Turners Firewood

[William C Rogers]

It all started out fine. I'm still learning and wanted to add some wood burning decorative feature to this bowl. Cherry about 10" X 5 1/2". Rough turned inside and outside. Wanting to see the effect I finished turned the outside and sanded it. Then added the band. All was well.

.338616

started the inside, just taking light cuts when I heard that dreaded hollowing sound. Sure enough it cracked. I glued it, but knew the outside would now need additional work. Taking even lighter cuts it happened again. The first crack was near the pith, but the second was not.
338617

The first glue held so why not a second time. Got the inside done and went to take some light cuts on the outside. When I got to the bottom of the glue line BAM. I now know by experience why I wear the face shield. I was too the left, but still felt a piece hit the shield. The bionic shield did fine, but I will wear some safety glasses in addition on larger bowls as I don't believe the shield is rated for impact. Speed was 1400 rpm.

338618

Kindking has has been made. Lessons learnt: 1. finish turning before investing time in adding nice touches and sanding. 2. Sometimes it's best not to make your kindling smaller. Just quit and burn a larger piece.

[Randy Red Bemont]

It was a beautiful bowl. So far I have not had that happen.

Red

[Dick Strauss]

I'm sorry that you lost that one...it looks like it would have been a very nice piece. I suspect that either the cracks were there all along on the outside and you didn't see them or possibly the stress of removing the interior caused things to move. We are very glad you are safe!

As a post mortem here are some things I noticed that might help others with less experience to stay a little safer:

1) 1400 rpms is too fast for a 7" and larger bowl IMO.
2) Once you have a known crack (especially one that has been repaired), it is time to slow the lathe down to slower than normal. This makes the audible tick of a crack opening more noticeable because the frequency drops with speed (so instead of a almost hiss noise of ticks close together, it sounds like a series of rapid ticks that are distinct).
3) It is a good idea to wrap plastic wrap or fiber tape around the outside of any repaired piece to try to contain any possible glue joint failure after the first wood repair. I never assume my fix is permanent or secure!
4) The design of your bowl probably had you hanging out over the tool rest in the corner more than you would have liked also.
5) Ideally a piece that size and thickness would have been turned to depth in steps to limit vibration.

Just food for thought and safety discussion.

[Fred Belknap]

Sorry, it was a very nice bowl. Dick,s advice covers pretty much what happened I think. I see that part of the break is along one of the burn lines, maybe it got to hot. Heat build up from sanding the outside could contribute and internal stress in the wood probably didn't help. I was wondering how you got the area between the burn lines darker than the rest of the bowl?

[Reed Gray]

In the second picture, I can see another crack under the first two. My first thought is that the cracks were already there to begin with, and opened up more as you turned the piece. That many cracks off the pith, even with the pith removed makes me think it was trouble to start with. With any unsound wood, turn slower, and with any piece of wood, stand out of the line of fire. Nice decorations on it though...

robo hippy

[William C Rogers]

I'm sorry that you lost that one...it looks like it would have been a very nice piece. I suspect that either the cracks were there all along on the outside and you didn't see them or possibly the stress of removing the interior caused things to move. We are very glad you are safe!

As a post mortem here are some things I noticed that might help others with less experience to stay a little safer:

1) 1400 rpms is too fast for a 7" and larger bowl IMO.
2) Once you have a known crack (especially one that has been repaired), it is time to slow the lathe down to slower than normal. This makes the audible tick of a crack opening more noticeable because the frequency drops with speed (so instead of a almost hiss noise of ticks close together, it sounds like a series of rapid ticks that are distinct).
3) It is a good idea to wrap plastic wrap or fiber tape around the outside of any repaired piece to try to contain any possible glue joint failure after the first wood repair. I never assume my fix is permanent or secure!
4) The design of your bowl probably had you hanging out over the tool rest in the corner more than you would have liked also.
5) Ideally a piece that size and thickness would have been turned to depth in steps to limit vibration.

Just food for thought and safety discussion.

Dick,

I appreciate the advice and the reason I posted. 1,2, and 3 are very helpful. Yes, I should have been down to 800-900 rpm. 4, I was ok on tool rest. I bought the Robust bowl rest that gives me coverage. 5, I'm not sure what you mean or how to do that.

Fred,
i don't think the wood burning contributed to the failure. I am also very careful regarding heat build during sanding. I think Reed is right and there were cracks to start, but I didn't recognize the signs. As far as the dark lines, I just used a wire to burn the wood.

