A challenging piece of molding

[Dave Falkenstein]

I have been asked by a friend of a friend to make 4 pieces of molding - for a fee. Here is my plan, and I need input on my technique:

The molding is 8/4 oak cut into a roughly semi-circular arc that is about 20 inches across the bottom and 15 inches high. The finished molding will be 1-3/4 inches thick and 1 inch wide. I plan to make a template of the arc first. I will glue up 8/4 oak into a rectangle about 20 by 15, and then rough cut the arc on a band saw. Using a 2 inch long flush trim bit in my router table, I will rout the oak to final size and shape on the router table, using double-sided tape to tape the template to the oak. Finally, I will use a 7/8 inch roundover bit to round the outside edge into a half circle in multiple passes on each side

Any helpful comments appreciated.

[Dave Richards]

It would probably be fine if you are careful to match the grain between pieces so the seam lines don't show. Keep in mind you'll have those seams crossing the molding at what might look like a funny angle.

Any chance of ripping the oak into thin strips with a bandsaw and then bending and gluing over a form? If you keep the strips in order and use epoxy or some other adhesive that won't leave dark glue lines the lines won't be noticeable and the grain will run around the arc rather than across it.

[Andy Hoyt]

Dave - If I understand your intent correctly, I believe you'll end up with a ton of end grain showing. My suggestion would be to miter cut the lumber into the appropriate shape, assemble end grain to end grain with biscuits, bandsaw to rough shape and then flush trim from an mdf template. This would also be much less wasteful of material.

[Vaughn McMillan]

Dave, to echo what Andy suggested, here's a post (http://www.sawmillcreek.org/showthread.php?t=33239) Fred Voorhees posted recently about doing arched moldings. His explanation later in the thread (post #6) of why you'd do it in segments made a light bulb go off for me. Maybe it'll help you out.

- Vaughn

[Dave Falkenstein]

Andy and Vaughn - Thanks for the approach of gluing up the arc in rough shape, rather than as a rectangle. I'll factor that into the project. I think I'll be able to use one biscuit in the center of the joints, and still be able to rout the half round edge without the biscuit showing through. Strength is not an issue, since the molding will be glued onto a flat surface in the finished piece - it is totally decorative.

[tod evans]

dave, this is something i do daily so hopefully i can give good advice... first leave the biscuits in the oven, they cause problems when woodworking:) . if you have the ability to finger joint segments of the radius this is the quickest method, if not a brick stack is actually a stronger and more attractive method, just make sure the horizontal glue lines fall in a fillet of the mould. here`s links to what i do;
http://www.sawmillcreek.org/showthread.php?t=29781
http://www.sawmillcreek.org/showthread.php?t=29782
http://www.sawmillcreek.org/showthread.php?t=29783

hope this helps? .02 tod

[Dave Falkenstein]

Tod - Your threads are helpful - but... The molding I am making is a bit different. The first part of the process would be the same - make a template, form the rough shape using strips of oak and cut to rough size on the band saw. My molding will be glued onto a curved surface - think the vertical surface of a round drum - and the only flat side left after shaping will be the side that glues onto the curved drum surface. Also, my tool inventory includes a router table, not a shaper and/or molding machine. So my challenge is to form a half round surface with the router table and a roundover bit on a curved arc of molding. Any suggestions?


dave, this is something i do daily so hopefully i can give good advice... first leave the biscuits in the oven, they cause problems when woodworking:) . if you have the ability to finger joint segments of the radius this is the quickest method, if not a brick stack is actually a stronger and more attractive method, just make sure the horizontal glue lines fall in a fillet of the mould. here`s links to what i do;
http://www.sawmillcreek.org/showthread.php?t=29781
http://www.sawmillcreek.org/showthread.php?t=29782
http://www.sawmillcreek.org/showthread.php?t=29783

hope this helps? .02 tod

[Andy Hoyt]

Oy!

You're gonna have to post some pics or sketches of that since my head can't wrap that tightly!

[tod evans]

Tod - Your threads are helpful - but... The molding I am making is a bit different. The first part of the process would be the same - make a template, form the rough shape using strips of oak and cut to rough size on the band saw. My molding will be glued onto a curved surface - think the vertical surface of a round drum - and the only flat side left after shaping will be the side that glues onto the curved drum surface. Also, my tool inventory includes a router table, not a shaper and/or molding machine. So my challenge is to form a half round surface with the router table and a roundover bit on a curved arc of molding. Any suggestions?

dave, i`m trying to put this into terms i understand..... are you doing double curviture? or just single? if single then on a horizontal plane, at least that`s what i get from the drum analogy...if this is the case, single curve, horizontal, like a plinth of a column....then brick stack segments oversized clamp and let glue dry. then use a router mounted to a trammel bar to cut the outer radius first then the inner never moving the pivot point..here`s a picture of a p/c edge guide i converted into an adjustable trammel...
34565
if you`re doing double curviture work let me know, it starts the same way but a bandsaw is pretty important......02 tod

[Dave Falkenstein]

Tod - thanks for your reply. The molding is a single curvature measuring about 1-3/4 inches square - the inside radius of about 15 inches is the same as the radius of the "drum", and the larger (or outside) radius is about 1-3/4 inches larger than the inside radius. The molding will be glued onto the drum when machining is completed. The curvature is not circular, so I cannot use a trammel arm. I will make a template from the drum curvature using stiff cardboard and then transfer that inside radius template to 3/4 inch MDF, adding 1-3/4 inches for the outside radius. I was planning to glue up 8/4 oak pieces in the rough shape of the curvature, cut the curvature on the band saw, and use a flush trim bit on the template I made to cut the curved molding to final size on the inside and outside radius. I think I will then attach the molding to a carrier with the shape of the inside curvature with double-stick tape, and rout a half round on the outside radius of the curvature with a 7/8 inch roundover bit in multiple passes, flipping the molding and carrier to create the half round shape on the outside radius of the molding. Does this make sense for my situation???


dave, i`m trying to put this into terms i understand..... are you doing double curviture? or just single? if single then on a horizontal plane, at least that`s what i get from the drum analogy...if this is the case, single curve, horizontal, like a plinth of a column....then brick stack segments oversized clamp and let glue dry. then use a router mounted to a trammel bar to cut the outer radius first then the inner never moving the pivot point..here`s a picture of a p/c edge guide i converted into an adjustable trammel...
34565
if you`re doing double curviture work let me know, it starts the same way but a bandsaw is pretty important......02 tod

[tod evans]

dave, best i can tell it sounds workable? i try to avoid doublesided tape `cause i`ve had it shift in the past but your approach sounds sound..02 tod

[Dave Falkenstein]

Tod - Thanks again for your feedback and advice. I see no way to aviod using double sided tape in this instance, since the finished piece will have a half round edge, and very little flat surface to support the piece as it is run through the roundover bit.


dave, best i can tell it sounds workable? i try to avoid doublesided tape `cause i`ve had it shift in the past but your approach sounds sound..02 tod