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Sanding segments (Read 1,445 times)
 
Steve Law
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Sanding segments
Mar 10th, 2013 at 12:27am
 
Sanding segments has and is a major pain. What is causing my segments to have more taken off on the ends than the middle. I am using a Delta 12 inch sander with a sanding jig that I have seen on different sites. The segments are approximately 4 inch in length. I have not had any problems with segments 2" or less.
The fixture is clamped in place, I take the time to ensure that the angles are correct before I start sanding.
I appreciate any help.
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Ron Sardo
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Re: Sanding segments
Reply #1 - Mar 10th, 2013 at 6:46am
 
Steve Law wrote on Mar 10th, 2013 at 12:27am:
What is causing my segments to have more taken off on the ends than the middle.


It sounds like the segments are rocking. This could happen for a variety of reasons from a fixture that is not perfectly flat to wood dust collecting between the table and fixture to the way they are being held down. While unlikely, it could even be that the sandpaper and or disk are not flat.

FWIW - I use a sheet of sandpaper placed on my table saw and hand sand each piece. This takes just as long as when I use my disk sander... and I beleive I get better results.
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Gary Hostetter
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Re: Sanding segments
Reply #2 - Mar 10th, 2013 at 8:53am
 
Quote:

FWIW - I use a sheet of sandpaper placed on my table saw and hand sand each piece. This takes just as long as when I use my disk sander... and I beleive I get better results.


X2
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Ed Weber
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Re: Sanding segments
Reply #3 - Mar 10th, 2013 at 9:59am
 
If it is only happening on the 4" pieces and not the 2" pieces and everything else is the same, than I suspect it's your jig.
I would do some experiments with scrap wood until I figure out whats throwing off your alignment.
A picture might help us help you.
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john Taylor
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Re: Sanding segments
Reply #4 - Mar 10th, 2013 at 4:43pm
 
Does the jig you are using feed the segment across the sanding disc or into the face of the disc?  If your jig feeds the segment across the sanding disc (most do), then there are two possible issues: 1. any slop in the sliding mechanism can create the rainbow effect you are experiencing.  2. the feed rate you are using is too fast and "pulls" the segment in at the ends.

If your jig feeds the segment into the face of the sanding disc, then there are still two possibilities: 1. slop in the slide mechanism of the jig  2. segment movement in the fixture itself.

Fitting segments is all precision machining and a few thousandths of error magnifies itself times the number of segment "faces". 

The fix?  Make sure your fixture is ultra "tight".  Any slop in the movement will show in the face of the segment.  Make sure that the segment is locked down before presenting it to the sanding disc.  Also, blow all dust away from the fixture and sanding disc before positionng a segment for sanding.

If this all sounds a bit anal, it is.  BUT... every tiny detail spells the difference between failure and success.  I found that to be successful is to apply the same rigorous procedures as one would if doing precision machining of metal.  That's why I gave up segmented work except on leap year... Grin
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steve rost
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Re: Sanding segments
Reply #5 - Mar 11th, 2013 at 8:42am
 
smiley=thumbsup.gif on the previous comments.  I would like to add that I cut my segments on my table saw with a accurate home made jig.  My jig is adjustable and once I get the angle dead on I lock it down and never move it again. I build a new jig for each angle I use.  I use a premium blade and get glass smooth cuts.  The only sanding I do is knocking off the fuzz.  If you are using a miter saw thats a different story.  Blade run-out is a common problem and makes for a visable glue line if you don't touch it up on a sander.  But if you have to do more than a touch up your saw may not be giving you the precise angle.  Cut test rings in scrap till you get a ring with no gaps!  And flip every other segment too!  That will   eliminate any compound angles your saw may be giving you.
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Mike Fisher
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Re: Sanding segments
Reply #6 - Mar 11th, 2013 at 11:39am
 
I use to make my own sleds. To consolidate I broke down and purchased the Incra miter express cutting sled with one of the beter miter gauges. $200. Once the sled is set up it has been making spot on angle cuts. I like having one sled for doing a different segment angles.

If your jig is good. Is it possible your miter track on your sander is not square to the sanding disk along the full leangh of the track.
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« Last Edit: Mar 11th, 2013 at 11:43am by Mike Fisher »  
 
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john Taylor
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Re: Sanding segments
Reply #7 - Mar 11th, 2013 at 4:21pm
 
Ron & Gary,

Question: Quote:
FWIW - I use a sheet of sandpaper placed on my table saw and hand sand each piece. This takes just as long as when I use my disk sander... and I beleive I get better results.

Quote:
X2
  I can see how this would work, but do you maintain the exact same number of strokes each face receives on the sandpaper?  I suppose it would make no difference on any segment ring up to maybe 12 segments, but rings with larger numbers of segments could easily end up oval instead of round.  Of course, oval becomes round when turned, but different outer lengths on the segments could alter intricate patterns.  Just curious if you've ever run into problems with pattern match...  I haven't the patience to perform the experiment.  I like looking at segmented work, making them, not so much.
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Ron Sardo
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Re: Sanding segments
Reply #8 - Mar 11th, 2013 at 4:59pm
 
The only way you would get an oval is if you change the angle and that can happen when sanding on a machine or by hand.

I work with 12 -16 or 24 segments and glue up enough segments to form a quarter circle which I then true up to 90.

Also, I don't count the strokes when sanding by hand or the revolutions when sanding by machine. The idea is to remove cut or burn marks left by the blade and sometimes you gotta take off a little more than expected. That's why you calculate in a fudge factor (make it a little big than needed in case you screw up).
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« Last Edit: Mar 11th, 2013 at 5:00pm by Ron Sardo »  

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Re: Sanding segments
Reply #9 - Mar 12th, 2013 at 9:21pm
 
I always cut a few extra segments so I can test my angles before committing other pieces.  Angles are critical for segmenting.  I agree with Ron and think your angles are off or you are not cleaning your jig in between each piece.
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Jim Tankersley
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Re: Sanding segments
Reply #10 - Mar 14th, 2013 at 10:06am
 
Steve,
I'm new here but this sounds exactly like something that was happening to me on my first try at segmenting a few months ago and no one has mentioned it yet.

On my craigslist purchased disc sander I did not realize the disc was loose. That is hard to believe but it didn't really chuck around or sound loose but it was by the tiniest fraction. The sander is one of those made in Taiwan and is a green color, it works but is not perfect and the general vibration didn't tip me off. The 'shick shick shick shick' sound while sanding finally did.

When I first started making segments I had difficulty getting exactly straight edges too and they would kind of curve on the ends by a 64th or less. It wasn't until I realized the disc was ever so loose (maybe not loose but mounted incorrectly?) and was wobbling that I started getting flat pieces. The wobble occurring more on the outer rim of the disc is what ate away the ends and made the rainbow effect for me. I too thought my disc was warped, but thankfully it wasn't.

Now segments, staves and such of 4" or more are good to go with little sanding and I don't have the rainbow problem any more.  Since then I have had to retighten the set screw twice (in 90 minutes total use) on the drive shaft to the disc since I discovered the problem so until I get a better machine I have to keep an eye out when things start happening. Delta might be a better engineered machine though and not have this problem.

Good luck with your segments, I agree it is monotonous at times but with an awesome outcome! I like the "wow how did you do that??!!" I have received so far.

Jim
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