[Doug Ladendorf]

My first thought is what Dick mentions in number 5. When turning the inside start by turning the first inch down, finish that and go the next inch down. Finish that and don't go back to the rim. Continue on this way for the inside. I also finish sand the outside beside going to the inside so I'm working with solid wood there.

[William C Rogers]

My first thought is what Dick mentions in number 5. When turning the inside start by turning the first inch down, finish that and go the next inch down. Finish that and don't go back to the rim. Continue on this way for the inside. I also finish sand the outside beside going to the inside so I'm working with solid wood there.

Am I doing this wrong? I put a start hole usually with a forester bit about 1" about 1/2" above where I think the bottom of the bowl should end up. Then start Turing starting about 2-3 from center working my way toward the rim. When I get the rim to about thickness I usually have a medium amount of material I still need to remove from the bottom half of the sides and bottom of the bowl to get a somewhat uniform thickness.

If if I understand the above I should finish the first couple of inches sown to the approximate depth and then start moving toward the rim.

[Doug Ladendorf]

The center doesn't matter so much. There are many people who leave the tailstock up for more support and leave a column in the center that needs to be turned out last. What I mean by turning the first inch down I mean on the rim. Turn the first inch down on the rim to final thickness, then move down the second inch of the rim to final thickness. You will be removing some from the rest of the bowl as well but this way you are turning the rim while it is still well supported. Afterward it will not be supported and likely start to move/warp a bit with the release of tension. Hopefully that's clearer.

[William C Rogers]

The center doesn't matter so much. There are many people who leave the tailstock up for more support and leave a column in the center that needs to be turned out last. What I mean by turning the first inch down I mean on the rim. Turn the first inch down on the rim to final thickness, then move down the second inch of the rim to final thickness. You will be removing some from the rest of the bowl as well but this way you are turning the rim while it is still well supported. Afterward it will not be supported and likely start to move/warp a bit with the release of tension. Hopefully that's clearer.

Got it, thanks

[Brice Rogers]

Bill,

I too often use a Forstner bit to start my hollowing and establish the bottom (to within about 1/4 inch or so). So, if you continue to do so, just leave more "meat" it the lower portion of your bowls, thin out the top section first, don't go back to the rim, and thin out the bottom last. If I am making something quite thin, and go back to the top of the bowl, I've heard howling (chatter) and get a bunch of chatter marks. So, now I avoid going back to the thin sections on the top.

I recently watched David Ellsworth make a hollow form. What I found interesting (and a departure to how I usually did things) was he completed the hollowing of the bottom inside before he finished the bottom outside. He left some extra meat on the outside until last. He mentioned that it is generally easier and safer to make make the final cuts on the outside where you can see what you're doing. I hadn't been doing this. While he was generally discussing hollow forms, I think that it is also applicable to bowls.

[John K Jordan]

I hate it when that happens. I keep a Box Of Shame for things that break or I mess up. However, that last picture looks like it could be an artistic composition in a gallery, probably with a big price tag! Name it "angst-giving" or "expectations" or something. :-) I'm glad no humans were injured in the making of this piece.

JKJ

[David Delo]

Glad your okay William. Anyone of those pieces could have put a serious hitch into your giddy-up. Stay safe.

[robert baccus]

Read up on twice turned bowls. Drying pieces is a necessary art in turning.

[Dick Strauss]

One more quick note...

It looks like you got very thin on the inside just below the beauty ring. This happens to be in the area of the first repair.

Have fun and be safe!

[William C Rogers]

Read up on twice turned bowls. Drying pieces is a necessary art in turning.
Robert
Im not sure what you mean. The wood was dry. I checked it before starting and it was around 7% MC.

Dick
it was around 5/16 thick and I was just trying to clean up some tear out when the first crack happened. It got thin after my repair attempts.

I appreciate all the comments. I have a hickory bowl in the lathe now and following advice do far so good. Trying to decide if I do something similar to enhance the rim or not. Just a little more out of the bottom and sanding.

[Dennis Peacock]

Well, over the course of the last several years, I've had some really fancy firewood for the old woodstove. :)
Bowls, platters, and etc....damaged, flew apart, cracked, etc, etc,etc....all would end up as heat for the house in the winter. :)

[Dick Strauss]

William,
A piece of wood that measures 7% moisture at the outside 1/4" layer does not mean it measures 7% at its core. Unfortunately solid blocks of wood used for turning bowls rarely have a consistent moisture content even if they have been sitting to air dry for 10 years or more. Think about a slice of an apple...the outside of the slice can be dry from sitting on the counter for an hour while the inside in still pretty juicy. The same can be true for wood.

