Drying a flat bowl.

[Alie Barnes]

I started to make a flattish bowl for a Xmas present for my dad, i used a bit of green oak that i picked up last week. however it was only gonna be a practice run for a dry piece of wood that i have had stored away for some time.

My problem is this, i really like the bowl ive made and would actually like to keep it to use as Xmas pressie for dad, however being green oak i know its gonna warp and possible crack, is there any way i can stop it or at least minimise chances of warping/breakage.

Is this microwave method a good shout and how does one go about it?

Thanks all

Ill post some pictures at some stage.

 

[colin macdiarmid]

is the bowl at the finished size? if not you could try this method, I am trying it out the now nd have good success but not tried it on oak, try this link for a read, scroll down to the heading Experimental New Treatment for Wood http://www.ronkent.com/techniques.php

 

[PAC]

I love microwave drying. Here's the method...

1. Weigh your item with digital scales (to nearest gram)

2. Wrap it in a microwave safe plastic bag or simply wrap in kitchen roll (this keeps a fairly humid environment next the wood and keeps your oven clean) and pop it into the microwave oven.

3. Cook on full power (mine is 1000 Watts) for 30 seconds (over-cooking for several minutes might be a bad idea).

4. Remove (careful, it will be hot) and allow to cool for 5 minutes (might still be warmish after this period, but that's ok).

5. Re-weigh and compare to previous weight. It will probably lose about 6g of water but each piece is different.

6. Repeat the above steps until there is no loss of mass between the present and previous session. Small (thin) pieces take about 5 cycles, thick ones many more. In my experience, the final mass of the wood will be about 2/3 of the fresh (green) mass. So a green 100g piece will reduce to 66g when dry.

7. I've not had any cracking yet but sometimes get distortion. If this is undesirable the dried piece needs to be returned to the lathe.

8. You could apply the finish at the this point. I would wait until the piece has been in the house for a few days in the dried state.

Hope this helps.

 

[Alie Barnes]

I love microwave drying. Here's the method...

1. Weigh your item with digital scales (to nearest gram)

2. Wrap it in a microwave safe plastic bag or simply wrap in kitchen roll (this keeps a fairly humid environment next the wood and keeps your oven clean) and pop it into the microwave oven.

3. Cook on full power (mine is 1000 Watts) for 30 seconds (over-cooking for several minutes might be a bad idea).

4. Remove (careful, it will be hot) and allow to cool for 5 minutes (might still be warmish after this period, but that's ok).

5. Re-weigh and compare to previous weight. It will probably lose about 6g of water but each piece is different.

6. Repeat the above steps until there is no loss of mass between the present and previous session. Small (thin) pieces take about 5 cycles, thick ones many more. In my experience, the final mass of the wood will be about 2/3 of the fresh (green) mass. So a green 100g piece will reduce to 66g when dry.

7. I've not had any cracking yet but sometimes get distortion. If this is undesirable the dried piece needs to be returned to the lathe.

8. You could apply the finish at the this point. I would wait until the piece has been in the house for a few days in the dried state.

Hope this helps.

thanks a lot i shall try this in the next few days

 

[PAC]

Great, hope it works for you. Let us know how you get on.

 

[robo hippy]

With the micro wave drying, one note of caution, do not use the house hold microwave, or she who must be obeyed will be quite upset. It does work though.

On the soap soaking, I use it on all my bowls. The biggest benefit I can see is that it makes the sanding a lot easier. I turn to final thickness, soak for 24 hours or more, then let dry. It takes a 1/4 inch thick bowl about 10 days to come to equilibrium (as dry as it will get). I haven't noticed that it does anything to prevent movement, or cracking. Rule of thumb on drying; if it cracks, you are drying too fast, and if it molds it is drying too slow. One thing I do, and I picked this up from the people who soak in DNA (denatured alcohol) is to wrap the outside of the bowl in news paper, but leave the inside open. I wrap the rim in that plastic film that you wrap around boxes on a pallet to keep them from falling off. The theory is that the inside will dry first, and in shrinking, it pulls the outside in towards it, and the bowl dries in a compression mode. The plastic film helps with some compression on the rim. Do round over your rims a bit as compared to leaving the rim edges square and sharp. These delicate edges are more prone to splitting than rounded edges. This tecnique seems especially helpful for woods that are more prone to splitting, like the fruit woods, or for me, my favorite wood, Pacific Madrone (arbutus menzizi I think). Sanding a warped bowl can be a chore. You need a lathe that turns very slowly, in the 10 rpm range or so. If it is spinning any faster than that, you can't keep your hands, the abrasives, or a power sander on the wood. Rechucking it can be a chore as well as the recess or tenon will move considerably as well. I use a recess, and smaller extended chuck jaws to remount for sanding. You don't need as secure of a grip on the bowl for sanding as you do for turning. I love warped bowls.
robo hippy

 

[Alie Barnes]

I love microwave drying. Here's the method...

