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Bowl blank advice, cracking.

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Forum topic by GM3 posted 02-16-2020 03:58 PM 542 views 0 times favorited 11 replies Add to Favorites Watch
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GM3

2 posts in 46 days


02-16-2020 03:58 PM

I am pretty new to turning, I have been turning pens for about a year now. I decided to try to step it up and turn some bowls. I bought some waxed bowl blanks from a local Woodcraft and some from a local sawmill that sells kiln dried and sealed blanks. I picked up some maple, cheery, and guanacaste (? it was on sale at Woodcraft). Accepting that my first few bowls would fail in the name practice.

Last weekend I got home, cut 3 of the blanks to rough circles on the band saw. I mounted one of those my lathe, shaped it, put a mortise in it, sanded it and left it for the night. It was a couple days before I was able to get back to them and all the ones I cut have cracked…. I am going to try to fill the cracks with resin so that it is not a complete failure.

The sawmill dates their blanks, they were kiln dried in October 2019. No info on the Woodcraft ones.

How can I prevent this in the future? Do I need to let them dry longer? Should I not cut them until I am ready to make the bowl? Any advice is appreciated, I’m just a self taught newbie!


11 replies so far

View OSU55's profile

OSU55

2600 posts in 2665 days


#1 posted 02-17-2020 03:16 PM

I find most all sealed blanks are not dry, even if kiln dried. Regardless, whether sealed blanks or green wood, when not cutting wrap the blank in plastic. Even 5 min is long enough to cover the blank. I just wrap a trash bag around it. You want to prevent water evaporation from the blank.

What to do when you have finished cutting – one of 2 choices, cut the piece thin 1/4”-3/8” and let it warp (green or once turned), or leave the wall about 10% of dia (1” for a 10” bowl), dry it, then finish turn. I use kraft paper bags or sheets to wrap the turning and usually throw in a lot of chips, tape it closed, weigh it, when it stops losing weight its dry. I keep the bagged turnings inside the house

View Wildwood's profile

Wildwood

2824 posts in 2810 days


#2 posted 02-17-2020 08:07 PM

Any time turning blanks completely seal in paraffin wax consider it wet wood. Not sure where you live but if scrap that wax from the sides and let it hang out for awhile might have more success.

If remove wax and weigh blanks and set aside so out of direct sunlight with air circulation weight each week until stop losing weight those blanks reached EMC for your area and safer to rough turn.

If scroll down to page 5 and look at Figure 1 then down to table 13-2 think will understand what am talking about.
https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr190/chapter_13.pdf

-- Bill

View Washam's profile

Washam

11 posts in 294 days


#3 posted 02-19-2020 12:16 AM

Try rough turning and then soak the blank in denatured alcohol for about 24 hrs. then remove and leave it to dry. I’ve had pretty good luck with this process. Either of the methods Osuss described will work very well too.

View bobvilla's profile

bobvilla

16 posts in 1773 days


#4 posted 02-19-2020 03:05 PM

I bought a dehydrator and I put rough blanks in it over night. I put it on a fairly low temperature, about 105 degrees. I still get some cracking but not nearly as much. I think it must be the constant flow of air around it that helps the evaporation occur more evenly. I don’t really want to wait months to finish a rough piece so I’m willing to live with some cracks. It’s actually the nature of the beast and that’s what wood wants to do. I don’t want cracks in furniture pieces, but in lathe pieces, I’m fine with them.

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Phil32

980 posts in 579 days


#5 posted 02-19-2020 06:12 PM

I visited a Myrtlewood bowl factory in Oregon years ago. They would air dry their rough planks for years, the bandsawed blanks for months, the rough turned bowls for months, and unfinished bowls for weeks. Nothing has changed in the behavior of wood. It is us (we) that have gotten in a hurry.

-- Phil Allin - There are mountain climbers and people who talk about climbing mountains. The climbers have "selfies" at the summit!

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LesB

2414 posts in 4119 days


#6 posted 02-19-2020 06:16 PM

As you can see from other responses this is a whole can of worms. First I agree about wax covered blanks being treated as “wet”. There are so many ways to approach this I don’t quite know where to begin but even the most experienced turners have failures due to wood movement. I have had bowls that I thought were dry slowly warp over a period of months after they were finished.

A common method for turners who are what I will call semi commercial is to rough turn a whole bunch of blanks and put them away to finish drying. A variety of methods are used in the drying process from paper bags to a cool room. It can take months.

A faster method involves rough turning and then drying using a microwave oven and a paper bag. This functions sort of like a steam kiln and can be done in a few hours. I won’t go into details here as there are lots of videos on the internet about it. It usually takes several heatings in the oven. I use it often for wet wood but your wife may not like chunk of wood in her oven so check out the second hand stores for a used one.

Another method is to treat the blank with polyethylene glycol (Petacryl is one brand) to soak the wood and displace the moisture. I would not recommend this for items to be used with food.

