How do you do this?

[Otter]

I vote for this approach.

I second that..

[radhak]

The proper tool here is a shaper. If you can locate a right-sized router bit, can be done on a router table.
http://www.grizzly.com/catalog/2007/Main/468 - see 'internal radius' bits. Available in 3/16, 1/4, 3/8, 5/8, 1 1/8" cutting radius. If the groove is shallower than a full semicircle, you'll need to do one of the following:
Install a larger guide bearing.
Enlarge the bearing by winding thin strip of tape around it.
Then, use a beading bit to round off the edges.

Could I use a fence on the router table to control the depth of the groove/cove? I see that Grizzly's bits have a cutting height of 3/8", so if i place the fence carefully, and set the bit height appropriately...?

[bthere]

If the groove in the center isn't a huge deal to match the rest of the design, what about making 4 brackets, replacing the existing ones, also? Then you have all the brackets match exactly.

[JR]

Could I use a fence on the router table to control the depth of the groove/cove? I see that Grizzly's bits have a cutting height of 3/8", so if i place the fence carefully, and set the bit height appropriately...?

Yes, you could do it that way. I'd thing you'd get a sort of flattened curve doing that.

BTW - Your comment about cutting height is specific to two of the bits shown in the referenced chart. With available cutting heights of 3/8", 1/2", 3/4", 1", and 1.5" I'd think you could find one that would come close to your original, no?

JR

[LarryG]

(Deleted. Wasn't thinking.)

[LCHIEN]

Could I use a fence on the router table to control the depth of the groove/cove? I see that Grizzly's bits have a cutting height of 3/8", so if i place the fence carefully, and set the bit height appropriately...?

The curve ball in your original problem is that the groove is in a curved surface.

That means that the most obvious suggestion, using a round-nose bit and a fence and the piece on edge cannot be used. Because of the curved edge against the table height changing issues.

That means that an edge cutting bit, not a top cutting bit is needed. Also a bearing for pattern following is required.
I imediately though that a bullnose bit was right but the wrong direction and needs a bearing. The MLCS catalog did not even list such a bit but Scorrpio found one called an inside radius bit.
So being a side cutting bit, the bearing chosen sets the depth of the groove, the bit height is set to center the groove in the edge of the workpiece. Of course you have to precut the curve.
You'll have to make final cuts with an elevated roundover bit to soften the edges of the groove.

[LarryG]

That means that the most obvious suggestion, using a round-nose bit and a fence and the piece on edge cannot be used. Because of the curved edge against the table height changing issues.

Oh, you're right ... I completely forgot about the concave portion (ironic, because it's the same limitation that would keep this from being done using a table saw).

EDIT: Okay, I've been thinking about this and sketching it out, and I think the best way to do it would be:

Pass #1: bullnose bit to round (fully) one edge. The bearing of the bit rides on the center of the workpiece's edge.
Pass #2: bullnose bit to round the opposite edge. The bearing of the bit rides in the same place.
Pass #3: fluting bit to remove the middle, concave portion. The bearing rides on the crown of one of the rounded edges.

A roundover/beading bit MAY work, if the straight (beading) portion of the cutter isn't so long that it gets into the opposite edge, and/or the bit's body isn't too large to nestle into the center groove. But I'm thinking both of these may be issues with a workpiece that's only 1" thick.

[Tom Miller]

It looks like these pieces are going to be painted(?)

If so, here's one more flog for the dead horse:

How about making the pieces by face-gluing two pieces of 1/2" stock? Then, use a cove bit and a round-over bit, as shown:





NEXT!


Regards,
Tom

[BasementDweller]

Bingo! I'm with you Tom.

It looks like these pieces are going to be painted(?)

If so, here's one more flog for the dead horse:

How about making the pieces by face-gluing two pieces of 1/2" stock? Then, use a cove bit and a round-over bit, as shown:




NEXT!


Regards,
Tom

[scorrpio]

Could I use a fence on the router table to control the depth of the groove/cove? I see that Grizzly's bits have a cutting height of 3/8", so if i place the fence carefully, and set the bit height appropriately...?

Can't really use fence because of the shape of the piece. The concave portion will not reach the bit.

You might want to invest in a bearing kit from MLCS which includes many different size bearings that will come in handy on quite a number of projects for depth of cut tweaking. The Grizzly bits I linked come in a fairly wide variety of heights. and for 1" thick piece, a 3/4" bit (G1272) seems like a good fit. The default bearing on it is 13mm OD/5mm ID, which results in full 3/8" deep groove. The MLCS kit includes 16 and 19mm OD/5mmID bearings, which can be used with above bit to produce respectively, ~5/16 and ~1/4" deep groove.

[radhak]

Can't really use fence because of the shape of the piece. The concave portion will not reach the bit.

You might want to invest in a bearing kit from MLCS which includes many different size bearings that will come in handy on quite a number of projects for depth of cut tweaking. The Grizzly bits I linked come in a fairly wide variety of heights. and for 1" thick piece, a 3/4" bit (G1272) seems like a good fit. The default bearing on it is 13mm OD/5mm ID, which results in full 3/8" deep groove. The MLCS kit includes 16 and 19mm OD/5mmID bearings, which can be used with above bit to produce respectively, ~5/16 and ~1/4" deep groove.

Yes, now I realize/remember the futility of using the fence - the very reason I had to post for help in the first place, duh ! But your suggestion about the bearing kit could be the answer, thanks.

Tom's idea about of using two pieces makes sense too, but i want to try (even if fail) the 'tougher' way first. Mebbe just for the excuse of buying those extra bits / kits.

Thanks everybody for the education!