First Build Log - OM 6-String

[Bryan Bear]

I like it. I think it goes better with the cedar than the maple mockup. Definitely use the maple line inside the back!

Thanks, Bryan. Do you mean that I should use the same maple as purfling on the back?

-Eric

No, that was a type-o. I meant inside te bLack line.

[Eric Knapp]

No, that was a type-o. I meant inside te bLack line.

Ah! Yes, I will certainly be doing that. I did several mockups with different schemes and that's the one I liked best.

-Eric

[Eric Knapp]

Today I made a radius dish. I needed to make my own to save money but most of the DIY methods involve a lot of dust and have to start with some sort of reference radius that I don't have. I finally found a reference to the method I used. I used math instead of a long chain. The formula is pretty simple, to find the height of a spacer for a distance from the center it is:

Code: Select all

h = R - sqrt(R^2 - r^2)

R is the radius of the dish, like mine at 25'
r is the distance from the center of the dish to the spacer
h is the height of the spacer

I made 12 spacers for each distance from the center. The top section that gets screwed down to a backing board is 1/4" hardboard. The backing board is 3/4" MDF.

25' Radius Dish

Here you can see the outside spacers.

Side View of Spacers

Here's the spacer layout and the heights for 25' and 15' radius dishes. I made the 25' one first to work on the top.

Spacer Layout

It seems to be plenty accurate and fully spherical. It was also very cheap and easy to make with no dust.

-Eric

[Eric Knapp]

I'm fully on break and trying to make good progress before summer school starts. I have the braces mostly in place, I think.

Braces in Place

I am starting to carve them and this pic shows that a little better.

A Little Carving

Still looks rough and not elegant. I'm not sure how perfect I want to try to make it since I have no idea what perfect means yet.

The plans I'm using don't that that flat brace near the head stock. Should I add one anyway?

-Eric

[Barry Daniels]

The main braces can be taken down in height a bunch. The two lower tone bars should taper down at the rim end instead of being parallel to the top.

[Eric Knapp]

The main braces can be taken down in height a bunch. The two lower tone bars should taper down at the rim end instead of being parallel to the top.

Thank, Barry. I have just started carving the braces and I will take them down slowly and get some feedback as I go. I'm tapping for tone as I go but I can't hear much difference. It seems like there are about 5 clear frequencies. I guess that's better than a thud.

-Eric

[Eric Knapp]

I made progress today on the braces. I am trying to know when I'm done.

Carving Progress

They are trimmed, shaved, and shaped.

Looking Up

Am I getting closer?

Looking Down

I suspect I'll have to make a lot more to know if this is any good. I did keep tapping it and I can't hear any change in the tones.

Thanks,

-Eric

[Randolph Rhett]

Those tone bars look tall to me, but only you will know when you are done. For the scientific approach you can use Trevor Gore's method. I don't know it at all, but obviously many feel it is excellent.

The 100 year old approach is to hold the guitar about an inch or so in from the perimeter at many locations, hold the guitar up to your ear, and rap on it with your knuckles. Does it sound musical? Do you hear musical notes or the plink of wood? Do you hear low notes that would be at the bottom of your ability to hum, or just higher notes? If you hear deep drum like notes mixed with some sweeter high notes stop. If not, try shaving the tone bars, then maybe the lower legs of the x. Flex the board cross grain and long grain from the soundhole to the tail. Rule of thumb is that they should be roughly the same. No obvious bias towards one or the other. You can't really affect long grain at this point, but shaving down the legs of the x can help balance the cross grain. Don't just hold it in one place, move your hand around the perimeter checking.

Obviously there is nothing scientific about this approach. Everybody develops a slightly different method and ear. In the end, after a dozen or three dozen or ten dozen guitars you will develop an intuitive sense on how to voice the top. In the mean while, if the top sounds like a musical instrument when you rap it with your knuckles it will probably make a better guitar than almost any factory guitar. Just the fact that you listened to it, checked to hear it sounded musical and carved the braces trying to get you there, will place it head and shoulders above a factory guitar that is not voiced at all. Imagine if you had just glued the bracing down and closed up the box without even trying to voice it! Most guitars sold are built that way.

[Eric Knapp]

Those tone bars look tall to me, but only you will know when you are done.

I was starting to think the same thing when I saw these photos. It's funny how perspective can change like that.

For the scientific approach you can use Trevor Gore's method. I don't know it at all, but obviously many feel it is excellent.

I think I need to use the 100-year-old approach.

The 100 year old approach is to hold the guitar about an inch or so in from the perimeter at many locations, hold the guitar up to your ear, and rap on it with your knuckles. Does it sound musical? Do you hear musical notes or the plink of wood? Do you hear low notes that would be at the bottom of your ability to hum, or just higher notes? If you hear deep drum like notes mixed with some sweeter high notes stop. If not, try shaving the tone bars, then maybe the lower legs of the x. Flex the board cross grain and long grain from the soundhole to the tail. Rule of thumb is that they should be roughly the same. No obvious bias towards one or the other. You can't really affect long grain at this point, but shaving down the legs of the x can help balance the cross grain. Don't just hold it in one place, move your hand around the perimeter checking.

