Radiused Dishes

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Graham McDonald
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Radiused Dishes

Post by Graham McDonald » Fri Nov 23, 2007 7:12 pm

Ok, here is a short how to to make radiused dished workboards to whatever radius you want . Total cost under $20

Materials needed are two pieces of MDF or plywood 600mm/2' square, one 18mm/3/4â€
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Post by Graham McDonald » Fri Nov 23, 2007 7:18 pm

The top layer is glued on the the go-bar deck. I just use big blobs of glue on each of the radial slats. Any slight inconistancy evens itself out if you are mostly using it to sand the sides to fit domed tops and backs. I stick on strips of 60grit paper (cloth backed will last longer) with contact cement and drill the hole in the middle out to take a length of 15mm curtain rod which fits into a hole in the middle of the main building workboard.

Image

cheers

graham
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Post by Allen » Sat Nov 24, 2007 7:13 am

I used a router sled to make mine Graham. Wish I knew about this back then. The dust that is created by my method is truly something to behold. :cry:
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Post by Dave White » Sat Nov 24, 2007 7:48 am

Graham,

That's a very elegant solution. Thanks for the tutorial.
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Post by martinedwards » Tue Dec 11, 2007 2:58 am

I gotta say I like that!!!
Sorry I'm not from the Southern Hemisphere.....

I have an aunt in New Zealand and another in South Africa, can I still play?

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Post by Hesh1956 » Tue Dec 11, 2007 5:45 am

Very cool solution Graham = thanks my friend for the excellent tute! :cl :cl :cl :cl

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Re: Radiused Dishes

Post by Graham McDonald » Sun Apr 24, 2011 4:50 pm

As most of this seemed to disappear in the Great Server Crash of '10. Here it is as it is (more or less) in my mandolin book. Remember this is for something the size of a mandolin or ukulele, so just make it bigger for a guitar. For whatever reason, the pics don't want to load in order, but I have added a note on each one for those who can't work it out :D

The credit for this should go to John Calkin, who published it in American Lutherie a few years back.

Radiused dished workboards
These are available commercially in a number of different radii, usually designed for guitar building use, but it is a simple and cheap device to build. A 15’ radius is suggested for both the front and back of a mandolin, but a tighter, 12’, radius could also be used (or a 24' radius for a guitar). Materials needed are two pieces of MDF or plywood 500mm (18”) square, one 18mm (3/4”) thick and the other 3mm (/8”) thick as well as twelve pieces of dressed 2x1” pine that are around 215mm (8.5”) long. For a guitar you would want the MDF 600mm/2' square and longer bits of 2x1.

Drill a 1/4” hole in the middle of both pieces of the MDF/ply and cut a 450mm (17”) diameter circle. A piece of wood with a 1/4” hole at one end and another 225mm (8.5”) away to take a pencil makes a simple compass. Using the 15’ radius pattern in the plans at the back of the book, cut curved strips from the lengths of 2x1 pine. The pieces should end up 5mm (3/16”) thick at one end and 10mm (3/8”) thick at the other. Glue the first two so they butt together in the middle, and add the others shortening them as required, as pictured below.

Once all are in place sand any unevenness out and glue on the piece of 3mm MDF/ply, using a short length of 6mm or 1/4” dowel to line them up. The best way to apply pressure is with go-bars in a go-bar cabinet. This is simply a rigid structure with a floor and ceiling and lengths of dowel the same length as the distance between floor and ceiling. Suppliers offer wood or fibreglass bars 24” in length, though longer ones are not a problem. Mine are 42’ in length and made from 10mm (3/8”) dowel.
Attachments
dish9.jpg
And last
dish9.jpg (109.26 KiB) Viewed 19106 times
dish5.jpg
Third picture
dish5.jpg (102.53 KiB) Viewed 19106 times
dish1.jpg
The first pic
dish1.jpg (65.4 KiB) Viewed 19106 times
dish3.jpg
The second pic
dish3.jpg (88.41 KiB) Viewed 19106 times
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Re: Radiused Dishes

Post by Kim » Sun Apr 24, 2011 5:15 pm

Thanks for taking the time to put this tutorial back together Graham, its pretty obvious quite a few people have found it helpful in the past and now are sure to in the future as well.

Cheers

Kim

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Re: Radiused Dishes

Post by Graham McDonald » Sun Apr 24, 2011 8:06 pm

You're welcome. One of the other forumees (is that a word?) sent me a message saying he couldn't understand it, so it wasn't hard to add the necessaries.

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Re: Radiused Dishes

Post by charangohabsburg » Mon Apr 25, 2011 12:49 am

Graham McDonald wrote: [...] Using the 15’ radius pattern in the plans at the back of the book, cut curved strips from the lengths of 2x1 pine. [...]
I don't know if "how to draw part of a circle with a great radius" a has yet been discussed on this forum. Those who don't have the book's templates or want a different radius might find interesting the (for me) easiest way to draw such circle lines. When I was going to make my first solera I was told that I could make a compass with a pencil and a loooong thread or wire. Although I had my difficulties to believe this would work well I gave it a try. Now I know how much different threads and wires stretch under even low tension... and I ended up drawing the line by calculating the coordinates of some of it's points :lol: - it's one of the hard ways to do it.

