Cutting segments...are these segment lenghts close enough?

[dirk martin]

I'm messing around with some segmented ring cutting.
I realize the segment length, governs the diameter of the ring.
When cutting segments for any given ring, I know it's important to get every segment the same length.

I'm making a 8 segment ring that will be 8" in diameter. So the segments need to be 3.1416" long.
I'm cutting my segments, from 1.5" wide sticks of maple.
I mount a small stop block to my table saw fence, that I bring the tip of my stick up, and touch the stop block, and then I slide the sled and stick through the blade, cutting a segment. Works good. I cut a bunch of segments, and then move on to other woodworking tasks.

Now, tomorrow, I wish to cut more segments, and so I need to re-setup my table saw. The key is getting that stop block in the exact same place as it was yesterday...so that my new segments are the exact length of the previous sessions segments. So, I measured the distance from my saw blade, to my fence, on the first session, and now on the next session, I just need to get that fence and stop block, back to the same spot. I'm wondering how close, is close enough? I'm measuring with a digital calipers. Is 2 decimal places close enuf? 3? 4?

Jet 12" tablesaw with Xacta fence.
Incra 5000 Meter Gauge
Digital caliper.
Stop block is a 1/2" brass setup block clamped to the fence.

I make my rings using the 1/2 ring glue-up method, and then trim the half rings on my tablesaw for the final glueup.



Side question:
With all my messing around, I've got some test segments sitting here, so I measured them.
Segment lengths:
3.169"
3.128"
3.149"
3.156"
3.145"

Would you glue those into the same ring, or are each of their lengths not close enough to each other?

[curtis rosche]

Depending on what shape your form is, every ring is a different size isnt it? Make enough for each ring of the same size when its set up. Do a different size each day? You wouldnt attempt to change a setup in the middle of other precision woodworking activities and then come back to the same thing.

[dirk martin]

Yeah, I see what you're saying Curtis.
I need to make a ton of 7" rings, as an example. I'll be cutting dozens and dozens of those segments today, and then continue cutting dozens more, a few weeks later. Then, I'll go on to some 7.5" rings, and some 4" rings, etc.

I guess, as long as I keep the segments from each session together, and don't mix them up with other sessions, I'll be ok.

[Bill Bulloch]

You are making this too complicated. Your glued up rings do not have to be the exact same size. Make them a little over size and then size them on the lathe. My Segmented Project Planner tells me if I want an 8 inch diameter ring to cut my segment lengths to 3.412 lengths and that will give me a glue up diameter of 8.941 inches. Then you will turn it to the exact 8 inches on the lathe. So a segment length of 3.40 will give me a 9.02 inch glued up diameter, no problem, just size it to 8 inches on the lathe. Just don't mix your yesterday cutting with todays cuttings; In-other-words, don't try and mix the different size segments -- that will not work.

[Quinn McCarthy]

If yuo haven't already done it. Buy Malcolm Tibbit's book on segmented turning. It is a wonderful reference and very inspireing. He also has 7 DVD's that you can get later. He really harps on cummulative error. Which is if you are .001" of on the bottom ring you could be .010" off on the topr rings.

Hope that helps.

Quinn

[John Beaver]

Those are pretty close, and should work. When you square the half rings you will lose a little anyway, so try to put the longer segments on the ends. I assume you don't have a disc sander where could touch them up and make them exact.
The only real issue is when you stack multiple rings, the joints might not line up perfectly vertically.