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Segments not aligning (Read 513 times)
 
Bill Neff
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Segments not aligning
Aug 15th, 2016 at 6:29pm
 
I'm working on a commissioned pet urn.  The customer liked a small jewelry box I had but she wanted it bigger (finished size will be 5" across & 4.5 tall).  The segmented pieces will be 4 inches tall, so I guess it might be better called staves since the sides will be vertical and not slanted. 

I went through my table saw making sure everything was square and aligned (hadn't used it since the move last fall), then set the blade angle using a digital angle finder to 75 degrees. 

It's 12 segments, and the calculators said long side 1.5 (or 1.4737) long side and 1 1/4 (or 1.2294) short side measurements.  I marked the board with those measurements and ripped it size. 

After cutting pieces to length, I put them together & there were gaps all around.  Is it possible the digital angle finder is off?   Any suggestions will be appreciated.
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« Last Edit: Aug 15th, 2016 at 6:30pm by Bill Neff »  

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Gary Hostetter
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Re: Segments not aligning
Reply #1 - Aug 15th, 2016 at 7:29pm
 
Hello Bill            
When I do a 12 segment ring I set for 15 degrees on each side...
                Gary
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Ed Weber
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Re: Segments not aligning
Reply #2 - Aug 15th, 2016 at 7:41pm
 
Bill, first of all a picture would he helpful.
I'll try to explain this how I would approach it.
Bill Neff wrote on Aug 15th, 2016 at 6:29pm:
It's 12 segments, and the calculators said long side 1.5 (or 1.4737) long side and 1 1/4 (or 1.2294) short side measurements.  I marked the board with those measurements and ripped it size.


I'm guessing "long side" means outside face and "short side" means inside face.
Bill Neff wrote on Aug 15th, 2016 at 6:29pm:
After cutting pieces to length, I put them together & there were gaps all around.  Is it possible the digital angle finder is off?   Any suggestions will be appreciated.

Are the gaps on the inside or outside?

The first thing I would do is make a test cut and then measure that. The segment is the end result and must be perfect regardless of anything else. It really doesn't matter if you aligned your saw or your sled or whatever, the segment is what counts. I've never heard of a digital angle finder being "off" to the degree your having.
Next thing IMO, Don't concern yourself with the short (inside face) length. If the outer face is the correct width and the angles are correct, the insideface has no choice but to be correct. I perform all my cuts and calculations referencing the outer face,
How are you cutting these staves? I would make a simple sled with a stop block for easy reputability. The sled in the image is for a compound stave but you can see the high-tech  Roll Eyes sled, simple but effective.
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Ron Sardo
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Re: Segments not aligning
Reply #3 - Aug 16th, 2016 at 8:10am
 
What is the diameter of the base? I'll check your numbers. On staves it can make a difference.
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« Last Edit: Aug 16th, 2016 at 8:10am by Ron Sardo »  

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Bill Neff
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Re: Segments not aligning
Reply #4 - Aug 17th, 2016 at 10:09am
 
Here are a couple of pix.  I ripped the board lengthwise using a 15 degree cut on both sides.  Don't know if that affected the angle since it was a long cut.  Building a sled will be my next step.

Ron, the finished size of the base will be 5.25 inches (outside diameter). With a wall thickness around .25 inches.

I will be putting an 1/8" thick walnut slice between each segment so whatever the final measurement for the long side will be shorted by that much.

Thanks
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« Last Edit: Aug 17th, 2016 at 10:10am by Bill Neff »  

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Re: Segments not aligning
Reply #5 - Aug 17th, 2016 at 10:46am
 
Bill Neff wrote on Aug 17th, 2016 at 10:09am:
Don't know if that affected the angle since it was a long cut.


That could have had a slight impact.

Also remember, you don't have to glue it all at once.
I would suggest making sub assemblies of three staves and three spacers. You can then refine these (making sure each is 90 degrees), typically by sanding only. Then join two sub-assemblies together to make a half ring, checking for a flat even 180 degrees and then glue the two halves together.
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Ron Sardo
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Re: Segments not aligning
Reply #6 - Aug 17th, 2016 at 11:56am
 
Bill

When you mentioned stave I wrongly assumed the diameter of the top and bottom were different.

When there is a gap on the outside (like the ones shown in your photo) it usually means the angle was too small. In other words the angle may have been 14.5° (75.5°) instead of 15° (75°). A spec of sawdust can knock out an angle ever so slightly.

But when I look at your photo and see the pith all bets are off. Wood moves. Wood near the pith moves more. Damp wood moves even more. Damp wood near the pith is a disaster.

On top of all that, when I look at the endgrain of your segments and see wide growth rings I know the wood will not be stable and would expect a lot of movement.

So even if you cut the segments perfectly, nature took its course and the wood moved.
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Bill Neff
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Re: Segments not aligning
Reply #7 - Aug 17th, 2016 at 12:22pm
 
Thanks Ed & Ron.

This was a piece of pine board that I used to check to make sure everything was working.  The final piece will be of oak & walnut.  I didn't want to waste the oak running a bunch of tests.
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« Last Edit: Aug 17th, 2016 at 12:22pm by Bill Neff »  

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Ron Sardo
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Re: Segments not aligning
Reply #8 - Aug 17th, 2016 at 1:15pm
 
I use MDF
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