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Fail at 1350 RPM

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It was Dramatic

I found a hunk of walnut, Was turning a nice bowl going for thin walls ( thin for me anyway) and had removed the center support post and was finalizing the shape of the inside.

http://i1002.photobucket.com/albums.../Lathe Fails/walnut bowl-000a_zpstruczyzt.jpg



http://i1002.photobucket.com/albums...p/Lathe Fails/walnut bowl-001_zpsc3j3jnxx.jpg


http://i1002.photobucket.com/albums...p/Lathe Fails/walnut bowl-002_zpsw6bj9jdq.jpg


And all the kings horses and all - - well - - you get the drill.

http://i1002.photobucket.com/albums...p/Lathe Fails/walnut bowl-004_zpsnjq9fmwu.jpg

Gosh~!! Golly~!! and some other really succulent salty language.
I was really happy about the shape I was getting
 
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The lathe speed may have been too high for the size of that bowl, particularly if the wood has a defect(s) and/or you might (inadvertently) make a "horrific" catch!
According to the late & great Dale Nish …(May he RIP)... his upper limit safe turning speed rule of thumb, …. defined as the maximum safe turning speed RPM, is equal to 9000,
divided by the bowl's diameter. (The 9000 number is not RPM, but a derived safety constant number that is generally agreed upon by many turners.)
As a guess, your bowl looks to be in excess of 10" in diameter, so as an example, 9000/10"diameter = 900 RPM. In this case 1350 RPM would be 50% faster than the max safe speed for a 10" bowl.


Lee Tourtelotte

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Bill Boehme

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Not a failure, it's a learning opportunity

thanks for showing what can go wrong. I am glad that you weren't injured. Any of those pieces could have had very serious consequences if they had hit you.

Since you are in NJ, there is a good chance that you are within reasonable driving distance to a club where someone could give you some pointers that would go a long way in reducing the risk of a blow up. I will offer a few suggestions, but they won't be nearly as helpful as having somebody looking over your shoulder.

First of all, I see two really bad catches on the interior and one lesser one on the rim. One of those catches was probably where things went south on you. In this bowl I think that theses catches began with the wood chattering. There are several factors that contribute to chatter:
  • high speed -- the speed should have been much slower in my opinion. Personally, I would have reduced the speed to less than 400 RPM. As the wood gets thinner, start thinking about slowing things down and also keeping your tools sharp.
  • thin walls -- I have several thoughts about some mistakes that I see (I see them because at one time those were my mistakes)
    • The exterior shape wasn't finalized before you started working on the interior. Here's something to be mindful of -- wood has built in stresses and when you remove wood, the wood that remains is going to shift a bit to get internal stresses back in balance. So why is this important? When you remove wood from the interior, the inside will be round, but the exterior isn't -- so if you go back to the exterior the tool will be making interrupted cuts -- interrupted cuts on thin wood can be the beginning of trouble. So next you go back to the interior and find that it isn't round .....
    • You've removed supporting wood in the bottom of the bowl while the upper portion of the interior is still uneven and has greater wall thickness than the bottom part. A better procedure to avoid chatter is to turn the interior in steps. Divide the interior into about six zones. Complete the upper zone and finalize the wall thickness before proceeding to the next zone. Never go back to a previous zone to touch it up because the wood is thin and no longer circular and it will chatter and then .......
    • Flat bottom/vertical sides -- can be done, but it has inherent stability problems. My opinion is that a continuous gentle curve works best.
    • Recess vs tenon -- The dovetail recess on your bowl has very little supporting wood. It would not take much of a catch for it to be ripped out of the chuck and my guess would be that is exactly what happened because I see some exposed chuck jaw in the shot showing what was left on the lathe. A recess is fine if you have plenty of supporting wood, but a tenon is much stronger.
Anyway, it's not a failure because it was a learning experience. It's only a failure if you don't try to learn how and why things went wrong and then do something towards preventing that problem next time. Save the pieces and put them in a prominent place in your shop. That's what I do and I suspect that many others also do the same.
 
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john lucas

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The problem to me seems like it might be coming off the bevel and getting that catch. That shape can be challenging to keep the bevel rubbing. Since there was a bark inclusion in the middle it's possible it had hidden cracks running out toward the side. Once you got the wall thin enough it was probably thinking about blowing up. Having the increased speed and then getting a catch was all it would take to make it decide to go.
 

