension Nut over the top of the string nut, and retune.
Check for rattles and buzzes
When set-up is complete, check all of the coverplate, tailpiece, and tuner mounting screws to make sure they are snug. Don't overtighten, or you may strip the wood out. Many pros will actually start the screw backwards with a small screwdriver (don't use a screw-gun or drill-you may strip the holes) and feel when the screw drops into the threads, just like finding the threads for a fine machine screw or bolt. This insures that the screw is using the original threads, and doesn't cross-thread the wood.
If you find any screw holes that are stripped, dip the end of a round toothpick into some wood glue and insert it into the screw hole. After the glue dries, carefully cut the toothpick flush with the top of the instrument. Re-drill the hole to the correct size for the screw and reinstall the component.
It may be necessary to put a small piece of foam rubber under the tailpiece if it rattles against the coverplate. If you hear a rattling in the cone, it could be caused by a loose spider bridge tension screw. Tighten the screw until you feel it contact the spider, then give it 1/4 to 1/2 turn. Experiment with the tension of this screw after you have completed the set-up procedure. You shouldn't tighten the screw more than one turn.
If the nut and saddle slots are too large, the strings will sustain poorly, and may even buzz or rattle in their slots.
It's also recommended to use a piece of felt or the softer loop material from hook and loop (Velcro) self-stick tape under the tailpiece where the strings' ball-ends will rest. This eliminates string rattling at the tailpiece.
National guitars and biscuit bridges
Much of the set-up of a National or biscuit-bridge guitar is the same as a Dobro-style spider-bridge instrument. A biscuit-bridge is a little easier since it doesn't need the tweaking a spider-bridge requires.
Be sure the cone seats correctly in the soundwell and that the soundwell is clean and level (refer to "Fitting the Cone" above). The ridge of the cone that contacts the underside of the biscuit must be flat. Place a piece of 180-grit sandpaper on a flat surface and level the bottom of the biscuit.
The saddle on the biscuit should be slotted and shaped in the same manner as a spider-bridge saddle. If the slots in the biscuit are too deep or wide, carefully remove the saddle from the biscuit and make a new saddle. If the saddle cannot be removed (it's usually glued into a slot in the biscuit and then the assembly is painted black), purchase a new #4330 biscuit, or make a new one from hard maple.
Once you have trued the cone, biscuit seat, and biscuit, attach the biscuit to the cone using the small wood screw. Some pros attach the biscuit to the cone with a thin bead of glue.
Check out StewMac's selection of pickups for resonator guitars.