Tear out on inside of Koa bowl

Re: Tear out on inside of Koa bowl

Brad Vietje

>John,

If you soak it a bit with soap/water, or mineral oil (might depend on the intended finish), you might have good results with very gentle shear scraping... If it's curly Koa that may not work at all. Can you post a pic. ?

Safe Spinning,

Brad Vietje

Thetford, VT

Re: Tear out on inside of Koa bowl

Mike Schwing from Md.

>John, I'll try to help.

There are many wears to deal with tear out, and sometimes nothing works other than sandpaper. Before resorting to that though...

Try stiffening the fibers instead of lubricating them, since that didn't work. Applying a coat of CA over the areas prone to tear out may help, as may any stiffening agent, white glue, shellac, sanding sealer, etc.. I have had better luck with stiffening fibers than softening them with oil, but others report exactly the opposite. Be mindful that any thing you add to the wood now may have an effect on the finish you choose later. For me, this is another reason to not use oil as it is harder to turn completely away than something that dries. I also find that thin CA goes everywhere it was not intended, so sanding sealer, such as Mylands Cellulose Sealer, winds up being my favorite choice.

Tool approach can also help (as can quality of sharpness). Not sure what type of gouge you're using, but if I use the roughing/shaping cut on my ellsworth grind to finish off a bowl I might get tear on the interior, but if I use his "flutes up", bevel rub cut (can be a bit of a pucker factor if you're not used to it), I can normally totally eliminate tear out, even on interior curves.

You may also find that different lathe speeds affect tear out. I tend to find slower speeds produce a finer surface for finishing cuts, but tool movement must change accordingly or you get ripples. I _think_ this is because the wood fibers are hitting the gouge with less force and tend to slice off cleanly rather than being pulled (torn) out by the sheer force of the speed at which then enounter the cutting edge.

Hope some of this helped (or made sense)

Re: Tear out on inside of Koa bowl

John

>Brad thanks for the response. It's not curly Koa,and I'm probably one of the last people in the USA who does not have a digital camera. Thanks for the idea though.

Re: Tear out on inside of Koa bowl

John

>Thanks, Mike

Re: Tear out on inside of Koa bowl

Doug Leite

>John, I turn a lot of Koa, and as Mike suggested, hardening the fibers with sanding sealer or thin super glue is usually the only way that works for me. On some Koa,not all, if you turn a piece with an inner radius, like a Calabash, you can't turn it clean without toughening the wood. I use an modified Ellsworth grind with about a 45 deg. angle for going around the curve and doing the bottom. Keeping the bevel rubbing is a must to support the fibers from being torn. If your final cut has already been done and you are at final thickness,then use the super glue to toughen the area and start sanding with 40 or 60 grit. If you don't toughen the fibers first, sanding will continue to lift the fibers and you will soon be sanding air. All of the previous has pertained to inside problems. If you are having the problem on the outside, using a standard Ellsworth grind in a shear scraper mode should suffice. You may still have to toughen the area. Don't worry about the color change from the glue, as it will disappear when you sand.

Aloha

Doug

Re: Tear out on inside of Koa bowl

John

>Thanks Doug, I was in the islands back in January and picked up a box full of Koa and am excited to turn some of them.