Later I found this description and drawing on Jon Sevy's website:

Image

I need to draw such circle lines so seldom that I make these compasses (two so far) out of 30 mm wide cardboard strips and throw them away after having used them.

EDIT:

I nearly forgot to present the math...

Image

R = radius of the dish's curvature
D = "diameter" of the radius dish
Pmax = maximum depth (the letter "P" stands for the spanish word "profundidad" - I'm too lazy to draw the whole thing again with "letters in English" ... ;) )

Image
=>
Image
=>
Image
=>
Image
=>
Image

You can also use one of Jon Sevy's instant solutions:
1) Excel (PC), Excel (Mac)
2) Java Script
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Re: Radiused Dishes

Post by Graham McDonald » Mon Apr 25, 2011 8:46 am

Thank you Markus, I had forgotten about the actual curves. I have 15" and 25" radius curves as jpgs, but the images are over 4000 pixels long, so I will have chopped them up into four sections as the site limit is 1200 pixels. They are numbered 1-4 and there are vertical line which can be used to reassemble the whole curve. There is some doubt about what radii curves these actually are. Someone emailed me a couple of months ago complaining that he had done the maths and these were not 15' and 25' radius curves. Perhaps they are not, and if someone wants to do the maths and let me know, that would be great. ALternatively they work quite well as they are and lots of people have used them since the Bouzouki Book was published 7 years ago :D There should be eight images below.

cheers

graham
Attachments
25'_4.jpg
25'_3.jpg
25'_2.jpg
25'_1.jpg
15'_4.jpg
15'_3.jpg
15'_2.jpg
15'_1.jpg
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Re: Radiused Dishes

Post by Kim » Mon Apr 25, 2011 9:19 am

I downloaded this pdf. file a while back but never ended up using it so you may wish to check accuracy. However as I recall the document was drafted on some wizz bang plotter so they should be right. But with that said it is more important that the radius be consistent than dead accurate anyhow.

As to the file it has a range of radii covering those in common use. The document prints as 4 adjoining pages each with alignment marks so they can be accurately tape together, glued to some thin ply, and cut out to use as templates.
Multicurve dish.pdf
(44.51 KiB) Downloaded 703 times
Cheers

Kim

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Re: Radiused Dishes

Post by auscab » Thu May 05, 2011 12:26 am

I came across this circle calculator and it helped my understanding out .
http://www.1728.com/circsect.htm

cheers Rob.

Just checked this link 21 5 11 and it has been changed, it now links to some clothing shop from China by the looks of it, A freind told me this happens if they dont pay their bill to who ever is hosting their web site, wait and see ? Rob
Last edited by auscab on Sat May 21, 2011 11:09 pm, edited 2 times in total.

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Re: Radiused Dishes

Post by What Democracy? » Sat May 21, 2011 8:39 pm

Hi to all,
I have to make a couple of Radius dishes soon. The tips here will be most helpful.
I went to a seminar at The International Guitar Festival in Adelaide in this year to hear Luthier Jim Redgate (http://redgateguitars.com.au/)
talk about his radical guitar designs and some of his building techniques. You guys are probably familiar with his work, with the double wave tops, lattices and nomex bracing amongst other innovations. Amazing sounding guitars too. Blown away!

You will have to excuse my inexperience here, but I clearly remember Jim saying that if you want a 25 foot radius disc, he explained that he got 25 feet of rope, with which he suspended a router from the roof and away he went. Lots of noise, dust and One 25 foot radius disc.
I don't know if this works or whether it is a good way to create one very dangerous power tool.

Just checkin...

Cheers, Ben.

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Re: Radiused Dishes

Post by charangohabsburg » Sat May 21, 2011 9:49 pm

So he didn't show pictures or even a video or live presentation of that method? :? :(

Before you try this you might want to get a smooth curve with that rope and a pencil...
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Re: Radiused Dishes

Post by Nick » Sun May 22, 2011 9:35 am

Don't get too carried away by what other's refer to as innovations Ben, most everything has already been tried/used in one variation or another down through time, but sure it's clever to see how some people incorporate these things.
As far as radius dishes go I've used the same method as Graham with great success & without having to find a barn with a 25 foot roof beam! :wink: :lol: All I needed was a bandsaw & a belt sander.
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Re: Radiused Dishes

Post by What Democracy? » Sun May 22, 2011 1:42 pm

Sorry guys,
Showing my inexperience here I know. I am very new to this but committed to it for the long haul (health permitting).
I am certainly not going to arrive on here and start telling Grandma how to suck eggs. Really keen to sit back, read, watch and learn from a group of people who are FAR more experienced than I. I don't have a barn either and the swinging router sounded simple - simple to knock my head off with! I will follow your advice and try the easier proven methods. I have only just got the floor space to work in, so I am gathering tools, materials and looking at jigs, molds templates. All this will largely hinge on what exactly it is that I am to build of course.
I have an LMI HD-28 replica kit ready to go, so I suppose I better set up for that one.

