Replies

1. 
   Kim_Carleton_Graves | Jan 26, 2001 10:54pm | #1

   *
   Hi Dave,

   As I understand your post, you are building a racetrack ellipse with solid wood edging on the inside and outside of the table.

   < Obsolete Link >

   As you feared the inside curve is not the same as the outside one which necessitates a second pattern. (1 and 2) Unfortunately, the situation is even more complicated. Not only do you need to cut the outside concave curve and the inside convex one for the table substrate, you also have to cut their negatives on the molding so the molding fits correctly - two more patterns. (3 and 4) Then you have to cut the outside of both moldings (5 and 6) for a total of six patterns. In truth, the sequence for cutting the negatives involves an interim pattern - so the two negatives are really four giving you a total of eight. Luckily these are all quarter patterns - though large ones. My drawing shows you need two 4 by 8 sheets for each pattern and two 5 by 10 sheets make it easier - the sheets go together square.

   The two negative patterns are no problem. You should make them directly from the positives so you're assured of a perfect fit. I have a posting < Obsolete Link > here describing that procedure. Cutting the four positives is harder. My feeling is that the patterns should all be cut with some sort of jig to ensure a fair curve. There are commercial jigs available, but I'm not sure they are capable of cutting at this scale - you might have to make one yourself. (good commercial jigs go for +$700 plus extension arms the last time I looked.) The other option is to use a "modified ellipse" as described in FWW #147 February 2001,page 18. This combines cords from two circles and so is much easier to cut using a simple pivot jig. While a close approximation to an ellipse, I don't personally like the curve formed by this method - it's just not as beautiful as a true ellipse. But you'll need to look at it yourself and make you're own assessment.

   The final method is to lay out the patterns in CAD, as I have in my illustration, and print out the drawings full size. The advantage to this method is that you get a true ellipse. Though not as accurate as a router jig, a pattern carefully made from a full size CAD drawing should be fine for this application.

   Finally, you could rent time on a CNC router and let the router cut the positives directly on the substrate using the CAD drawing as a pattern. It could also give you patterns for the remaining curves - this is probably the best methodology.

   And if you think you've had all you can stand with making patterns for the table wait until you have to make them up for the veneer. Assuming you layup 12" wide veneer I estimate you'll need 16 patterns for the veneer to get the 64 way sunburst! ;-) (I did this quick and dirty so don't quote me!)

   If you'd like us to make the CAD drawings or would like consulting help, give me a call in the shop - I'm there this weekend.

   Sorry to be the bearer of bad news, but I hope this helps.

   Best,

   Kim Carleton Graves
   Carleton Woodworking

1. 
   CStanford_ | Jan 27, 2001 12:23am | #2

   *If I was in your shoes I'd subcontract this job to Kim. My head hurts just thinking about it.

1. 
   Sgian_Dubh | Jan 27, 2001 07:16am | #3

   *I too did some headscratching over this. Not too much, because I didn't feel like getting into all the technicalities, but I was intrigued by the fact that a job this complex was ready for production, and no-one (perhaps) had so far been able to work out how to make it. Which makes me wonder how it was priced. After all if you don't know how to make it, how do you know how long the job will take to complete? How does anyone price something like this? Let's say you guess at 500 hours, and it actually takes 650 hours at $50 per hour, just as a couple of figures. And say you make insufficient allowance for jig materials, and so on, and so on. I'm intrigued at how such wild guesstimating can be done, if that's the case here, and who gets eaten alive if the guesstimate is wildly out. Maybe I'm talking out of turn, in which case ignore my musings. Sliante.

1. 
   CStanford_ | Jan 27, 2001 05:12pm | #4

   *I'd still sub. this to Kim and humbly ask him if I could watch him build it........Like Sgian, I trust you have not given a final bid on this job. This could be a real wallet buster.

1. 
   Kim_Carleton_Graves | Jan 27, 2001 08:16pm | #5

   *Hi Richard,I think your questions are real good one. I've opened up a new post on the main board. Would you and Charles give me your comments? Thanks.Best,Kim Carleton GravesCarleton Woodworking

2. 
   John_Nolte | Jan 28, 2001 02:24am | #6

   *Dave:To simplify the project, I would build it in knock down sections, four like Kim's drawing, or six with the two short radius ends in identical pieces and the long sides in four identical (mirror image) pieces. I would make thw substrate first, using the first piece as a pattern for a flush cutting router. Then I would add and trim the veneer. Then I would rabbet the solid edge the thickness of the top and leave the exposed edge thin enough to bend to the curve. Kerf the edging almost to the rabbet, and clapm both the inside and outside edging at the same time. You can also add reinforcing blocks to the bottom of the substrate or crosswise rails as needed. The key concept is to build it from the inside out and let the fill be the form. Another option is to laminate the inner and outer rails. For this you would have to add sufficient reinforcing blocks to use as forms and clamping surfaces. Adding a cut to fit false bottom might be a nice touch. You did not specify the leg design. If the legs are joined to the rails, that is where sections can come together. Then either hide the joints, or emphasize them with radial end rails on each section.John

3. 
   Sgian_Dubh | Jan 28, 2001 10:51pm | #7

   *I posted, and realised I'd got the wrong end of the stick, so I deleted because the information I gave was useless. I'll go back to mulling it over. Sorry about that. Sliante.

4. 
   Sgian_Dubh | Jan 29, 2001 04:55pm | #8

   *Dave, A little time sometimes results in some inspiration, and I came up with these thoughts for you to consider. Firstly you need to be able to develop these six ellipses accurately. In order starting from the inner ring they are:*1. The outside face of the inner hardwood lipping.*2. The inside face of the inner hardwood lipping to match,*3. The inside edge of the veneered man made board to match 2 above.*4. The outside edge of the veneered man made board to match 5 below.*5. The inside edge of the outer hardwood lipping to match 4 above.*6. The outside edge of the outer hardwood lipping.Various ways exist to develop ellipses. Kim in his first answer I'm sure used a version of CAD, but in the workshop two methods are most common, the first being three pins, a piece of string, and a pencil. The second is to draw out the two axes, make three marks on a trammel to match half the length each axis, etc., as per Ernest Joyce and others. One of the mail order suppliers like Rockler, or Woodworker's Supply sells a smallish router jig based exactly on this latter principle, and cabinetmakers also make their own. It's basically a board with T slots or similar perpendicular to each other with a trammel mounted on a pair of plastic or aluminium T extrusions that fit the T slots in the board.My suggestion is to make one of these jigs but on a giant scale where the router is attached to the trammel. Here is the nifty bit. You make two trammels. *7. The first trammel places the router cutter exactly right to cut 1. above, the outside face of the inner hardwood lipping. *8. The second trammel places the router exactly right to cut 5. above, the inside edge of the outer hardwood lipping.In both 7 and 8 above the router must be moved further out to make the two additional matching cuts on both the inner ring and outer ring. I think this might be done by making the trammels a bit shorter than you need and fabricating a series of router sub-bases that attach to the end of the trammel, to account for each of the sets of measurements. Okay, that was my idea, and it does nothing to address exactly how you locate the ellipse jig in relationship to your various parts, but I have a feeling these problems are not insurmountable. I also suspect that you would need to lay out your elliptical top full size in your workshop on a huge base or jig to make this work, but I'd have to assume that if you guys are making a table this big, you also have the space in which to do this. I'll leave the rest up to you, and maybe other contributors, but I hope this helps. I've been long winded enough, and I've work of my own to get to. Sliante.PS. Interestingly, I hear there is no known method of precisely calculating the perimeter length of an ellipse using maths. I find that fascinating.