Moisture Content Question

[Mark Kelly 92040]

I am not an experienced woodturner by any stretch, hence this question: What is an acceptable moisture content for a turning block that can be turned from start to finish in one go? I'd like to make some peppermills for Xmas and some of the blanks I'm looking at are between 17 and 20% MC. I live in Southern California if that makes a difference. Any help would be appreciated.

Mark

[Dennis Ford]

The easy answer to moisture questions is that "it depends". If a peppermill warps, that is likely to be a problem so I would consider 17% too wet for almost any wood (mesquite would probably be OK).
Turning green wood to finish works fine for pieces that can warp and still be OK. Sometimes warping makes an art piece better.

[John K Jordan]

I am not an experienced woodturner by any stretch, hence this question: What is an acceptable moisture content for a turning block that can be turned from start to finish in one go? I'd like to make some peppermills for Xmas and some of the blanks I'm looking at are between 17 and 20% MC. I live in Southern California if that makes a difference. Any help would be appreciated.
Mark

Almost everything I turn is dry. Seasonal wood movement is bad enough and I don't want to deal with shrinkage and warping from wood that is not completely dry.

I process a lot of green wood into turning blanks and air dry everything. Small spindle squares (1" or so) of many species will dry nicely in a few months to a year. Larger blanks for boxes and peppermills and such take much longer and some species take longer than others. The dogwood I'm using now has been drying for about 10 years. The the same size of eastern red cedar or sassafras is ready MUCH quicker.

Just as needs to be considered when making furniture, what is the intended environment for the object? If it is in someone's heated/air conditioned house I like to see between 9-10% moisture. I live in East TN where it gets quite humid, but my shop is has heat and air - wood stored in my shop will eventually hit 9+% . For things that won't matter if they warp a little I might turn at 15% or more.

I suspect it might be a problem to turn something with critical dimensions in the desert then ship it to a humid climate. A good sealing finish should help slow down but not stop the moisture.

Note that for things like turned boxes that can't handle any warping, I learned from reading Raffan to turn it twice even if dry. The stresses in a solid blank, even when well dried, can be released after it is cut into. It's not possible to know if a certain blank has internal stresses so I treat it "sort of" like a twice-turned bowl: hollow the box but leave it a little thicker than needed. Let it sit for a while, preferably over night, and any stresses should be relieved. Then turn to finished.

This also works for wood that is not quite dry enough inside the blank and quickly if the walls are thin - hollow and let it dry, just like turning a green bowl but it much quicker. If in a hurry you can also rough turn and use the microwave drying technique. When I was making a lot of boxes I had a bin full of hollowed box blanks I let dry for a month or two before finishing.

For your peppermills could you rough turn then drill out the center a little smaller than needed? This would let them dry a lot quicker. The microwave method should get them way down in one day. (Maybe not use the kitchen MW - I have one in the shop.) Then drill to final size and finish turning. ???

JKJ

[Pat Scott]

I'd like to make some peppermills for Xmas and some of the blanks I'm looking at are between 17 and 20% MC.

That is way too much MC to make a peppermill. I cut my peppermill blanks into 3x3 x whatever length, and using the "1 year per inch" guideline, I let them air dry for a minimum of 3 years before I even look at them. Some species may dry quicker than others, but I still wait at least 3 years. Since it takes so long to dry, this is why I always seem to be cutting peppermill blanks. I don't want to count how many blanks I have downstairs but it's several hundred.

If you were to make a peppermill out of the blanks you have, your tenon between top and bottom could oval slightly once the wood completely dries and you stand a chance of the top binding. You could make the fit real sloppy, but IMO then you have a lesser quality peppermill. If your top binds even a little, then you have a lesser quality peppermill.

To speed up drying you could drill a smaller hole through the middle but I don't as I'm too lazy and that would take too much time for all the blanks I have. Another reason is what size hole do you drill? Usually the finished through hole is 1" or 1-1/16". If you drill out a 3/4" hole for drying, it's possible the blank could move enough that the hole isn't centered on each end anymore, and that your 1" bit isn't big enough to true it up. If your hole isn't true, then the alignment for the shaft is thrown off. You could drill a smaller hole, say 1/2", but that sure seems like a lot of work to go through. And I don't know how much air movement there would be through a 1/2" or 3/4" hole, so in the end is all that work really worth it and did it really save that much drying time?

Also remember that in order to drill a hole for drying, you have to predetermine the top and bottom length and cut them apart so you can drill a hole through the bottom. What if the ends crack or check during drying? Your proportions could be thrown off. What if once you start turning the blank round you see nice figure that you really wish were at the top of the mill and not the bottom? I leave the blanks whole, and once they dry and I turn them round, then I can decide which end is the top and which is the bottom.

One way to speed up drying is to remove the corners from the blank. This removes quite a bit of excess wood that will be turned off anyway, and air has to dry through the corners before it can get to the center to dry it. You can mount the blanks on the lathe and turn the blanks round, or take them to the bandsaw and cut the corners off. It takes too long to mount each blank on the lathe, so I try to cut the corners off at the bandsaw. I leave the bandsaw table flat, and I made a V-jig to angle the blanks. The cut off triangle corners are also more useful than a pile of shavings. I can use the corners as fire kindling, or as scraps to raise things off the bench. For example if I cut the corners off one 12" blank, I have four 12" long triangle shaped scraps. When I Anchorseal a piece, I can use two of those triangle scraps to set it on to dry.

[William Bachtel]

Southern CA should be around 8 % to 10 %