Day 6: Filling Tuner Screw Holes

A few years ago we acquired a Grizzly "Wood Mill" and it has proven to be a valuable tool for guitar repair. Here I have the peghead clamped in the milling vise, and I can mill off the protruding mahogany plugs to within about .010" of the finished surface with ease and security:

I'll trim them the rest of the way with this fine little Japanese single bevel knife:


The back side of the knife is ground and polished very flat so it can skate along on the flat finished surface and slice off anything that sticks up - in this case, the remaining bits of the mahogany plugs:


It's delicate work, requiring a firm hand, strong pressure, and thanks to the flat surfaces, good control.



Hey everbody, come have a nice drink of fresh hot hide glue!

While there are only six extra tuner mounting holes, some of the originals are enlarged or stripped, so I figure on filling all the screw holes to get the best results when I mount the new tuners.

While there are only six extra tuner mounting holes, some of the originals are enlarged or stripped, so I figure on filling all the screw holes to get the best results when I mount the new tuners. You don't have to look closely to see that I've made mahogany pegs to fill the holes, and that I'm hammering them right in:

Square pegs in round holes?

Well yes, and I guess it's time for another little side trip:

Some 25 years ago I was visiting my old college roomie, Gary Stanton, who lived and studied in Bloomington, Indiana. He's a folklorist, and at the time, was involved in early local achitecture. He took me on a trip around the county and we stopped at an old house that was being systematically dismanted and studied. It was down to the framing - all hardwood with mortised and pegged joints.

When I remarked that the pegs were square an that it must have been terribly inefficient for the builders to make square holes for all those joints, he said that wasn't the way it worked. Turns out that if you drill a round hole in wood and hammer in a square peg, the corners of the peg really bite into the wood, making for solid construction that's less likely to come apart with time and shrinkage of the wood.

So I figure if it's good enough for those old houses, maybe it would be cool for this old guitar.

Anyhow, this kind of plug can make a good presentation - not that anybody will see it, particularly after I drill and drive screws into the holes. After wiping up the glue with some warm water and rags, I put the neck away again for a night's rest.





Day 7: Cleaning Up That Damaged Tuner Hole

First, here's a quick look at a filled tuner screw hole from yesterday's work, after I trimmed the plugs with that thin knife:


This next photo is just a reminder of the veneer damage at the sixth tuner hole:

All the holes have been filled from the back side but I need to clean up the front of the hole so I can inlay some new wood so I can redrill it for the small Waverly bushing that I'll press in place.

In our shop, we have a fair selection of end mills, and drill bits, reamers, and all the rest, but what I need for this job is a flat bottomed bit that will drill a hole exactly big enough to round it to a regular shape without enlarging any more than necessary. A quick bit of measuring with my digital caliper produced a maximum reading of .460" so that's the size bit I'll use to drill it out.

Except, we don't have such a bit, nor a lathe to make one, and we certainly don't want to wait to order a special tool. In fact, I really wanted to get this job done right away, so I set about making a single-use cutter. As I was doing this particular operation, the other guys in the shop noticed, and suggested I'd gone nuts, and was "showing off." Indeed, I guess I was, but we have to get some fun out of our work, don't we?

Looking through scrap hardware drawer, I couldn't find anything particularly well suited for the job, so I decided to get just a little crazy and selected a simple hex head bolt, which I mounted in a mill collet:

With a regular lathe tool clamped in the mill vise, I was able to manipulate the X-axis table screw and the quill down feed to turn the head to the .460" diameter I needed:


After some hack sawing, and filing, I had a really simple little cutter:

Now, this cutter is just mild steel, so it won't compare with the long term utility of a high speed steel drill, but it did the job very easily, and it went back into the drawer, labeled for whenever.

After taking pains to center the drill exactly over the damage, I plunged it very slowly, stopping my cut just after clearing out all the rosewood veneer:

Here's the result, a nice shallow flat-bottomed hole into which I can inlay a piece of matching rosewood:

Day 8: Homework - Making a Plug Cutter

This is what I do on my "days off." I make tools and fixtures in the never ending process of learning to be a machinist.

Today's project is a plug cutter that will make a precise .460" diameter disc to inlay into the sixth string tuner hole I just cleaned up.

First, I drilled and bored the end of a short 1/2" diameter O-1 tool steel rod:

O-1 is a wonderful material for making woodworking tools. It machines nicely in its annealed state, and it can be hardened in a home shop easily to make long lasting cutting tools. I make some knives, chisels, drill bits and other cutters with it.

On the milling machine, I slotted the turned end of the rod so that when I got a disc cut, I could push it back out with a screwdriver or other blade>

Then, working strictly by eye and hand, I filed a series of sharp teeth in the end of my new little plug cutter:

Here's the simple hardening process I use. I get the tool about as hot as I can with a regular propane torch:

If I'm unsure about the temperature, I test the heated section with a magnet. When this steel is at about the right temperature to harden, it suddenly becomes nonmagnetic. You'll notice that I'm only heating the business end of the cutter - there's no need for any part to be hardened except the teeth that do the actuall cutting.

