I have just finished a new project to build a small steel string guitar (Parlor guitar). This is mainly because I hadn’t built a steel string before and also because I have a friend who may be interested.
I looked at a variety of commercial designs and listened to lots of demos before arriving at an outline specification. The main thing that appears to affect tone quality is scale length so I chose towards the longer end of the spectrum whilst keeping the 12th fret at the body for a compact design. Body shape was arrived at using a parametric drawing package (solvespace) until I got something that looked right and was neither too large nor too small.
|Fret# at body||12|
|Sound hole dia||98mm|
|Sound hole centre from heel||179mm|
|Fingerboard width at nut||46mm|
|Fingerboard width at 12th fret||55.4mm|
|String width at bridge||54mm|
|Neck thickness at nut||21mm|
|Neck thickness at heel||25mm|
|Top radius||25 ‘|
|Back thickness||2.5mm nominal|
|Back and sides||Indian rosewood|
|Neck||Mahogany with centre maple splice|
|Top bracing (X style)||Spruce|
|Bridge||Rosewood. Ebony pins with abalone dots|
|Sound hole||Abalone ring|
|Back centre strip||Maple bounded by abalone & purfling|
|Neck centre strip||Maple bounded by 0.6mm black|
|Headstock||Ebony facing with inlaid crossbow|
|Pick guard||Tortoise shell pattern|
|Tuners||Gotoh 510 18:1|
|Nut & saddle||Bone|
|Strings||D’Addario EXP17 (XT 56-13)|
The drawings as pdfs are here:
- Parlor p01 headstock (two alternatives – I used the curvy/pointed one)
- Parlor P01 body template
- Parlor P01 sideview
- Parlor P01 purfling
- Parlor bridge P01
I started by cutting a body template from 4mm clear polystyrene sheet which I finished on the vertical oscillating sander and then drilled to show positions of the sound hole and braces.
I decided to build a body form with expanding clamps inside to hold the sides built up from several (4) layers of 12mm plywood. I rough cut a template on the bandsaw and finished on the vertical oscillating sander. Then I used this piece with a router follower cutter to make the other 7 pieces which were then glued together, finished on the vertical sander and sealed.
Finally I drilled dowel holes between the two mating halves and tied it all together with some latch style toggle fasteners. To increase the stiffness I epoxied in a length of carbon fibre rod to a routed out slot on each long edge.
I then marked out the inner cauls and built them in a similar way, facing them with 3mm cork and connecting to some turnbuckles to make expanding clamps.
Side bending jig
I already have a jig for sidebending from making classical guitars so all I needed to do was build the body mould part for the new design. I cut out the two sides from 12mm plywood and connected these with 10 lengths of 15mm aluminium tubing glued into mating holes with epoxy.
Neck joint dovetail jig
After reviewing commercially available jigs I decided to design my own 2 part jig:
- a lower part for securing a guitar body (or neck) at a controllable angle so that this could be worked on separately for example when working on the end splice.
- The dovetail template table that can be slotted onto and then bolted to the lower part ready for cutting the dovetail male and female halves
The design drawings are here:
I had the template plates for making the dovetails with a dovetail follower router bit laser cut from 6mm acrylic based on this design:
I decided to make the top slightly domed at the lower bout and so built a solera from 25mm plywood that I built up with basswood on the lower bout and then shaped to give me a 25′ radius concavity. I also domed the top bout slightly to give me 0.8mm of dome at the top of the sound hole to match the designed angle on the fingerboard.
Building the guitar
First I thicknessed the sides (indian rosewood) to 2.2mm on the drum sander. Then I used my old bending jig with a thermostatically controlled heated silicon blanket at 120C to bend each one after moistening and wrapping in greaseproof paper.
After bending I cut to length and marked and cut the side profile with a saw before clamping into the body form.
I then cut and shaped the top and bottom blocks and glued into place.
Next I trued up the edges of the top and bottom edges of the sides by using 2 large radiused sanding blocks until the desired side depth had been reached at the two end blocks.
For the linings I used the bandsaw and drum sander to make mahogany strips for laminating before glueing and clamping (with string) to a former made of 18mm mdf.
Once dry I shaped the linings on my router table (laminate trimmer mounted upside down on a plywood base board) before gluing into place onto the sides. Once dry the excess linings were planed flush with the sides and then finished with the radiused sanding blocks.
I then removed the inside clamps in order to clean up the insides with scrapers before sealing with shellac.
