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John:

I'm planing on using 3 clips to secure the router, two fixed clips and one removable (t-nut & thumb screw). I have not been able to think of a better way to advance the sled than Chris's clamp method. The sad thing about all of this is that we've spent so much time and brain power on a jig that we will use rarely and will take a lot of space to store to save $160. I must truly be a geek to get such a kick out of this jig.

I know, in our guitar brochures we can advertise that we adjust our top and bottom guitar radii to suit the individual player, a degree of customization not available from other builders.

That would justify us using our jigs to make unique dishes for each guitar and to really trick them out.

Stay tuned. I want your critique of my jig this weekend!!

I had the box from tapering a solid form (buck) for my Tricones and it leans against wall with my plywood behind my drafting table. The sled unscews and stacks easy enought. Took me a day to put the sled together and adjust the ends of the box and figure out what to do to get the sled to clear. Do you all get about how the rails of the sled just sister on to each other for a different radius dish? The smallest radius is the inside rails. You have to have fun and time to build these jigs.
Yeah that simple cheap HF bar clamp was a neat idea that made the job alot easier nicer end product I think.

I really do not understand the complexity of this design. The design I used was based on one I have seen elsewhere. I put a pin (dowel) in the center of my 2x4' go-bar deck and put the dish on that so it would spin. Then, I built a gantry (bridge) the went over the dish (just clearing it) and locked down on either side of the dish (with some side clearance) to the go-bar deck floor. That gantry is just wide enough for the router, sides keep it in place. Then, put the arc templates in the gantry. Start with the router (bowl bit) at the outside edge of of the dish, bit just touching the dish. Spin the dish and slowly move the router towards the center. 30 minutes later I am done. Sand, shellac, and ready to apply sandpaper.

If you want pics, I will post...

There are always 10's of ways to skin a cat.

Mike

It's one way to skin the cat that doesn't rely on cutting an accurate radius curve on the gantry and minus the router bit extension. You would never know the differences being off in the real world with either approch. That's why I say you could raise the gantry on this design and entend the bit so that the gantry or sled would clear the dish and it won't really be noticed. I guess it all depends on how accurate you fill you want to be. You could also just do the masonite method too. I like the fact that I can cut the straight angle rails and to make another radius I just cut new rails and sister them to the sled. I also like the fact that I didn't have any nasty dust or mess to clean up as the dust collection system worked well for me.
Just another choice.

I tend to make things way more difficult than they need to be. For me building the jigs is getting me used to living in my workspace and figuring out what I need, or need to change, as far as my tooling or process goes. Now that I have done this, I could probably do it differently, easier, and more efficiently. But at least now I know that I can do it.

The cheap clamp idea really makes this a smooth operation. I need to find one that I can use for the full length of travel for the sled. The difference for me was night and day.

Chris,

I follow you on the adding the rails. Once I had them both cut it seams sort of obvious that if you build the sled with the 15' rails you can just add a larger radius rail on top of that one to do other radius sizes for the dishes.

Danny,

For attaching the router to the sled, just make sure the constant vibration of the router does not cause it to work loose. You will see this in the dish when you are done if it does. I know what you mean about the time it takes to save some cash. I sort of feel like an idiot because while I was doing, this Chris offered to let me use his proven setup. One day, a three hour dive each way and some dish blanks and problem solved. But I already know I can drive, so here I now know I can make a dish too. I may not want to, but I can.

Mike,

The appeal of this system is that I didn't have to cut the radius in the rails. I like the idea of the smaller setup that others have shown, but with the tools I have I can cut a straight line and feel confidant that it is straight. To cut rails with a radius already in them, I'm not sure if I could pull that off accurately. If I were to do this again I might try to come up with a way to use a setup like you are describing or is in Vincent’s pictures, but have the router ride on a straight rail. In theory it should work. Most of the complexity that comes across in this thread is just me trying to wrap my head around the math of the long compass system and actually using a router for more that following a template.

John

Here's the thing now that you know how to make a long compass and understand it you can make a long compass that is your router base as the compass base sits flat and rides on two dowels sitting vertically . Place the board for the gantry under the router and cut the radius. It's just like using it to draw an arch but instead of a pencil you use the router to cut. You know what I mean? You could probably use this idea in a lot of ways if you are aware of it.

Chris:

Obviously you are more adept and experienced at this stuff than I and put it together quickly, using scrap, etc. Like John said, the challenge to me is understanding and applying the math and then the accurate conversion into a workable product. I was just joking about the waste of time stuff, although my wife ....

Mike:

I did my first 15' dish as you did, but I just stapled masonite to two 15' radiused rails. The result was not great because the rail/masonite set up flexed too much, I had some slippage with the bit, and tried to salvage it all with sanding and wood filler. My first guitar was fine. Now I am starting a batch of six guitars. I am improving all my jigs (I hope!) to improve my methods and get more consistent results. I have one design surprize for Chris and John I'm waiting to unveil this weekend (only if it works, of course)...

Hey, the great thing is you all are staying engaged in the thread so if the weekend is a failure, I can be consoled and make corrections.