O-1 steel is so named because in the hardening process, the ideal quenching medium is oil. So, I dunk the red-hot piece into a can of used motor oil (stinky - you bet) and swish it around until it cools down some:

As it comes out of the oil bath, the steel is what's known as "file hard," meaning it's about as hard as it can ever get, like a file. I test it with a file, which won't even scratch the surface, so I know it's hard. Like a file, any steel in this condition is very brittle - too brittle for most uses because it could break if dropped, or even while it's cutting wood.

I need to temper most of the wood cutting tools, and my kitchen oven is just the place to do that:

An hour in the oven at 400 degrees Fahrenheit, and I've drawn the hardness back to a point where the tool is still hard for lots of repetitive use, yet tough enough to avoid cracking as it's used. From here, the cutter teeth get a little touch up honing with a carborundum slip or diamond pocket hone, and it's ready for tomorrow's adventure.

If it seems I'm going overboard with this effort, then I ask you, If a 1937 D-28 doesn't deserve the effort which guitar does?

Day 9: Inlaying the Oversize Hole


I spent a bit of time rummaging through my assortment of Brazilian rosewood scraps to find one that had similar grain and color as the original peghead veneer. To make sure I'd have a decent match, I applied a bit of finish to my piece to bring out the color:

Over on t he wood mill, I used my new little plug cutter to make a thin disc for the inlay:

With no set to the teeth, and precious little chip clearance, I made sure to "peck" lots of times as I drilled the veneer, stopping to clear the gummy rosewood dust out of the cutter teeth. Once the cutter broke through, I used the little access slot to push out the disc.

Into the hole went the disc, with a bit of glue:



And, after clamping up with a flat plate and waxed paper on top, the neck was ready for another overnight nap:




Using steam to release the neck dovetail glue joint has its hazards. I've already talked about the obvious effects of steam on finish, but, as the steam fills the dovetail cavity, it often also separates the glue joint between the spruce top and the neck block. That's what happened with this guitar, so before I even think about doing more on the neck resetting process, I attend to that bit of business.

Fixing it was simple enough. After warming the wood with a hair dryer for a few minutes to raise its temperature to about 90 degrees, I worked some hot hide glue into the joint with a broad palette knife:

I mix my glue weeks in advance, and keep it in these little hot sauce cups - like Jell-O in the refrigerator. When I need to use hot hide glue, I nuke it in the microwave, float it in a cup of hot water, and I'm good to go. Heating the wood gives me a little extra time to clamp up the joint before the glue starts to return to its gel state.


Clamps must be tight before the glue gels to get good adhesion and squeeze-out. One of these "Quick-Grip" clmaps is just the thing - fast and easy:

As always, I try to control the clamping pressure by using an appropriate block or pad over the joint - in this case a sheet of acrylic helps distribute the pressure and maintain flatness. With very few exceptions, I leave all wood gluing operation under clamps to dry for a minimum of 12 hours to make sure I get the strongest joint possible.



Day 10: Locating and drilling tuner holes


Today's little adventure involves a really swell set of precision machined steel rods, called "plug gages." (Lots of folks use "guage" but it seems that most machinists prefer "gage" when referring to sets like this.) These gage sets are used for measuring the diameter of small holes, and they are quite accurate - this set works from .251" to .500" in .001" increments.

Five of the original holes in the peghead veneer are still very close to their original diameters, and, after checking the peghead of another 1937 D-28 that's in the shop for repair, I determined that their locations are within spec. But, I wanted to be precise in redrilling through the plugged peghead as I could, so I set about being as accurate as I could. My new drill hole would be 1/4" - much smaller than the holes in the veneer - I couldn't count on locating the hole accurately by eyeball, so I got out the plug gages, and for each hole, I selected the rod that fit tightly:

All five holes were slightly different, so I used five different rods.

Back to the wood mill. After clamping the peghead parallel to the mill table, I locate each hole by using the appropriate plug gage, and moving the table X- and Y- axis cranks to get the plug centered so that I could bring the chuck downward, and the pin would press right into the hole with ease:

Then, leaving the table adjustments set, I raised the quill, exchanged the gage pin for a 1/4" drill bit, and drilled through the plugged peghead hole:

Here's the first one - dead center:

I did the remaining four holes the same way. When I got to the sixth string hole, I spent some time measuring and marking center, using the other holes as data points. Then I drilled through with the 1/4" bit.

After all the holes were drilled, I used the official Stewart MacDonald counterbore to drill for the Waverly tuner press-in bushings:

Check out my high-tech depth gauge - a turn of low-tack masking tape.

Now that the peghead is all set for its new gears, take a look at the back side:

Seems the oversize holes weren't exactly concentric with the originals. No matter - the back plates of the new tuners will cover that:

The footprint of the new Waverly tuners is just a tiny bit different from the original Grovers, but they are so close that nobody much complains:

More, on day 11 . . .