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Anyway, it's not a failure because it was a learning experience. It's only a failure if you don't try to learn how and why things went wrong and then do something towards preventing that problem next time. Save the pieces and put them in a prominent place in your shop. That's what I do and I suspect that many others also do the same.

Yes, this definitely a learning experience, and Bill has a good suggestion about saving it for reference....for the time being, anyway. If I saved every failure I ever had, I'd be complaining about the space in my shop!:eek:

IMHO, the center post is useless. It gets in the way, and doesn't support anything but the most supported wood in the bowl. Raul, you didn't say what tool you were using, but for roughing purposes prior to seasoning, a scraper is more likely to catch than a gouge. Make no mistake, a gouge is capable of some catastrophic catches, just as well. The point I'm making is either can be used, but the scraper for roughing purposes is much less forgiving, especially if not used with strict adherence to best technique.

ko
 
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If I'm doing larger pieces, especially if there are any areas of concern, then I wrap it up in plastic tape. It's similar to seran wrap, about 2-3" wide and very strong, although slightly stretchy. That allows it to wrap around sections and hold tight. (Make sure you wrap in the right direction.....)

Occasionally I put duct tape over top to eliminate any stretch.

Btw kinda looks like maple to me....I've got a huge pile outside waiting....
 
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I found a hunk of walnut, Was turning a nice bowl going for thin walls ( thin for me anyway) and had removed the center support post and was finalizing the shape of the inside.

Granted I have to squint from 3000 miles away to see this clearly, but that doesn’t look like walnut to me. A chunk that large should have visible dark heart and light sapwood demarcation. Anyone else agree?

Too, that large decayed (buggy?) looking area at the outset makes me think the overall piece was compromised. For it to come so completely apart at that thickness is concerning.

… but like I said, it’s kinda hard to see from way over here.
 

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Granted I have to squint from 3000 miles away to see this clearly, but that doesn’t look like walnut to me. A chunk that large should have visible dark heart and light sapwood demarcation. Anyone else agree? .....

I didn't think it was walnut either, but that wasn't the main issue. I thought that it could possibly be hickory, but trying to ID wood from a snapshot is risky. The only time that I run across walnut around here is sitting on a shelf at Wood World, Woodcraft, or Rockler Hardware.

BTW, I think that Odie and John both have a valid point about the wood being scraped rather than cut. One of the pictures shows a lot of torn grain fibers sticking up. From the dig-ins it looks like a bowl gouge was used, but if a bowl gouge is used like a scraper then it might as well be a scraper.

I agree with Odie that nub in the middle should have been removed much sooner because it wasn't very useful by the time that most of the wood had been removed from the interior. From Raul's description, it wasn't clear to me whether "center post" was referring to the center nub in the bowl or to the live center.
 
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According to the late & great Dale Nish …(May he RIP)... his upper limit safe turning speed rule of thumb, …. defined as the maximum safe turning speed RPM, is equal to 9000,
divided by the bowl's diameter. (The 9000 number is not RPM, but a derived safety constant number that is generally agreed upon by many turners.)

Thank you so very much for that.
I'd not seen that before.
 
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I agree with Odie that nub in the middle should have been removed much sooner because it wasn't very useful by the time that most of the wood had been removed from the interior. From Raul's description, it wasn't clear to me whether "center post" was referring to the center nub in the bowl or to the live center.


I left a column of material in the center to bring the the center to bear.
When the bowl burst I'd already removed it.
Yes it was a bottoming gouge I was using. There was a catch and I suspect that and speed is why the bowl burst.

If I'm doing larger pieces, especially if there are any areas of concern, then I wrap it up in plastic tape. It's similar to seran wrap, about 2-3" wide and very strong, although slightly stretchy. That allows it to wrap around sections and hold tight. (Make sure you wrap in the right direction.....)

Occasionally I put duct tape over top to eliminate any stretch.

I rather like that idea Olaf..... thanks



I've learned a lesson.
Actually a couple lessons.


I cut and mounted the other half of the log.

This time I was going to go for a more refined shape. I wanted a more dramatic recurved lip. Sort of a hollow form as a turner might define one.
But I don't own a hollower yet.

