I take back every mean thing I’ve ever said about my LDS.

[lairdb]

Wood. For sand casting at least, the plugs are normally wood. You can do it with wax, but I don't think you need the fine detail that you get with lost-wax casting (and carving something that big out of wax will be a bore). You could probably make something suitable with some stacked plywood and some bondo. Don't forget to include holes for locating and alignment pins.
Probably an hour on a laser cutter, or if you have access to a slightly larger 3D printer, a day or two... some bondo and some sanding.

I'm really struggling with casting making sense here -- it smacks of cut/punch/press.

 

[The Ruttmeister]

I'm really struggling with casting making sense here -- it smacks of cut/punch/press.

Casting the pressing tools.
Casting the plates wouldn't make any sense at all. But the finished plate is a relatively low precision part and isn't from a particularly hard metal. So a cast iron press tool would make a lot of sense.
Its not done that much any more because people are trying to get higher precision, which cast iron isn't ideal for, when you can usually justify milled tool steel.

 

[lairdb]

Eric, is the profile the same among the sizes? (I'm not sure I'm asking clearly -- let me phrase it another way.) Before the rails are added, do the shapes of different sizes nest? Where I'm headed is this: could a single forming die with common central locating pins be used for all the sizes?

 

[lairdb]

Casting the pressing tools.
Casting the plates wouldn't make any sense at all. But the finished plate is a relatively low precision part and isn't from a particularly hard metal. So a cast iron press tool would make a lot of sense.
Its not done that much any more because people are trying to get higher precision, which cast iron isn't ideal for, when you can usually justify milled tool steel.

Ah, ah -- got it. Agreed, although quantity drives service pricing: machining has gotten so common that it might be cheaper than casting.

 

[Eric Sedletzky]

I’m thinking about a cast iron lower block (the female part) that is heavy enough to hammer on.
The upper part (male part) could be hardwood or cast iron too, doesn’t matter because it will only be used for pressure. The lower block will have line up pins or some sort of 1/4” whatever that will slide through the plate slots for alignment. The top die has cutouts where these alignment pins go into. You drop a flat already cut out plate onto the line up pins onto the lower block that is sitting on a 20 ton press and then you locate the upper block onto those pins and drop it into place. Then you press the plate down into shape in between the upper and lower dies or blocks. Then while it’s pushed in between the two blocks and under pressure you hammer the perimeter roll that is part of the shape of the lower block, that’s why the lower block needs to be iron and heavy. The top block sets back in from the edges about and inch or more to leave room for hammering. When you release the plate from the press it should hold shape.
So this is my idea for a semi automated setup that I can do on a budget in my garage. The press can be purchased at Harbor Freight Tools.
The cast iron blocks can be ground and cleaned up with a flap disc grinder and made slick and shiny. I could make a bondo casting of the inside of a plate in all three sizes from a well formed plate that looks to be about as perfect as I can get it, and those would be the plugs for them to cast me my blocks. I have plenty of experience from my fiberglass part making days. The casting plug could be further scanned by a laser and machined on a C&C machine if I wanted to be that anal about it. But I don’t think I have to get that fancy.
I’m making all these right now by eye balling each and every one of them and hand bending the curves and hand hammering the roll, so a well shaped block would be fine.

 

[lairdb]

I’m thinking about a cast iron lower block (the female part) that is heavy enough to hammer on.
The upper part (male part) could be hardwood or cast iron too, doesn’t matter because it will only be used for pressure. The lower block will have line up pins or some sort of 1/4” whatever that will slide through the plate slots for alignment. The top die has cutouts where these alignment pins go into. You drop a flat already cut out plate onto the line up pins onto the lower block that is sitting on a 20 ton press and then you locate the upper block onto those pins and drop it into place. Then you press the plate down into shape in between the upper and lower dies or blocks. Then while it’s pushed in between the two blocks and under pressure you hammer the perimeter roll that is part of the shape of the lower block, that’s why the lower block needs to be iron and heavy. The top block sets back in from the edges about and inch or more to leave room for hammering.

Are you thinking about hemming the edge, or when you speak of hammering are you just forming the perimeter curve?

 

[The Ruttmeister]

I don't know how much force would be required to completely press the shape (removing the need for hammering)... Plus I've not actually seen a freedom plate in person so I have no idea what the edge geometry is. But hammer formed metalwork, using a buck or form goes back a long long way. You could probably do that and add a pneumatic tool of some kind to do the actual hammering. Holding it in a press while you hammer it will probably also eliminate any spring-back from the pressing.

I did think about hydro-forming, but I'm not sure that would make sense. Too much additional cleanup.

 

[lairdb]

I don't know how much force would be required to completely press the shape (removing the need for hammering)... Plus I've not actually seen a freedom plate in person so I have no idea what the edge geometry is.

freedom plate scuba - Google Image Search

 

[Eric Sedletzky]

Are you thinking about hemming the edge, or when you speak of hammering are you just forming the perimeter curve?

Just the edge roll.
The way these are formed, the strength relies on the edge roll. It’s actually amazing how strong and ridged these get when a few compound curves are introduced. The same theory can be seen with how body panel shapes are formed now days with new car designs and very thin lightweight sheet metal. It just so happens that the Freedom Plate shape was designed for comfort before I realized just how strong that particular shape actually was. But it makes sense since there are several opposing compound shapes at play. When I realized the strength is what lead me to experiment with lighter gauge material to make travel plates that fit nice and are comfortable.
Back in the 60’s I think it was Voit who made a stamped thin aluminum backpack that had an edge roll too and this is what kind of gave me the idea.

 

[happy-diver]