Tuesday, May 27, 2014

Attach the top to neck

 Before I attach the sound board to the neck, I pre-shape the heel so I don't have to worry about damaging the sides or sound board once everything is assembled.

Once the heel is shaped, I cut the top portion of the sound board that will meet the neck.

To ensure alignment, I draw a center line down both the neck and sound board, the dry fit the two together and tac two small nails to mark my position.
 The two nails prevent the sound board from shifting out of alignment when I glue the pieces together.
 Clamp it up......
 Make sure I am centered..... Done.
 Next, I glue the tail block to the sound baord. 

Here's a pic of the tenor 'ukulele in progress as well, note the similarities :-)

Next up..... Attach the sides to the sound board and neck......

Tenor Guitar Fret Board

 This tenor guitar has a 23" scale length.

To determine the spacing between the frets and from the nut to each fret bar you have to do some math.

Who doesn't love a good math equation =)

The magic number to figure this out was derived from the Greek Philosopher/Mathematician Pythagoras and refined over the years to 17.817.

A good article to read about calculating fret positions can be found here. If you want to totally geek out, click here.

To find the fret spacing on any stringed instrument, you divide your scale length by this magic number to get your first fret position from the nut.

Next, subtract your first fret position from the nut from the total scale length, then divide by the magic number, 17.817.

Repeat until you reach the total number of frets you plan to cut. I used Excel to create this sheet and a conversion chart of decimal inches to find the closest fractional inch.

The first fret should be 1-9/32" from the base of the nut slot, the 12th fret should be at 11-1/2", and the 14th fret should be at 12-3/4".....

Side note: When I checked where the neck meets the body I noticed my drawing was 3/8" off, so I'll have to redraw my plans for my next tenor guitar build.

Once I drew all the lines with a straight edge and 90° square, I made a few photo copies at a local drafting shop and cut out my fret board template.

Prefab 23" fret board templates can be found at Stew Mac or LMII, but I chose to do it from scratch so I could, theoretically, reproduce any scale length going forward.

I cut out a little over 2" wide plexiglass and taped my template over the top and used scarp pieces of wood on the top and bottom so I could clamp to my work surface.
I notched the plexiglass with a hack saw and another small scrap piece to line up with my fret line. I tried to line up the saw blade with the middle of my line as close as possible.

Note: I had to re-cut this template because I cut the middle of the nut line at the top of the fret board instead of using the inner most width of nut line as the end point.

If I didn't re-cut the nut line to make a new template, I would have been 1/64th off at the 1st fret, then it would've thrown out the spacing and, most likely, the intonation across my entire fret board :(

Using a cross cut jig with a razor blade as my marker, I methodically slotted a couple fret boards using the Stew Mac fret table saw blade.
Next up..... attach top and neck...

Friday, May 23, 2014

Tenor Guitar Neck

 As mentioned earlier, this tenor guitar will have a Spanish neck joint to the body. This means that the sides will be tucked into heel slots on the side of the neck where it joins with the body of the guitar.

Read more about neck construction here.
These heel slots are cut 12-3/4" from the nut, 90° to the center line of the neck and 11/16" deep. I am left with about a 9/16" of wood in the middle of the neck.

The truss rod is 7/16" thick, so there isn't much room for error..... This is probably why a different neck joint is used with truss rods....

 The truss rod will be accessible from the sound hole for future adjustments.

Since this is a Spanish heel joint, there will be a shelf on the end of this neck block the thickness of the soundboard.

I will have to rout my truss rod channel deep enough so the soundboard will lay flat to the neck when I attach both of them together. 

This is probably another reason why other neck joints are done with truss rods.

Using a router table and a test piece, I rout a shallow channel to check for depth and alignment.

I used a 3/8" straight bit to rout the 7/16" wide channel in successive passes till I reached my desired depth. 

 Once the channel was cut, i chiseled out the shelf for my soundbaord.....
 Check if it is level....
 Drop in the truss rod and dry fit all pieces....
 Now that I have a shelf on my neck I have a gap over the truss rod to cover down the middle of the neck.

Good thing I didn't burn all my scrap wood....
note the end of my scrap wood is charred.
 Plain it to thickness....
 ....and width.....
 Check for accuracy....
 All good....

 Trim off the end...
Next, I use a heel nibbler on my table saw to rough cut the heel.... huge time saver... Thanks Hana Lima 'Ia!

 Once the heel is roughed out, I epoxied the truss rod into the channel, then glued the scrap piece in to cover the truss rod.

This should prevent any glue squeeze out that can ruin the truss rod function.
(Note to self: Next time don't use a plastic container with epoxy. I think my tray started to melt or something... the smell was kind of nauseating.)

Next up.... Fret board........

Tenor Guitar and 'Ukulele Necks

I built 2 tenor guitar necks with the same process as I use for tenor 'ukuleles that have a Spanish Heel joint to the body.

This is not a typical construction method that I have found online, so I am kinda hoping for the best. The tenor guitar necks will also have a one-way truss rod installed for future neck adjustments.

*** Note about neck joints....... on steel string instruments, the most common neck joint to the body would be either a dovetail, mortise and tenon or bolt-on attachment.

The Spanish heel joint is commonly found on classical guitars with nylon strings, hence, my "hoping for the best" result.

I chose this method because this is the only method I have used in the past....  The third tenor guitar I build will have a dovetail joint.
 First, I cut my stock into the following pieces;
1) Main neck
2) 2 Heel blocks that measure in hieght-3"
3) Tail block
4) 2 ears for the headstock

Using a neck scarf joint jig, I cut the main neck block at a 15° angle.
 Making sure the joint is tight I sanded the scarf joint flat.
Glued the scarf joint then the heels blocks together.

Here are the three rough shaped necks side by side.

From top to bottom
1) Philippine Mahogany
2) African Mahogany
3) African Mahogany

Tuesday, May 20, 2014

Tenor Guitar - Bending the sides

 Here I am prepping the side by pre-cutting to my final dimensions, at the head is 3" and the tail is 3-3/4". Also note the waist line about 9-1/4" from the head. Total length is about 23-1/2"
Using a taper jig on a table saw with auxiliary tabletop.
Here is the finished side molding jig with all-thread and star knobs.
Before the bending starts, I layout all my materials and open the side molding jig so I don't have to rush when I transfer the bent side from one jig to the next.

1) Side Bending Jig
2) Side Molding Jig
3) Heat Blanket
4) Water Bottle
5) Clamps

1) Plug in the heat blanket. (wait 5 minutes or so)
2) Spray some water on the blanket to see if it starts to steam.
3) Spray water on both front and back of the side piece you about to bend, then line up waist line to the middle of the waist on the side bending jig.
4) Sandwich the second mesh piece on top of the side piece and the heat blanket on the jig.
5) Turn the waist clamps down slowly.....
6) Once the waist is all the way down, bend the tail end, then head.
*** This is a fickle process that I do not rush or force the side to bend too quickly. The worst sound you can hear is cracking......
 7) Once all the clamps are secured, turn off the heat blanket and wait about 5-10 minutes.

8) Release the clamps and transfer to the side molding jig.
9) Cut the side to the center line on the side molding jig.

Repeat process for the other side.........

 Once both sides are bent and cut and in the jig, secure with clamps....

Next up..... The Neck...............