OK, I give up - need help

[John Thorson]

The hard-to-notice tail ends of the cracks from the pith area are like a loaded gun. It is often hard to know where to stop to make sure you don't leave them in the bowl blank. When turning any bowl you relax some stress areas and focus stress into others... the bowl always moves at least a little bit. My bet is that this is the cause of your cracks.

[David Gilbert]

OK, I'll toss in my two cents. Since the blank had been drying for several years, I am guessing that the bowl blank had these checks already in them. Drying large blocks of wood without any checks is difficult and only appear as you turn away the wood. The other thought is that if you were spinning these at 3000 rpm and the flexing could generate some cracks. (My guess is that you weren't doing this.)

Since I normally turn green wood, my cracks like this are usually seen as the bowls dry and after I have done most of the work on them. I did have a recent fresh cut cherry bowl blank that had a check in it. I turned it down so the crack was gone (I thought) but it reappeared as it dried. My guess is that your cracks were there too but you either missed them or they were too small to be seen.

Cheers,
David

[robert baccus]

Charge extra for character points.

[Faust M. Ruggiero]

Michael,
Just out of curiosity, when you say the wood was drying for several years, I assume you mean it was a rough out. If so, may I ask how you dried the roughed out bowl? Was it anchor sealed on the end grain or stored in a bag or possibly both? I'm feeling like the cracks were there but not visible in the rough out and were a result of the drying process. I expect turning the end grain thinner merely allowed them to open further. Sorry that happened. It looks like it was a nice peace of walnut. There is not even a hint of sapwood showing. You were definitely approaching the hollowing properly. I see you were finishing the wall thickness closest to the rim while you still had mass in the bottom. That's what leads me to feel the end grain cracks were there all the while.
faust

[Pat Scott]

I've had this happen before as well, and it's always a bummer when it does. You've already made this into a jam chuck - good idea, I would have put it in the firewood pile. Meaning you already "saved" the bowl.

A few years ago I had several large (15"+) Walnut bowls that all of them cracked on me a few weeks after I roughed them out. I later chalked it up to Anchorseal 2 not being as good as the original Anchorseal. That might have had something to do with it, but I also might have had the bottom a bit too thick. On a 10" bowl using the 10% rule means the walls should be 1" thick. That's OK, but make sure it's a consistent 1" all the way down to the bottom. If you use a tenon, don't forget to count the tenon thickness.

What I do now is make the walls 1" thick, but I try to make the bottom a little thinner - say 3/4". The bottom isn't going to move and distort like the walls will so it doesn't need the full 1" thickness. If the base is thicker than the walls, it will prevent the walls from moving and cause them to crack. I think this is what happened with my Walnut bowls. This might have happened with yours also. I'm thinking the walls were under a lot of stress and when you thinned them down that was all it took.

You might try a 3/8" gouge with 45 degree bevel for the upper 1/3 of the bowl instead of your 1/2" gouge. A 45 degree bevel will cut through the fibers cleaner than say a 55 degree gouge. You didn't say what bevel you had on your gouge, but I used to use my 1/2" gouge with 55 degree bevel all the time. With the bigger gouge you end up pushing against the side wall harder while trying to maintain bevel contact. This can lead to problems. Using a smaller gouge with 45 degree bevel reduces the pressure against the sidewall and produces a cleaner cut. It's amazing what the difference is. Learned this from Glenn Lucas in one of his classes. I use Glenns GL5 for the top of the bowl (3/8" flute, 1/2" diameter bar).

[Michael Watson]

More explanation---
the "blank" had not been roughed into a bowl
I started with a "half-log" shape( several inches outside of actual pith), but my moister meter showed it dry even when i got to the stage as shown in the pictures.
Would it have been better to turn to an approx 1 inch thick bowl, then let it rest a few days, before thinning to final size?
I'm doubting that existing cracks just "opened up" because there was a loud, snap like a firecracker. I stopped the lathe and saw the cracks.
They outside was sanded to 400 grit and appeared to be perfectly true. Would it have helped to apply a coat of finish?
Thanks for all your comments-----Mike

[Michael Watson]

Pat - thanks for the hint, I'll try it.
My 1/2 inch gouge is about 62 degrees, but so is my 3/8's.
Both are Thompson bowl gouges and I've attempted to leave the grinds as they came new.

[Richard Coers]

sanding to 400 grit can put a lot of heat into the wood. Penturners crack blanks all the time by pressing too hard with fine sandpaper and putting heat into freshly turned wood. Your moisture meter may have read dry, but they aren't very accurate with thick wood. Still could have been wetter in the center.

[Eric Gourieux]

I agree with the possibilities outlined previously. I have been turning quite a bit of aging ambrosia maple and have found a lot of "hidden" cracks. I worked on this hollow form for about 4 hours. It was completely hollowed to an even thickness of 1/4-3/8" when this crack appeared. I think that the crack was there all of the time and just opened up with the stress. I feel your pain, man. Yours will make for a good jam chuck. Mine, well lets just say that it may reappear later as an experiment.


