Bowl explosion

[artful bodger]

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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[Simplicity]

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.

[Bushmiller]

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
Paul

[artful bodger]

No Bushmiller, there was no heart.

[tony_A]

Thanks for posting AB. Its a reminder that even an experienced turner working with solid wood can have this sort of thing happen.

[Nubsnstubs]

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.

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)

[wood spirit]

Some pieces I tend to stand a bit out of the line of fire shall we say. just in case!

[Mobyturns]

I can't recollect seeing a "bowl explosion" with such complete destruction as this example. :o

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.

[Old Croc]

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.

[artful bodger]

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.

[Simplicity]

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)


Jerry,

My apologies it was just a typo mistake.(Bloody auto correct).

It should have been “Changing”

Cheers Matt.

[Skew ChiDAMN!!]

My apologies it was just a typo mistake.(Bloody auto correct).

It should have been “Changing”

Maybe so, but I suspect "charged my pants" is going to work it's way into my vocabularly at least. :D

[Mobyturns]

Maybe so, but I suspect "charged my pants" is going to work it's way into my vocabularly at least. :D

More genteel than saying "I just $hit my dacks." :rolleyes:

[The Spin Doctor]

I can't recollect seeing a "bowl explosion" with such complete destruction as this example. :o

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.

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.

[The Spin Doctor]

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.


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.

[Mobyturns]

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.

Good advice on wearing a high impact rated face shield. It will certainly minimize potential injuries.

However, the real focus should be on eliminating the hazards that contribute to such catastrophic failures - like reducing lathe rpm, inspecting the blank regularly, etc.

[brainstrust]

great wood for a resin combo though :U

[hughie]

I have had only one of these fairly early on in the wood turning game. It literally exploded and threw wooden shrapnel all over the workshop, totally my own fault, too thin, too fast. Luckily I had just stepped away to get some more sandpaper so I was well out of the line of fire. Since then, I turn much slower on dangerous pieces and have learned to turn and be out of the line of fire. Its not hard, now its second nature for me.
Which is a good thing as I have got a passion for the impossible pieces, or air turning as some folk say. This has all come about with some luck initially and these days a fair amount of experience.

[hughie]

Good advice on wearing a high impact rated face shield. It will certainly minimize potential injuries.

However, the real focus should be on eliminating the hazards that contribute to such catastrophic failures - like reducing lathe rpm, inspecting the blank regularly, etc.

Absolutely!

[artful bodger]

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.

Generally I do sand at lower speeds, Just find that you can get a much better off the tool finish with a scraper at higher speed.
Probably should have had a face shield on I agree. Have worn a motorcycle crash helmet before when turning large heavy columns.

[The Spin Doctor]

Good advice on wearing a high impact rated face shield. It will certainly minimize potential injuries.

However, the real focus should be on eliminating the hazards that contribute to such catastrophic failures - like reducing lathe rpm, inspecting the blank regularly, etc.

Preachin to the choir mate ��

[The Spin Doctor]

I have had only one of these fairly early on in the wood turning game. It literally exploded and threw wooden shrapnel all over the workshop, totally my own fault, too thin, too fast. Luckily I had just stepped away to get some more sandpaper so I was well out of the line of fire. Since then, I turn much slower on dangerous pieces and have learned to turn and be out of the line of fire. Its not hard, now its second nature for me.
Which is a good thing as I have got a passion for the impossible pieces, or air turning as some folk say. This has all come about with some luck initially and these days a fair amount of experience.

I've had a few over the years. First one was when I was demonstrating at a show. The lathe had a speed control that was opposite to mine. Was going to slow it down to start sanding. Instead I cranked it up to about 2500rpms. I knew to step aside and just as I did the bowl just vanished, it shattered and flew apart so fast.

Had a few at home. One where I was turning a 24 inch spalted oak piece. Something just wasn't right so I stood to the side and sure enough about a 3lb chuck came off and smashed through the drywall. Even a face shield wouldn't have help. At that time I had a 900lb really old Powermatic customised to take 24 inches. The risers alone weighed about 80lb. It was hoping all over the place till I hit the kill switch. I was young and laughed it off and kept on dodging lots of other pieces.

Used to turn for a guy on his really old Oliver. The lowest rpm on that was about 600. I used to turn 6 foot pedestal bed posts. I would mount the head stock end in a chuck to try and help stabilise it. Now you really have to have cat like reflexes when one of those snaps. The end attached to the chuck gets kinda crazy and smashes all over the place till the chuch loses grip. I used to drop to the floor as the tool rest usually stopped it from battering me to death. Good times!!

[Mobyturns]

Preachin to the choir mate 👍

Probably, but do they listen? :)