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Silicon Carbide vs Aluminum Oxide

John Tisdale

John Tisdale

Joined
Apr 11, 2014
Messages
462
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Location
Dallas, TX
Currently working on a 26" tall mesquite vase - beautiful wood and great pattern with the inclusions but seems like the worms had a field-day before I got there. My normal routine is to fill the worm-hole and problem areas with black G-Flex epoxy, cut it off, and then apply TimberMate water base, black of course, as needed in the finishing applications. This time I changed the process: due to the number of pits and holes, I spread on black G-Flex epoxy over the sealer knowing I would have to sand it off.

Jury is still out on final results but I can tell you sanding a big piece with troweled G-Flex makes for a bad day - I use a 5" dual-action pneumatic w 3/32-orbit - great for fine finish work, lousy for the task at hand. Instead of the recommended 220, I went with 150. After the first hour I knew what I'd be doing for the next 5 or 6.

Then I remembered some sagely advice: LIGHTEN UP WHEN USING SILICON CARBIDE. The stuff is so sharp that, if allowed to do the work, it cuts like crazy. In fact, the weight of the little sander was too much - I found that if I didn't allow it to compress the soft, worn-out, 1/2" pad, it removed both epoxy and sealer faster. I finished in less than 2-hrs.

Not sure if silicon carbide has an advantage on wood but, on finishes, my experience is "no comparison". While it's great for lacquer, you got no choice if you use catalyzed urethanes. The stuff is expensive compared to aluminum oxide - a good source is www.turningwood.com - Steve carries Kovax / Eagle product
 
Have you tried using a cabinet scraper instead of abrasives?

You might also look at ceramic abrasive discs like 3M Cubitron.

A larger orbit DA or a disc sander might speed things up.

Are you wet sanding?
 
Last edited:
John Tisdale said:
Currently working on a 26" tall mesquite vase - beautiful wood and great pattern with the inclusions but seems like the worms had a field-day before I got there. My normal routine is to fill the worm-hole and problem areas with black G-Flex epoxy, cut it off, and then apply TimberMate water base, black of course, as needed in the finishing applications. This time I changed the process: due to the number of pits and holes, I spread on black G-Flex epoxy over the sealer knowing I would have to sand it off.

Jury is still out on final results but I can tell you sanding a big piece with troweled G-Flex makes for a bad day - I use a 5" dual-action pneumatic w 3/32-orbit - great for fine finish work, lousy for the task at hand. Instead of the recommended 220, I went with 150. After the first hour I knew what I'd be doing for the next 5 or 6.

Then I remembered some sagely advice: LIGHTEN UP WHEN USING SILICON CARBIDE. The stuff is so sharp that, if allowed to do the work, it cuts like crazy. In fact, the weight of the little sander was too much - I found that if I didn't allow it to compress the soft, worn-out, 1/2" pad, it removed both epoxy and sealer faster. I finished in less than 2-hrs.

Not sure if silicon carbide has an advantage on wood but, on finishes, my experience is "no comparison". While it's great for lacquer, you got no choice if you use catalyzed urethanes. The stuff is expensive compared to aluminum oxide - a good source is www.turningwood.com - Steve carries Kovax / Eagle product
Click to expand...

May I ask why didn't you just cut it off by turning ?
 
John Tisdale said:
Currently working on a 26" tall mesquite vase - beautiful wood and great pattern with the inclusions but seems like the worms had a field-day before I got there. My normal routine is to fill the worm-hole and problem areas with black G-Flex epoxy, ...
Click to expand...

I don't know if placosternus difficilis has thick skin, but speaking down to the larval stage of the mesquite borer as a "worm" might not be well received. As collaborators in mesquite objets d'art, they should be allowed to share the credit. :D

My favorite filler for borer tunnels is brown Starbond cyanoacrylate. It's medium thickness and the color is actually translucent amber.
 
B5185_88.JPG
The 4 bowls above were turned from a mesquite burl from west TX and as you can see they had voids as well as borer tunnels. The burl was supplied by a resident of TX with a summer cabin in my area and the bowls were payment for a ride in his Stearman biplane.
The technique used to fill the voids was to first fill the voids with epoxy putty then turn that smooth, undercut about 1/16th", then apply powered turquoise and solidify with thin CA. The undercut technique and use of soft minerals was borrowed from Stephen Hatcher Who I saw at the 2011 symposium and I keep the handout book for reference. The use of the Epoxy putty was my idea to require less mineral and get a fill that didn't require dams like regular epoxy.
DSC00645.JPG
There are two areas on the replacement grip for this Colt 45 revolver out of the same Burl that had borer shit left behind that I solidified with thin CA. That was done about 4 years ago and I talked to him about a month ago and he said there were no problems with the grips.
 
Mike Pindzola said:
May I ask why didn't you just cut it off by turning ?
Click to expand...
Normally I "turn off" epoxy as I do the final outside cuts. I had finally got both smoothed out and the thickness at about 1/4" so went ahead and shot with barrier and one coat sealer. The roughness of this one was such that I thought epoxy the better choice over TimberMate - I also gambled that I could do a final troweling with maple veneer constantly dipped in acetone and reduce the thickness above the fix - worked pretty good.
My thinking when doing the post was to comment how silicon carbide is faster with less pressure which, to my thinking, is counter intuitive. When I started, the old habit of "bear down and git'r done" prevailed. When I finally practiced the "less is sometimes more" advice, and not just a little, the G-Flex was quickly reduced and put "in plane"
I plan to shoot again on Saturday and will send pics.
The Starbond cyanoacrylate material sounds interesting - will let you know how that works out.
 
Thanks John. So, just a normal procedure. I can do that ! Really did like the point of the post about 'Less is Better' for the Si carbide paper. Hope I can remember it ! Thanks again.
 
Worm poop is also called frass. Spell check doesn't like that, but that is what I have always heard it called.... Dictionary liked it.... Spell check doesn't know what spalt is either....

robo hippy
 
robo hippy said:
... Spell check doesn't know what spalt is either....

robo hippy
Click to expand...

That's because "spalted" isn't the past tense of "spalt".

"Spalted" is an adjective that means, as well all know, is the black lines caused by the fungal decay of wood.

"Spalt", on the other hand, is a noun that might be borrowed from the German word "spalt" which means "gap" in English. I also found a definition that means the left-over pieces when cutting wood shingles. It seems to be one of those rarely used words that aren't recognized by spell checkers.
 
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