HEY!
that's incredible! i wake up this morning and i found your answers..
guys, you're great!
thank you very much!
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| using radius dishes http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=11760 |
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| Author: | bolix [ Mon Apr 23, 2007 8:44 am ] |
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hi everybody! i'm new in the forum.. write from switzerland... i'm learning making guitars and at home i'm starting preparing all the stuff for the guitar construction. i've recently routed four MDF radius dishes (15" and 25") but there's something that i can't understand.. how do you prepare the (4) back bracing? they have to be carved in different radiuses..?? or every brace as a 15" radius? thank you very much bolix |
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| Author: | TonyKarol [ Mon Apr 23, 2007 8:51 am ] |
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All the braces woudl be the same, 15 foot radius .. you can sand them to that int he dish if you like, or plane them ... whatever suits you. I use a bracemaker jig first, then plane them, the bowl is only for sanding the rim and then as a clamping caul. |
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| Author: | Michael Lloyd [ Mon Apr 23, 2007 10:10 am ] |
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[QUOTE=Hesh1956] I layout the back or the plan for the back in the radius dish and using a pieces of masking tape I stick the tape to the sides of the dish where each respective brace will go. Then I number the braces and sand each individual brace, between the pieces of tape, in the exact location on the dish that that brace will be on the back. By the way I do this on tops too.[/QUOTE] I do it the same way as Hesh and I number the braces. Though you don't need a brace maker jig it sure reduces the time and the aches and pains. Welcome to the OLF! |
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| Author: | old man [ Mon Apr 23, 2007 1:45 pm ] |
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Hello, Bolix, and welcome to the forum. I'm with Todd on this. I used to use the same argument as Hesh, but caved in and decided that it works great to sand them all flat bottomed at 15'. When the back is bent to follow the taper, the braces aren't vertical anyway. Below is a link to a progress journal for the guitar I'm currently building. On the second page you can see how I do my braces. Old Man's Progress Journal Ron |
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| Author: | crazymanmichael [ Mon Apr 23, 2007 2:55 pm ] |
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whereever you sand them in the dish the bottom will/should have the same shape. the dish is spherical after all. the possibility of sanding unevenly will be the same wherever you do it if you do it wrong. i rough out the radius for the top and bottom braces on the router table using a radius jig first and then just give a few passes in the dish to finish off. |
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| Author: | bolix [ Mon Apr 23, 2007 6:37 pm ] |
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HEY! that's incredible! i wake up this morning and i found your answers.. guys, you're great! thank you very much! |
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| Author: | Billy T [ Mon Apr 23, 2007 7:10 pm ] |
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Welcome Bolix!! [quote]It's true that the radius on the bottom of the braces will all be the same but there is a slight conical component to each brace too.[/quote] Thank you M'Man!!
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| Author: | Dominic [ Mon Apr 23, 2007 7:25 pm ] |
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A sphere is a called a sphere because of its symmetry which means anywhere you sand as long as it is at 90 degrees to the tangent it will be the exact same shape. The only reason to use a different part of the form is to get to fresh sandpaper  .
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| Author: | old man [ Mon Apr 23, 2007 11:26 pm ] |
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[QUOTE=ToddStock] Bolix: Good luck...bracing is my favorite part of building, right after cutting a new body mold. Todd [/QUOTE] My favorite thing is routing the MDF radius dishes.
Ron |
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| Author: | TonyKarol [ Mon Apr 23, 2007 11:32 pm ] |
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Yes, Domenic, the key point in your sentence is the " 90 degrees to the tangent" part - Hesh doesnt do that, which is why his braces are different - he is sanding them to keep vertical on the back which requires sanding in dofferent parts of the bowl, keeping the brace vertical - it changes the angle of the curve on the brace bottom. I dont bother as Hesh does - why - because when I shape the brace, I plane the vertical into them removing any lean that results from a flat gluing surface on the brce bottom to the curve of the back in the bowl - the end result looks the same. |
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| Author: | JJ Donohue [ Mon Apr 23, 2007 11:41 pm ] |
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Is this purely for asethetic purposes or is there a structural difference? |
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| Author: | TonyKarol [ Tue Apr 24, 2007 12:16 am ] |
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I cant see there being much of a difference structurally at all JJ, the delta is too small. IN fact, there is an article in GAL away back where our friend Ervin tested bracewood, and found the stiffest pieces werent perfectly quartered at all (all cut from the same board I believe). Aesthetically, it may look a bit wierd if you could see the brace leaning a touch ... |
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| Author: | JJ Donohue [ Tue Apr 24, 2007 12:44 am ] |
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We debated this ad nauseum some time ago and never resolved the issue either theoretically or through actual measurements. Tony, I too feel that if there were any difference it would be slight but I could be wrong and was hoping that someone smarter than me would have some actual facts. If it makes a significant difference I'll be happy to adopt the method. Until then, call me a "leaner". |
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| Author: | joe white(old) [ Tue Apr 24, 2007 1:04 am ] |
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I don't have any solid proof having not built a guitar yet but I think Hesh's idea makes sense to me. I respect your attention to detail too! 