IMG_7187.jpg

[Pat Scott]

Pat - thanks for the hint, I'll try it.
My 1/2 inch gouge is about 62 degrees, but so is my 3/8's.
Both are Thompson bowl gouges and I've attempted to leave the grinds as they came new.

Wow, 62 degrees is pretty blunt! That angle is best used for the bottom of a bowl. Using it on the top of a bowl means the handle is way out there away from your body, and whether you think you are or not, there is a lot more force being applied to the rim. If anything that's making your job harder.

Try changing the 3/8 gouge to 45 degrees and see what happens. I think you'll be pleasantly surprised how easy and clean it cuts the top inside 1/3 of a bowl. Then you can switch to your 1/2 gouge the rest of the way (but change the angle to 55 degrees).

Glenn Lucas really has a nice thing going with his gouges, check them out at Craft Supplies to get more info. He simplifies things by only using two angles, and two sizes of gouges. All of his tools come with sharpening instructions so you can replicate his grind no matter what jig you use. He's made a believer out of me and it's sure a lot simpler at the grinder. A 3/8 gouge with 45 degree bevel for the top 1/3 of a bowl (his GL5 gouge), and a 1/2" gouge with 55 degree the rest of the way (GL4). If you want to add a 3rd gouge, a 1/2" gouge with 55 degree grind for the bottom of the bowl (GL6).

If you started with a solid chunk of wood, shaped the outside, and then sanded while the inside was still solid, (like Richard said) sanding creates heat and there is no where for the heat to dissipate. I learned this from Mike Mahoney as well. Whether this caused or contributed to your cracking is hard to say, but it isn't a good practice.

[steve johnson]

I drill holes in the center at the beginning and end of the crack...more in between if needed,...turn a plug/ dowel of a contrasting wood as dry as the bowl and insert it into the hole using ca or yellow glue. Once dry, I continue to turn....works for me...no returns yet😀.

[david privett]

you can always try jamming as much glue in the crack as you can and using a ratchet strap to pull it back together and leaving it for a few days and let the stresses fade, I have had to use c clamps to hold the strap where I wanted it on the edge. Use wax paper to keep the glue off the strap which adds a level of aggravation, I have had fair luck with doing this. Then give the bowl to a person that you do not think that much of, they will think it is great and make some points for future favor's if needed and you will learn how to salvage a split bowl. win win

[Reed Gray]

Hmm, I have never had one crack on me while I was turning it. It has been a while since I turned dry wood though. I have discovered hair line cracks in the wood as I am turning that I didn't see when I started. Maybe it was sanding the wood to finish on the outside before you did the inside. If that was the culprit, then how you sanded would be the problem. Main thing with sanding is to use slow speeds, and it makes no difference if you hand sand or power sand. Abrasives need traction to cut, and if you are spinning too fast, the grit doesn't get a chance to dig in and cut. For power sanding I have the lathe as slow as it will go (warped bowls need to be down around 15rpm), and drill speed at half speed or slightly less. For hand sanding, I would want no more than 500 rpm, or even slower if I could. If you are hand sanding and your hand gets hot, so is the wood. Do not use a pad to insulate your fingers/hand. The heat is still there, slow down and use less hand pressure. This heat build up can cause checking in the end grain. If you hand sanded and it got hot, that could have put some stress on the wood because the outside would have gotten hot, but the inside stayed cooler. Removing the inside would have reduces wall strength to the point where the heat stress was relieved by cracking. Only thing I can think of.... Tool pressure can generate heat, but I never considered it making the bowl hot, just the shavings and the tool, but it makes sense that some of the heat would go into the wood. Don't know if that would make it hot enough to crack though.

Some people do all of their bowl turning with 60 degree bevels. I only use that for the transition and across the bottom of a bowl, and not the walls. I prefer a 45/45 gouge for the finish cuts when I can use them. Scrapers for all of my roughing.

robo hippy

[Kyle Iwamoto]

Seems to me that the cut you're doing is pretty aggressive, you're taking off a lot of wood. In a single pass. Just my $0.02. As mentioned, perhaps taking the entire bowl evenly down could be the key to success.
As for the bowl, I know it's too late, but some drilling as mentioned and a couple butterfly patches, and you got an art exhibit! Again, just my $0.02.

[Mark Greenbaum]

Not sure if this applies, but here goes another theory: Wind Shake? I've had cherry which looked absolutely perfect shaped into a uniform cylinder; when I stepped away for a few minutes to sharpen my bowl gouge, and I came back to see it had split from end to end. My instructor told me to not even turn the lathe back on, and toss the wood into the firewood pile. Some hard straight grained woods build tensions on the vertical trunk pieces that once the wood surrounding is removed the tensions show up as cracks. Maybe?