Tiling an oval

[Alex Zeller]

So I want to make an oval that's going to be about 24" x 54" which is larger than I can make without splitting the cut up into two halves. It's going to be a cheval mirror frame. Here's a rough sketch that shows were the finger joints are. It would be nice to use the two red joints as the break for the two pieces but I'm not sure how to get it accurate enough. The other option is to add a finger joint at the center (blue line) where the mirror will pivot. The 3rd option that I haven't sketched out yet to see if I can do it would be on the yellow lines. I know finger joints are strong but I would rather not add extra joints if needed. How would "you" do it? I'm using Fusion 360.

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[Jim Becker]

I suspect that tiling the way you propose will be difficult, if it can be done at all. It's purely software dependent, however. I don't believe that the Vectric software I use can tile that way...the divisions between tiles are straight lines across the material as your centerline is shown.

I'd probably calculate the sections you're intended to make (for grain direction reasons) and just cut the pieces independently instead of tiling. Joining them would be via splines, either visible or hidden (IE lose tenons)

[Kevin Jenness]

I think I would make a template of mdf assembled with splines from tiled sections and use that to trim the assembled frame. The template parts will be easier to register than fingerjointed sections and you can tweak them as necessary rather than cutting frame parts and hoping they go together in a fair curve. Clearly you need a bigger cnc :).

[Alex Zeller]

The only reason for going with a finger joint vs splines was because I've never done finger joints. They seem very simple but until I do it it's still an unknown. I'm thinking that it's one more thing to complicate making this project though. If I wanted to cheat (and waste wood) I could just get a 12"+ wide board and make just one joint. But I'm looking to copy how it would have been done years ago. So I've been looking around at antiques shops for ideas.

My plan is to make all the joints and glue it up except for the two joints that will get glued after the cnc work. That would require getting both halves mounted exactly the same spot on the table. If I was to split it at the center, the blue line, it would be much easier. But that would put a glue joint where the insert for the pivot bolts has to go. It looks like I have enough room on my cnc and can make the two halves the long way (perpendicular to the blue line). Also if I go with a splines I can make them so they line up with the rabbit for the mirror so they would only be visible from the outside edge.

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[Jim Becker]

Keep in mind that the act of tiling the workpiece on a CNC generally means indexing and moving the material parallel to one axis, most usually that would be the Y axis (front to back) but on some machines it's reversed. Tiling on an angle would be a "tough row to hoe"...

[Alex Zeller]

I'm thinking that the best way to do it is to make a very fine line on the spoil board at the correct angle so I can make the cuts. I'll then glue up the wood in the pattern below. As long as the two pieces of wood are exactly flat along the red line I should be able to make two halves that can be glued with splines together.

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[Wes Grass]

Finish machine everything, especially the ends that butt together. Placement on the machine becomes 'close enough'.

I'd glue one end first, if the 2 don't meet up perfectly. After it's cured, wrestle the 2nd into alignment and dog/clamp whatever way required to hold it. It's wood, it'll flex.

Finger jointing would be more complicated. I'd machine up a piece, cut it in half, and measure the width across the pair mated together. And then shave the faces of blocks screwed to the table, compensated for half that width, to position the halves with the finger joint spacers in place.

A spline, I'm not sure how to handle that without it showing. A t-slot cutter maybe. Basically, use the cnc to 'biscuit join' them.

Fusion I'm not at all familiar with. But it's a top level Cad/Cam system, so you should be able to simply pick the joint lines as you create your toolpaths. Might have to split the ellipse at the intersections. I *think* if I picked the ellipse in Surfcam it would 'pause' at the intersection and ask for the next element. Maybe not.

And I'd consider doing it as 3/4, and 1/4 sections on your red lines. But probably no advantage vs the yellow, other than possibly letting you set it up 'straight' with the long axis of the machine. That would simplify it a bunch I think. Maybe.

[Alex Zeller]

So here's where I'm at. The oval is made but I haven't routered a detail around the outside edge. yet. Here's the final design I came up with and a picture of one half of the oval.
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[David Buchhauser]

That looks nice! You are making great progress, and I will look forward to seeing your finished result. Lots of work there.
David