1. Weigh your item with digital scales (to nearest gram)

2. Wrap it in a microwave safe plastic bag or simply wrap in kitchen roll (this keeps a fairly humid environment next the wood and keeps your oven clean) and pop it into the microwave oven.

3. Cook on full power (mine is 1000 Watts) for 30 seconds (over-cooking for several minutes might be a bad idea).

4. Remove (careful, it will be hot) and allow to cool for 5 minutes (might still be warmish after this period, but that's ok).

5. Re-weigh and compare to previous weight. It will probably lose about 6g of water but each piece is different.

6. Repeat the above steps until there is no loss of mass between the present and previous session. Small (thin) pieces take about 5 cycles, thick ones many more. In my experience, the final mass of the wood will be about 2/3 of the fresh (green) mass. So a green 100g piece will reduce to 66g when dry.

7. I've not had any cracking yet but sometimes get distortion. If this is undesirable the dried piece needs to be returned to the lathe.

8. You could apply the finish at the this point. I would wait until the piece has been in the house for a few days in the dried state.

Hope this helps.

I tried this tonight and 30 seconds is no were near long enough, my oven is 800W and it barely warmed it for 30seconds, ive been doing it in stinits off 3 mins. progress is ongoing!

 

[PAC]

I tried this tonight and 30 seconds is no were near long enough, my oven is 800W and it barely warmed it for 30seconds, ive been doing it in stinits off 3 mins. progress is ongoing!

If using a sealed plastic bag to hold your wood, a good measure is to heat on full power until the bag fully inflates with steam (keep watching through the window and stop cooking when inflated). Note the time, and heat all further cycles for that duration. Choose your bag carefully as some don't like to be elevated to steam temperatures.

Forgot to mention before, during the 5 min. of cooling I wrap my wood in a fresh piece of kitchen roll to slow down water loss a little. Don't know if it really does anything but it's a nice idea...

 

[Wanlock Dod]

Hi Alie,

In your situation I think that I woudl recommend using PEG (PolyEthyleneGlycol?). This chemical can (apparently) dimensionally stabilise wood whilst in its wet state simply by soaking the piece in a solution. To be honest I've never tried it myself, although I believe that Craft Supplies used to sell the necessary.

I suggest this because as a piece of wood dries from green it will often split and warp. Perhaps warping on it's own isn't so bad, a nice kind of natural wobble . As far as woods go in terms of having a tendency to split, oak is pretty bad. The large medullary rays can cause splitting radially from the pith. So I'd say that if you dry the bowl, by whatever means, the chances are that you will end up with a split and wobbly bowl. This might be rescuable after drying if you turned a really chunky bowl in the first place, lots of folks rough turn bowls so that they will dry more quickly. If you want to preserve it's current shape/form (I'm assuming that it's still fairly green wood), then a PEG soaking probably offers you the best chances, although I would expect that the treatment would probably have an influence on the range of finishes you could use.

If you've already microwaved it, how did it go?

Cheers,

Dod

 

[PAC]

In your situation I think that I woudl recommend using PEG (PolyEthyleneGlycol?).

Hi Dod,

I think that PEG is also used for car radiator antifreeze. It's pretty toxic stuff and I'm guessing might not be a good idea if used for a bowl intended for fruit/food. Not entirely sure, though... :?


And Alie, how's your microwaving going?

 

[PowerTool]

Hi Paul - antifreeze is mainly Ethylene Glycol and colouring.
PEG (polyethyleneglycol) comes in several grades,including pharmaceutical.
It's uses vary from a swab solution for phenol burns,to a constituent of shower gel,depending on grade - so it's a whole lot safer than drinking antifreeze :wink:
Note - still don't drink it :shock:
Don't know where to get small quantities,but know several places to get it by the tankerload.

Andrew (who works in bulk chemical transport)

 

[PAC]

Hi Paul - antifreeze is mainly Ethylene Glycol and colouring.
PEG (polyethyleneglycol) comes in several grades,including pharmaceutical.
It's uses vary from a swab solution for phenol burns,to a constituent of shower gel,depending on grade - so it's a whole lot safer than drinking antifreeze :wink:
Note - still don't drink it :shock:
Don't know where to get small quantities,but know several places to get it by the tankerload.

Andrew (who works in bulk chemical transport)

Thanks for clearing that one up, Andrew.