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maybe im too hard on myself
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10102&t=13198		 Page 1 of 1
Author:  Heath Blair [ Mon Aug 13, 2007 3:05 pm ]
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well, with the wood for my first on its way, i thought id get to work making some radius dishes this weekend. cutting out round sheets of MDF for the dishes is simple easy. making a jig to cut the dish is easy enough. the rails that the router will ride on... AngryAngryAngry! my first try at drawing the arc for the rails was with a pencil and string. after numerous tries and no satisfaction, i thought i would move on to another method. i ended up plotting some points and measuring real accurate like with my dial calipers. turned out ok i guess. after lots of hours in the shop this weekend and today i decided to call it good enough. i guess i just want to know, what is good enough. i am a very meticulous person and i really want well, whatever i do, to be perfect. i think a certain degree of this is good, but when is it over the edge? are you all satisfied with the dishes you made? i may just buck up and spend some cash, but i was really hoping to use my limited budget elsewhere. what do you think?
Author:  WaddyThomson [ Mon Aug 13, 2007 3:16 pm ]
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Chris Oliver did some radius templates that can be printed from Adobe Reader.  I was able to print them by setting my paper size to a custom size of 8 1/2 x 22" (22 is the length of a piece of poster board).  I cut the 8 1/2 width and put poster board in my Epson printer and it printed great.  It has to be a printer that feeds paper from a back feeder in a straight through pass with limited bending.
Author:  Bruce Dickey [ Mon Aug 13, 2007 3:34 pm ]
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Of course for this method you need a wood deck over 25 feet long. I tack a nail, hook my tape, walk 25 or 15 feet from the nail. Lay down an arc on my blank which is tacked to the deck with some #4 finish nails, hold the pencil steady on the tape edge and draw an arc. Easy as falling off a chair.

Good luck, you have a great future ahead of you. Don't be so hard on yourself.
Author:  Michael Dale Payne [ Tue Aug 14, 2007 1:10 am ]
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All you need is a flexible straight edge over 24" long, 3 finishing nails a hammer and a pencil. Nail two nails 24"+ thicknes of straight edge apart draw a straight line between them, this is the chord. measure 12"+ halt the thickness of the straight edge from either nail along this line and draw a line perpendicular at this point this is the rise line. measure up .2401" (this is the rise)-thickness of the nail. Now flex the straight edge around the outside of the middle nail and around the inside of the outer nails. There you go you have an accurate 25' radius arc on a 24" chord.

For a 24" dome dish the chord will always be 24"
The rise changes with the radius
15' radius the rise on a 24" chord length is .400
Author:  Chris Oliver [ Tue Aug 14, 2007 3:38 am ]
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Heath,
I know exactly what you're talking about. I made my own first template and couldn't play the following evening because my hands were too stiff and sore from rasping and sanding. I followed up by purchasing the other template I needed and making my runner with the flush trim bit.
By the way, Christian actually posted those adobe template files, although I think it was on Hesh's last discussion about 'What's on your bench.'
If you continue on your own, I feel for you.
chris
Author:  JohnAbercrombie [ Tue Aug 14, 2007 4:21 am ]
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[QUOTE=Hesh1956]
It is pretty important that your radius dishes be true and uniform [/QUOTE]
Why?
I doubt that anyone who is checking here at the OLF would do such a rough job on a dish that it would affect the quality of the guitar they build.
Whether the top radius is 24, 25 or 26 feet makes little difference by the time you get to the finished guitar. You should be checking the neck set in relation to the bridge height anyway, 'as you go'.

The top wood will not bend to follow every little waver in the radius dish, when you use the dish to support the top during gluing. Often, dishes with sandpaper attached are cushioned for use in glue-up anyway.

If you are using the dish for sanding, the sanding movement will tend to 'average out' any small irregularities.

I've built 4 guitars in my home-made dishes (and 1.25 inch particle board) and the dishes haven't caused any problems. My advice is to make some rails using reasonable care (use the hints in the posts above and smooth by hand with a sanding block), set up your router jig and carve the dishes, then smooth with a RO sander. Check with a flexible batten, and then worry about something else.

We're working with wood here, not billets of titanium, so let's not let the CNC ethos get us measuring to 0.0001 inch. Many, many good guitars have been built using flat workboards with a perimeter spacer to develop an 'arch'.
And, of course, you can profile your rims with a plane and a sanding stick, without using a dish at all.

As one of my bosses used to say: "Finish up yer coffee and lets get at 'er, boy!"

