Microwave Drying

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Forum topic by CSmithWoodturnings posted 09-29-2014 08:21 AM 2621 views 0 times favorited 13 replies Add to Favorites Watch
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24 posts in 2793 days

09-29-2014 08:21 AM

Topic tags/keywords: woodturning green bowl bowls lathe microwave drying question

Well this is my first forum on Lumberjocks and I’m pretty excited about it. I am a junior at Clemson University, but in my free time I have been turning bowls for about a year now. I have some friends in the tree cutting business where I have gotten the majority of my bowl blanks from, but I recently cut down a Sweetgum tree that was on our property where we hunt.

I typically tend to rough turn my bowls to about 3/4 of an inch thick, then I proceed to through them in a 50 gallon trash bag filled with shavings to dry out in my garage. This particular sweetgum blank I was turning had some awesome figure near the tenon, so I figured what the heck, lets try to make this as thin as possible to show the figure and maybe it will dry a bit quicker. I don’t have a fancy laser, so I mounted a led light and thinned the walls until I could see the shadow of my hand on the other side. I don’t have a bowl caliper, but if the walls are uniform, my dial caliper read about 3/16 of an inch thick. Later on that day, about 6 hours after rough turning, I noticed the bowl had gone from a 9 inch diameter to 9 1/4 inch from end grain to end grain, and about 8 3/4 from side to side. I figured I would try to microwave this bowl since it was already pretty thin. I did this in very short segments about 10 times.

After the sum of segments were complete, the bowl feels exponentially drier. My only dilemma with the bowl being dried that quickly is the warping. I can’t recheck and reshape it due to how thin the bowl is. Does anyone with experience in this situation have any advice on the best way to sand this bowl? I feel that if I remounted and sanded on the lathe it would only hit the grain because it has a shorter diameter, and not the end grain which has expanded.

13 replies so far

View Ronbarnes's profile


1 post in 3017 days

#1 posted 09-29-2014 09:44 AM

After drying in the microwave, I hand sand the bowls. Before going to the Microwave, I sand down to 220 so there isn’t that much sanding to do after drying.

View Charles Maxwell's profile

Charles Maxwell

1110 posts in 5262 days

#2 posted 09-29-2014 01:47 PM

Welcome to LJ. Good to have a young man sharing in this forum. Since you’re in the student mode, I would recommend visiting a professional kiln dryer where they do microwave drying all the time. I’m pretty sure you can shorten your learning slope by talking, even interning, with one of the ‘old bulls.’ Keep chargin! Hope to hear more from you soon.

-- Max the "night janitor" at

View CSmithWoodturnings's profile


24 posts in 2793 days

#3 posted 09-29-2014 05:44 PM

Thanks Max, I buddied up with one of my girlfriends dad’s best friends who happens to be an expert at duck calls in particular. He also knows beyond his fair share in most topics of woodturning. Ive been doing research and I would love to visit a kiln, just not sure where one would be in the area, or how to even locate one.

View Wildwood's profile


2959 posts in 3590 days

#4 posted 09-29-2014 10:11 PM

If sand before microwaving might make life easier. Only way to put it back on the lathe after bowl has gone oval is jam chucking. Easier to hand sand while mounted on the lathe.

I do not use a microwave bowls, tried many years ago and was not impressed with the results. I have turned many thin bowls and have had good luck with many of them and many ended up in firewood pile. Oval bowls draw a lot of attention at craft fairs. The successful ones sanded and finished on the lathe. Unsuccessful ones never made it off the lathe.

You might switch to paper bags or carboard boxes to store bowl blanks. Once lived in zone 5 worst part of the country for mold on wood, according to Forest Product Labatory now their new chart say in the 80%,

Only use plastic bag while wood is on the lathe for very short period of time. I just rough turn bowl blanks and set them on floor in back of the shop, may use paper bags & shavings wood is really wet, bit only for week or two.

-- Bill

View CSmithWoodturnings's profile


24 posts in 2793 days

#5 posted 09-29-2014 11:11 PM

Thanks Bill. I really wish I would’ve known that. The bowl already seems really dry, and I was sanding it yesterday and it was pretty tough to get some of those tool marks out, but then again being an oval shaped bowl, I guess it looks best rustic.