I temporarily removed from the side mold in order to cut the V-shaped slot for the back strip which I made from 2 pieces of maple binding. This will be fitted after I have attached the bindings.
I first planed the edges of the book matched pieces of spruce for the top to give a perfect fit and glued up before using the drum sander to a graduated thickness of 2.0-2.2mm.
Then I fixed to a workboard and used the router to cut a 1.8mm groove in the top to take the abalone pieces that make up the rosette ring. This was first sealed with shellac to prevent the super-glue from discoloring the top. Once the abalone was in I secured with thin super-glue before routing a 1.2mm channel either side to take two strips of 0.3mm black veneer sandwiching a 0.6mm strip of maple which were then fixed with thin super glue.
Finally This was planed and sanded flat before routing out the sound hole.
The top could then be turned over and taped to the solera ready for fitting the braces and the 3mm maple bridge patch after marking their positions from the template made earlier.
Once fixed in place I scalloped the braces to give a basic profile before making some frequency measurements and comparing with the back.
The book-matched indian rosewood was first planed to give a perfect fit before gluing together and thicknessing to 2.5mm on the drum sander. I routed a 6mm channel (using a guide-rail with my laminate router) to take the maple centre strip which was glued in place and sanded flush before routing 2.6mm channels either side to take the abalone strips and purfling. Once dry this was flattened on the drum sander before turning the back over and taping to my back building board which has a 15′ radius on it to match the desired dishing on the back.
First I made up the mahogany cross grained banding strip 3mm thick and glued in place. Once dry this was sanded to it’s final rounded profile using a profiled sanding block. Then I shaped the cross braces on a profiled sanding block to give a matching 15′ radius and planed/sanded them to their pointed profile before gluing in place. Once dry these were scalloped using a chisel before making some resonant frequency measurements and comparing with the top plate. Once adjusted the back was cleaned up with scrapers and the label attached.
Tuning the plates
I used the same setup I have used for Cellos and violins but the process did not seem so clear to me as there were so many resonant frequencies and the back mostly resonated in bar modes with lateral node lines. In the end I thinned the top braces to the point where there seemed to be plenty of free resonances in the top.
I ended up with these resonant frequencies:
Back: 102Hz (G2), 199Hz (G3), 269Hz (C4), 302Hz (D4 and also tap tone)
Front: 143Hz (C#3), 183Hz (F3 and also tap tone), 231Hz (A3)
Assembling the box
I started by fixing the top to the sides whilst the sides were still contained in the side mold. I marked the position of the X-braces on the linings and cut recesses in the linings to match. Once it was all fitting snugly I glued and clamped it up.
Before fitting the back I cleaned up the glue joints on the top and gave the inside of the top a coat of shellac. Then I removed the side moulds and marked the position of the back cross braces on the sides and notched out recesses in the linings to match. Again, once it was all fitting snugly it was glued and clamped up.
Purfling and banding
I used my laminate trimmer on my purfling cutting jig with a 3mm down-cut router bit to cut first the banding and then the purfling channels. As I am using abalone in the purfling I first sourced some 2mm PTFE sheet and band sawed into 2mm high strips that could be sandwiched between the black/white purfling strips. This sandwich was first glued into the purling channel fastening with masking tape before bending the banding strips to shape and gluing into the banding channel again fastening with masking tape.
When dry, the PTFE strips were extracted and then the abalone strip (actually lots of short pieces on a very thin plastic backing strip) pressed down into the open channel left by the PTFE before flooding with thin super glue and leaving to dry. The last stage was to plane and scrape everything flush.
I started by truing up the mahogany blank before slicing in half and fitting in a centre maple splice (made from a used cello neck blank) sandwiched between two pieces of black veneer.
Then I tapered the blank on the drum sander before cutting the neck lap joint and gluing back together. Finally I added a few short pieces that will form the heel.
Next I routed a 7/32″ groove down the centre of the neck ready to take the double neck truss rod and opened the slot with files until the truss rod was a nice tight fit.
The Neck dovetail
This joint had been worrying me for sometime but I finally took the plunge. I started by ensuring the top end of the guitar was totally flat and square before cutting the dovetail mortise on the jig I had built.
I then rough cut the neck profile on the bandsaw before routing out the dovetail neck tenon on the jig I had built earlier. Then I put the body upside down on the jig to set the neck angle so that the neck projection gave me about 2.4mm clearance at the bridge position. With the angle set I proceeded to carefully cut the neck dovetail tenon so that the fingerboard was still a bit proud of the body. I then used files and chalk to fettle the joint until it was a snug fit with the fingerboard flush with the body.
