Laying Out, Routing, or Templating an Ellipse
From contributor K:
A better way to do this is with jig that uses a router to cut a pattern. You have a long radius of 36, and short of 21" in trammel arm. If you cut two tracks in a piece of MDF that cross each other. The length of each leg needs to be 15" or the difference between the long and short radius. A T- slot, or dovetail, will keep the little slides that you screw to the trammel arm in the track. If you make a 1/2" MDF pattern, to guide the router, you don't have to worry about trying to chase every little bump and dip that spoils the edge of trying to saw and sand the edge otherwise.
From contributor F:
I think an oval and an ellipse are basically the same thing. I have never seen separate instructions for drawing them. If you do any electronic drafting you can draw the shape you want in your drafting program and then make a template for it with standard size printer paper.
What I do is take one quarter of the full ellipse or table top outline and then draw a series of grid lines at right angles to one another in a different color ink right through the ellipse. Then I scale the quarter section drawing so that it will print at full scale. Now it's a matter of printing as many pages as necessary to have the entire quarter section of your tables outline on the pages you print. I number the sheets so that I can instantly see their relationships to the entire plan as I work with them in the shop.
Back in the shop, using spray adhesive, I start gluing the printed sheets onto a sheet of quarter inch thick MDF or similar material. Start with the bottom left corner sheet and then add the remaining sheets one at a time by carefully aligning the grid lines and placing a weight at the edge. Lift the rest of the sheet back and spray it with adhesive. After sticking, spray and stick the previously weighted section of the page. Once all sheets are in perfect alignment and glued to the MDF you can cut the ellipse outline and fair the curve with a sanding block if necessary.
All that remains is to use the quarter table outline template on the table top itself flipped four ways or use it to make a full sized routing template from a piece of quarter inch material as large as the top will be by flipping it four ways from a set of perpendicular center lines.
A bit of a hassle but very accurate when done correctly and I have used it with great results. I like the fact that I have control over the whole process and it can all be done in house and any goofed up printed sheets can be duplicated if necessary in minutes.
From contributor D:
For all the trouble, why not have your local CNC guy make a MDF template that you can run a pattern bit around? I would think it would be cheaper than the labor to set up an elliptical trammel and the trial and error. I would think that less than a few sheets of 1/2" MDF and 20 minutes of machine time and you'd be in business. But thanks, everyone, for the layout tricks I am sure I will use in the field!
From contributor F:
It's funny how often people assume everyone has a shop in the middle of a large metropolitan area with a guy with a CNC or beam saw on every block. It would take me a 2 hour round trip to get to the nearest CNC I know of. This does not include time for phone calls, loading and unloading. I also must assume the CNC guy won't magically have a program ready for my project, so more time either making him an electronic drawing or giving him a sketch so he can draw it. That only leaves tool pathing to be done.
As far as local shops with large machines go... I called a local shop (30 minutes away) to ask if he would do some widebelt sanding for me. He laughed and asked if I thought he was crazy enough to "help his competition." There are shops around that aren't ignorant enough to think they can do all the cabinet work in the universe, but I think I made the point that sometimes it's faster to use a low tech method when you don't have a high tech machine at home.
From contributor D:
If you want an ellipse 42" x 72" cut from 1/2" MDF to use as a pattern with a template router bit, I can cut it for $60.00. Shipping is the question, as I do not know where you are, but I doubt it would be any more than the cost of the template. The CAD is no big issue if you want a true ellipse with the stated dimensions. Prior to getting our Flexicam CNC, we would have paper patterns printed on a billboard printer at a local sign shop. The nice thing about sheet good templates is you can use it over and over with a good smooth edge produced when routed with a pattern bit. I could have your pattern out the door in less than 30 minutes.
From the original questioner:
Thanks for all the help! Contributor F, I agree, there is too much time coordinating a CNC guy to make up a template. It sounds like contributor D is one of the rare guys that would quickly and easily make up a pattern on his CNC. If only he was within a half hour of me, that would work out great! Shipping on that would make it cost prohibitive. If this was a pattern for a production run, that would be one thing, but for one table I don't know that it would be worth the expense. I think I will try the string method first, since it is low tech and quick to try.
From contributor U:
I'm with contributor D on this one. 20 minutes, but our shop minimum is $75.00 plus material - 1 sheet for this.
There is a difference between an oval and ellipse. Most people will be satisfied with the ellipse (red) when they want an oval (blue). I drew the red one in 2 seconds. The blue one took 2 minutes. (I had to change the color :) I'm saving the notes on the string way 'cause someday everything will not work.
From contributor I:
I just had a local copy shop print a full size drawing of an oval window I have to build. They could print something like a sheet 5' wide by 150' long. It cost me about $200 for 2 copies of the oval, though. I just e-mailed them the CAD file and picked it up that afternoon.
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