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Green round blank blew apart

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Forum topic by JoshNZ posted 06-29-2015 11:13 PM 1014 views 0 times favorited 12 replies Add to Favorites Watch
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JoshNZ

53 posts in 529 days


06-29-2015 11:13 PM

I had an unfortunate accident on the lathe today where I’d just got done rounding a green blank, when it blew apart in two pieces. No tool engaged, I was just standing next to it. Unfortunately clipped my head on it’s way off the bed, then blew through the canvas shelter I was working in. I found it outside almost 25ft from the lathe when I got back from the hospital.

What do you check for before you start turning… Below is a photo of a piece cut off the same blank. Is it bad enough that you wouldn’t mount it?

The two pieces show the fault clearly, and the first picture is obvious after seeing the second.

Sucky day anyway… 9 stitches and a hospital bill later… Not to mention the confidence knock.


12 replies so far

View gwilki's profile

gwilki

121 posts in 933 days


#1 posted 06-29-2015 11:38 PM

In a word, YES! That piece – currently in one piece – is bad enough that I would not turn it. You can see rot pretty much all the way through it. The piece that broke must have looked similar. This looks like a crotch piece, and it is not unusual to get punky wood between the two branches. As you have unfortunately found out, they are not worth the risk.

-- Grant Wilkinson, Ottawa ON

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JoshNZ

53 posts in 529 days


#2 posted 06-29-2015 11:44 PM

It is a crotch piece of maple. Are you saying crotches in general aren’t worth the risk?

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Nubsnstubs

826 posts in 1190 days


#3 posted 06-30-2015 02:02 AM

Hmmm, bounced off your head, tore through a canvass sheet, and landed about 25 feet away…. What was your rpm?
Your piece of wood is now safe to turn if there is any size left. On the piece that hasn’t been on the lathe yet, split it and turn whatever you can with the pieces.
I got nine stitches once from a piece coming apart. Not fun. You’ll heal and now you’ve gotten some education on what to look out for when setting up wood to turn. Good luck in the future…..... Jerry (in Tucson)

-- Jerry (in Tucson)

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JeffP

573 posts in 851 days


#4 posted 06-30-2015 10:59 AM

Hmmmn, maybe plug the lathe in from a distance, and just let it spin a little faster than you plan to work it for half an hour before you approach?

No guarantee of course, but seems like a prudent risk enhancement.

-- Last week I finally got my $*i# together. Unfortunately, it was in my shop, so I will probably never find it again.

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gwilki

121 posts in 933 days


#5 posted 06-30-2015 02:57 PM

Josh: I was not saying that crotch pieces are not worth the risk. However, you do need to thoroughly check them out before you make the decision to turn them. I’ve done several that were fine. I’ve had many more that, like yours, were obvious disasters waiting to happen.

Also, how did you mount yours? If it was just mounted between centers with the headstock center in the crotch, you were helping it to split – just like using a wedge. If you had it held on a faceplate, with screws in both legs of the crotch, at least you had screws holding it together. It would still not be “safe”, just “safer”.

-- Grant Wilkinson, Ottawa ON

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JoshNZ

53 posts in 529 days


#6 posted 06-30-2015 03:02 PM


Hmmm, bounced off your head, tore through a canvass sheet, and landed about 25 feet away…. What was your rpm?
Your piece of wood is now safe to turn if there is any size left. On the piece that hasn t been on the lathe yet, split it and turn whatever you can with the pieces.
I got nine stitches once from a piece coming apart. Not fun. You ll heal and now you ve gotten some education on what to look out for when setting up wood to turn. Good luck in the future…..... Jerry (in Tucson)

- Nubsnstubs

Sorry to hear it.
I had it going fairly quickly, I had it round and true so I’d turned it up from where I’d roughed it. I’m not sure of my lathes RPM range but somewhere around 60% of it maybe. I think it not only blew apart but probably did a loop hanging out wide off the face plate screws before they broke free too so it sling shot a little, and it was the big piece that hit me =/.

In general, can you turn a whole bowl without ever spending ‘working’ time in the line of fire? Are you supposed to? And going back to the crotch issue, are they just a no-no or what? I thought pieces with knots and burl wood were what we were all after.

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JoshNZ

53 posts in 529 days


#7 posted 06-30-2015 03:10 PM


Josh: I was not saying that crotch pieces are not worth the risk. However, you do need to thoroughly check them out before you make the decision to turn them. I ve done several that were fine. I ve had many more that, like yours, were obvious disasters waiting to happen.

