Cutting Curved shelves?

[Ryan Cassidy]

I seem to be having a bear of a time cutting curves.... And I can use some help. I've attached a crude picture (yeah it's bad) of the frame for the shelving unit for reference. The legs and rails are 5/4 square, I used two piano hinges mortised on the back legs so it is collapseable. Now I'm trying to cut the shelves. I'm putting a square on the back of the legs to find my corner and am measuring the radius from there to the front of the center leg + 3/4 inch. But when I do that, the center of the shelf is narrower than the ends where it butts up to the legs. All the legs/rails are the exact same measurements. Could there be something funny with the geometry and how I hinged the legs?

The first shelf was OK, not great but OK. I'm still going to redo it. I can chalk to up to dusting off the old math cobwebs I guess.

Is there a trick to this or does someone have a set of steps they go through? I prefer to limit the height of my scrap pile and get this right on the 2nd try. Any thoughts would be great!

Cheers,
Ryan

[Dewey Torres]

I can't understand from your post and pic what it is you are building.

Do you have any pics?

[Ryan Cassidy]

I can get some a little later. In short it's a set of 3 tiered shelves. The frame consists of 3 matching stepped frames and it is attached by 2 piano hinges in the back so that the frame can collapse and be easily moved. This will sit in a corner.

Ryan

[Jeff Bratt]

Some guessing here - if you had a good, scaled drawing it might help answer any dimension questions you have.

If you need to draw an accurate circle, you can use trammel points, or a compass; or make a compass using a nail and string or a nail and a board. If you want to cut a circle with a router you can use a jig like this, or easily make something equivalent. Also, something similar could also attach to a jigsaw.

If you're asking some other question - try again...

[Derek Tuchscherer]

If I am reading it correct, you are trying to make a three tiered corner shelf. Essentially a quarter round converging staircase. I think you are measuring the radius from the wrong point, rather than measuring from the back of the rear upright of the center leg, you should be measuring from the front of the rear upright. By measuring from the back you are giving yourself too large of a radius. Also, because of where your hinges are located if you built all three of your "supports/stringers" the same size, the side ones will have a greater radius than the center one. This then gives you more of an oval than a circle.

[Todd Crawford]

Sounds like your actual curve is a different radius than your measured dimension from the corner. Use a compass or a string to make sure you are carrying the same radius all the way around. Just because your curve intersects that measured dimension doesn't mean that is your radius if that makes any sense.

[Ryan Cassidy]

Hrmmm.. Yep. I think Derek hit it on the head. Thinking through the whole geometry thing, I think I'm measuring from the wrong spot. I've got a 1/2 sheet of 1/2 ply downstairs I'll do some testing and all with when I get back there. I think what I'm finding is that this oval shape is more pronounced the larger the radius gets. So on my Top shelf it wasn't that great, but as they get larger and I go down to the bottom the oval shape gets more pronounced.

I'll keep you posted on how it turns out.

Ryan

[Joe Chritz]

Without CNC, laying it out with the actual parts or a full scale drawing is the way to go without doubt.

I made some full size drawings for a couple desks I am doing right now and they help a lot.

Joe