I'd been looking at the Sorby Soverign and they Flexiform. Supposedly both "catch proof."

But while looking I stumbled across one of George Watkin's posts from 2009 some where else
His hollowing tools are shop made with tiny tips.
His work isn't tiny so I figured there had to be a reason.

Turned drilled and tapped a hole form 1/4-20 grub screw in the end of a length of 5/8" bar stock I had laying around.
The cross drilled it 0.1875" to take a busted end mill so the grub screw would lock it in place.
Then I ground the end of the end mill like a little radiused scraper

It works pretty well. Lacking a proper handle, I put a vice grip on it. The tiny tip is in the form of a scraper and held at the right (downward inclined) angle it doesn't catch and if it does, it's tiny so the energies involved will be smaller than say a 3/8" gouge.

I'm getting right proper little lip.
http://i1002.photobucket.com/albums...k/walnut bowl/20150701_182819_zpsvbodhy67.jpg

There's a carpenter ant nest hole in the piece so an interrupted cut and imbalance issues inhere.


What species is the wood? Well, I can't say for sure. The wild walnut we have around here is American Black walnut and the color is not like European English walnut.

The wood smells sort of weirdly minty.
I get long fuzzy stringy tear out unless I have a really sharp tool.
There's acid in the wood. It's acts on steel faster than other wet woods I've cut.
So, I sort of suspect it's black walnut
 
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So you are using an end mill. A ball end or flat, or some other. Busted?
I have used ball end mills mounted as you describe.
They can give a pretty good cut when held at the right angle.
There is a bevel to rub, so it is not a scraping cut. If the angle is right.
Not the best tool for the job, but they work.
There are no real 'catch proof' tools, marketing is wonderful.
Some can be configured to limit the amount of the cut, but there are still rules to be followed.
Having made my share of flat bottom bowls with rather straight sides, I know they can be very challenging at the points of transition.
Lots of catch potential.
Platter forms are perfect for thinner wood, although avoiding unsound wood at higher speeds is a good rule of thumb.
A thicker blank turned with gentle curved walls will a more satisfying form.
If you have not looked into a bowl gouge, it would be a good investment. Along with some mentoring in it's use.
Have fun, turn safe.

Mark
 
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Hmm, well, for sure, when turning at higher speeds, things get much more dramatic. The calabash forms are a lot more difficult to do than standard open bowls. I couldn't find the link some how, but turned up a broken bowl picture in your photo bucket series, and there was a definite gouge dig in right before the break, and the dig in was in the transition area. It looked like it might have been a different piece though. This happens to many turners. When turning out the inside of the bowl I always roll the flutes away from the cut, so they would be pointing to around 2 or even 3 o'clock. What this does, is make it impossible to come off the bevel and catch the wood side wing of your gouge. It also gives a higher shear angle for a generally cleaner cut. If the flutes are pretty much straight up and down, when you go through the transition, the wood side wing is very easy to catch.

If I had to guess, I am thinking that that piece of wood may be butternut, which is also called white walnut. What little I have had smelled kind of like vinegar. It does cut rather fuzzy, and it has acid in it, so every tiny metal dust particle leaves black freckles all over the wood, and your hands can get black as well. We don't get much of that around here.

robo hippy
 

hockenbery

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Doesn't look like walnut. Maybe butternut but it is usually darker.
These two species are the only ones in North America with a chambered pith.
Cut with a saw to expose the pith center and there will be little chambers exposed.



I encourage al new bowl turners to get some basic instruction or at least spend some time watching someone turn bowls.

We all have powerful machines which when used properly can in rare cases cause serious injury
Used improperly, chance of serious injury becomes probable.

Mastery of the basics makes turning safer and more rewarding.
And once you master the basics you won't get a catch unless you ignore the basics.

Be safe, have fun
Al
 

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I consulted Hoadley's Identifying Wood and it seems like Black Walnut can be ruled out because black walnut is a semi-diffuse porous wood. The 100% crop shown below was taken from one of Raul's full size shots and it clearly shows the wood is ring-porous. Anyway, I don't have any good idea of what it could be. Hoadley says that Butternut is semi ring porous. All of the torn grain make it hard to tell about pore distribution, if any, between rings.

mystery_wood2.jpg
 
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hockenbery

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Raul,

Looking at your pictures I'm concluding you have a couple of issues that led to the blow up.

