Radius dish

[xsnrg]

Hello, I am tring to make a radius dish which are used in making of acustic guitars. Guitar tops and backs are typically not flat. Although you may not notice it, most acoustic guitars have a slight outward bow in the top and the back. This bow is created by contoured bracing and the use of a radius dish. I am new to Solidworks and thought this would be an easy first project...haha, man was I wrong. The radius dish is a 24" diameter and 1.5" thick with a concave 28' radius cut into the top surface if the dish. I can't seem to get a concave radius, its more of a valley.

 

I can upload a file but not sure what extension to use, I have it in a .SDLPRT

[shift1313]

To upload a file here you would have to make it a .zip file or load it onto another site.

 

As far as your dish goes there are several ways to achieve this. The dish isnt going to be the entire back of the guitar(rather the 24" diameter wont be consistent over the entire back of the guitar).

 

I would definitely work with surfaces. I would either do a swept surface or a boundary surface using two guides. Make these guides both arcs then after you have your surface you can trim the surface to fit your shape. If you can link or upload a picture of the guitar you are trying to draw i can make a few screen shots to show you this method.

[xsnrg]

If you can link or upload a picture of the guitar you are trying to draw i can make a few screen shots to show you this method.

 

Thanks for the reply.I am not tring to draw a guitar...rather a jig that is used in guitar construction. I hope it is ok to post a youtube link http://www.youtube.com/watch?v=a63uOKkEE1I ....this is one persons way to make a radius dish. I only have rar....I will look for a upload site.

[Dana W]

Thanks for the reply.I am not tring to draw a guitar...rather a jig that is used in guitar construction. I hope it is ok to post a youtube link http://www.youtube.com/watch?v=a63uOKkEE1I ....this is one persons way to make a radius dish. I only have rar....I will look for a upload site.

 

Listen, xsnrg. Check out luthierforum dot com. It is a great forum with great people and you WILL be able to build a guitar with what they teach you about them over there.

 

EDIT: This one has great people on it too, and they try here as hard as the guitar guys do to give us good info.

 

Wait, I just hit your link. That's Greg Nelson. Great guy!! I have one of his rosette trim rings from about 5 years ago. You must have already found luthierforum dot com if you know about Greg. Awsome buncha people ain't they? I haven't been on that forum for a while because I am about not building a guitar in the 5 years I have been a member.

 

I don't know much about solidworks but I have made a radius dish. Made mine with a router jig having arc'ed runners equal to the guitar back radius minus the distance from the tip of the router bit to the router base. The hardest part was building the LONG COMPASS router base, and routing the jig runners.

 

Try drawing a 2D profile (cross section) of the dish and spin it around to make the shape. I have seen tutorials on here that start out that way for a wheel. All you need is a wheel, flat on one side and dished on the other, right. 'Course, you could put your back radius on one side of the dish and your soundboard radius on the other side, I did.

 

I have been working on building a drednaught myself. Not gonna say for how long. I have also tried to draw the daggum thing in AutoCAD too. Where's the little sweaty faced emoticon? Ah, there it is.

 

Gotta go before I hijack the thread. I could talk about guitars ALL DAY.

[Dana W]

To upload a file here you would have to make it a .zip file or load it onto another site.

 

As far as your dish goes there are several ways to achieve this. The dish isnt going to be the entire back of the guitar(rather the 24" diameter wont be consistent over the entire back of the guitar).

 

I would definitely work with surfaces. I would either do a swept surface or a boundary surface using two guides. Make these guides both arcs then after you have your surface you can trim the surface to fit your shape. If you can link or upload a picture of the guitar you are trying to draw i can make a few screen shots to show you this method.

 

The guitar back and soundboard are actually guitar shaped sections of the surface of a sphere with a radius usually more than 20 feet.

[xsnrg]

Thanks Dana for the advice. I can build a guitar the old fashoned way:wink: so now I want to incorperate CNC into my guitar building. I am using solidworks to build my electric guitars and then mastercam to get the g code for mach3. I thought it would be faily streight forward in building a radius dish in solidworks....lol, not. I guess I have a long road ahead of me.