Also, how did you mount yours? If it was just mounted between centers with the headstock center in the crotch, you were helping it to split – just like using a wedge. If you had it held on a faceplate, with screws in both legs of the crotch, at least you had screws holding it together. It would still not be “safe”, just “safer”.

- gwilki

It was mounted on a faceplate with no tail stock in place. I ran it slow till it was pretty round then dialled it up and was pretty rough on it hogging a bit more out. I’m surprised that didn’t cause it to fail. I didn’t even know the line through the middle was rot to tell you the truth. I didn’t spend that long checking the piece of wood either. The photo below is the surface I screwed the face plate into, it looked like healthy wood and I noticed colours in the centre which I thought would result in a pretty cool bowl but didn’t give it much more thought than that.
Lesson learned anyway

View LeeMills's profile

LeeMills

271 posts in 761 days


#8 posted 06-30-2015 06:43 PM

First, I’m glad you were not more seriously injured.
In looking at your first pic it appears you slabbed off the outside and left both piths in the blank.
Typically it is cut through the pith(s); this would allow you a look a the inside to determine better how far the inclusion went.
I do not know the speeds of your lathe but most go up to at least 3,000 rpm. If you were turning at 60% that is way way too fast IMHO. I will try to post below a chart from Teknatool (Nova) on their suggested turning speeds.
At 10” diameter I would start at the 200 or 400 max for rough-out.

I keep the tailstock in place until I have to move it out of the way. From the blank I assume you rounded it on the lathe. Which comes to your second point of being in the line of fire. There is no need to “round” the exterior because it will be turned away anyway. If you set the rest 45 degree to the bed you and turn the outside without being directly in the line of fire. You can also rough turn the inside and stay out of the line of fire.
About the only time I am in the line of fire is when final turning and I true up the base for the chuck and remount, then I have to be in the line of fire to finish the outside.

Crotch wood and be very nice and I love turning them. Check well to start with and then recheck often if there is an inclusion of any type.

If you didn’t have one I’m sure you have a good quality face shield on order.
Not to scare you but just to be aware. Lynne had a similar accident. Just think if a corner of your blank caught you in the eye rather than elsewhere. http://www.lynneyamaguchi.com/wordpress/

Here is another very similar to yours. Notice he is standing out of the line of fire until he leans in and down for a closer look. He had a face shield on so little damage.
https://www.youtube.com/watch?v=FlhWF4M9CO4

Here is the speed chart from Teknatool

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

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JoshNZ

53 posts in 529 days


#9 posted 06-30-2015 09:24 PM

Thanks for the table. The second video is pretty similar to what I did. Lynnes accident is sad, sucks to hear. You’re right I was still lucky all things considered, position right it would have been the end of my eye sight in that eye.

View ForestGrl's profile

ForestGrl

445 posts in 546 days


#10 posted 07-02-2015 02:28 AM

May I suggest you watch the following video from Reed Gray? I found it quite attention-getting and educational, and suspect it might save me from a similar hospital visit!
https://www.youtube.com/watch?v=F4qIM_-Jzgk

-- My mother said that anyone learning to cook needed a large dog to eat the mistakes. As a sculptor of wood I have always tried to keep a fireplace. (Norman Ridenour)

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JoshNZ

53 posts in 529 days


#11 posted 07-05-2015 02:12 PM

Thanks ForestGrl I watched the whole thing. For the most part I am usually out of the way like that. It’s laziness that got me… I got back on the lathe yesterday, goes without saying I am keeping out of the way now. And switching off the lathe for a look. It just isn’t worth being lazy.

I’ve never seen someone crank the scraper so much haha interesting style he has.

From the looking around I’ve done I’m actually really lucky. The piece that hit me was twice the size of his “wall-dart” and although the temple isn’t the greatest place to be hit, it’s a whole lot better than the eye. And anywhere on the chest would have been broken ribs, maybe broken collar bone etc, which takes a whole lot longer to heal up than a gouge on the head. How it didn’t knock me out cold I have no idea. Seems like a guardian angel teaching me a lesson as gently as it could…

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ForestGrl

445 posts in 546 days


#12 posted 07-06-2015 01:43 AM


Seems like a guardian angel teaching me a lesson as gently as it could…

- JoshNZ

Seems like it, so glad you weren’t really, really hurt!

-- My mother said that anyone learning to cook needed a large dog to eat the mistakes. As a sculptor of wood I have always tried to keep a fireplace. (Norman Ridenour)

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