Next I glued on the headpiece laminations with suitable cauls.
Once dry I marked out the headstock shape and rough cut on the bandsaw before using the laminate router and a fingerboard template made from perspex to get the final shape and as a guide for drilling the tuner holes with the pillar drill. Then I moved onto routing out the headstock decorations and rough carving the heel.
I started with a nice ebony blank that I first thicknessed to a little over 6mm on the drum sander and planed square ready for marking and cutting the frets for the 635mm scale length. The frets were cut by hand on my fret cutting jig before bandsawing the rough shape and then using the laminate router with a perspex fingerboard template I made which was also drilled for the locating dowels.
I used the same template to mark out and drill the neck before rough fitting the neck assembly to the body to check what material needed removing from the underside of the fingerboard over the guitar body. Once I had scraped that area to give a good fit I glued the fingerboard in place on the neck. When dry I used the laminate router with a follower bit to trim the neck flush with the fingerboard and finished carving the heel and headstock. The last job on the heel was to fit a rosewood heel cap.
Then I used a concave sanding block with a 16″ radius to give the correct profile on the face of the fingerboard and marked and drilled the 6mm holes for the fingerboard dots which I each secured with a drop of superglue leaving them slightly proud ready for cutting back flush.
Then I re-cut the fret slots to the proper depth, used a V-file to open up the top of the slots and then fitted the frets with a touch of Titebond. Once fitted, I trimmed them, filed the edges at a chamfer and filled the exposed slots with hot black shellac before final sanding and french polishing the neck and linseed oiling the fingerboard.
Finally I glued the neck assembly to the body with Titebond.
I cut the bridge from a rosewood blank to my own design with bandsaw and files. I designed it to take a 3.2mm saddle with a Fishman undersaddle pickup (PRO-AG1-125). The bridge pins are set back about 13mm and kept parallel with the saddle for consistent pressure on the saddle/pickup with an approx 20 degree string break over the saddle. The top of the saddle was radiused to match the fingerboard. I discovered that there are 2 standard sizes of bridge pins with a 5 degree taper (Martin) and a 3 degree taper. The reamers I used for violin pegs have a 1:30 taper which is about 1.9 degrees. Sods law had it that the bridge pins with abalone tops I had sourced from Planet Waves had a 3 degree taper while the chinese reamer I had bought was of course 5 degrees so I had to order a new one. Unbelievably I couldn’t find any in the UK and had to order one from the USA! – such is the state of UK industry!
Once shaped I sanded the underside concave to match the 25′ radius of the top before giving a couple of coats of finishing oil and polishing with fine wire wool. I positioned the finished bridge carefully on the top using a template and marked the position with masking tape before scraping away the finish to give a gluing surface. Then I glued up using special bridge clamps and a made up caul ti fit under the bridge plate inside the guitar.
To mark the position of the saddle correctly I made up an intonator jig (copied from the StewMac design) using rosewood and 2mm brass rod with 3mm and 4mm tubing sleeves that would allow me to record the correct saddle position on each string on a fully strung up instrument.
I also built an adjustable jig that could be clamped to the guitar top to guide the router and cut the saddle slot.
Before stringing up I levelled and polished the frets using diamond fret files and emery paper. The instrument was then strung up using 13-56 phosphor bronze strings from D’Addario (EXP 17 which have been discontinued but you can get the same now called XT 13-56) using the intonator jig and once adjusted for tuning I marked the position saddle position for each string before carefully cutting the saddle slot with a router and the saddle slot cutting jig shown above and then cutting a 1/8″ bone saddle blank with the correct string positions. I then drilled a small hole at one end of the saddle slot to take the Fishman under-saddle pickup (PRO-AG1-125) wire and once fitted I soldered up the jack socket and fitted to the hole drilled in the bottom block and used a clip stuck to the linings to stop the wire flapping round inside the guitar. The neck relief was set to 0.25mm at the 6th fret and the action at the 12th fret to about 1.5mm (top) and 2mm (bottom).
The finished instrument weighs 1.8kg, has a big tight sound for such a small body, has great sustain, is very well balanced and easy to play and also works very well with an amp. The friend who had first refusal is absolutely delighted with it and is selling his Martin HD28 to make way for his new acquisition!