A Blow Out that was a Blow UP

[tmhawk]

It can be exciting when a Pen blows out. (Had a Slimline blow out this weekend, my reaction was, “Oooops.) This was a sake cup that blew UP and OUT. My reaction was, “HOLY COW, am I lucky this thing didn’t take my head off.†This wood is like super green. Turning it was literally getting my hands wet. It was a tree limb cut from a small tree yesterday. I was testing my new Barracuda Scroll Chuck. The chuck works great! As you can see from the left side my Skew touched at JUST the wrong angle. LOL. My other learning experience from this was that I’d been turning it at 1240 rpm to get the shape, then adjusted to 3975 to begin smoothing down all of the wet little slivers sticking out. WAY TOO FAST. Funny thing, I have NO IDEA where the other half of this cup is. My garage has a lot of tote boxes in it next to my shop area and maybe when we move someday I’ll find the other half, unless it flew through to ceiling and is in my son’s room. Turning Green Wood was fun, learned some stuff. NOW it’s time to do some reading and research so that I get a wee bit closer to not throwing wood around the shop.
This particular test was 2½†across and 2†tall. Any and ALL comments regarding this little experiment are more than welcome. I am most grateful for all of the fantastic information we all share on this site.
Thanks,
Tony
Phoenix, AZ

 

[JimB]

I don't know much about turning (I'm a newbie) and I just started taking some bowl turning lessons. I've only roughed out two bowls. What I do know from my first two lessons ( I think this applies to your sake cup as well) is when you are working with green (wet) wood you are only roughing out the shape leaving the walls quite thick. You then need to let the bowl (cup) dry. Even a small bowl takes months for the wood to dry. Then you do the final shaping.

When turning this I believe you should be using a bowl gouge. A skew or spindle roughing gouge or many other tools will catch as you experienced. You already know what happens then.

You should also be turning at a very slow RPM. It's not like turning a pen. The first 2 bowls I roughed out (one dry, one wet) were both turned at the slowest speed on the lathe. You are removing a lot more wood than you do when turning a pen and you are working with a larger piece of wood so always safety first (slow).

You may want to do a bit more research before attemting anything else as this type of turning is a different experience. I've only touched on a few basics and my turning experience is extremely limited. During my second lesson I saw another student's bowl break and the piece flew about 20 feet and hit the band saw.

Have fun but be safe!

 

[maxwell_smart007]

The reason you use bowl tools is that they have a thicker cross section and stronger tang...spindle tools can snap when they catch while doing faceplate work...

 

[Aderhammer]

Tooo FAST! if you think about it, when the diameter gets larger, although it is still running at the same rpm the speed at the cutting edge of the tool gets smaller. So a 1 inch diameter at 1250 will have a surface speed of about 44mph whilst an 8 inch diameter object will have a surface speed of about 357mph

 

[dalemcginnis]

From looking at what's left of the cup it appears that you had the scroll chuck inside the dovetail and expanded to hold the cup in place. If so, then it was not necessarily a catch that got it to explode. As the wood got thinner it could no longer take the stress of the expanded chuck and blew apart. I've had a couple do that
And has previously been mentioned, with green wood you turn to about 10% of the final thickness and let it dry before final finishing. That is unless you WANT a warped bowl which in some cases is fine.

 

[darrenjttu]

How long should they dry before finishing?

 

[dalemcginnis]

Time varies. I typically soak it in DNA till the next day then put it in a paper bag full of wood shavings and let it sit. I had one I was able to finish in a week, but most take a month or longer. Others have different techniques for dying their bowls. I've even read of a technique involving boiling the bowl that allows you to finish it much sooner. Haven't tried it yet, but it sounded intriguing. I'm sure others here can give more methods. If not, do a search, you'll find all kinds of useful ideas.

 

[tmhawk]

Here are several methods for Drying Green Wood:
http://www.turningblanks.net/servlet/the-template/greenwoodturningmethods/Page

 

[Glenn McCullough]

If your sons room is like my daughters, you'll never find the other half there, either. Live and learn.

 

[hilltopper46]

I’d been turning it at 1240 rpm to get the shape, then adjusted to 3975

I'm curious as to what the recommended top speed is on that chuck? I won't deny that I push the top end on my Nova chuck occasionally, but I would never dream of running it that fast. Wood is bad enough when it goes whistling past your ears at light speed, but steel is another proposition altogether.