Official Luthiers Forum!

Hello again. I'm in the process of getting "jiggy" with it (I'm an idiot). First of all I'm brand new to guitarmaking, and am trying to acquire tools fast...and make jigs faster! My questions are laughable because I am so inexperienced, so bear with me.

I'm looking to make a bracing jig and need to make the radiused pieces. There are a ton of places that sell radiused templates, but I was wondering if anyone has a "simple" way of drawing a large radius? I know the math behind it will vary depending on your jig size, but wanted to see if someone has an easy way of doing this.

The sizes I'm looking to make are 15' & 28' for a bracing jig. It looks like the length of my pattern is going to be around 24" long.

Again....my apologies for the dumb question.

Jordan

There is a simple tool that ship builders used. I did search on the net and could not find it. I'll see if I can find it somewhere.

_________________
"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

   Other than trig plotting or a pencil with a tape measure, I don't know any! The chordal height would be a difference of about .400" at 12"/15' is this what your looking for?


    I don't know how accurate you have to be for braces but you could print a radius from a graphics program, that matches a 6" segment of the radii, and use that for a pattern.

Perhaps somebody else has a better idea.

    I would like to see the ship builder tool that's for sure! Do you have a rough explaination how it works Steve. Billy T38875.2153472222

_________________
Billy Dean Thomas
Covina, CA

"Multi famam, conscientiam, pauci verentur."
(Many fear their reputation, few their conscience)

Check this out, particularly the 'long compass' bit.

http://edge.cs.drexel.edu/GICL/people/sevy/luthierie/luthier ie.html

Also has an excel spreadsheet you can use to plot out arches, pretty simple. Bit fiddly, slow, but it does work. Alternately, someone may be willing to draw up the curves for you in CAD, which you could have plotted/printed at a local copy shop.

I use a fiberglass go bar, bent between to pins set at each end of the 24 inch distance on the 2x4 that is used to make the rails - math will tell you what the height of the arc needs to be, then you flex the rod to that distance and draw a line - cut, smooth the arc, then split the 2x4 - you now have matching rails for the routing jig to make the bowls.
Here are the needed numbers: arc height for a 24 inch curve
15 ft - .4 inches
18 ft - .33
25 ft - .24
28 ft - .21

Happy dust making - MDF is awful stuff!!!

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Go here this is the simplest brace maker out there works with either a table saw plane or sanding board. I make up a guitar set in a couple min. You will love this thing

brace maker

Its really pretty easy, although messy. I used a method similar to Tony's. I had a piece of square steel rod (1/8 inch I think). Put two nails 24 inches apart in a piece of plywood that would be the pattern for the rails. Bend the rod by the amount needed to make the desired radius and trace a line.

Use the plywood as a template to make a second rail (splitting a 2X4 is a good idea if you have a table saw). Use the rails to make a jig for your router to ride on. Set the jig over your piece of MDF and route out the inside of the bowl. Do this outside and use a dust mask. It makes a ton of MDF dust that will go everywhere.

_________________
53% of all statistics are made up on the spot
http://driftwoodguitars.blogspot.com/

There are several ways of going about this. Although I sell the dishes and the brace maker jig, I don't mind it when people want to make their own. In fact, I'll be the first to say, "go for it", rather than buy it from me. The reason...because after you build one, you will appreciate my jigs! Here is a good site for how to build a dish making jig. We make ours on a CNC machine using a calculated program. But this will work too! Good luck!
Tracy

I wrote a PostScript program to draw an arc. It draws a 24-inch long template across three 8 1/2" X 11" sheets, and you have to do a little cutting and pasting. I used it to print templates for 15', 20', 25', and 30' radii.

For those not familiar with PostScript, it's a programming language for controlling printers. You can just print the file if you have a PostScript printer. If you don't, there are various free software packages (e.g. GhostScript) that will interpret a PostScript file and format it for other printers.

I'd be happy to send a copy to anyone who would like it. Just send me a private message with your email address and I'll send it to you.

_________________
John Cavanaugh
Saint Paul, MN
"What could possibly go wrong?"

If you have access to Adobe Illustrator, draw a 12 inch diameter circle.
Cut off most of the circle so you are left with an arc you think will
ultimately be long enough. Multiply the arc by whatever radius you want,
say 25, and the resulting arc will have a 25 ft. radius. You can't enlarge
the circle first and then cut it to the chord length you want because
Illustrator won't let you make a shape that large. That's why you need to
remove the unwanted part of the circle first. Then just print it out on 8.5
x 11 sheets and tape them together, or take the file to Kinkos and they
can print them on big paper.

I have created an Illustrator file with the 2 arcs you're looking for. You can
PM me and I will email the file to you. If you don't have Illustrator, take
the file to Kinkos or whoever locally has wide format printers.
Craig

Thanks for responding everyone!

I believe John is going to e-mail me some of his templates to be printed (Thanks John!). There are still a lot of great ideas here though. The only one that I thought of before was making a string long enough to manually draw my line, but knew there had to be a better way.

I'm definitely going to try the idea of marking two points 24" away from each other, mark the correct height for the middle point, then bend something to make the curve.

Thanks again for your ideas and time!

Jordan

I just tape the end of my tape measure to my drill press and pull the tape out to whatever radius I need and use a pencil held with the tape measure to move and mark through an arc. Very simple.

Ron

_________________
OLD MAN formerly (and formally) known as:

Ron Wisdom

Somewhere in the middle of Arkansas......

Hi Jordan,

I posted a simple spreadsheet to calculate the chord length of any specified included arc radius a while back. I used it to layout the arcs I needed for my radius jigs.

http://www.luthiersforum.com/forum/forum_posts.asp?TID=5275& KW=spreadsheet#forumTop

I hope it can be of some value to you. You can download the spreadsheet from the link in my post.

Pete

_________________
Peter

I use my 15 & 25 Sanding dish to sand the radius into my braces and also use them on the Go-Bar deck for glueing, plus alot of other tasks. The best one I have seen for making braces is the same as MichaelP showed the link to one of our sponsors.

Mike
White Oak, Texas