Scratch build , intonation

[jbonecapo]

Hello all ,
Building a reso from scratch. Round neck , 25" scale , low action.  Forms are made, the steel has arrived , the woods on its way and the hardware is being dispatched.

However I still have some questions that are in need of answering.(every day I find a new hurdle)
Today's is intonation , I know its been done to death but seeing as I'm doing a scratch build , I might be able to get it as close as it can be.

My question is should i seat the bridge and cone a couple of mm away from the where it should be while I have the opportunity ?

And then rotate the bridge anti clockwise a degree or two as I've seen in other posts.


Planning on making a detailed build thread also that hopefully might be of some use to someone out there , even if it goes terribly wrong!

[pete1951]

Sounds like you know what to do. The best way on a new build is to copy an existing guitar. Find a guitar with an action similar to the one you want and with the same scale and strings that plays in tune. Then take careful measurement and your done. The bridge should finish 2 or 3mm behind the scale length.
Pete

[jbonecapo]

Cheers pete.
I don't have a 25" scale guitar or plans unfortunately. I have drawn up some plans myself which I feel confident are good enough.

I have found a compensation calculator online , although all variables will have to be estimations.

Continuously converting inches to mm is getting to me!

[pete1951]

Have just posted on the mandolin reso thread an example of how I find the right place for the cone, though I think you have already got there.
Pete

[Darryl]

I hope no one minds me barging in, but I am in a similar situation. (Building my first resonator - single cone biscuit - from scratch and wondering about bridge placement.)

I have an Ibex steel rule with four scale lengths and their respective fret positions marked on it - extremely useful. However, the closest to a 25" scale length that it offers is 25 11/32 or 24 27/32. It seems that 25" is the universal law on reso scale lengths, for cone pressure and tone, so I'm disinclined to argue. StewMac provides a handy calculator, so I'll use that and mark the fret position 'manually'.

My question is more of a clarification of what has already been said (and any pearls of wisdom jbonecapo can hand down as he's recently been through this). The StewMac calculator provides a distance from the nut to the breaking position of the first string and the sixth string. Should I take the median of these figures to give me the centre of my cone?

[Michael Messer]

Measure from the inside of the nut to the 12th fret, then go the same measurement plus 2mm from the 12th to the bridge saddle.

You really do need a National or something similar in your hands before you start to build one. It's a heck of a leap from just looking at photos and asking questions on here.

Shine On
Michael

[Darryl]

Thanks for that, Michael. And, yes, I'm starting to realise that a comparison model would be extremely useful.

[Michael Messer]

Darryl, There must be someone in Cardiff with a National or an MM. Put a post up on here in Talking Blues, I'm sure someone on here either lives nearby or knows someone that does.

Shine On
Michael

[pete1951]

Perfect intonation is very hard on an acoustic guitar as the extra length you need will change with string gauge and action. A reso , where the bridge can rarely be moved more than 1mm or so is particularly problematic. Normally the cone is a fairly tight fit in the well, you could give it a couple of millimetres extra to give yourself some adjustment? Though not ‘good practice ‘ on your first build it would be fine. But my recommendation of finding a guitar of the same scale and fitting the strings you want , with the action you want and measuring it is the best way .
Pete

[linkous]

Darryl, I'm currently building a reso that connects the neck to the body at the 13th fret. The body itself has the National '12-fret shape' (one day I will burn in Hell). This means that the soundwell has moved about 18 mm towards the neck. So I don't have an existing model at home to build  (the plan to build my first resonator guitar consisted of nothing more than a photo printed in full size).


Building a (reso) guitar is not rocket science, but I admit: you better be handy. You also have to take your time, think logically, collect information as much as you can and ask (yourself) a lot of questions.


To answer your question: I do indeed use the average measure between 'the bridge placement distance' that a (Stewmac) fret position calculator gives of the first and sixth string as the center of the soundwell. So you have reasoned well.

In case of a 635 mm (25 inch) scale, this is 638.5 mm (+ 3.5 mm) to be exact (from the fretboard edge of the nut, to the center of the soundwell). Then you can file the correct intonation within the thickness of the saddle.


As soundwell diameter I take 245 mm, then you still have some space when adjusting.


Good luck!

[Darryl]

Oct 1, 2021 11:55:29 GMT linkous said:

Building a (reso) guitar is not rocket science, but I admit: you better be handy. You also have to take your time, think logically, collect information as much as you can and ask (yourself) a lot of questions.

The 'collecting information' part is actually very rewarding. It seems that all the answers are out there, somewhere, so each stage is a bit of an Internet treasure hunt. There are also differing takes on construction techniques, which makes things interesting. 

Thanks for your help.

[bluesdude]

If you need measurements for the body taper let me know, the 12 fret Nationals had a better neck geometry because of it!
\

Kenny,,,,,,,,,,

[Michael Messer]

Oct 5, 2021 16:17:43 GMT bluesdude said:

If you need measurements for the body taper let me know, the 12 fret Nationals had a better neck geometry because of it!
\

Kenny,,,,,,,,,,

Good point, Kenny!

Body taper is 80mm at the tailpiece to 70mm at the heel. That is an important design feature.

Shine On
Michael

[Darryl]

Thanks, both. That's good to know.

[lexluthier]

Hi! That measurement over and above the scale length was said to be 1/8'' as the rule of thumb in th'old days.

Google informs me that's 3.175mm. I don't find 1/8'' to be quite enough personally.

The treble side of the bridge needs to be at least 1/8'' further than the scale AFTER the bridge is angled for some intonation. That angle is.....

....while I was looking up what that angle traditionally is on say a flat top,('cos I suddenly wasn't sure, it may be 3 degrees?) I found this, which explains exactly what I was going to try and convey, only better!

Chris