Miters at arbitrary angels?

[Michael Sobik]

I have a little problem with some moldings I'm trying to apply. The molding is an arch that intersects with two straight pieces like so:

http://www.sawmillcreek.org/attachment.php?attachmentid=123474&stc=1&d=1248351908

The angle formed at the intersection is some arbitrary angle determined by the radius of the arch and the width of the molding.

Anyway, I fought cutting/fitting these for a few hours yesterday and I have a lot more insight into what doesn't work :mad:. But I'm no further along getting them fit properly.

How do you accomplish this? For 45° miters, I saw them rough by hand then clean them up on the shooting board. I tried this method with this piece, but have no way to accurately shoot them. And just to tick me off both sides are just a tad different :rolleyes: Any tips would be greatly appreciated!

[John Keeton]

Michael, my "angels" are arbitrary, too!! Somedays they seem to be there - others not so much!:D

I just had to say that!

To the original question, I have always bisected an angle, drawn a line for the bisecting cut, and then cut each piece to the line - not really knowing what angle it actually measures. I'm not sure I recall doing this with an arc on one side, but I certainly would try it. Here is a pic (http://www.gogeometry.com/geometry/euclid_book_i_9.gif) of the process.

[Michael Sobik]

Haha! Yeah, I have the layout correct. I've bisected the angle and I can measure it, but doing the actually cutting and trimming is the problem. I mean do I make a dedicated shooting board, try and plane them freehand, hold them on the shooting board without using the fence, use the belt sander (gasp!)?

To make things worse the molding will be right at eye level so it has to be perfect.

[John Keeton]

Michael, I would have to admit that this is where my power (dirty word in this forum!) miter saw comes to play! I use test pieces, and mark them, then sneak up on the mark.

[Don McConnell]

Michael et al,

This isn't going to solve any technique problems (i.e. special shooting boards, &c.), but it is my understanding that when a curved moulding and a straight moulding meet, the miter is actually a curved line. Oddly, two equally curved mouldings curving in the same direction will meet in a straight miter.

In any event, the area at the miter needs to be drawn full-size, including accurately placed/drawn lines indicating each element of the respective moulding segments. As I guess is probably obvious, the lines on the curved segment need to accurately follow the curve. The curvature of the miter is determined by a series of points produced by the intersection of those accurately drawn lines. A slow, uniform, curve drawn through those points will be the true miter line.

If you need visuals for this, Charles Hayward touches on this, using text and illustrations, on pages 86 - 88 in his _Woodwork Joints_.

As to technique, my first thought is that this may call for some careful work with a coping saw and clean-up with a very slow gouge on the concave miter line and a block plane on the convex miter line.

Hope this helps a little.

Don McConnell
Eureka Springs, AR

[David Keller NC]

The angle formed at the intersection is some arbitrary angle determined by the radius of the arch and the width of the molding.

How do you accomplish this? For 45° miters, I saw them rough by hand then clean them up on the shooting board. I tried this method with this piece, but have no way to accurately shoot them. And just to tick me off both sides are just a tad different :rolleyes: Any tips would be greatly appreciated!

Assuming that you're talking about relatively flat moldings (if not, such as the case of a large cove on both the straight pieces and curved molding, the curved meet line that Don references would be the case), you can make the pieces meet at an arbitrary angle that's determined by the intersection of the outside edges of the molding with a line drawn from the inside corner.

When I've done this, I haven't measured anything - I worked to knifed layout lines and "snuck up" on the fit by repeatedly shaving off the miter on the straight piece until it fit the miter on the curved piece. It's a somewhat tedious process, but does result in a good fit in the end.

Anyway, to take shavings off of the straight miter, I simply used my regular shooting board with inserted shims between the workpiece and the shoot board fence on the side opposite to the one that's being planed. So long as the molding is relatively sturdy and doesn't flex significantly under the force of the plane, supporting it at two points (the shoot board fence on the side that's being planed and the opposite side of the shoot board with the shim) is sufficient to allow small shavings to be taken. Once I've gotten this mitered edge straight, adjusting the angle is a straightforward process of inserting or taking away additional shims.