[shift1313]

 

Here is a picture I found online. Basically what you need to do is draw the arcs that are on the right side image. When making a boundary surface you will use one arc as Direction 1 and the other as Direction 2. Then in a third sketch you can draw the shape of your guitar body(if needed for the jig) and trim the surface.

 

To get a solid from a surface you can either thicken it or you can create closed knitted surface comprised of several surfaces and this will make a solid.

[shift1313]

Also if you plan on doing a lot of NC work using your solidworks files you may look into SolidCam. I love using solidcam and dont really like using mastercam:)

[xsnrg]

Hey Matt take a look at this. It wont let me post a link under 9 posts. I am trying to follow what you are doing but cant seem to understand how to apply it to what I am doing. I may not be explaining it well enough....forget for a second that it has anything to do with guitars....the end product that i want will be a 24 inch round disk which is 1.5inches thick and have a concaved surface with a 28 foot radius routered out of the surface.

 

Xxx DOT 4shared DOT com/file/eeWnAQcI/radiusver2.

 

[shift1313]

Well if thats the case Dana is spot on. You will want to draw a 1/4 cross section of your radius disk and then use the Revolve function. This screen shot wasnt SW but the procedure is the same. I drew some reference lines starting at the origin. I created a horizontal line equal to the radius of the disk. Then two vertical lines. The one on the right is 1.5" tall. The one on the left will be driven by the arc. I then drew a horizontal reference line from the top of this vertical line so I could apply a tangent relation for my arc. draw the arc, add the tangent then give it the radius 336". I offset that arc and connected everything together to make a closed region.

 

In the revolve command you will make that vertical line at the origin your rotation axis and voila.

[Dana W]

Thanks Dana for the advice. I can build a guitar the old fashoned way:wink: so now I want to incorperate CNC into my guitar building. I am using solidworks to build my electric guitars and then mastercam to get the g code for mach3. I thought it would be faily streight forward in building a radius dish in solidworks....lol, not. I guess I have a long road ahead of me.

 

Cool. Electrics do lend themselves to CNC methods. It should be a fun trip to take.

 

I am an old fashioned kinda guy myself, even though my favorite artists all play electrics. I am also probably as much about the process as the result. I love the zenlike process of hand carving necks and doing inlay work. I also get a kick out of designing and building jigs and fixtures to do some of the special processes found in Luthiery. I have about a dozen custom shop aids and only a 1/3 finished guitar after 5 years:lol:.

 

Good luck with the project. Go post some of your work over at the Luthierform. I am sure they'd love to see your building process as well as the finished instruments. For that matter, there is a showcase area here you can post your work on. You'd be one of the few that could post drawings and actual finished stuff.

 

Also, Thanks Matt for saving me. I don't even own 3D software except for Sketchup free version and only have a minimal understanding of some of its functionality. I just jumped on this because I knew what a radius dish was without having to read the explanation.

[shift1313]

I have a few guitars myself but never even considered making one:) I like to learn about stuff like this and maybe years down the road make one of my own:) I find this kind of thing fascinating myself:) I will also say this. I have cnc'd some wood before and it wasnt pretty:)

[Dana W]

I have a few guitars myself but never even considered making one:) I like to learn about stuff like this and maybe years down the road make one of my own:) I find this kind of thing fascinating myself:) I will also say this. I have cnc'd some wood before and it wasnt pretty:)

 

Well, then. It's time you explored luthierforum.com too. It ain't rocket science, but there are a few guitar makers who like to make it seem like Quantum Physics, and a few others who think it is magical smoke and sparkly dust. That particular forum is full of realistic, and intuitive people who like to make it possible for beginners to understand the basics, and get hands on with it right away. Nobody needs to know which river Stradivari found his spruce trees submerged in, nor the meaning of "Tap Tone".

