# Segmented Bowl Question



## Tfoster100 (Feb 22, 2012)

I've got a question about cutting segments. I have built a jig for my table saw and set it for 15 degrees. I measured the angle with a digital angle tool as well as a simple angle guide on a protractor. I have it really close to 15 as best I can tell. 

When I put all the pieces together though After cutting i have just a slight variation though. I have watched tons of videos and use the technique of gluing up to two 6 piece half circles then sanding those. That gives me a pretty good complete circle
But I would really like it to be more precise. Any suggestions? Should I mess with the jig and the cutting? Or try to improve on the sanding of each individual segment. Just seem to have too many gaps in the final glue up and want to try to get it as clean as possible. Thanks.


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## Lilty (Dec 20, 2006)

You are probably have to do both.


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## john lucas (Sep 18, 2007)

There are 3 things (maybe more) that affect the accuracy of the cut. Then length, how your blade cuts and how hard you push, and the angle. 
to get the angle down what I do is put a screw in on the blade side of my fence. I clamp the other side. Then I cut up a bunch of scrap that's been planed and jointed (did I mention that the boards must be perfect as well) I tap the loose end with a mallet to fine adjust the fence. I cut half rings until they are perfect, then I cut whole rings. When everything is perfect I drill and put a screw in the loose end of the jig. I cut a lot of different segmented rings so mine is adjustable. What I've done is add a fine adjusment screw and 2 brass pins. I can measure between the brass pins with a dial caliper and nail the accuracy within a few thousandths for repeatabililty. 
Then I have a stop that I adjust for the length of the segment, this solves that problem. You have to practice getting the exact feed rate of a good sharp blade. A blade that doesn't cut very easily and cleanly will flex during the cut and not give you an accurate cut. 
Even with all this you may not get a really accurate cut every time. I do 32 segmented rings and they are challenging. I can nail 16 segments most of the time but I finally invested in a cabinet makers saw and Forest blades. It makes a difference.
the half ring glue up works but when you flatten both sides the rings are almost never equal in diameter. For most projects this isn't a problem but for projects where every ring must accurately meet the next one your lines won't line up. That sucks. So you much better off trying your best to get everything accurate for a complete glue up.


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## Dave Paine (May 30, 2012)

I have only done one segmented bowl so far.

My observations from this project was that EVERY detail matters.

Did you flip the wood between cuts for efficiency, or did you always use the same side against the jig because you were emphasizing the grain?

If you flipped the wood, then any small difference in width of the wood due to the initial cut of the strip not being exactly parallel contributes to the end result.

John mentioned the blade can make a difference. It can and does. Did you use a thin kerf or full kerf. A thin kerf may flex more than a full kerf. Not likely to see in a single cut, but with the many cuts for each ring, it may be another contribution to being off.

I saw one site where the person glues quarter segments together and has a jig on his disc sander to get these to be exactly 90 deg.

I glued half segments together and sanded these to be flat on my 12in disc sander.

I did tweak my mitre gauge between the first and later rings. I then improved the later rings, but they were still not perfect, just needed less sanding. I checked and did have very slight deviation in width/thickness, and since I was flipping the pieces this was perhaps the main contribution to the gap after I calibrated the mitre gauge.


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## john lucas (Sep 18, 2007)

Malcolm tibbets in his book on segmented turning shows how to use the disc sander to true up segments. It works very very good. If you adjust it properly the rings will fit perfectly and you won't need to do the true up on the disc sander. Before I started using his jig (which I don't do all the time) I used to divide my rings into quarters. Then I could would glue up enough segments using the rub joint concept, to make 90 degrees. True all of those groups up and then glue them into 180 and then true that up before doing the final ring. It works great. 
Here's my version the Malcom Tibbets sanding jig. The one big advantage of that jig is you can cut segments on the bandsaw so the grain matches better. you cut close to line and then sand one side flat. Then place it in this jig and sand the other side to perfection.


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