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 Post subject: radius dishes
PostPosted: Sun Sep 18, 2016 7:07 pm 
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Joined: Sun Jun 28, 2015 7:00 pm
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i have been watching a lot of Blues Creek Guitar videos.Are the top and back different radii.And are the parts in the kit already radius ed. Do I need to buy these dishes


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 Post subject: Re: radius dishes
PostPosted: Mon Sep 19, 2016 6:35 am 
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John can give you the Official Word, but based on my (limited) experience, yes, the top and back are typically different radii. The top radius seems to be usually in the range of 25 feet, and back radius about 15 feet.

You need the radius dishes to establish the proper radius on the sides and kerfing. It can't be done in advance.

There may be some way around buying the dishes, but I don't know of any reasonable alternative to using radius dishes as part of hte construction process. In addition to sanding the sides and kerfing to the proper radius, you'll use them when gluing the braces to the top and back. You'll put the back or top in the proper radius dish, then press it down into the dish when you apply clamping pressure to the braces.

There are directions floating around about making your own dishes, but it seems like an astounding amount of work.

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 Post subject: Re: radius dishes
PostPosted: Mon Sep 19, 2016 6:44 am 
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Joined: Fri Mar 03, 2006 7:09 pm
Posts: 5419
Location: Hegins, Pa
Most use a 28 foot top radius , but the entire top isn't radiuised. We use this to set the angle and to true the kerfed lining for a tighter fit for the glue joint.
The back is usually a 15 foot. I don't believe there is a tonal inference as much as it is for fit and finish. Of all the disks I seel 15 and 28 are the most used for steel strings.
jh

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Blues Creek Guitars Inc
Authorized CF Martin Repair Center
Board of Directors of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com


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 Post subject: Re: radius dishes
PostPosted: Mon Sep 19, 2016 6:53 am 
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Joined: Mon Jul 28, 2014 7:50 am
Posts: 424
Location: Chadds Ford, PA
LeftyAl wrote:
i have been watching a lot of Blues Creek Guitar videos.Are the top and back different radii.And are the parts in the kit already radius ed. Do I need to buy these dishes


You will get a really nice fit as John says with the sides to the top/back and in a few minutes of work. Other methods will work, too, but sometimes at a higher cost of time and aggravation. I couldn't believe how easy it was when I did my first with the dishes. If you go this route, also get another sandpaper disc so you can make the 28' a flat disc on the other side which is needed to set up the top geometry just right.


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 Post subject: Re: radius dishes
PostPosted: Mon Sep 19, 2016 8:52 am 
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Joined: Wed Aug 13, 2014 12:14 pm
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Other thoughts:

The curvature adds strength,. It also gives the expansion and contraction due to seasonal changes someplace to go. If it were totally flat, there would, I think, be more tendency for the wood to crack as it shrank in low humdity. With a radius, the curvature just flattens out a bit when it's dry, or increases a bit when it's damp.

John, how do you not radius the entire top? I've radiused the tops on both guitars I've built...maybe that is why I need the thin wedge under the fingerboard extension. If the top is radiused uniformly, the top drops off about 0.05" at the body/neck joint.

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Everybody is ignorant, only on different subjects. -- Will Rogers
There are lots of people who mistake their imagination for their memory. - Josh Billings
Anything is possible if you don't know what you are talking about.


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 Post subject: Re: radius dishes
PostPosted: Mon Sep 19, 2016 1:03 pm 
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Joined: Sun Jun 28, 2015 7:00 pm
Posts: 17
thanks, I'm seriously thinking about building an acoustic guitar. It may be a little over my head ,so I'm doing some serious research.I've been watching all of the Blues Creek Guitar videos for over a week now.Some videos more than once.


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 Post subject: Re: radius dishes
PostPosted: Mon Sep 19, 2016 3:50 pm 
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Joined: Fri Mar 03, 2006 7:09 pm
Posts: 5419
Location: Hegins, Pa
https://www.youtube.com/watch?v=pz6xzVRA51E
here is my video
I found that fully radiused tops often will change the neck angle and this results in a high condition at the bridge. An overset neck will lock the top up and harm the tone
I am looking for about 1/2 in overall height at the bridge and saddle when I am finished.

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John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
Board of Directors of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com


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 Post subject: Re: radius dishes
PostPosted: Mon Sep 19, 2016 8:22 pm 
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Joined: Thu May 24, 2012 8:03 am
Posts: 637
Location: Chestertown Maryland
Lefty

I have built 6 guitars without radius dishes and the method I found is cheap and easy enough I will not invest in them. I have a batten with the curve in it - 15 ft for the back and 28 for the front. These are not critical numbers - I understand that Martin does 52 ft on the top at the lower bout and flat at the upper bout

Just take a 15 or 25 foot string, put a weight on one end and wrap the other end around a pencil, draw the curve on the edge of a 2X4 for about 24", cut it on a band saw and sand it smooth, then glue on some 80 grit. I have a lathe, so I turned a round handle at either end.

I glue the braces on against the batten, and don't have or feel I need a go-bar deck for the few minutes of gluing required for braces. Once the bracing is done, I put a carriage bolt at the center of the back board and spin the batten around the rim before gluing the back and top.

Here are a few shots - look for about 15 or so to see the batten used as a gluing base and as a dish replacement:

https://www.flickr.com/photos/ruby1638/7998042889/in/album-72157631562735639/

Gibson does uses battens but works them up the length of the back, and it makes curved cylinder out of the back instead of a dome - lots of ways to do it, none "right".

This method is free but for your time, and after you build one or two instruments you can always upgrade to the minor time savings of dish and deck.

Ed


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 Post subject: Re: radius dishes
PostPosted: Tue Sep 20, 2016 7:34 am 
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Joined: Fri Mar 03, 2006 7:09 pm
Posts: 5419
Location: Hegins, Pa
I have used the battens early in my building. I found them to be less accurate then a dish and more time consuming but I agree it is a way to start . The dishes increase the accuracy and in most cases I am done is less than 5 min . The main point is that you have a way to control the fit and neck angle.

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John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
Board of Directors of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com


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 Post subject: Re: radius dishes
PostPosted: Tue Sep 20, 2016 12:53 pm 
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Joined: Fri Jul 03, 2015 2:45 pm
Posts: 143
I started with 2 x 4 curved cauls too and they did work. Radius dishes are just a step up. With a dish, you will get a constant curvature across the kerfing and sides, making for a better glue joint there. It is just a more controlled way of building than with cauls. Very easy to use for both sanding the sides and gluing the braces. A go bar deck can be shop made in a couple of hours at most with little investment. I have used oak bars for over 30 years and they work great. If you are so inclined and have a router, you can also make your own dishes. There are formulas on the web to determine the points of an arc for various radius, and IMHO, they work better than the string and pencil method. The work is in making the router jig. Making your own dishes is pretty cool. I'd say the whole process of making the router guides and then making the actual dishes could set you back about 6-8 hours of work. It is noisy and dusty routing the actual dishes, but it is still fun if you like making your own jigs. Buying them would of course be easier.


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