 

I have a feeling that CNC'ing a radius dish is more programming and finish handwork than it is worth for mass production, but fun for the one-off builder. I can see a computer cutting out an electric guitar body and even the neck, but any router bit is going to leave a network of gullies all over the inside of that dish. I did my dish with a manually operated, home built router sled that had curved runners. The bit could hit every point in the dish surface but I still had to finish it up with a hand scraper. The outer edge of the rotating bit does not follow the same arc path as the center of the bit.

 

Looks like I've successfully hijacked xsnrg's thread so I'm outa here, for now.

[bhamze]

This is cool!!! I too find this topic very interesting. I modeled the dish and found that Matt's suggestion is probably your easiest modeling approach. Once you get your model completed, programming the geometry should be straight forward in MC. Without seeing the completed model its hard to tell but I'm guessing the surface parallel option should do fine, assuming you have the correct post. I use SW and MC on a regular basis, most of the prototypes that are generated are cut out of wood. Depending on the type of wood being used, the feedrate and spindle speed need to be adjusted accordingly. You stated your using a Mach3 CNC. Is that CNC manufactured by KOMO? I ask because I use a Mach2 CNC and maybe you could use the post. Either way, I hope your project is successful. Goodluck.

 

Bill

[shift1313]

Hey bill. Its been a little bit since i have used mastercam. When you setup a 3d milling operation did they have spiral and modified spiral? Thats probably how i would machine the dish using SolidCAM, but heck a 28foot radius is a very small amount of Z travel and with a reasonable step-over and a larger radius bit probably anything would leave a decent finish.

[Dana W]

Hey bill. Its been a little bit since i have used mastercam. When you setup a 3d milling operation did they have spiral and modified spiral? Thats probably how i would machine the dish using SolidCAM, but heck a 28foot radius is a very small amount of Z travel and with a reasonable step-over and a larger radius bit probably anything would leave a decent finish.

 

Welcome to cadandLuthiertutor.com:lol:

 

Well, you don't really need to worry about the finish as long as the high spots are close together and they all hit the surface of the sought after spherical section. We are building a shop jig, or fixture to be precise. Most of us are using MDF for these fixtures. I used pine because MDF dust makes me hoarse for months after I inhale some of it. Routing a radius dish in MDF creates dust clouds on a biblical scale.

 

What happens is that a ~1/10" thick sheet of spruce gets lightly pressed into this finished radius dish until full contact is made, while longitudinal braces are glued to the resulting concave surface of the spruce. All is held in position until the glue dries. Then, the spruce is removed from the dish, and holds the dished shape (if all the stars are where they belong), and the resulting convex surface on the other side becomes the outside of the guitar top or back.

 

Larger bit, Really? When I did mine without embarassing a simple minded CNC machine:P, I found the larger dia. bits would actually lengthen the radius, thus deepening and widening the dish. I guess you could call it a paralax error from the edge of the cutter to the center of the bit. What part of CNC commands handles this problem?

Or am I overthinking the whole thing? It is not a huge error when thinking in terms of a 27 foot radius, but we are actually dealing with a chunk of wood 24" in diameter with a dish in it, a little less than 1/8" deep. Any error there is HUGE and it has a not small effect on the sound of the guitar. In theory, the tighter (shorter) the radius, the brighter the sound.

 

So, when you guys finish with xsnrg's radius dish on the CNC, try mine. I've attached a gif of it under construction. It is mounted by one of the two router sleds I built to achieve the dishes in it. The board rotates below the sled on a 1/2" dowel center pivot pin, one pass, rotate one cut width, another pass, and so on for about a half hour.

 

It's made of 1 1/2" thick clear pine glued up slabs. Mine also doubles as a guitar assembly workboard, or Solara which is usually a separate fixture for asembling the guitar body upon. That means it has to be shaped like the guitar but a bit larger all around. My radius dishes, 1/8" deep for the soundboard, and 1/4" deep for the back, reside on oposite sides of the workboard. The dish is not changed by the curves of the guitar shape. The result is my workboard is thinner at the waist than the other areas. In the wider areas of the upper and lower bouts (guitar speak for fat parts) the radius leaves the surface of the board before reaching the edges. My longest cord length is 20 1/8" wich is also the overall lenght of my drednaught guitar body.