View Wildwood's profile


2959 posts in 3590 days

#6 posted 09-30-2014 09:58 PM

Forest Products Laboratory Wood Handbook about the best reference for a woodturner. While no chapter addresses woodturning, still great reference for anyone harvesting or buying wood to turn. Just take what you learn and apply it to wood you turn.

If have indexing feature on your lath could try power sanding great way to get rid of tool marks but need the right supplies. With bowl mounted on lathe with jam chuck & tailstock support and lathe off can get rid of those tool marks. Only secret to power sanding is not applying too much pressure and not using too coarse grit sand paper.

You often here turners & woodworkers start their sanding sequence with 80 grit paper I say depends upon tool marks, other imperfections, and wood species.

Just me, but would start with 100 or 120 grit sandpaper on Gum and go through the sequence until have uniform scratch pattern and no tool marks.

-- Bill

View dozer57's profile


92 posts in 2955 days

#7 posted 10-14-2014 03:43 PM

Not that I know much about microwave drying of bowls but if you leave 10 percent of your material you can rechuck it and reshape you bowl. If your blank is 7 inches rough turned out side then leave the wall thickness 3/4 inch thick and the bottom the same. I found if you microwave slow at first, about 15 seconds and gradually increase to 30 seconds take your wood out of oven and let stand for 20 min. each time. Weigh it after cooling each time and when weight doesn’t change you can finish your project. After you sand it let it sit for a day before applying finish, this helps with hair line cracks to close up. This works for me but have not tried this on larger pieces yet. Good luck

View Woodmac's profile


5 posts in 5405 days

#8 posted 10-22-2014 03:28 AM

If you take the green wood down to final thickness and sand it to 220, you can have success drying in the microwave. Weigh the blank first. Use cycles of high power long enough to just get the wood really warm but not hot. Allow to cool between cycles. Usually 7-8 cycles is sufficient. If the blank is not changing weight you are done. Some warping adds charm. Mounting your bowl with a recess in the base instead of a tenon allows you to jam chuck the bowl and reround the recess to allow remounting. You will not be totally concentric but can sand at slow speed on the lathe. Judicious use of a plane alllows you to relieve the high ends of the bowl if iit warps. Keep the bowl mounted in the chuck, which in turn is mounted in your bench vise, to steady it for planing.

View hairy's profile


3366 posts in 4987 days

#9 posted 10-22-2014 12:39 PM

I’ve often wondered, but never tried, about making a form to put a bowl on while drying. Basically the exact opposite shape of the bowl. I think I remember seeing something like that watching “How it’s made” on TV. In that case they were making hats.

What could happen? It could shrink and be so tight you can’t get it off? Crack? Just a thought…

I have done microwave drying on a few spindle blanks without a problem. Nuke it, cool it, repeat until it quits losing weight.

-- there's someone in my head but it's not me...

View Woodknack's profile


13593 posts in 3835 days

#10 posted 10-22-2014 03:29 PM

Wonder how well steaming in the microwave wood work. Commercial wood bowls are sometimes steamed to control warping and cracking while drying. If I had a microwave in my shop, I would try it.

-- Rick M,

View TheDane's profile


6055 posts in 5118 days

#11 posted 10-22-2014 06:43 PM

If I had a microwave in my shop, I would try it.

Trying to talk SWMBO into a new one for the kitchen … she wants a new sewing machine instead!

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

View hairy's profile


3366 posts in 4987 days

#12 posted 10-22-2014 07:51 PM

I tried to get $5 for one at my yard sale this past summer. Nobody wanted it. It went to St. Vincent de Paul.

-- there's someone in my head but it's not me...

View Dallas's profile


3599 posts in 3942 days

#13 posted 10-22-2014 08:24 PM

I have an itty bitty convection oven. 26” wide and 18” deep. The temp will go to 150° and hold with an accurate reading.
Cut green lumber up to about 12/4 seems to dry nicely in about a day and a half. That is with a caveat….. let the wood cool off every five or six hours or you’ll get a lot of twist and warp.

-- Improvise.... Adapt...... Overcome!

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