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Thread: Bowl explosion
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24th May 2023, 07:26 PM #1GOLD MEMBER
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Bowl explosion
Have been working on a few largish bowls lately (will post pics when they are finished). Today I was working on a blackwood one about 460mm dia nearly had the turning done, just taking a final few finishing scrapes on the inside when without warning "BANG" as the bowl disintergrated in to many bits. This bowl had been rough turned maybe 3 years ago and had with stood that but the final turning was too much for it. The timber did have a darker band or streak through it where water had got into the tree and it looked like the early stages of rot. Pretty sure this is where it let go.
Luckily I escaped serious injury. A fragment hit a finger but no broken bone and a big part hit me in the stomach which might be a bruise tomorrow but nothing major.
One fragment shot across the shed and broke a cast iron miter clamp the other bits went everywhere.
Glad that sort of thing does not happen every day.
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24th May 2023 07:26 PM # ADSGoogle Adsense Advertisement
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24th May 2023, 07:44 PM #2
Wow,
Glad no serious injuries happened, personally I would have been charging my pants definitely.
The pieces really must have been moving to break the cast iron clamp.
Cheers Matt.
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24th May 2023, 07:56 PM #3
Artful
Good to hear you are still in one piece (unlike the bowl).
Did the Blackwood have any of the heart in it? If it did, that would be the cause of it breaking up. Hardwood logs should have the heart removed from any boards or turnings. It may look solid when first cut, but it will break up eventually. On a lathe it can be very serious. Our son during his early adventures with a wood lathe was turning an Ironbark bowl and did not appreciate he should avoid the heart. It let go on the lathe, nearly took out his heart and went through the side of his shed!.
Regards
PaulBushmiller;
"Power tends to corrupt. Absolute power corrupts, absolutely!"
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24th May 2023, 08:39 PM #4GOLD MEMBER
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No Bushmiller, there was no heart.
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24th May 2023, 09:12 PM #5SENIOR MEMBER
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Thanks for posting AB. Its a reminder that even an experienced turner working with solid wood can have this sort of thing happen.
You can't use up creativity. The more you use, the more you have. ~Oscar Wilde
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24th May 2023, 11:13 PM #6SENIOR MEMBER
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Matt, I agree about your concern about the seriousness of the incident Bodger posted, but as not being from Australia, I have to ask whether Charging is another term for Loading or the real 4 letter word beginning in S? It's a term I gonna be using when a situation arises like Bodger's. It's just plain funny and makes it publicly acceptable. ......... Jerry (in Tucson)
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25th May 2023, 01:08 AM #7Senior Member
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Some pieces I tend to stand a bit out of the line of fire shall we say. just in case!
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25th May 2023, 07:14 AM #8
I can't recollect seeing a "bowl explosion" with such complete destruction as this example.
Then to smash a cast iron clamp across the room??? (looks like a good quality Record too??) That requires some serious energy from the shrapnel, mass by velocity sort of physics.
460 mm is a decent sized bowl so it is not difficult to reach a staggering rim velocity as lathe rpm increases.
Time to reassess how you turn methinks.
Using a Dale Nish proposed rough rule of thumb bowl speed formula that, RPM x diameter (in inches) = 6,000 to 9,000 suggests that upper rpm should not exceed 500 rpm for a sound blank.
The old road safety message - Speed Kills - applies in wood turning too.Mobyturns
In An Instant Your Life CanChange Forever
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25th May 2023, 08:33 AM #9GOLD MEMBER
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We're you using old fashioned positive rake scrapers doing your final scraping? If so, it's very easy to get a catch and get that result. Since I changed to negative rake scrapers I have felt much, much safer doing inside bowls.
Rgds,
Crocy.
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25th May 2023, 09:10 AM #10GOLD MEMBER
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A couple of replies.
Nutsandstubs. Did not have to change my underpants I am glad to say but I did say "FUDGE" out loud or something similar. Then had to sit down for a minute to try and process what had just happened.
Mobyturns, I did have the bowl spinning way more than 500 rpm. Generally I like to have the work going as fast as it can go before vibrations kick in. It is a large heavy lathe and is very capable for larger jobs. Luckily at the time I was standing on the opposite side of the lathe where the edge of the bowl facing me was rotating from bottom to top and most of the shrapnel went the other way. Did thank the lucky stars that nothing hit me in the head or eyes even though I did have safety goggles on.
Old Croc, It was a regular type scraper and there was no catch. You would be able to see the tell tale signs of a catch on the fragments. I have lost the odd bowl from catches in the past and would have been happy to own up to it if it was one. Personally negative rake scrapers do not float my boat. I remember some older patternmakers using that type back in the day but never saw the real need to use them. Maybe I am a bit set in my ways.
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25th May 2023, 06:27 PM #11
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25th May 2023, 08:07 PM #12
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26th May 2023, 06:14 AM #13
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26th May 2023, 04:16 PM #14SENIOR MEMBER
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A good face shield is required. Not the sh%t sold by bunnings and others that is more token than good. My shield is about 2mm thick lexan. And I wear a half face respirator. So, if something crashes into my head the energy will be mostly absorbed by the forehead head band and respirator.
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26th May 2023, 04:24 PM #15SENIOR MEMBER
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Don't want to sound like I'm lecturing you, but it has nothing to do with a large heavy lathe. It has all to do with centrifugal force and the defects in the wood (which are extremely unpredictable). You got lucky, this time. You should be thinking the opposite and have such large platters going as slow as possible, but still allow for a good cut and or sand. Sanding is another issue in that so many think you should crank up the speed. When in fact, if you think about how sand paper works, you should slow the rpms down. And if your project lets go, your fingers are right there when it does... Not a pretty sight.
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