Processing SegPRO Summary Output for the Shop

GrahamJ46

PRO Member
I output 2 summaries to Excel. The first is the default summary and the second is with BW grouped. In both cases I check the optimize BW and SEL. I take those 2 Excel files and produce an Excel spreadsheet ready to take into the shop. I also take a screen shot of the bowl and past it onto the spreadsheet. The Cut List rounds up board lengths to the nearest whole number and adds 3" for safe cutting. Below is a copy of a typical output for the shop. This is all done with no manual input and only takes a few seconds. I use the Segeasy sled and setup the distance to the blade using setup blocks. I use the tangent method but as has been previously pointed out the SEL in SegPRO uses the ring circumference divided by the number of segments. In practice the difference is not important. Being numbers oriented (engineers can't stop being engineers) I couldn't resist comparing the 2 vs number of segments for the interest. The table shows the % difference vs number of segments.

Bowl6.jpg
table.jpg
 

mfisher

Super Moderator
Staff member
I did something similar years ago when I first got started. I quickly came to realize that it doesn't matter because the ring is going to get turned down to the final dimension. So a 6" ring may be built as a 6. 125 and turned round to 6.0"

Thanks for posting your comparison.
 

GrahamJ46

PRO Member
I agree. I wasn't trying to be precise for the sake of it. In fact I add 1/8" to the SegPRO output for the reason that you indicated. Right now I am still learning how to turn down from 6.125 to 6.0 :). So ending up with a bowl in one piece is my immediate target!
 

Chuck Margeson

PRO Member
I would be interested in the formulas that you used to obtain these calculations. I am not and engineer, and I am not a programmer.
 

mfisher

Super Moderator
Staff member
Chuck. It looks like Graham is exporting the summary sheet from SP and just organizing the results a bit in Excel.

As far as the formulas SP or WTP uses.
  • The circumference of a circle is the Diameter x Pi (3.1416)
  • Circumference divided by number of segments equals segment length (SEL)
  • Segment Angle = 360 / number of segments / 2 (because the angle is cut on each end). A simpler way to say it is Segment Angle = 180 / number of segments.
 

Chuck Margeson

PRO Member
I thought this was all done automatically with no manual input so I was thinking he had a macro that he was using to format the new output. In the first column the rows are reversed and I think that would require a manual input. Guess i am confused. Not a programmer, just a simple retired Border Patrol Agent.
 

GrahamJ46

PRO Member
Sorry for delay in responding. Thinking through COVID fog right now. Firstly, to address the table (segs vs % diff). It is intended to display the difference between the tangent method (see attached diagram) to calc seg length vs simply dividing the ring circumference by the # of segs. The tangent method is more accurate but as the table shows as you increase the # of segs the difference is small and well within the ability to turn to a specified size. In other words it does not matter from a practical standpoint. Thus SP uses the simpler approach of dividing the ring circumference by the # of segs.

The output is all automatic, including the re-ordering of rows. I am fortunate to have some programming experience. I wrote a program in Excel VBA (Visual Basic for Applications). It takes the 2 output spreadsheets from SP and creates the output that you see above ready to take to the shop. Of course, this is not essential and most of it could be done manually in Excel or elsewhere. The main purpose for me was to create the setup blocks for setting the distance to the blade for my Segeasy sled, so that no measuring is required. The rest is just for convenience. For example converting dimensions to something that I can comprehend, and the cut list is useful. HTH.
 

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  • tangent method.jpg
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GrahamJ46

PRO Member
It is quite a complex piece of code. I am loathed to let it out because that implies supporting it, which I am not willing to do. I am retired and looking for a simple life these days! However, if there is interest I will look into whether I could provide the part that determines the setup blocks but no promises until I see what that entails. Separating that from the rest might be tricky.
 

mfisher

Super Moderator
Staff member
OK. Never mind. Sorry to bother you.
Never hurts to ask. I was thinking about asking also.

I have never had the summary sheet in WTP or SP fail me in its calculations. I still tend to over build and carve away the excess. In SP one can
increase width to give some buffer.
 

Lloyd Johnson

Administrator
Staff member
Defending the accuracy of my calculations has always been a challenge. In 22 years, I can’t even guess how many times I’ve had someone tell me that my calculations were wrong at which time I would start the process of proving they were correct either by using SketchUp to create segmented rings to-size so that I could drop measurements on them or by providing the trigonometry formulas that every programmer uses and verify the results using a scientific calculator.

After doing this for years, I changed my approach. I tell them to use the simplified calculation used by most chartists as shown in the attachment from Graham (above) where circumference divided by the number of segments gives a close, but wrong, Segment Edge Length. This calculation is always a little less than the formula produced SEL. In simple math, a 10” diameter with 12 segments gives a wrong SEL of: pi * D / 12 or 3.14 * 10 / 12 = 2.62” and the trigonometry formula:
SEL = tan(miter angle) * radius * 2 or
tan(15) * 5 * 2 = 2.68”
This is simply a quick way to show that my calculations are correct. I always end by telling them that if they ever think that my numbers are wrong, drop that thought and focus on why the length of the segment they just cut isn’t what was specified by the Summary Sheet.

