How to cut concave dome into wood?


RickPick

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Hi folks. Totally new to this site and far from an experienced woodworker. I’m wanting to cut/rout/drill/gouge a shallow dome-shaped hole into a piece of 3/4” hardwood, and I don’t know the best tool/method to use. The diameter of the hole is 2 1/4 inches, and the depth at the center about 3/8 inch. I own a router but never used it before, and thought this would be the tool for the job. But as I look at the router and the few cutters I own, I’m not so sure a router is the best approach. I’m not sure if I need a specific cutter for this size depression, or some other approach entirely. Any guidance would be appreciated.         P.S. I’m probably looking at making a dozen or so of these concave domes.

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How critical are those dimensions? The measurements stated require a diameter of 3.75", if I did the math right. 

A tablesaw is great for milling spherical depressions, just spin the wood over the center of the running blade while slowly raising it to the desired height. You might substitute a biscuit cutter or angle grinder in a shop-made jig to do the same thing with an appropriately sized blade. Far simpler than making a router pendulum, for sure!

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1 hour ago, Tpt life said:

Scorp? Honestly, I’d look for the right size sphere. Then I’d use sand paper on it in a drill press. 

Thanks. I’d never heard of a scorp, but thanks to you and google, I’m now much better informed! Can you explain what you mean by “the right sized sphere,” please?

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28 minutes ago, wtnhighlander said:

How critical are those dimensions? The measurements stated require a diameter of 3.75", if I did the math right. 

A tablesaw is great for milling spherical depressions, just spin the wood over the center of the running blade while slowly raising it to the desired height. You might substitute a biscuit cutter or angle grinder in a shop-made jig to do the same thing with an appropriately sized blade. Far simpler than making a router pendulum, for sure!

Thanks, but not sure where you got 3.75”. If this depression were actually a hole through the piece of hardwood, the hole would have a 2 1/4” diameter. But it is not a hole; it is only a concave depression (shaped like an inverted dome) that is 3/8” at its deepest. I don’t have a table saw or a biscuit cutter (which, I assume, is not a dinner knife from an 18th Century man-of-war).   ;)  I’ll try to post a picture in a minute.  

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16 minutes ago, RickPick said:

Thanks, but not sure where you got 3.75”. If this depression were actually a hole through the piece of hardwood, the hole would have a 2 1/4” diameter. But it is not a hole; it is only a concave depression (shaped like an inverted dome) that is 3/8” at its deepest. I don’t have a table saw or a biscuit cutter (which, I assume, is not a dinner knife from an 18th Century man-of-war).   ;)  I’ll try to post a picture in a minute.  

image.thumb.jpeg.eaa2d2ad70d97f10c15dd374dc9da4e5.jpeg

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Well, that didn’t go as planned.... But there’s a picture. You can see the concave part on the right. On the left side, there is a similar-sized piece of wood with an identical depression turned down, not up. I had planned to make the depression as a dome in one piece of wood, then saw it in half. I see now, however, that the depression isn’t truly a half circle, but more a half oval.      To respond to the question about how critical? Not much, but I was impressed and amazed at the engineering possibilities of holes in wood!              For the curious, the picture is of a simple tool for holding oysters for shucking. I saw one back east this fall, and took some pictures in hopes of making a few for Christmas presents for friends. But shaping those depressions into which the oyster shell fits has stumped my limited woodworking knowledge. Thanks for your help. I’ve already learned a lot today!

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Since those are separate pieces and the exact profile is not critical, I’d just grab a rounded file or rasp and do it that way. Draw a couple reference lines and go to town, it would only take a couple minutes. Then smooth things out with sandpaper. 

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53 minutes ago, K Cooper said:

OP, the end product will be just one piece though, right? 

Speaking of shucking oysters, I picked this up in Louisiana a couple of months ago and unfortunately, I haven’t had a chance to use it yet. It’s made of lead. 

EF430782-7A3B-488F-B53E-20A47195B820.thumb.jpeg.1a343836a1b564f0bbcc5f0ee5a004e2.jpeg

“End product”? Yes, the completed shucking tool is one piece, made of 4 separate pieces attached together. Two of those pieces are identical, and have the scooped sections. I had planned to use some dark mahogany I salvaged from an old bar top for the base, and use a lighter hardwood for the other pieces. Maybe pegged with dowels of contrasting colour.       I generally prefer working with hand tools and prefer a surface that has been planed to a sanded one, but I might be “mass producing” quite a few of these scooped pieces, so I was thinking I might finally learn how to use a power router I bought 40 years ago and have never used! Sounds like it’s not even a job for a router though.     Think I’ll see if I can find a scorp. Interesting tool maybe up my alley. And by the time I’ve scooped a few, I’ll have gained a bit of skill at using it.  ???
 

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I googled scorp and all I found referenced S Corp.

if it were me, I would draw the od of the circle on the board and then draw the id. Then find the center and drill several 1/4” holes close together in the center, to the depth that you’re wanting the thickness of the bottom to be. Using a inexpensive Dremel Rotary Tool and a ball shaped bit to grind down to the depth of the holes that you drilled. Then, using the same tool, shape out to the id line that you drew. Then cut the board in half. 

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To do this with hand tools you could use carving gouges. Basically chisels shaped for this kind of work;

https://www.highlandwoodworking.com/carving-tools.aspx

Scorps do fit into this category and I actually own a few for chair making. A correct sized scorp used with a gouge or two would work well.

https://www.highlandwoodworking.com/hirsch-scorp.aspx

 

Now if you want to do this with a power tool than a company named Arbortech has a sweet lineup of carving and shaping tools. Most are attachments that are used on an angle grinder. Looking at their lineup I think the Ball Gouge would make quick work of your job. Here's a link;

https://www.arbortechtools.com/us/woodworking/

Boy, after watching the video on that link I think I have some ideas for my Christmas List!!

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