Machining spherical convex and concave surface on flat stock

Hi,

Hope I am posting this in the right forum.

I have just a general question. I want to design a part out of either aluminum, or high density plastic and I was wondering,...before I do the print...

Is it feasible to take an hunk of aluminum 4 inches wide and 15 inches long, and machine a spherical convex surface on one side only - leaving the other side flat? And on a second piece, a concave side on one side and convex on the other having the same radius? The spherical radius on both pieces would be anywhere from 24 to 36 inches. The material would be around 1 - 1.5 inches thick after machining.

I am assuming it is possible but I am mainly wondering if this sounds like it would be expensive due to tooling problems. I am assuming some kind of spherical mill bit would be involved. I am assuming this would be nearly impossible to do on a bridgeport so it would be a CNC machine? Would the part be difficult to hold? What about a cheap grade of steel?

I am wondering if I should go with this design or try a different approach for my situation if it is cost prohibitive for low volume machining. I am talking about a few hundred pieces a year tops.

Thanks for any input.

So you want to machine a shallow dish-shaped depression and a matching boss in your 4" x 15" pieces of material? How high a piece would this be? Is the intention to press something in between them? It's hard to talk about alternative approaches unless we know what you're trying to do.

The tooling wouldn't be a big problem; you'd use a 2-flute ball-nose endmill, as large in diameter as your mill would hold. If you decided to do this in steel, you'd use a 4-flute tool. It wouldn't be hard to hold onto if you left some margin on the ends for clamps.

A CNC Bridgeport mill or an equivalent clone would be a good machine to use for this. A manual mill wouldn't work unless it was pretty large, because you'd have to revolve the stock on a rotary table.

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Originally Posted by awerby

So you want to machine a shallow dish-shaped depression and a matching boss in your 4" x 15" pieces of material?

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Yes...If what you mean by "Boss" is a support base for the top plate (not all that up on names of machined parts...)? I want to make a plate that has a flat surface on top of it, and the convex shape on the underside of that flat topped plate will rest in the concave depression or is cradled by the lower support plate. This way I can slightly tilt the surface of the top plate on two axes. On the underside of that lower support plate I want a spherical convex shape that exactly matches the two above radii. The support or bottom plate with the two radii will be held in place for the application via the ends and not the underside - and will support the top plate.

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Originally Posted by awerby

How high a piece would this be?

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Both pieces maybe no more than 1 inch thick tops - thinner if possible. I would go thicker if machining requirements are such.

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Originally Posted by awerby

Is the intention to press something in between them?

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No, top plate resting in and cradled by the bottom dish.

Quote:

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Originally Posted by awerby

The tooling wouldn't be a big problem; you'd use a 2-flute ball-nose endmill, as large in diameter as your mill would hold. If you decided to do this in steel, you'd use a 4-flute tool. It wouldn't be hard to hold onto if you left some margin on the ends for clamps.

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I can leave margin no problem and cut it off later.

Quote:

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Originally Posted by awerby

A CNC Bridgeport mill or an equivalent clone would be a good machine to use for this. A manual mill wouldn't work unless it was pretty large, because you'd have to revolve the stock on a rotary table.

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That's good to know - I was thinking a Bridgeport would not work because they are manual machines and could not be programmed and a CNC machine would be required but I guess things have changed since the last time I used a Bridgeport which was around 1978 LOL.

Does this sound like a fairly simple machining application or does it sound like it's going to be be time intensive and would wear out the mill quickly?

This would take some time, since there's a fair amount of material to remove, but it's not the sort of thing that would wear a mill out prematurely. CNC mills do this all the time; I wouldn't suggest doing it as a manual mill project, though. What you need to do next is to make some drawings, or ideally a CAD model, so you can send it to machinists and get quotes.

The part I don't understand is the "two radii". If this is a spherical depression (or rounded boss) there would just be one radius, right?

OK thanks....the rounded boss part would have the same radii on the underside.

Think this could also be done via 3D printing?

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Originally Posted by nadsab

OK thanks....the rounded boss part would have the same radii on the underside.

[This sounds like the parts underneath an old-style monitor, that allow it to swivel.]

Think this could also be done via 3D printing?

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[Sure, but in plastic it wouldn't have the same strength as in solid aluminum an inch thick, if that matters to you (although you could print it in metal if cost was no object). The surface probably wouldn't be as good either, although whether that matters depends on what you're doing with it.]

Thanks for all the info last year awerby.

I am re visiting this..... so I am assuming that the 2 or 4 flute ball-nose endmill does not actually have a spherical radius to match my radius - and putting very large concave or convex spherical radii on metal is done by clamping the part on a table - the table turns and the end mill projects further into the stock as is goes toward center in the convex piece and opposite for the concave piece. Kind of acts as a bit cutting stock on a lathe - is this about correct? I would assume the most economical way to have it machined is by a CNC machine? If I was running several dozen or a hundred parts or so?

printing don't gives precision like machining..