Thanks

Cool, I'm always interested in advancements to design or devancements if it doesn't work. Sometimes you learn from what didn't work too. Don't ask me how I know. Funny thing is I had to do the geometry as I wasn't aware of the tables that was out there till after I made mine. Did all the figuring out of the span rail heigths by putting the dish down in the bow an setting the sled on the box and measuring from the apex to the top of the outside edge of the dish and cutting that space off the box rails. I didn't understand what was happening with the math untill later when I had time to think about it and people were asking me questions about it. That like alot of my jigs are done a bit on the fly. I have the general idea where I'm going or want to go with it and figure it out some what on the way. There always seems to be some curves in the road but that makes the ride a little fun sometimes. Just like John says now that he has it built he knows how to build one probably better but it works. And Danny is doing just that , improving his jigs to make his work easier and better.

What ????

Cutting radiused arc rails is no big deal once you understand how to use the long compass. To me, that was the hardest part. I finally built a long compass out of 30" long, .75x.75 poplar beams. Used a mortised joint with a bolt and wing nut to lock it into posotion.

I experimented with popsicle sticks until I got it down. The beauty of this system is the simple gantry jig to hold the rails.

Mike

Mike if you have a long compass rigged up maybe you could a test for me? Could you set it for a 15' or 25' radius and draw it and then draw it again with the pencil an inch beyond the apex and see what the difference is between them.

Hmmm, I posted a pic of the rails in the "Whats on your bench" thread. The difference is 1/4" in height (the smaller radius is taller) They both come to the same chordal points. Does that make sense?

Mike

Chris, if you have the pencil an inch beyond the apex then you are going to have an arc that is an inch longer in radius, or 25'-1" for the 25' long compass setup. Not a big difference, but there it is.

Well, i promised photos of my jig, but my daughter and her digital camera weren't available until tonight. I got the jig complete and did my first 15' radius dish. I advance the sled 1/4" at a time, with a 1/2" bit and ended up with "terraces" that were easily sanded down with a random orbit sander. All told, I'm happy with the result.

I was disappointed in my dust collection. I thought I had improved on Chris's design by mounting the 4" dust collection to the sled. It got some of it, but way too much dust exited from beneath the sled and to the right. I used a straight bit, not a spiral up-cut and wonder if that would be helpful. I'm thinking about a right-side mount for the dust collection. On the good side, the dust didn't get out of the box.

My surprize addition was a trammel arm to provide for an adustable rise between the pivot and end of the sled. it works well. Right now it will adjust to anything between straight and a 15' radius, but I can alter the sled rails to say a 10' radius for a larger range of dishes.

Thanks for the warnings about the router spinning the dish. I was apprehensive, but it wasn't too bad.

I'll try to post pictures tonight, but have not done that process yet.

You will always need the radius dishes for final sanding and glueing of the braces. But after reading that thread on using a table saw to cut the shape into the braces, well, I think I have discovered my desired approach. That justs looks so easy!

Mike

Barry, I don't think the long compass works like that because it is riding on straight angled rails not curved rails . As a matter of fact if you want a larger radius then the sag or rise is less. I did a test and extended the pencil 4" and the 2 lines I drew on 2 sheets of paper overed laped close to perfect as far as I could see. I think that extending the pencil pretty much draws the arch lines parallel to each other and not concentric. But I could be wrong. The point is that it would work fine. So one could just make the sled without worrying about removing part of it to clear the dish and just raise the span rails an inch and extend the bit an inch below the apex. That would make it a lot easier and faster to build.
Better late then never.

Chris,

I think you are right there. As long as you have the rails at the appropriate distance and the rise cut accurately in the sled, it doesn't matter how tall the rails are as long as the bit can make the reach and cut the final depth. I had made some shims to raise the sled by 1/8" for my 15' dish and didn't end up using them. My dish still came out exact. So the height of the box rails is more of a convince sort of thing. Making them higher, would simplify the jig. That would be way more manageable for storage of the jig than the route I took with the wide sled to avoid clearance issues. It is all part of the balancing act.

John

OK, I'm trying to post the pictures. Gimme a minute.....

OK I'll look at a tutorial and try again.

I'm trying again to send a photo or two of my long compass radius dish jig.

Dan I think you should try and advance it only 1/8" and you wont need to do any sanding. But it looks good in the email. I like the adjustment and good improvement. Also try the dust collector on the other side and see what happens as I'd like to know because that's where the chips are going to be thrown when they clear the bit and dish. The lower right corner that you feed from. If that doesn't help then try and do it like I did as I had no dust problem at all as you can see in the video. If you keep that top of the sled pretty well covered it might help too buy acting like a duct. I had to clean the dust collector filter after the 4 dishes were cut.

Chris:

You're right about the dust collection. After a few turns, I saw the dust coming out of the right side and put a shop-vac with a floor attachment there with an elastice strap. With it and the 4" dust collection it got almost all of the dust. That said I will move the 4" to the side next time and try to eliminate the shop-vac.

I really enjoyed the exercise. Thanks for your help. I guess I'll try to email John with the pictures, as well.

Danny

What is the problem you are having with downloading them here? You should be able to go down the page below the message window and click the Browse button and get to your picture folder and picture file and enter it. Hit add the file for more then one picture and then submit.

Chris:

I've tried that. The file shows up in the browse field, but in subdued text (you jnow, like in a drop down menu and that option is not available). When I hit the add button it goes to the upload screen, then I hit the submit button, go back to the forum and no picture. I chatted with Lance about it and tried the Img button, but ran out of time. I'm sure it is one of those, "aw, sh*#" simple omissions on my part.