I have Pete Marken's sled and need to adjust to cut 48 open segments. I know the cut angle is 2.75 for 48 open segs. The plan shows a 2 degree gap.
Can I just measure using an angle finder and adjust the sled arms or do I have to make a wedgie?
I tried with using the angle finder and just adjust the arms of the sled but I must be doing it wrong because it is not leaving me much of a gap in between segments.
So, where do I measure the angle(s)? In between both arms or inside on the bottom arm and outside of the top arm?
*A visual would help
Second question first. The sides of each fence arm are absolutely, strictly parallel, right? Therefore the angle from one side of either fence to the other side of that same fence is always 0.0000 degrees. Therefore it doesn't make any difference where you measure the angle from one arm to the other. The wedgie, of course, measures it (actually controls it) between the inside edges while your cut depends on the accuracy of the fence parallelism. Fortunately, ripping a very parallel fence is easy.
First question next. My Wixey angle gauge wouldn't work very well to set a fence but it claims both an accuracy and a resolution of +/- 0.1 degree. I looked up two digital bevel gauges (I don't have one) and they both claimed an accuracy of +/- 0.13 degrees. If you were making a closed segment ring where the tolerance on the included angle adds up, a 0,1 degree error, repeated 48 times, would cause an error of 4.8 degrees or 2/3 of a segment by the time you close the ring. Now the good news. Open segmenting doesn't really care much about the precise angle on the ends of the segments. That angle controls the shape of the open window that nobody really studies. What matters more is the glue surface you have left between a segment on one row and the segment above it on the next row. For example, if you cut your segments squarely (yes, a 7.5 degree error in the included angle!) and had a 1/2" wall thickness, you would have an overlap error of 0.328". If you set your gap correctly at the OD, the gap would get smaller as you go in, giving you more glue area but less gap. If you set it at the ID by using a Segeasy plate, the gap would get bigger as you go out and you would lose glue surface. I expect that if you get anywhere close to the correct cut angle, it will be good enough.
The question you didn't ask last. 360 degrees / 48 segments = 7.5 degrees per segment. If you want a 2 degree gap, your included cut angle must be 5.5 degrees or a 2.75 degree cut on each end. Your arithmetic is correct. The problem is that a 2 degree gap is not very big at the rim of a bowl and gets downright tiny near the bottom. Compare the geometry to your expectations to find the confusion. Remember that gap width as a percent of segment width and glue area are devout enemies of each other. If your gaps look too small, you might be locating your segments on too small a radius.
