Cutting and Gluing Segments - Woodworking Talk - Woodworkers Forum
 
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post #1 of 10 Old 08-03-2011, 02:28 PM Thread Starter
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Cutting and Gluing Segments

I am fairly new to turning and woodworking (less than a year). I am trying my hand at a segmented vessel from some scraps I was able to dig up and a piece of Butternut that I bought. I am cutting 8 pieces per layer on my radial arm saw. I have a sacrificial table that is held in place by double faced foam tape. After a pile of firewood and several days later, I think I have the 22.5į angle set.
On one layer, I am alternating Walnut and some green (color) Poplar. 1/2" thick. The next row I glued up a thin sheet of Cherry sandwiched between thin sheets of Maple. 21/32" thick. The Butternut I will use as the main part of the vessel and it is 25/32" thick.
After setting up with scraps, I cut the Walnut and Polar and glued it up. I saw a TV program by Tim Yoder doing a segmented bowl and they glued up the pieces on a sheet of plywood in two half rings then ripped it on the table saw to get a good fit. I didnít want to waste what little plywood I have so I glued up on card stock as a complete ring allowing the glue to set up for at least 10 minutes between pieces. The last piece was off a little bit so I sanded the angles to get it to fit.
I barely tweaked my saw angle and cut the sandwiched strip and glued it up in the same manner. The fit was as close to perfect as I could ever imagine. Then I cut the pieces for another ring of the sandwiched material. It was off a tiny bit, but I think I didnít have the points of one of the segments lined up just right.
Next I moved my stop block about an eighth of an inch for longer pieces and cut some Butternut and glued it up. The last piece was too tight on the short side and had a thin gap on the long side.
I am fairly certain that I have the angle set correctly but that the problem is in my glue up and not aligning the corners exactly. With the Butternut being a little thicker, I wondered if I donít have the blade perpendicular to the table, but when I flipped the last segment, it fit about the same.
Could my sacrificial table be causing a problem since there is a tiny gap between it and the permanent table?
Is my glue up off?
Should I use some sort of fixture for aligning the corners during glue up?
Could my angle be off?
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post #2 of 10 Old 08-03-2011, 02:46 PM
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I made 1 segmented bowl (so far) and I used masking tape to hold it together. If the angles are right it should work out fine.

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post #3 of 10 Old 08-03-2011, 03:28 PM
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I do a lot of sanding and dry fitting of segments before the glue comes out. Using a sled on your tablesaw will make cutting the segments a lot easier. You'll want a nice clean fit on every joint from the inside to the outside, and then you'll spend a lot of time sanding down the entire ring so that the joint to the next ring is nice and tight.

For keeping pressure on the ring during the glue up I use large hose clamps that you can find in the HVAC section of most hardware stores. You don't need to screw it down real tight, just enough so that it keeps equal pressure around the ring, and you'll want to be careful a segment or two doesn't try and pop out of the ring on you. I use titebond II for all my segmented gluing and it starts to be pretty solid after even just 10 minutes so you'll want to make sure everything is pretty well set before then.

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post #4 of 10 Old 08-03-2011, 03:32 PM
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Cutting segments is very exacting. There are lots of things that can go wrong. Of course the angle can be incorrect. This is hard to narrow down at first because the other factors also cause problems.
The length of each segment is crucial. If only one segment is a hair longer or shorter then the circle won't close properly.
Saw blades, the rigidity of your saw and how you cut can all cause the angle to be off every so slightly. magnify that by 8 times and you have a ring that won't close up.
I just bought a new Makita sliding miter saw. I'm using the 15 degree factory setting for 12 sides. The first 3 rings did not fit perfectly. I found it was the feed rate. I slowed down and let the saw do the work and got 3 more rings that did fit perfectly but have very slight defects at the start of the cut. I'm pretty sure it's the thin kerf blade and probably me as well. I'm going to order a higher quality full kerf blade.
for many years I did the 180 degree sanding or sawing because my saws simply weren't high enough quality. I've done it several ways.
I made a sliding table for my table saw. I clamp the half ring to this with almost nothing hanging over the edge. Then I run this through the saw. You could make a table that has a cut in the middle and clamp both halves down and cut them at once.
I have used a disc sander to flatten each half ring. Along that same line I took a 2x4 that had been flattened. I attach 120 grit sandpaper to it and then hold it against the edge of my work bench. The I sit the half ring on the work bench and sand the end flat. It doesn't take much if your joints are close.
If final alignment of details is really important divide your glue ups even further. glue up 45 degrees and check it, adjust this for fit. Then glue up 90 degrees, then 180. this removes less material each time so the elements stay closer to proper alignment.
Ideally you find a saw, blade, and technique that works to give you perfect segments.
One of the best methods is to use whatever saw to rough out the segments. then fine tune them with a jig and the disc sander. You can even cut the segments on the bandsaw for this method which allows you to orient the grain anyway you want.
I highly suggest buying Malcolm Tibbets book on The Art of Segmented turning. It answers an awful lot of questions and shows how to build the sanding jig and how to use it.
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post #5 of 10 Old 08-03-2011, 08:36 PM
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I agree with John on the Malcolm Tibbets book. I've been working on some segmented bracelets and am having the same problems. I've got a disk sanding setup on the lathe and sand the individual pieces, ensure a tight fit and then glue up the 2 halves of the rings. Those two usually don't fit so it's off to the sanding disk after the glue is set to get them to fit. This stuff is fun but it can be frustrating at the same time.