As to cracks. I have had very good luck using medium or thick CA glue; with fine sawdust packed in the crack first if the crack is over 1/8” or alone for smaller cracks. For the fine sadust filler I usually treat it with thin CA glue followed immediately with the thicker stuff. The thin glue acts as a wicking agent for the thick glue. I don’t always use the saw dust but sometimes just fill the crack with glue, applying it in layers. Occasionally the glue filler will chip out some as you turn, just refill the chip and continue. Oh, in wet wood the glue may get hot and give of little vapor, don’t breath it. Also as I turn an item I watch for fine cracks and if I see them I immediately treat them with medium CA glue and can usually stop their progress while I finish the piece. You can also use this on for cracks in rough turned blanks while they dry.

By the way, once other people know your are turning things from “fire” wood you will probably get lots of offers for free wood….I have collected piles of it that way. When that happens you can get more casual about drying the wood and just put it in a cool dry place for a year or so they sort out those that dried well and burn the rest.

-- Les B, Oregon

View GM3's profile

GM3

2 posts in 46 days


#7 posted 02-20-2020 07:18 AM

Thank you all for the detailed responses. I see I have a lot of homework in front of me. I will try all the methods listed and maybe one day in the not so far future have some successful pieces to come back and post here for you. Thank you again everyone!

View OiBowyer's profile

OiBowyer

24 posts in 668 days


#8 posted 02-26-2020 09:33 PM

Wood drying is a matter of removing the free water over time. There are some calculations that you can make to see what the drying rate of your species of. That’s really only to give you a basic idea though as every piece of wood is different and figured wood is unpredictable

R. Bruce Hoadley had a few books on the subject of you’re real nerdy about it.

When wood cracks from drying it’s because the outside dries faster than the inside. That makes the outside shrink faster than the inside so the outside cracks. It’s called checking.

So keeping your word from checking becomes a problem of drying the outside and the inside at similar rates. This can be done in a bunch of ways but if you bought the blanks and just want to turn them sooner rather than later I would
only cut the one that I’m about to turn.
Turn the bowl in one sitting
Turn it to quarter inch thick (expect warping) or
Turn it to 1 inch thick (expect warping and possibly cracking)
Do not attempt to sand it
Then either
Bury it in its own shavings in a paper bag
Put it in a damp basement
Place it in a plastic bag
Or anything else you can think of to slow the water from running out.
You can also dry by microwave of the piece is already turned but if you heat it too much the water will turn to stream and the wood will crack. (I wrap a damp town around it) check it often and if you see cracks start to form cool and dampen the wood.

Get out a strong magnifying glass (I use an app on my phone) and look at the end grain the more solid it looks the longer it will take to dry. If it looks like a bunch of straws or Swiss cheese it will take less time to dry.
There are exceptions but generally speaking soft woods (with needless) dry faster than hard wood (with leaves). If you have questions about wood stats and drying rates you can find them in a free pdf of “the wood handbook” on the USDA website.
Feel free to ask questions
Good luck

-- Matt Bielenberg- turning student https://www.etsy.com/shop/Turning4SchoolMoney?ref=search_shop_redirect https://www.facebook.com/Turning-4-School-Money-213112446187330/?modal=admin_todo_tour

View Furnone's profile

Furnone

17 posts in 811 days


#9 posted 03-02-2020 05:20 PM

I too, am new to bowl turning. I cut some blanks from spalted maple, rough turned them and then put them in a $30 craigslist microwave. I nuked them on high for 60 seconds, let them rest in the microwave for at least 1/2 hour and repeated about 10-12 times. They came out perfect. Only 6 bowls so far, so this is not a long term test, but early results are good. I think the walls should have been a little thinner, but I was a little hesitant after blowing out a couple of bowls.

-- I will not lower my quality standards, so up yours!

View MrUnix's profile (online now)

MrUnix

7828 posts in 2875 days


#10 posted 03-02-2020 05:27 PM

Drying in the microwave is a fairly common technique… I’ve done it a few times and it seemed to work well, but most of my wood is already pretty dry anyway – I cut up the blanks, paint the ends and stick them out in my pole barn for a few years :)

Anyway, here is a 3 minute video that may be useful:

Drying Wood In A Microwave Oven - A WARNING – YouTube

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

View ShapingGrain's profile

ShapingGrain

16 posts in 1490 days


#11 posted 03-04-2020 12:24 AM



Drying in the microwave is a fairly common technique… I ve done it a few times and it seemed to work well, but most of my wood is already pretty dry anyway – I cut up the blanks, paint the ends and stick them out in my pole barn for a few years :)

Anyway, here is a 3 minute video that may be useful:

Drying Wood In A Microwave Oven - A WARNING – YouTube

Cheers,
Brad

- MrUnix

Good video MrUnix. I had not seen that one before but have watched some of Gord’s other videos.

-- Ken, New Hampshire, www.shapinggrain.com

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