You can turn a piece of green wood to final thickness all in one shot but count on it finshing as an oval bowl. It is easiest to sand green at the same time it is turned before it goes oval. However, decorative detail like you added to your piece will often result in disaster because the stresses of drying may cause the bowl to crack at its weakest point (your nice beauty ring detail!)

Kiln dried wood will move some as you remove the supporting wood inside and internal stresses are released but it doesn't move much from the change in moisture content that happens as you turn green wood. In this way, we have two forces working against us with green wood.

Robert B was referring to the twice turned method for green wood turning. We usually turn the green wood once leaving it thicker than we would like in the finished product. Let it dry (through a variety of methods that may or may not work based on your local climate). Any sharp transitions (corners, lines, etc) in green wood can lead to a crack forming from the localized wood drying at vastly different rates at the surface (especially corners and edges) versus the inside of the wood. Once again think of an apple wedge where the edges are very dry while the center is still juicy setting up a moisture induced stress. Once drying is pretty complete, we re-turn the now warped piece back to round and finally to our final thickness.

Feel free to ask any questions if I didn't do a good job of explaining something.

Have fun and be safe!

[William C Rogers]

William,
A piece of wood that measures 7% moisture at the outside 1/4" layer does not mean it measures 7% at its core. Unfortunately solid blocks of wood used for turning bowls rarely have a consistent moisture content even if they have been sitting to air dry for 10 years or more. Think about a slice of an apple...the outside of the slice can be dry from sitting on the counter for an hour while the inside in still pretty juicy. The same can be true for wood.

You can turn a piece of green wood to final thickness all in one shot but count on it finshing as an oval bowl. It is easiest to sand green at the same time it is turned before it goes oval. However, decorative detail like you added to your piece will often result in disaster because the stresses of drying may cause the bowl to crack at its weakest point (your nice beauty ring detail!)

Kiln dried wood will move some as you remove the supporting wood inside and internal stresses are released but it doesn't move much from the change in moisture content that happens as you turn green wood. In this way, we have two forces working against us with green wood.

Robert B was referring to the twice turned method for green wood turning. We usually turn the green wood once leaving it thicker than we would like in the finished product. Let it dry (through a variety of methods that may or may not work based on your local climate). Any sharp transitions (corners, lines, etc) in green wood can lead to a crack forming from the localized wood drying at vastly different rates at the surface (especially corners and edges) versus the inside of the wood. Once again think of an apple wedge where the edges are very dry while the center is still juicy setting up a moisture induced stress. Once drying is pretty complete, we re-turn the now warped piece back to round and finally to our final thickness.

Feel free to ask any questions if I didn't do a good job of explaining something.

Have fun and be safe!

Dick
I recently cut a piece of hickory sitting on the ground for about 2 years. I thought it was "dry", but when roughing it out it felt "damp". Rough to size, but next day it was warped. MC was about 16%.

This piece of cherry I only checked as the blank, 7%. It was cut in 2012 and had been in my shop 3 months on a shelf. There was no sealer on the wood.

So are you saying I should check MC when rough size? What is a safe MC, and does it depend on the wood.

I turned my first green bowl about 8" diameter, sealed it and bagged it on Feb. 2. Checked today and some expected warp age and the MC is about 13-14%. I figured I would wait until 10-11% before finishing. I think it is box elder, but not sure.

[Dick Strauss]

William,
Moisture content is sometimes hard to determine in a roughout without leaving vampire marks from the probe tips.
Depending on the design, you may be able to use a moisture probe in an area like a tenon that you plan to turn away in the second turning for the finished product to get a good idea where you are. I shoot for around 8-10% in my area depending on the season. Your area may have a different RH where the wood has reached equilibrium and is relatively stable. Also most inexpensive meters can show a range but don't have really good accuracy. The RH number isn't really important but it is important that the wood is no longer losing moisture (see below for alternative method).

I also paper bag my roughouts (but don't seal them) to prevent them from drying too quickly (I sometimes add a second bag if needed when it is hot/dry). Sometimes I weigh them from day one just for fun of it. I always write the date it was turned on the outside of the bag on day one. I try to remember to weigh the bagged roughout at about the one month mark and continue every couple of weeks until it quits losing weight. When it no longer loses weight it has reached equilibrium with the local climate and can come out of the bag. At that point it shouldn't move much more from moisture loss and can be re-turned and finished.

This is what works for me based on the wood I turn, my storage method, my designs and my local climate. You may need to take a completely different approach to be successful given all of the variables!