Cheers

John
Author:  Wayne Clark [ Tue Aug 14, 2007 7:53 am ]
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I can second Michael's approach. I made two dishes using the same approach. It worked pretty well, and made one heck of a mess. If you are making them out of mdf, try to do it outdoors.
Author:  crazymanmichael [ Tue Aug 14, 2007 10:50 am ]
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i find it much simpler to buy a radius template from one of our sponsors and use it and a patern following bit to route the rails. my time is worth far more than the $20 or so the template costs me.
Author:  Heath Blair [ Tue Aug 14, 2007 10:52 am ]
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[QUOTE=JohnAbercrombie] [QUOTE=Hesh1956]
It is pretty important that your radius dishes be true and uniform [/QUOTE]
Why?
I doubt that anyone who is checking here at the OLF would do such a rough job on a dish that it would affect the quality of the guitar they build.
Whether the top radius is 24, 25 or 26 feet makes little difference by the time you get to the finished guitar. You should be checking the neck set in relation to the bridge height anyway, 'as you go'.

The top wood will not bend to follow every little waver in the radius dish, when you use the dish to support the top during gluing. Often, dishes with sandpaper attached are cushioned for use in glue-up anyway.

If you are using the dish for sanding, the sanding movement will tend to 'average out' any small irregularities.

I've built 4 guitars in my home-made dishes (and 1.25 inch particle board) and the dishes haven't caused any problems. My advice is to make some rails using reasonable care (use the hints in the posts above and smooth by hand with a sanding block), set up your router jig and carve the dishes, then smooth with a RO sander. Check with a flexible batten, and then worry about something else.

We're working with wood here, not billets of titanium, so let's not let the CNC ethos get us measuring to 0.0001 inch. Many, many good guitars have been built using flat workboards with a perimeter spacer to develop an 'arch'.
And, of course, you can profile your rims with a plane and a sanding stick, without using a dish at all.

As one of my bosses used to say: "Finish up yer coffee and lets get at 'er, boy!"

Cheers

John
[/QUOTE]


i really need people like you in my lifeBig smile. sorta the yen to my yang... or something like that. i was just thinking to myself, if this dish isnt perfect, then the braces i sand in it wont be perfect, then the top wont be perfect, and so on and so forth. one big snowball. thanks for bringing me down to earth. i just figured that i need all of the help i can get to do this thing right. ive started out with less than adequate tools before and cussed the whole way. this should be a happy buildBig smile!


what i found with the straight edge and nails routine is that you end up with a flex in the middle of the straight edge and much flatter as you move away from the center. not a true arch. so i used numerous points along the arch and drove nails into each one. then flexed the straight edge across that. like i said, it worked out ok. im gonna give it a go in the next couple of days if i can find some time. ill let you know how it goes.


thanks for the help and encouragement guys.

Author:  Alain Lambert [ Tue Aug 14, 2007 12:47 pm ]
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Check with a printing or copy business if they can take Autocad files and print them for you on large paper (36")

If yes, I or other members here can send you a drawing to print a template.

Or use the long compass method to draw them.
Long Compass
Author:  JohnAbercrombie [ Tue Aug 14, 2007 3:24 pm ]
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Heath-
Thanks for the comment!
When I re-read my post, I thought; "oh, oh...I'm gonna get it for saying this!" Glad it didn't sound too bad.
Unfortunately I haven't been able to blame any of my (many) mistakes in building on my dishes and workboards
For example- my latest was putting some dings in a cedar top (already finished with FP) when I was peeling off the masking tape after gluing the bridge. Moral: Fingernails are (much) harder than cedar. So don't worry, your future path will be full of 'experiences'.....

Cheers
John
Author:  Heath Blair [ Tue Aug 14, 2007 4:39 pm ]
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alain, thank you for the offer. very kind of you. the long compass is so very cool! ive heard the term before, but had no idea what it was. now i know. and i might one up g.i. joe and say knowing is more than half the battle! 
Author:  Chansen [ Tue Aug 14, 2007 4:57 pm ]
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The compass is a pretty cool trick! So do you have to know how much "higher" the middle point is?
Author:  Mike Mahar [ Wed Aug 15, 2007 2:25 am ]
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[QUOTE=Chansen] The compass is a pretty cool trick! So do you have to know how much "higher" the middle point is?
[/QUOTE] Yes you have to know how much higher the middle point is. That is the variable that makes one long compass different from another. MichaelP gave the values for 15' and 25' above. Pythagoras will give you the values for other radiuses.

For 20':
20' = 240"
1'= 12"

240^2 = 57600
12^2 = 144

diff = 240 - sqrt(57600-144)
diff = 240 - 239.70
diff = .30" rise for a 2 foot arc


Author:  Alain Lambert [ Wed Aug 15, 2007 11:17 am ]
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There is a spreadsheet on the MIMF archive that calculate the rise of the midle point.

Radius.zip
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