Acoustic Guitar Construction

Hello everyone, I am new to the forum and have been reading up as much as possible before starting my 000 12fret build from Stewmac plans. I intend to build from scratch , i.e. no kit. I have 2 questions( for now) which I need answers for, before I can progress.
1. I've seen the posts relating to sanding the rim from neck block to soundhole area by pushing the upper bout up above the mold, using 8 3x5 cards to measure the required depth to be removed. I'm in the UK so I'm not sure what these are exactly, so could somebody translate that into a measurement, please?

2 I've searched high and low to find the top radius for the Martin 000 12 fret, and so far seen suggestions form various sources of 28ft, 30ft, 40ft and even 50ft radii. Rather confusing! What exactly should it be, and is it the same radius as used on the Kenneth Michael building build mentioned above in question 1?

many thanks in advance Mike

Hi Mike,
Welcome!

1.5 mm will work OK -- there is a tweaking process further along the way in the instructions.

Our (KMG) construction procedure assumes 40' radius for the major top braces. Martin factory spec is 52' even though they are proud to tell you they make "flat top guitars." The tighter radius (25, 28, 30) is a modern convention thought to be even more insurance against adverse humidity changes. Sound-wise the tighter radius will decrease bass response thus increasing perceived treble response.

Thanks Ken, is there a link where I can download a pdf template for a 40 ft radius? I've been searching around without success.
Mike
( I have one I downloaded a while ago with different radii, but it's largest is 30' )

This provides a formula for any radius you like and shows you how to draw it simply.
http://www.liutaiomottola.com/Tools/BraceArchJig.htm

Thanks Dave, I have used this before to make such a stick for a ukulele build. I was thinking it might not produce a perfect arc, in that the strip of wood wouldn't bend uniformly. However, looking at you link again, I can now see that calculations can be made for more points along the arc, thus making it more accurate. I'll give it a try.
Cheers Mike

I just used that formula to make some radius templates. I used a length of fiberglass rod (from a electrical wire snake set that I had) and it made for a nice consistent arc.

Mike, I've used a diagram of various radii to make a few wooden templates. A fellow on the ANZLF forum made this. You can print it out at 100% on a few 11x17 pages, carefully taped together, and then cut them out, trace onto wood, etc. It's a good exercise to use the formula Dave provided, and then measure the arch. Hopefully they match!
I think I have a different version at home with a 40' radius. I'll check later.