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post #6 of 10 Old 08-04-2011, 03:17 AM Thread Starter
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Thanks for the ideas. I since tried a ring using the masking tape. I felt better about ensuring they went together more evenly, but by the time I got glue on all of the joints, Iím not sure I was able to pull the tape together very tightly. Iíll know better tomorrow after I sand the ring and can see the glue joints more clearly.
I will have to see if I can find a large hose clamp. I like that idea. It seems like it would give even pressure to each piece.
As far as lengths go, I am using a stop block and blowing out any dust in the corner before I slide the next piece in to be cut so the lengths should be nearly identical. The 10" blade that came with the saw (it is a used saw) was so warped that it made a kerf that was .22" rather than 1/8". I am using an 8" thin kerf blade for plywood because I know it is free of warp.
It just occurred to me that the good joints were on narrower stock - 3/4". The iffy ones are showing up on wider stock 1-1/8". I think I need to do some test cuts on some wide boards to see if I really do have 22.5į.
I do have the Malcom Tibbets book on my shopping list. I seen several recommendations for it when it comes to segmented turning.
Thanks all for your tips. They have been a big help.
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post #7 of 10 Old 08-04-2011, 09:31 AM
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I often screw 2 or more screw clamps together to get the right size for rings. you can also buy a kit that comes with several screw pieces and a length of flat wire that you cut to length to make any size you want. I don't remember where I found that but it has been handy.
If you use screw clamps to glue up make sure the ring fits absolutely perfectly before you use the clamps. I use a short piece of masking tape to hold things together to check for alignment. That way if the ring doesn't close perfectly I can either sand the 180 or remove one piece and sand it to perfection.
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post #8 of 10 Old 08-05-2011, 06:22 PM Thread Starter
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I tried another ring today that was a little wider. I laid it out on a piece of masking tape to line up the pieces, painted glue on all of the joints, and rolled it up. I tightened the tape as best I could then laid the ring down on a piece of MDF with a sheet of paper between so I wouldn't glue the ring to the MDF. Then I put the hose clamp around the ring. Then I put another piece of MDF on top and put a heavy weight on that to keep everthing flat. Then I tightened the hose clamp. After letting the glue set for a couple hours, I undid everything and sanded it flat. The glue lines look tight and pretty even. I was very happy with this method of gluing up. It ensured that I had things lined up correctly. If my angles are off, it would be less than 1/64" over a 2-1/4" width.

Thanks so much for the tips.
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post #9 of 10 Old 08-05-2011, 08:36 PM
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Pretty good technique but use wax paper on the bottom the glue won't stick to it.
Another good method is to simply freshly wax your workbench with floor wax. Then glue up the segments on this. The glue won't stick to the waxed top either.
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post #10 of 10 Old 08-06-2011, 03:22 AM
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Quote:
Originally Posted by john lucas View Post
... you can also buy a kit that comes with several screw pieces and a length of flat wire that you cut to length to make any size you want. I don't remember where I found that but it has been handy ...
I bought THIS ONE from Leigh Valley but it seems to be discontinued. I hadn't thought of using it as a clamp for segment rings, thanks for the idea.

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