Lloyd
 

Chuck Margeson

PRO Member
The accuracy of the calculations from WTP are not in question here.
I have never had a problem with WTP which I have been using since 2015.
I am a woodworker with some 70 years of experience. I was not born yesterday.
Until about a year ago I used a miter saw to cut segments.
I have not had a decent ring since I started using a wedgie sled, which I thought would be a faster process for cutting.
It is faster . . . but it is also inaccurate. If I have learned anything over the past 7 years, it is that the segment angle (SA) and segment edge length (SEL) are critical measurements.
I am using Jerry Bennet's wedgies, so I think my SA is good. Only thing left is SEL.
Guess I just can't get it right.
 

mfisher

Super Moderator
Staff member
Interesting to read you have not had good luck with cutting rings on a wedgie sled. When I first built a JB sled I had a bit of an issue with a few rings. I was using some shop made wedges cut from a CNC machine. Before that I used a digital protractor to set the fence angles.

- the two fences used on a wedgie sled need to have parallel sides (as you know)
- stock used for cutting segments need parallel sides
- I set my SEL by using an extra stock piece. I make the first cut at the top fence. Then using digital calibers, I mark the SEL line on the stock. I then place the stock along the fence and line the mark to the cut side of the blade, then set the stop block. Make a test cut and measure. I then do any micro adjustment for the SEL.

I consider myself just an intermediate segment builder. I tend to over build. That is I will make my stock wider than some more experience builders would need. Easier for me to turn down the wood than build a bad ring. If I want a 5 inch ring I will make one 5.125 to 5.25 and turn down to size.

For me there are many factors than can mess up SEL. Debris between the end of the stock and the stop block. Not setting SEL along the segment angle but 90 degrees to the fence. Not placing the stock against the stop block or it moves as you begin the cut.

I have made all of those errors. I have learned to check SEL of the pieces being cut and make adjustments. I have found that DB system is good once you get use to it. Like you, one of my first segment bowls was cut on a miter saw. Then I switched to a table saw.
 

Chuck Margeson

PRO Member
Interesting to read you have not had good luck with cutting rings on a wedgie sled. When I first built a JB sled I had a bit of an issue with a few rings. I was using some shop made wedges cut from a CNC machine. Before that I used a digital protractor to set the fence angles.

- the two fences used on a wedgie sled need to have parallel sides (as you know)
- stock used for cutting segments need parallel sides
- I set my SEL by using an extra stock piece. I make the first cut at the top fence. Then using digital calibers, I mark the SEL line on the stock. I then place the stock along the fence and line the mark to the cut side of the blade, then set the stop block. Make a test cut and measure. I then do any micro adjustment for the SEL.

I consider myself just an intermediate segment builder. I tend to over build. That is I will make my stock wider than some more experience builders would need. Easier for me to turn down the wood than build a bad ring. If I want a 5 inch ring I will make one 5.125 to 5.25 and turn down to size.

For me there are many factors than can mess up SEL. Debris between the end of the stock and the stop block. Not setting SEL along the segment angle but 90 degrees to the fence. Not placing the stock against the stop block or it moves as you begin the cut.

I have made all of those errors. I have learned to check SEL of the pieces being cut and make adjustments. I have found that DB system is good once you get use to it. Like you, one of my first segment bowls was cut on a miter saw. Then I switched to a table saw.
 

Chuck Margeson

PRO Member
I am using a JB type sled made by one of our WTP members with a CNC machine. Works Great! No complaints.
I am using JB wedgies to set the angle.
It is the stop-block that is giving me trouble. Today I will use the method you describe.
Chuck
 

mfisher

Super Moderator
Staff member
I am using a JB type sled made by one of our WTP members with a CNC machine. Works Great! No complaints.
I am using JB wedgies to set the angle.
It is the stop-block that is giving me trouble. Today I will use the method you describe.
Chuck
Hope it works out for you.
 

Chuck Margeson

PRO Member
Made a small ring @ 5.5 inches.
Ring was near perfect with very minimal adjusting.
Adjustment was one the outside of the ring. I like any adjustments to be on the inside so will have to adjust for that.
Also the ring was 6 inches rather than 5.5 inches. SEL was too long.
I will keep trying.
 

mfisher

Super Moderator
Staff member
Made a small ring @ 5.5 inches.
Ring was near perfect with very minimal adjusting.
Adjustment was one the outside of the ring. I like any adjustments to be on the inside so will have to adjust for that.
Also the ring was 6 inches rather than 5.5 inches. SEL was too long.
I will keep trying.

What is the SEL of the cut segments compared to the SEL on the summary sheet?

When I set the SEL and begin to cut segments I generally will cut a couple and check the SEL. If the SEL is not right I make the adjusts, cut a couple of segments out of scrap and check the SEL. Once it looks good I cut from the good stock again. After a few cuts, I check the SEL again.

Another reason I make my board wider than needed. is if the ring comes out larger than needed i can turn it down to size.
Have not found a ring stretcher if the ring is too small. :D
 

Chuck Margeson

PRO Member
My SEL'S are the same, segment and summary.
I cut my segments as you describe. Cut, check, cut check, 'till I get it right.
Then get the good wood and go for broke, checking every 3rd or fourth SEL as I go.
Works good for me.
At this point I am thinking that I may have dropped my calipers too many times.
I have ordered a new one from my friends at Amazon.
 
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