First, the surface in the second picture shows a poor surface. A properly sharpen tool presented to the wood properly will give a much cleaner surface.
The first few inches of the inside are the hardest to do because a cut around the inside passes across the top of the end grain on each end and straight along the long grain on each side. Sharp gouge and repeated light cuts are needed here. The cut is begun at the rim with the flute pointing parallel to the floor just easing into the wood slowly with the bevel parallel to the outside wall. A heavy cut will cause tear out. Scraping with a negative rake scraper or a tool in a shear scrape angle can work ok. A scraper held flat will cause tearout and the edngrain can climb onto the tool causing a catch.

Tools need to be sharp and have a continuous convex cutting edge. Any dips or bumps will make the tool grabby and a big grab is a catch.
The ABC - Anchor, Bevel, Cut should be used every time the gouge touches the wood.
A- anchor the tool holding it on the tool rest
B - bevel on the wood rubbing gently cutting edge not touching the good
C- cutting edge by rolling the tool and/or lifting the handle


Second
The Bowl wall should be cut in steps so that thick wood supports the cut from the bowl mount.

Shape the outside.
Put it in a chuck or on a face plate.
True the outside, if necessary.
Cut the top of the rim
Hollow to an even thick wall of about 10 percent of wall thickness
The stair step the wall thickness about an inch at a time.
( In your final picture you have a thin wall at about the 4" in diameter
area you can only work safely on the bowl from just outside that 4" diameter toward the
center bottom. Areas up toward the rim can flex too much to be worked safely)
Reverse chuck the bowl and finish turn the foot.

In stair stepping. I would first turn a 10-12" diameter bowl with a 3/4" wall.
I would then make a 1/4 cut about 2" into the bowl. This leaves a wall 1/2" thick for 2 inches.
I would then make an 1/8 " cut about an inch into the bowl. This leaves a wall 3/8" thick for 1'inch.
I would then make reappeared finish cuts to my wall thickness of a fat 1/4"

I would then extend the first stair step another inch and repeat.
The last finish cut I could start just before the visible line of the stair step I am removing so that no transition line remain.

Find a mentor,
Work safely,
Have fun,

Al
 
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So you are using an end mill. A ball end or flat, or some other. Busted?
I have used ball end mills mounted as you describe.

Mark


Yah, and end mill busted on one end. So I ground that end to be a three sided cutter.
It's working out very nicely
 
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Raul,
When I started turning I joined a club and it was the best thing I did. The opportunities to work with experienced turners has made a big difference not only in my technique, but understanding the many, many points of safety. Depending on where you are in NJ there are some options. Run a search here to take a look:

http://aaw.site-ym.com/search/custom.asp?id=1509

Interestingly my club doesn't come up on a search for New Jersey through many of us are members: http://www.bucksturners.com/

Doug
 
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Raul,


The ABC - [...]

The Bowl wall should be cut in steps so that thick wood supports the cut from the bowl mount. [...]


The stair step the wall thickness about an inch at a time.

Al


Thanks Al.
I have thus far expressed a tendency to look at the inside as one continual form to be removed - as a unit.
Oddly it is something I'd avoid doing with a hollow form like a narrow throat vase, because I've seen videos of people describing that process, but ( for reasons that shall remain un-spoken) I never translated that same approach to a bowl.
 

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Thanks Al. I have thus far expressed a tendency to look at the inside as one continual form to be removed - as a unit. Oddly it is something I'd avoid doing with a hollow form like a narrow throat vase, because I've seen videos of people describing that process, but ( for reasons that shall remain un-spoken) I never translated that same approach to a bowl.

It can be done in passes from rim to bottom center in thicker bowls say a 1/2" wall on a 12" diameter bowl.
especially with dry wood when returning a twice turned bowl as long as you don't make a thin spot down the wall.

With wet wood it begins moving as you take out wood from the interior so you need to turn steps partly so that the thick wood keeps the part you are cutting in place.
With thin walls there is too much movement from vibration when the walls are past a certain thinness. Chatter Becomes a problem.

The best thing is that the stair steps let you get a really even consistent wall thickness.

