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You should have a look at expanded PVC sheets. I buy it in 1/2" 4X8 sheets that I use for jigs and other fixtures.

You can glue it with CA glue and you can use a router on it and it sands smooth. As I said I buy it in 4X8 sheets and cut it just like wood on my table saw. I have used this for a number of years for all kinds of things.

Here is a link to what it is but you can find it all kinds of places. Just search for Expanded PVC sheets.

https://www.vimapvc.com/product/pima-expanded-pvc-foam-sheet-4-x-8-thickness-1-2-12-7mm/

It can also be bent and shaped with heat but it is flexible enough that you could probably make a dish by just using shims to form the curve.

Maybe something you could use?

Cheers,
Bob

A generous offer, Brad! How about bringing just some scraps, so I can see what it looks like? I remember something similar being offered at Woodcraft or Rockler when it was super tough to get real BB plywood. I have some sources, but it is surprisingly hard to get great plywood here locally. We grow it and make it, then ship it out!

While I always keep some around the shop, I ordered some extra BB plywood last night so I can experiment with making radius dishes with it. Two thicknesses of 13 ply (18 mm each) should be thick enough to minimize warping. I made some dishes from MDF a looong time ago, and have preferred buying them since that time, but I’m looking forward to making them myself again, so I can make them exactly the way I want. Thanks to all for your input! Keep it coming for the sake of future experiments; again, I would love to hear about other materials that have worked for you, and we all benefit from documenting both successes and failures with different materials.

a piece of advice if I may...

wood is wood and prone to internal stresses in addition to it's propensity to moving after being milled up.

being in the middle of a project where I am having to mill up jambs out of 1" thick poplar the above concept is freshly in my head. that being said, I'd approach the final shape slowly, then attach the nearly finished dish to a flat backer board, then finalize it's shape. and remember the rule of wood glue I learned here: it takes a few days for wood glue to get close to being cured (I remember a post here where a luthier reported hearing changes in tap tone of tops up to 14 days after glue up)...e.g. let any glue up dry thoroughly before proceeding with shaping

if the marine grade plywood being referred to in a previous post is Meranti, then yeah, that's some good stuff in general. the thing about plywood is proper storage and handling...a prime example of bad handling is buying a 4x8 sheet and transporting it leaning up on the tailgate of a short bed truck in 100+ degree direct sun...a prime example of bad storage is leaning it up against a wall on the 8' axis.

just my two pennies

Message received, Mike. I was actually already thinking about ways of managing this. One way might be to use a structural epoxy to stick the two layers of wood together, and clamp it all down to my flat workbench for the full cure time (and then some). And if the pieces of plywood have a little warp in them, I can point any cupping to the inside. I was also thinking about screwing the dished piece of plywood to my workbench through dogholes during the dishing router cuts. That should keep it flat during the cutting. I appreciate the heads up.

Interesting pricing update—

I contacted someone (not an OLF participant or sponsor) who normally sells MDF radius dishes for around $70 USD, before shipping. I wanted to see if they would cut identical dishes for me made from Baltic Birch plywood, just to save me the time and hassle of doing it myself. They quoted me a price of $200 per dish, before shipping, and this is just for the 18 mm thickness of plywood, no extra layers for stability. Those would have cost extra.

I am going to dish these myself. I’ll gladly pay extra for special orders and good quality, but that markup was too much. I’ve cut dishes before. It’s a hassle, and I would love to pay someone to do it, but not when they price the job like this.

Don,
Twenty+ years ago I had access to some 3/4 marine plywood. I face glued two pieces, cut it into a round and the dished out 28’ on one side and 15’ of the other. I just recently motorized it and it has absolutely no wobble and runs true. Oh yeah, applied a sealer (probably a thin shellac) after dishing it.
Tom

Hey Don. I mentioned Luthier Suppliers earlier in the thread. I looked at their site last night and see the baltic birch dishes listed as out of stock. It might be worth contacting them (Tracy) to inquire about availability?

James—

It’s a good idea, but I have a better solution. Brad Combs is coming to the rescue. He wanted to tinker with new dishes anyway, so he’ll be cutting his and mine. Many thanks to Brad!

OLF for the win!

Another option for those with vac.
Should work on other flat, non porous surfaces too.
Mark my words, you'll never go back!!

Sent from my Pixel 5a using Tapatalk

David—

Vacuum is definitely cool; I see how it keeps even a thin dish flat. But it still involves manually driving the bus (rims over dish). I built a motorized sander, and I ain’t goin’ back! Photos and descriptions are here:

viewtopic.php?f=10101&t=51545&hilit=Motorized

Sweet set up Don!

I have my mom's old potters wheel in the basement.
I've seen really nice vacuum chucks for holding wood bowl blanks on lathes while turning. someday it could be the best of yours and mine at the same time!