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Well Folks I have made a 15' and a 25' radius sled ready to rout some dishes on the weekend. I have cut 4 600mm disk (24") out of some 36mm (1.5") MDF and have cut same in 19mm (3/4") ply. The ply disk have now been laminated to the MDF which gives me 4 x 600mm laminate disk @ 55mm (2 1/4")thick.

My focus is steel string guitars so the 15' and 25' radius combo seems the most useful. The choice, I can rout 2 of each and have say 1 of each with 80grit and another of each with say 120 grit to finess the profile. Alternatively, I could just make some other sleds for the router and have 4 different radii dishes all with 80 grit.

So, my questions are, which of these choices do you feel would be the most useful in the long term? If it were you, how would you proceed? If 2 more radii is your option, what extra radii would you choose and why?

Thanks all

Kim

Would be preferable to have more radius option than finer grit. I would make a 20' and a 28' or 30'

I use 20' and 28'.

Yeah, I'd go with more choices too. I think a 20' and a 28'. I build SS and use 15' and 25' and always use 80 grit paper. Don't really need to finesse the radius, when it's there it's there.

-Mark

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Pullman, WA

The more I know, the more I know I don't know.

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I agree with them all Kim. I make these dishes and sell them. I just ordered more radii from a friend of mine who draws them on Autocad. For me the most popular radii are 15, 25 and 30. I have done the odd 28. One of my customers uses 17 and 32, another is going very flat. I have a lot of dishes but have found that I am best to just use one dish for each radius, glue on a SINGLE sheet of sandpaper (joining small sheets was a proplem for me when edges started to lift, a single sheet is a must in my book) and if you use it as a go-bar deck then just slip a sheet of paper over the sandpaper.

Good Luck!

Shane

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Canada

Kim,

I have two each of 15' and 25'. I also have 30' dishes but Ive never used them. One set sits in the go bar deck and the other set is loaded up with sandpaper (120 grit).

I got my dishes from LMI...cant be bothered routing around with MDF/customwood.kiwigeo38953.0558796296

I make my own dishes as well and just have 15'and 25' as I've never felt the need for anything else. With mine though I made two of each from 18mm MDF and then glued them back to back with a 12mm ply centre. I then put 100grit (couldn't get 80 locally) on one side of each radius. No risk of a tear in the paper exposing sandpaper when I don't want it.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

I will approach the question like this. I have one dish of each radius with 100 grit paper. each dish is 3/4 MDF laminated to a 1/2 MDF flat disk to increase life and rigidity. I use these same dishes on the go-bar deck for brace glue up. I lay a piece of 4mil mylar over the sand paper to protect the wood. In my small shop space is a moderate premium.

As far as should you add other radii dishes to the assortment? That is a question that can only be answered by asking your self do you want to build a variety of dome radius's. My self I build all my models with 15' back domes and 28' top domes, but I have cosidered adding a 14' dome to the mix. If I do I will make me an other dish and brace shaping jig. I don't know any other way to answer that question.MichaelP38953.4644097222

Mine are like Colin's. Two 7/8" disks glued back to back, same radius on each, sandpaper on one side , the other plain. I have this in 15' and another at 28'.

Ron

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OLD MAN formerly (and formally) known as:

Ron Wisdom

Somewhere in the middle of Arkansas......

Perhaps this thread is too old, but I have a related question.

I am a relative newcomer to guitar building and have had to build some of my own forms and tools.

I built a 15' radius dish using 3/4" thick MDF and a router. Once I got it out of the jig to rout it, it almost immediately cupped, making the effective radius much smaller than 15'. I was able to flatten it out somewhat by gluing it to another piece of 3/4" MDF, but I never got it completely straightened out.

Anyone have a similar problem with cupping like this on an MDF form?

Any suggestions on how I should have built this to avoid the problem?

[QUOTE=Matt H] Perhaps this thread is too old, but I have a related question.

I am a relative newcomer to guitar building and have had to build some of my own forms and tools.

I built a 15' radius dish using 3/4" thick MDF and a router. Once I got it out of the jig to rout it, it almost immediately cupped, making the effective radius much smaller than 15'. I was able to flatten it out somewhat by gluing it to another piece of 3/4" MDF, but I never got it completely straightened out.

Anyone have a similar problem with cupping like this on an MDF form?

Any suggestions on how I should have built this to avoid the problem?[/QUOTE]

Hi Matt,

I used 3/4" ply as a sub-straight upon which I glued the MDF. I have routed the forms and they are solid as a rock.

Cheers

Kim

I just used two pieces of MDF, but I glued them together before I started routing (both sides), and haven't had a problem. I haven't even put any kind of sealer on it yet, though I intend to.

Ron

_________________
OLD MAN formerly (and formally) known as:

Ron Wisdom

Somewhere in the middle of Arkansas......

Larkin & Old man,

Thanks for the tips, I guess I will have to rebuild the jig I used to make the first forms. It will only allow for 3/4" thickness.

Old man,

As another Central Arkansas resident, Hopefully we can connect some day. I certainly would love to see your shop and what you are working on.

Terken,

I have cut two dishes, and I did it outdoors and can say I am glad I did.

Still curious as to whether anyone else has experienced the cupping problem without a backer board.

Thanks everyone for the help!

Matt
Little Rock

Been said here already, but I'm in the "put sandpaper on them and leave it there for everything" camp...I just slip my guitar plan in there when I'm go-barring things together...I use 15 and 25, two pieces of HDPB laminated...and if you make them yourself do it a a friend's house!

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http://www.presnallguitars.com

Matt,
This is a known issue when having wood that is made under pressure during the manufacturing stage. There is a way to relieve the pressure, and we do this when making our dishes. I don't want to give away our secret, but that is why are dishes stay flat longer, and come flat. You may still have issues with a stubborn board, but for the most part, it will stay flat. Sorry I couldn't be of more help. Best of luck in your building!
Regards,
Tracy

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Tracy
http://www.luthiersuppliers.com

[QUOTE=Matt H]

Old man,

As another Central Arkansas resident, Hopefully we can connect some day. I certainly would love to see your shop and what you are working on.[/QUOTE]


Love to meet you, Matt. You're welcome to visit.

Ron

_________________
OLD MAN formerly (and formally) known as:

Ron Wisdom

Somewhere in the middle of Arkansas......