If I'm roughing out a bowl to dry I never use stair steps because it will be a thick wall.

Al
 
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This is a short video clip on rough hollowing a bowl.

Quite the video. among the best explanations I've seen to date and I've watched quite a few clip on the basics
The over head shot at the beginning and at 3:33 was quite illustrative. The woman with the camera did a nice job especially at about 4:00 with the limited lighting inside the bowl
 

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This is a short video clip on rough hollowing a bowl.
It was part of a demonstration on gouges.

It shows how I use a side ground bowl gouge for hollowing a bowl.
The sound is a bit off but hopefully adequate.t

http://www.youtube.com/watch?v=flw8LwQqGQU

Al,

I just watched that video and it was very helpful, regardless of sound quality. It appears that you turned the inside of that bowl in about 3 minutes. In a 4 minute video. Humbling.

By the way, I'm taking your advice. Spheres, spheres, spheres every day. Well actually, they're not spheres yet :D
 

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Al, I just watched that video and it was very helpful, regardless of sound quality. It appears that you turned the inside of that bowl in about 3 minutes. In a 4 minute video. Humbling. By the way, I'm taking your advice. Spheres, spheres, spheres every day. Well actually, they're not spheres yet :D

I enjoyed meeting up again and talking with you.

By the way I looked for your bowl twice in the empty bowls and did not find it so I assume it has good home....

One aspect of spheres is it is a known shape.
You turn it or miss.
Turning balls really helped me get better with curves in bowls and hollow forms.

Eggs are good too but too hard for me....

Have fun! Al
 
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Quite the video. among the best explanations I've seen to date and I've watched quite a few clip on the basics The over head shot at the beginning and at 3:33 was quite illustrative. The woman with the camera did a nice job especially at about 4:00 with the limited lighting inside the bowl

Jan is terrific with the camera.....
Our club has the good fortune to have some terrific turners and a great videographer.

Al
 
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It's good to also practice turning eggs. :rolleyes:

Actually, turning a good egg is more difficult for me than turning a sphere.

Let's just say I'm turning a spheroid-like item. And I seem to have a knack for it. :D
 
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Raul, from looking at this picture it appears that there isn't any or enough collar on your tenon to properly support the bowl. The tenon needs to be made so that the piece is sitting on the face of the jaws too and the tenon must not bottom out on the chuck. You will have a lot more support that way. This is especially important when not using the tail stock. If your bowl that blew up was mounted like this, it was likely a contributing factor to the failure.
 

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Raul, from looking at this picture it appears that there isn't any or enough collar on your tenon to properly support the bowl. The tenon needs to be made so that the piece is sitting on the face of the jaws too and the tenon must not bottom out on the chuck. You will have a lot more support that way. This is especially important when not using the tail stock. If your bowl that blew up was mounted like this, it was likely a contributing factor to the failure.

I believe that he has a recess and not a tenon on that bowl. There is not enough wood on the outside of the recess to hold the bowl safely. It's pretty clear from the pictures that jaw pressure pushing outwards (note the jaw orientation showing what was left on the chuck) cracked the wood and then a little catch finished the job. When orienting the jaws in a recess, it is good practice to have the jaw pattern 45° to the grain direction. In this case, it was 90°.
 

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I believe that he has a recess and not a tenon on that bowl. There is not enough wood on the outside of the recess to hold the bowl safely. It's pretty clear from the pictures that jaw pressure pushing outwards (note the jaw orientation showing what was left on the chuck) cracked the wood and then a little catch finished the job. When orienting the jaws in a recess, it is good practice to have the jaw pattern 45° to the grain direction. In this case, it was 90°.

I only use a recess in something like a platter and rarely then. A recess wastes too much wood in a bowl unless an extra wide foot is part of the design and IMHO recess mounts are not as strong a mount as a tenon. Over tightening can split the wood and the long grain splits easily in many woods.

Al
 

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I only use a recess in something like a platter and rarely then. A recess wastes too much wood in a bowl unless an extra wide foot is part of the design and IMHO recess mounts are not as strong a mount as a tenon. Over tightening can split the wood and the long grain splits easily in many woods.

Al

I agree 100%. I very rarely use a recess.

