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Wedgie calculation

Rick Wize

PRO Member
I know this is probably a simple math calculation formula, but I'm stumped (probably has to do with age......).

I have several wedgies, I've purchased, but the highest segment number is 48 (3.75 degrees) & I would like to do a wedgie for 60 pieces. I know this would need to be 3 degrees, but I'm not sure how to do the calculation to be able to actually cut a wedgie.

I have a laser and a Shopbot, so I feel confident I can cut the actual wedgie accurately, but I'm stumped with the calculation to draw the actual wedgie in Corel or Aspire.

Hope I'm being clear, any help?
The wedge is basically a rectangle
wouldn't it work in the cad program to set the right leg of the rectangle at 87 degrees and the left leg at 93 degrees?
Rick, another way to think of the wedgie is as a segment, the same thing you do when you build a ring. In this case the wedgie is one of 60 segments. So you can use your Woodturner PRO or Segment PRO software to calculate the segment size. You will need to determine how big you want for the S.E.L., lets pick 3", also lets pick a width of 12" for the wedgie. The ring is 3 x 60 = 180", which gives the OD as 57.29565" (57.29565 = 180/3.1416). So now you need to figure out what the inside S.E.L. is. ID is 57.29565 - 2x12 = 33.29565". So with the inside diameter = 33.29565" the circumference = 104.6016" and the inside S.E.L. = 104.6016/60 = 1.74336". So make the wedgie with one end 3" the other end 1.74336" and length = 12". The bottom line think of the wedgie as a segment in a ring.
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Here's a simple no-math way to verify your wedge's accuracy using Woodturner PRO.
To follow the above example, if you want a 12" long wedge with the S.E.L. 3" or more. Do the following:
  1. Start Woodturner PRO and change Row 1 from a Disk to a Flat
  2. Set the Outside Diameter to 60" and the Inside Diameter to 36" (if turned, this would give a wall width of 12", but the actual trapezoid will be slightly larger because it won't be turned.
  3. Click the Ring View and scroll to the bottom of the page where the legend containing the calculations appear. You'll have to do a lot of scrolling and make sure the percentage at the top of the page is 100% so you'll be able to read the legend.
Three of these measurements are all you need:
  1. Segment Edge Length - 3.14"
  2. Segment Inside Edge - 1.89" (this is the edge opposite the Segment Edge Length. I actually added this measurement purely for this purpose but I may be the only one that has ever used it)
  3. Board Width - 12.02" (this is the actual measurement of how long the wedge should be.

You can vary the outside and inside diameters to give you a wedge with more or less width. Just make sure that the inside diameter is 24" less than the outside diameter.

I use this process to verify that my cutting angle is correct for making segmented sculptures. If I'm cutting a 3" 'segmented log' into slices that will make a 90-degree angle with 12 slices, I make a ring in Woodturner PRO that has 48 segments, has the outside diameter I want, let's say a doughnut that has a 12" outside diameter and an inside diameter of 6" (to yield a slice that is 3" in diameter). Now I cutoff the end of the log and then rotate it by 180 degrees and make make my second cut that will leave an outside slice width of .79" (the Ring View: Segment Edge Length). Now if I measure the narrow edge of that slice, if it is .39" (the Ring View: Segment Inside Edge), I know that my cutting angle for that slice is a perfect 3.75 degrees. If I make 12 of these perfect slices and glue them together, the angle of the 12 slices will be a perfect 90 degrees.

The following sketch shows a sculpture that needs 12 of these 90 degree corners and some straight runs:
LLoyd, Thanks for the explanation and instructions. Did you actually make the sculpture? If so, how long did it take?
I've built several of the corners already and have come up with some jigs and techniques that will make it fairly easy and fairly fast to build it. In fact, I think you'll be surprised at how fast you can build this. I will be making a Follow Along Project of this. I've made enough progress on it to show how to do it and will publish some measured drawings. It should be a fun project that should take 2-3 three weeks to build from scratch once the jigs are built.

There are four jigs. First is a jig for cutting the staves to make 'segmented logs' that will keep the grain going in the correct direction. Second is an optional jig for the lathe that uses a router to dimension them to identical diameters. Third is a jig for cutting the slices on a miter saw so that sanding isn't required. And finally, a jig that lets you glue the slices together at the proper rotation and uses a pin nailer to speed up the process. I think the most time consuming part of the project is making the stave logs. The rest of the project is quite simple.

I'm spending May with my wife in Australia and New Zealand and won't be able to get back to the project until I return, though.
Sounds like its very interesting. I can't way to see the project!, But enjoy the time with your wife 1st!!!