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| Author: | Rod True [ Tue Apr 24, 2007 1:11 am ] |
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Hey leaner, welcome back 
There are many builders out there who don't use a dish to set their braces. Rather they use actual radiused boards and glue the braces on with just a radius not a sphere. Charlie Hoffman (I've learned so much from that guy and he doesn't even know it ) has a great tutorial of this on his website. Every brace is perpendicular to the plate this way.
Here is a picture off his site. 
I'm seriously thinking of going this way too. Easy to make a gluing form for the go-bar deck. You can still use the radiused dish to sand the rims, the back plate will glue down just fine. There is actually very very very little longitudinal curve/arc to the plate once the back strip and the braces are glued on anyway, so really gluing the braces in the dish is not totally necessary. (crack......the sound of another can of worms opening up )
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| Author: | Todd Rose [ Tue Apr 24, 2007 1:20 am ] |
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Hesh, you could achieve the same effect (having all your braces stand up straight - that is, with their sides parallel to each other rather than pointing toward the center of the theoretical sphere 15' away [or whatever your plate radius is]) by simply tilting them slightly in the dish while sanding them. In other words, it has nothing to do with where in the dish they are sanded, since the contour of the dish is identical over its entire surface. However, I can see how positioning them in a certain place in the dish could help you visualize the tilt you need to acheive the result you're after. Whether you do it one way or the other, it will have no effect on how well the radius of the brace fits the radius you are creating in the plate. You can't sand anything but a 15' radius in a 15' radius spherical sanding dish. The only difference it will make is the angle at which the brace will stand up on the plate. OTOH, I have found that it is easy to end up with a radius on a brace that's different from what's intended, because the brace flexes as you sand. Whether you hold the brace near the center while sanding, or near the ends, the pressure will create a somewhat different result. If you want to be precise, you have to check the radius repeatedly and sand carefully to remove more material from either the middle or the ends to get the radius really right. Once the braces are glued to the plate, though, the plate will want to flatten itself, so it will fight against the braces, everything will flex, and the actual radius of the plate will be somewhere in between flat and the radius you've put on the braces. When the plate is glued to the sides, they will help to support the intended radius, but it's still not going to be exactly what you planned. If you really wanted to end up with a 15' radius in your back (I'm just using 15' as an example), you'd have to sand something like a 10' radius in the braces. Ultimately, string tension will always pull things into a new shape no matter what you do. So, we're not creating any "ideal" geometry, regardless. The wood has a good laugh at our efforts! And the strings really snub their noses at us! We're just trying to give it some dome-like shape to add a bit of stiffness and give the plate somewhere to go when it shrinks from drying out. It probably would not make a wit of difference if the braces tilted this way and that (within reason) or even if they were originally sanded to radii ranging several feet different from each other, since they're all going to flex and find a new equilibrium once the whole thing is assembled and strung up. And then that changes as soon as the humidity changes! See there, now the weather is laughing at our efforts as well! |
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| Author: | Lillian F-W [ Tue Apr 24, 2007 1:32 am ] |
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[QUOTE=old man] [QUOTE=ToddStock] Bolix: Good luck...bracing is my favorite part of building, right after cutting a new body mold. Todd [/QUOTE] My favorite thing is routing the MDF radius dishes.
Ron[/QUOTE] You are one sick puppy Ron. 
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| Author: | Todd Rose [ Tue Apr 24, 2007 1:38 am ] |
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[QUOTE=Todd Rose] Whether you do it one way or the other, it will have no effect on how well the radius of the brace fits the radius you are creating in the plate. You can't sand anything but a 15' radius in a 15' radius spherical sanding dish. The only difference it will make is the angle at which the brace will stand up on the plate. [/QUOTE] If you're still not convinced of this, just take any of your radiused braces and lay then on your radius dish, and you will find that, no matter where on the dish they were sanded, they will fit the radius of the dish no matter where you lay them on the dish (unless they weren't sanded accurately due to the flexing factor I was talking about). The only thing that will be different, as you lay them in one spot or another, will be the angle at which they stand up. |
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| Author: | crazymanmichael [ Tue Apr 24, 2007 1:48 am ] |
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the nature of this seemingly never ending discussion tends to remind me of those that took place over the imaginary question of when the calendrical second millenium ce ended and the third began, whether at the end of 1999 or the end of 2000. |
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| Author: | AStass [ Tue Apr 24, 2007 1:49 am ] |
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[QUOTE=Rod True]Hey leaner, welcome back Rod, thank you sooo much for posting that pic! |
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