Mike Mahoney was at our club a couple years ago and if I recall correctly, he like to use a very shallow recess or was it a very short tenon. Either way, I didn't agree with his rationale. For me, a " tenon is ideal.
 

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I agree 100%. I very rarely use a recess. Mike Mahoney was at our club a couple years ago and if I recall correctly, he like to use a very shallow recess or was it a very short tenon. Either way, I didn't agree with his rationale. For me, a ⅜" tenon is ideal.

I have seen mike use a very shallow recess. Mike does not put pressure on the recess.
Many turners would break a shallow recess with too much bevel pressure even if they don't get a catch.

A 3/8 to 5/16 long tenon is about ideal for jaws a 1/2" deep.

With dovetail jaws on solid wood I occasionally use a short tenon if there isn't enough wood.
I take light cuts and use catch proof wood.

Al
 
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I believe that he has a recess and not a tenon on that bowl. There is not enough wood on the outside of the recess to hold the bowl safely. It's pretty clear from the pictures that jaw pressure pushing outwards (note the jaw orientation showing what was left on the chuck) cracked the wood and then a little catch finished the job. When orienting the jaws in a recess, it is good practice to have the jaw pattern 45° to the grain direction. In this case, it was 90°.

I'm not sure about the first post, but the link I posted was from Raul's post #10 and that looks like a tenon to me. So does this "picture of putting the chuck on" while the bowl is still on a face plate or screw chuck.
 

Bill Boehme

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I'm not sure about the first post, but the link I posted was from Raul's post #10 and that looks like a tenon to me. So does this "picture of putting the chuck on" while the bowl is still on a face plate or screw chuck.

OK, I see what you are saying and I agree that the tenon shouldn't bottom out in the chuck. The first bowl that blew up had a recess without sufficient supporting wood on the outside and these two shots of the tenon on the second bowl show that there was not a shoulder on the tenon. Here is a crop from the full size image.

bowl_2_rough crop.jpg
 
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For sure, that tenon is not made correctly. One, it does not have a dove tail to match the dove tail on the chuck jaws. Two, it isn't wide enough, and should be another inch or so wider. Three, it is way too deep, which has it bottoming out in the chuck, and there is no contact with the shoulder of the bowl, so the leverage point is where the jaws meet the chuck.

Now, as for a recess, which is what I use 99.99% of the time, it will hold equally well as any tenon if it is made correctly, which is angle to match the chuck jaws, ample size for the bowl being turned, and ample shoulder for the jaws to expand into.

I have never understood the concept that a recess wastes more wood than a tenon. If the tenon and recess both measure 1/8 inch deep/tall, and you turn it off, they are exactly the same...

robo hippy
 

hockenbery

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. I have never understood the concept that a recess wastes more wood than a tenon. If the tenon and recess both measure 1/8 inch deep/tall, and you turn it off, they are exactly the same... robo hippy

Reed, two quick examples
1. a bowl from a half log the tenon made on the top of the log is less wood than if you cut down to make a recess with enough wood outside the recess to hold.
2. if you are doing a bowl or natural edge bowl with a foot less that 2" in diameter the foot can be in tenon versus turning away lots if wood to make a small foot inside a recess

In a platter type situation the recess can use less wood.
In bowls it often takes more and makes the shaping harder as you have to visualize the wood cut away where with the tenon the bowl shape is there to see.

I don't like having the recess or the tenon as part of the design of my work.
Just my thoughts.

Al
 
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Oh. It was a tenon. The tenon slipped a couple of times too. I'd apply some pressure and suddenly things'd get screwy.
Eventually I found the sweet spot.
 
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Raul, from looking at this picture it appears that there isn't any or enough collar


The work was bottomed out against the bottom of the jaws of the chuck. I suppose I might have been better off having it bottom against the forward edge of the jaws instead.

Machine shop practice and wood lathe practice often do not coincide.
I have the habits of a machinist/toolmaker.
Something Yoda said about unlearning?
 

Bill Boehme

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The work was bottomed out against the bottom of the jaws of the chuck. I suppose I might have been better off having it bottom against the forward edge of the jaws instead....

Absolutely! The registration face should be against the tops of the jaws. That give better leverage against the piece shifting than having the tenon bottom out inside the jaws.

Did bowl #1 have a tenon or a recess?
 
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