Obviously there is nothing scientific about this approach. Everybody develops a slightly different method and ear. In the end, after a dozen or three dozen or ten dozen guitars you will develop an intuitive sense on how to voice the top. In the mean while, if the top sounds like a musical instrument when you rap it with your knuckles it will probably make a better guitar than almost any factory guitar. Just the fact that you listened to it, checked to hear it sounded musical and carved the braces trying to get you there, will place it head and shoulders above a factory guitar that is not voiced at all. Imagine if you had just glued the bracing down and closed up the box without even trying to voice it! Most guitars sold are built that way.

I have started holding it and tapping. I can hear many tones from low drums to high notes. This cedar has produced pleasant and musical sounds even before I resawed it. It rings and rings and hasn't changed much throughout the bracing process. My viola playing daughter with great pitch sense says she can hear 6 distinct notes when I tap it. And that's was from several feet away. Is that unusual? The tones change depending on where I hold it but it always sounds nice to me. I have not tried flexing it and will tomorrow morning.

Thanks for the input, this is very helpful and encouraging.

-Eric

[Barry Daniels]

Take a bunch more off the lower end of the tone bars. They can taper down to a feather edge instead of being parallel to the top and then ending in a scoop.

[Eric Knapp]

After the feedback that the tone bars needed trimming I did this. Seems better.

Shorter Tonebars

-Eric

[Barry Daniels]

Much better. That will probably work just fine, but just for reference, I often take my braces a bit lower.

[Bob Gramann]

The bracing here is typical for one of mine. Yours still looks pretty hefty. Typically, nothing seems to change when you start carving the braces down until you have removed enough that vibration starts to get easy. When the sounds seem to change, that's the time to slow down and listen carefully with each pass. It gets more and more musical until it doesn't. At that point, it's too late. You will learn when to stop after you've done it many times. For my tops and my ears, I stop when I get a distinctive fifth difference in tone between tapping on the left and right sides of the bridge plate with the top hanging from my finger in the soundhole. I don't have a theory as to why this works, but with the Martin-style tonebar layout, there is a difference in stiffness and mass on the two sides.

[Beate Ritzert]

... It gets more and more musical until it doesn't. At that point, it's too late. You will learn when to stop after you've done it many times.

But if that should happen, the bars can be thickened again by glueing up some wood. Something i have recently learned here.

[Randolph Rhett]

My viola playing daughter with great pitch sense says she can hear 6 distinct notes when I tap it. And that's was from several feet away. Is that unusual?
-Eric

If she can hear them distinctly? Yes, that is unusual and a good sign (both for her and the top ).

[Eric Knapp]

OK, next installment is about my bandsaw. I have a finicky old Inca 3-wheeler. When it's set up just right it can do great resawing. Then the blade breaks. I was just starting to resaw my walnut and I broke my last blade.

Broke

That's the edge view of my 9" by 42" walnut board. If everything goes right I could get two guitars out of it. That didn't happen.

So, when all my blades break I have traditionally been stuck until I could get to a welding place to get them repaired. This is too frustrating and I have to be more independent. I decided to try to learn how to silver braze bandsaw blades. This seems like a fundamental skill of a guitar maker, especially someone who has a fussy bandsaw.

Short version of the story is I was able to do it.

Silver Braze

This feels like a superpower! Silver brazing is supposed to be better than welding. So far the blade is holding.

With the repaired blade I was able to resaw my walnut board and I'm making more progress.

-Eric

[Eric Knapp]

With a bandsaw that actually works I was able to resaw my walnut board for my back and rims. The cutting didn't go perfectly, though. I am still getting used to my bandsaw with the new blades I can find. They don't work the same as I remember and I have not fully adapted to them. There was some wandering and I will end up with one guitar instead of two from this board.

Once I got the board cut up I cut the sides out oversized. I started thinning them like this.

Thicknessing

I put a border of hardboard around the rim. Off the saw they were from 4mm to 6mm thick. The hardboard is about 3.3mm off the surface of the workbench. It is taped down and the walnut is loose inside. I planed down one side of each rim to 3.3mm. Then I removed the rim and planed down the hardboard to 3.0mm. I flipped each rim and planed them down to 3.0mm.

3.0mm

I'm going to leave them like there for a few days. Then I'm take them down to 2.0mm.

I think this walnut looks really good. It has a lot of quarter-sawn figure and some deep flame. I'm pleased I was able to get them to 3.0mm with no tear out or cracking. There are still some saw marks but they will come out before 2.0mm.

Looks Good To Me

I'll be repeating this for the back pieces sometime in the next few weeks.

-Eric

[Mark Swanson]

Yes that is nice looking walnut Eric! If you ask me, you are doing about as well as can be expected with a three-wheel bandsaw. They are hard to operate and hard to get a good result when using them to re-saw.

[Matthew Lau]

Nice thickness caliper.

Did you make one yourself?
I'd like to make one similar, but not sure how to do it with my digital dial gauge.

[Eric Knapp]

Nice thickness caliper.

Did you make one yourself?
I'd like to make one similar, but not sure how to do it with my digital dial gauge.

Yes, I did make that with the help of a machinist. I had an aluminum piece made that holds the gauge. I made the handle with a piece of sheet aluminum with some padauk glued to it.

I’m looking forward to getting back to this project. I’m having a very busy school year and my shop time is so limited I’m doing small projects.

-Eric