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I am setting up to make some dishes. Tomorrow I will get some extera, mdf, or mdf light. Any thoughts on any of these. I like mdf light. I have used Extera but never machined it much.
I am considering that mdf has a tempered "skin" or face and wondering if when I release most of that skin from one side how unstable will the disk be. I would seal with expoxy resin or poly. Extera is more homogenous. I believe they micro wave it unlike standard mdf which is pressed with heat.
So, mdf light, mdf regular, extera. What say you.
Link

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Cut to size.....Beat to fit.....Paint to match.

If I were to make my disk again, I'd use the MDF lite but I'd still double it up to eliminate the warp from a single 3/4" piece of MDF. Mostly to cut down on the weight. Mind you the weight isn't to bad with the normal MDF.

Seal with varathane and you're good to go.

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Link,
Just a little tip...if you are using any MDF, you will want to remove the case hardenening from the flat side of the dish before cutting the concave portion of the dish. When I first started selling dishes, I didn't know this, and we had some come back. It doesn't really matter how many pieces of the MDF you glue it to...it will still warp. If you remove the case hardening, then glue to another flat piece of mdf with polyurethane or epoxy glue, then you will be good to go. As far as what type of MDF...we use extira because of the water resistance ability, that is the only reason. Otherwise, I guess it doesn't really matter. Good luck!

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Tracy
http://www.luthiersuppliers.com

Thanks Tracy,
That was the skin I was talking about. I thought that might happen. Does the same apply to Extera as far as a outer skin. I haven't used it in a while but I remember it as being homogenous so that was why I was considering it to avoid any issues with warpage.
Link

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Cut to size.....Beat to fit.....Paint to match.

Hey Link,

I just finished another run of a dozen dishes. I use two layers of regular mdf, but I glue them together before I spin the dish. I have not had any warping problems at all with them. But I agree with Tracy, if you make the dish from a single piece of MDF and THEN glue it to a backing piece you may have trouble getting the desired radius back. As for weight, two ply dishes weigh bang on 15 pounds with two coats of Varathane Diamond Coat and no sand paper (that's how I ship them). I must also confess that I have never used MDF light or Extera for any project so I have no experience at all with it and they may indeed be better products but I like a bit of weight to the dish and have had zero problems with my dishes that related to the materials (I did have one returned once but that was a good while back and I found the problem and made the adjustments, it was not related to the MDF)

Shane

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Canada

i built 4 radius dishes over a year ago with plain old mdf. i glued two pieces together before i routed the dish, just as shane mentioned. i never coated the dishes with anything and they are still flat as can be. they are, of course, kept in my house where the humidity remains constant. they are a bit heavy, but i like them that way.

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sweat the small stuff.

Link,
Yes, same applies to Extira. You may not have problems by laminating to a bigger piece of backing without removing the case hardening, but in my experience, I don't take chances.

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Tracy
http://www.luthiersuppliers.com

Howdy Link,

I recently made two new dishes for my shop, 1 ea. of 15' and 28'. I used regular 3/4" MDF doubled, and glued them with
TiteBond. After gluing them I clamped them to my tablesaw for a couple of days to make sure they were dried well.

I then cut the radius into one side of each. I have not gotten around to coating them with Varthane yet but they
have remained very stable and warp free for over two weeks now. The most recent one I made before these
was a couple of years ago and I made it of a single 3/4" Melamine board (dense wood particle board center). I didn't coat it
with anything and it has never warped to this day. I do however try to keep my shop at a constant humidity of 45%.

Hope it goes just as well for you

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Bill Hodge


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