[Michael Sobik]

Thanks guys. David, how do you hold/clamp the curved pieces for trimming? I can saw them okay, but cleaning up the cut is giving me some trouble. I think I'm set on the straight pieces. I'll make up some shims for the shooting board to handle them.

[David Keller NC]

Thanks guys. David, how do you hold/clamp the curved pieces for trimming? I can saw them okay, but cleaning up the cut is giving me some trouble. I think I'm set on the straight pieces. I'll make up some shims for the shooting board to handle them.

On the curved piece, and again assuming that the molding is large enough/sturdy enough to take this without failing, I simply clamp it in the face vise with as little of the mitered edge sticking up over the edge of the bench as possible and still allowing me to take a shaving, and clean up the sawn surface with (usually) a block plane. If the radius of the curve does not allow access with the block plane, I will saw the miter line as carefully as possible in the manner of the second, marked cuts of a set of dovetails, then clean up the "fuzz" left from the saw with very light cuts of a paring chisel.

One way to establish the correct miter line on the curved molding for the initial sawing is to cut a piece of paper exactly the width of the straight molding, and place this piece of paper underneath the curved molding with both flat on the bench. Adjust the orientation of the paper molding substitute so that you've the proper angle relative to the curved molding (which can usually be determined by using the bench edge as a reference). Now you've two points to connect on the curved molding for your miter - the inside corner of the curved molding, and the outside point where the curved piece and the paper meet at the edge.

[Michael Sobik]

On the curved piece, and again assuming that the molding is large enough/sturdy enough to take this without failing, I simply clamp it in the face vise with as little of the mitered edge sticking up over the edge of the bench as possible and still allowing me to take a shaving, and clean up the sawn surface with (usually) a block plane.

Cool, that's what I've been doing. More practice required on my part :D


One way to establish the correct miter line on the curved molding for the initial sawing is to cut a piece of paper exactly the width of the straight molding, and place this piece of paper underneath the curved molding with both flat on the bench. Adjust the orientation of the paper molding substitute so that you've the proper angle relative to the curved molding (which can usually be determined by using the bench edge as a reference). Now you've two points to connect on the curved molding for your miter - the inside corner of the curved molding, and the outside point where the curved piece and the paper meet at the edge.

Ahh, very tricky. That's a great idea. I'm going to give it another try today at lunch. Will post pictures if I can get it right. Thanks guys.

[Michael Sobik]

Success! David, that paper trick worked great. I was lacking a good way to layout the cut line. Using the paper, I was able to knife a line in the back of the molding and then saw it close. I finished it up with a sharp block plane. I basically did the same thing with the straight piece, but used a sliding bevel to set the angle and then knifed the line on the piece right off that. Again, sawed to the line and cleaned with the block plane.

One other thing that really helped was to drive a couple of brads into the pediment board and clip their heads off. Then I laid the curved piece down where I wanted it and pressed it onto the brads to lock it in position. Yesterday I tried clamps and had no way to reposition the piece after trimming it. So I was going around in circles.

Couple pictures. This is without glue. I think they're going to come together nicely. Thanks guys.

http://www.sawmillcreek.org/attachment.php?attachmentid=123517&stc=1&d=1248385835

http://www.sawmillcreek.org/attachment.php?attachmentid=123518&stc=1&d=1248385835

[Richard Francis]

Now build a boat.

[Robert Rozaieski]

Looks really good! I'm guessing it's the top case of a tall clock?

[Michael Sobik]

Oops. Yes, it's a clock (in progress) :)

[David Keller NC]

"One other thing that really helped was to drive a couple of brads into the pediment board and clip their heads off. Then I laid the curved piece down where I wanted it and pressed it onto the brads to lock it in position. Yesterday I tried clamps and had no way to reposition the piece after trimming it. So I was going around in circles."

Ha! I figured that last sentence was a bit of a tongue-in-cheek joke. :)

The clipped-off brads is a good idea - I've been using small screws drivin through the back of the piece for jobs like that, but the extra holes on the back of the piece always bothered me.

Nice mahogany, btw.

[Doug Shepard]

In the past when I've had to cut 2 mating pieces at some oddball angle, I've lined up the 2 pieces to form the resulting angle then clamped them one over the other. Then with a fine kerf pull saw cut right down through both. Even if my saw angle is a little off, they end up with the same cut line.