 

Radius dishes are actually a new innovation about 10 years ago. Up until then, a luthier would simply raise the edges of the workboard by laying down 1" wide strips of cork around the edges and then mashing the guitar soundboard down into the resulting low area within the cork strips. Sometimes I think the radius dish is like using an M1A2 Abrams Main Battle Tank to go ah squirrel huntin'.

[shift1313]

Thanks for the good explanation Dana. Certainly keeps shedding light on the subject:)

 

On the topic of larger bits. When milling 3d contours you typically want to use the largest radius ball mill you can use with your design. If you have some high concave areas you will need a small radius bit but the surface finish will not be as good unless you have a really really really small step over each pass. I would probably take a large square or bull end mill to rough out the dish and do all the finishing passes with a large two or three flute ball end. 3/4" or larger diameter. 1.5" is probably about the largest you will find in a standard size. Since I dont typically cut wood i couldnt tell you what bits actually work the best but im sure bill knows since I think he deals with mdf and sound systems:)

[Dana W]

Thanks for the good explanation Dana. Certainly keeps shedding light on the subject:)

 

On the topic of larger bits. When milling 3d contours you typically want to use the largest radius ball mill you can use with your design. If you have some high concave areas you will need a small radius bit but the surface finish will not be as good unless you have a really really really small step over each pass. I would probably take a large square or bull end mill to rough out the dish and do all the finishing passes with a large two or three flute ball end. 3/4" or larger diameter. 1.5" is probably about the largest you will find in a standard size. Since I dont typically cut wood i couldnt tell you what bits actually work the best but im sure bill knows since I think he deals with mdf and sound systems:)

Thanks for the advice. I suppose my method is a bit different than a CNC router head would use. I only have one axis of rotation on the router and I used a flat ended 1/2" router bit. Since the router sled runners have a smooth arc cut into them, and the workpiece is rotated about a half bit width at a time, I end up with smooth flat bottom facets radiating from the rotation center point of the workpiece. I just smoothed them out with a cabinet scraper, and Bob's yer uncle.

 

:shock:A new round ball mill would cost more than my stinkin' router.

[bhamze]

Hey bill. Its been a little bit since i have used mastercam. When you setup a 3d milling operation did they have spiral and modified spiral? Thats probably how i would machine the dish using SolidCAM, but heck a 28foot radius is a very small amount of Z travel and with a reasonable step-over and a larger radius bit probably anything would leave a decent finish.

 

Matt,

 

There are several options available for spiral toolpaths in MC, particularly under the surface/rough/pocket area. I think there's a spiral option under high speed toolpaths as well. I never used this option so I'm not sure. In the surface/rough/pocket area you have........true,parallel,overlap,and morph spiral options. Keep in mind these are roughing toolpaths and not intended for achieving a decent surface finish. I'm sure you can adjust some settings to achieve this but you get the point. If your trying to achieve a spiral type toolpath as a finishing path you could use the scallop option. You can set the start point at the center of your part and it will create a toolpath in an outward circular pattern from that point, very similar to a spiral. I'm no expert in MC and I'm sure more options are available. I'm only sharing what I know. When I machine wood (MDF) I usually use a .050" stepover and a .020" stepdown. This may seem a lot but I usually cut large pieces and these parameters cut down on machine time. Since its MDF were talking about, there is no way to achieve a metal type surface finish with any toolpath option. Once you cut past the surface of MDF the material becomes grainy, its smooth but grainy. After the part is machined..... a little sanding is necessary. The parts I create are intended as a plug which then are used to create a fiberglass mold. After the mold is created the mold is sanded and buffed to a mirror finish. Its much easier to work on the mold than the plug.