Please excuse my ignorance guys. I am capital "L" for learner here.
Looking forward to your input.

Ben.

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Re: Radiused Dishes

Post by J.F. Custom » Sun May 22, 2011 11:03 pm

Hey Ben.

I'd certainly look at alternatives before hoisting a 25ft rope and router. :shock: For a start, rope can stretch so the accuracy of said results would be questionable. Of course, it does not need to be precisely 25ft either but that's another discussion.

I'd be buying one pre-made before trying that. You may even find a machining shop near you that will CNC one for less than the cost to import from a luthiers supply house. At least off the cnc you are guaranteed (as much as possible) of consistent even results. Considering the current dollar though, they are really not too expensive for what amounts to a permanent fixture. And that's not to mention the sheer volume of dust and time it takes to machine with a router by any method too.

But then, it does not get much simpler than Grahams method here for a lot less effort and trouble.

Finally, as Nick alluded to, both Nomex double tops and Carbon Fiber/Balsa or general lattice bracing are not Jim Redgates' creations. He may have adapted them somewhat to suit his style of build true, but he did not originate the deviations from "norm". He has simply taken them on as many other builders have too. Can't comment on the wave-top as further info on his designs is difficult to find. In fact, info on his builds period is pretty limited. Nice guitars though. 8)

As a side, I did see a short video on him years ago on ABC that showed some of his work and methods. Unfortunately, though the link on the ABC website still exists, apparently the video it links to does not... Gone and can't find any source for it now.

Cheers,

Jeremy.

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Re: Radiused Dishes

Post by charangohabsburg » Mon May 23, 2011 1:11 am

Ben jamin wrote:Please excuse my ignorance guys. I am capital "L" for learner here.
The one who asks a question may appear to be a fool for two minutes.
The one who does not ask questions will be a fool for the rest of his life.
Oh, and I nearly forgot to point out that this forum solely exists for showing off how good we are! :mrgreen: :roll: :dri (in reality it has nothing to do with guitars!) :toi
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Re: Radiused Dishes

Post by Lillian » Mon May 23, 2011 3:47 am

charangohabsburg wrote:
Ben jamin wrote:Please excuse my ignorance guys. I am capital "L" for learner here.
The one who asks a question may appear to be a fool for two minutes.
The one who does not ask questions will be a fool for the rest of his life.
Oh, and I nearly forgot to point out that this forum solely exists for showing off how good we are! :mrgreen: :roll: :dri (in reality it has nothing to do with guitars!) :toi
Let me give you a hand there Markus. Your hand must have slipped and the print got very tiny on you.




:lol:

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Re: Radiused Dishes

Post by charangohabsburg » Mon May 23, 2011 6:41 am

Thank you so much, Lillian! :lol:
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Re: Radiused Dishes

Post by Nick » Mon May 23, 2011 6:59 am

Please don't think I was having a go at you Ben, everybody has to start somewhere & asking questions is all part & parcel, we never bash people for asking questions unless they're really stupid questions :lol: but there are never any stupid questions when it comes to guitars. I was just pointing out that while everything is all new & alien to you it's easy to be convinced that something 'unusual' is all marvelous & should be the target to aim for. At this stage approach everything with a partial sense of wonderment & an open mind, observe as many 'innovations' as you can, this will shape how you eventually decide to do your builds, maybe even have an "innovation" of your own. I've been building for a while but acoustics not so long & I'm very much still learning. The day we stop learning is the day our guitars/builds become stagnant as far as I'm concerned. :wink:
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Re: Radiused Dishes

Post by charangohabsburg » Fri Apr 25, 2014 7:11 am

charangohabsburg wrote: [...]
Later I found this description and drawing on Jon Sevy's website:

Image

[...]

You can also use one of Jon Sevy's instant solutions:
1) Excel (PC), Excel (Mac)
2) Java Script
Bugger. Mr. Sevy loves to changes URLs and set up new websites.
OK, you can have my own drawing and spreadsheet:
radius.xls
radius.ods (the same in OpenOffice format)
a.jpg
The angle ACB is always the same.
a.jpg (58.51 KiB) Viewed 13792 times
More about my shipwright's compass here.
Markus

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It's only the others who suffer.

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Re: Radiused Dishes

Post by timbuck » Sun Apr 27, 2014 5:43 am

I don't know if this will help..Or you could have seen it before...It's just another way of doing it. :idea:
http://forum.ukuleleunderground.com/sho ... adius+dish

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