• Are you looking for a coupon code to buy my software? You can get one from lots of 3rd party sites but they won't work. My software never goes on sale and has never been discounted. The only coupon codes that are given is when I give a club presentation and I offer a discount to the attendees. Other than that, everyone pays the same price.

S.E.L. question

E

elayerr

PRO Member
I recently purchased the Segment Pro suite and am working on learning it. I have made several open segment candle vases and now am expanding to more challenging turnings. I use a double guide wedgie sled and to set the open segments I use a setup similar to Tom Lohman's rig. Now my questions. When cutting the segments I have been measuring the S.E.L. from the stop to the closest edge of the saw blade at the miter angle. This seems to be the correct way to get the correct S.E.L. If I measure perpendicular to the saw blade, then the length would be slightly longer than the desired S.E.L. Is this correct and which method is best, or am I overthinking it? I am currently building a more precision stop that incorporates a digital linear scale.

My second question is in reference to my segment setting apparatus. If I want to be able to turn the bowl to the design diameter, the segment must be placed accurately at the proper outside diameter. The setting apparatus uses a stop that is set at the outside diameter of that ring, but the segment is placed by its outside edge. If the segment outside center is the actual outside diameter, then my segments are actually being placed at a smaller diameter and the opening will be reduced in size.

It seems that if these errors could be corrected by downloading the design to Excel and calculating the perpendicular distance to the the desired S.E.L. and the adjusted outside diameter to be used to set the segments. Hope this is not to confusing. Tell me if I am overthinking it.
 
I think you are correct with both assumptions. I do export my segment data then apply the cosine correction for the error in setting the stop dimension because I have a DRO on my saw that reads the perpendicular dimension. On a 12-segment ring, that amounts to about 3.6% smaller. Using the SEL for the saw stop makes the segment too long. More segments per ring will make that error smaller.

Please check the trig for yourself but I think using the angled end of a segment to set the diameter instead of the center of the segment will make the actual diameter smaller by the same percentage that the cosine error in the stop made it too big. In other words, I think those two errors will cancel each other out.
 
Since the actual circumference of the vessel ring is going to be below the edge lengths surface such precision is moot. If you are worried about having a precise finished dimension you can make the sel a bit longer and the segment width correspondingly wider so you will have more room in the ring to hit your target.
 
This is exactly the solution I use.

I have 3 rules I follow for closed segment rows:
1) The included angle of the segments must be precise to achieve good joints in a ring.
2) Both sides of every ring must be dead flat to achieve good joints between rings.
3) Everything else is approximate. It just doesn't matter much.

For open segment rows, I have only 2 rules:
1) All segments in a row must be the same height.
2) Everything else is approximate. It just doesn't matter much.

As Gary said, radial spacing can be approximate as long as you plan ahead for it.
 
This thread may be of interest to the discussion of setting the sawstop for SEL.

SEL versus actual blade to stop distance

Have you ever considered adding the actual distance between the blade and the stop used on the saw to get the correct SEL for the angle the of the segment being cut. I have watched many videos of people using the SEL to set the saw stop. This gives a segment that is actually longer than the SEL...
woodturnerpro.com

The discussion talks about setting the sawstop for SEL when measuring at perpendicular instead of along the fence angle.
Excel uses radians and not degrees. hence degrees must be converted to radians.

SEl * COS(RADIANS(MiterAngle/2))
 
Ken Sherwin said:
I think you are correct with both assumptions. I do export my segment data then apply the cosine correction for the error in setting the stop dimension because I have a DRO on my saw that reads the perpendicular dimension. On a 12-segment ring, that amounts to about 3.6% smaller. Using the SEL for the saw stop makes the segment too long. More segments per ring will make that error smaller.

Please check the trig for yourself but I think using the angled end of a segment to set the diameter instead of the center of the segment will make the actual diameter smaller by the same percentage that the cosine error in the stop made it too big. In other words, I think those two errors will cancel each other out.
Click to expand...
I ran through an example calculation for 12 segments and an outside radius of 5 inches. Cutting with the stop perpendicular to the blade increased the SEL by 0.0945". Setting the segment by the outside edge decreased the radius by 0.1764". So they do not appear to cancel out each other. Of course, the shorter the segment SEL the smaller will be the error. In conclusion, I like your Rules you posted below. I think I will adopt them.
 
Gary Beasley said:
Since the actual circumference of the vessel ring is going to be below the edge lengths surface such precision is moot. If you are worried about having a precise finished dimension you can make the sel a bit longer and the segment width correspondingly wider so you will have more room in the ring to hit your target.
Click to expand...
I agree. I still tend to over build. If I need a 6" diameter ring I will build a 6.125" diameter rings and turn down to 6 inches.
 
You must log in or register to reply here.
Back
Top