Going nuts! Can't seem to NOT break a bowl!

[Bret Hinz]

The last 5 or so bowls I have made have broken right at the end of turning!

I seem to always get a catch, especially right in the area of just before where the sides meet the base on the inside (it is not due to catching the sides and base, just the sides OR base.

Anyone have any good videos showing tips/methods of bowl turning for beginners?

At first I thought it was because of my gouge ( so I purchased the vari-grind attachment, and that helped tremendously. Then I noticed it wasn't the bowl gouge, but more catches happened with the bowl scraper (which would explain why they are all breaking right at the end). It is a round-nosed scraper.

Happens with all types of woods, those with alternating grain types and patterns, those with tight grains, loose grains, whatever.....

I'm at a loss, just can't "get" this! Ugh!!

 

[Dave W]

Bret,

Without being there to see exactly what you are doing, my guess would be you are scrapping across the side, and the corner of the scraper comes into contact with the bottom (vise versa). You need to take care as to not have any gouge or scraper make contact at two points at any time. Common mistake, we've all done it. Just out of curiosity, how far back did you grind your side bevels on the bowl gouge? And do you know what the angle of the bevel is?


If you can deal with the commercials, you might find this of interest: http://www.ustream.tv/recorded/17839734

 

[robo hippy]

If you have a steep transition, as in straight sides, then a fairly sharp curve, then a flat bottom, the problem could be that when you sweep across the bottom, and then hit the side, you have the scraper suddenly in contact with the bottom and the side so you have twice as much wood on the tool in an instant.

I have a couple of short clips up on You Tube (type in robo hippy) where I turn a bowl with scrapers, and one with gouges. It might help.

robo hippy

 

[odie]

Bret.......

I no longer use scrapers in the interior of bowls, because an advanced tool finish is of a higher possibility with gouges. This, of course, all depends on the skill level of the turner.......and, of course, this is also my opinion......for whatever it's worth!

When I was using scrapers on the interior of bowls, I found that scrapers were more prone to catches with thin wall bowls than are gouges.

It's hard to say what your catches are caused by, because so many factors could be a part of the equation. Assuming sharp tools and good presentation, it could be that excessive rpm, tool height, thickness of the bowl, too much of a bite in a single pass, all could have an effect on how the wood resonates. At that point where resonating wood causes a catch, it could happen so suddenly, that it's really difficult to correctly assess the reasons why the catch occurred.

My first inclination is to reduce rpm.

Tool height is critical on interiors. On the inside, it's important to keep tool rest a bit higher, the further away you are working from the center of the bowl rotation. It's very easy to inadvertently angle a scraper downwards and not realize you've actually dipped below center. At this point the wood is rotating towards the cutting edge, and the chances of having a catch here are more likely.

Could be many things......but, these are a couple of things to think about.

I'm also adding a drawing that shows the best direction of cut, according to wood grain orientation. Not only does going with the grain produce the best cut, it also is less prone to a catch. This doesn't mean you can't cut against the grain, if you have to.......

good luck

ooc

 

[MichaelMouse]

When you say "sides" and "base" it does sound like you're doing the tough right angle move rather than the sweeping transition. Easy way out is to go to that sweeping transition, sacrificing a bit of capacity.

If you want to stick with near vertical sides, don't transition, just cut down to the bottom, then go out from center to meet your depth. Get the sides cut clean, because they have endgrain that's slow to sand. You can sand any residual ridging on the facegrain much easier. I don't have the precise shot, but you can see the gouge positioning here. http://s35.photobucket.com/albums/d160/GoodOnesGone/?action=view&current=Inside.mp4
Swing in, cut down with the bottom flute nearly horizontal until you get near what will be the bottom, then swing the gouge out from the side. You can see the prominent ridge perpendicular to the sides as a shadow. Narrow where it's round, but when getting lower where the bowl's still oblong, it is nearly 3/8 wide.

Have to do some mental gyrations on this one, because it was meant to show something else, but it's the right-hand side of an interrupted edge piece worked with a deep gouge just as the first. http://i35.photobucket.com/albums/d160/GoodOnesGone/7c6d6541.jpg As you can see, if the bottom portion were not hogged away already, it would make a nice flat bottom.

 

[john lucas]

Several people have given you the answer. The problem is the transition area from the side to the bottom. Quite often when using a bowl gouge you can't rub the bevel as you go through the transition area. It's just too abrupt of a corner. MM mentioned what I do. I turn the sides from lip to bottom and the bottom from center out. You just very carefully and gently stop when you reach the transition area and try to gently blend the two cuts.
A scraper will work just fine but you have to be very gently as you approach the transition area. This is the exact cut I use on boxes when using a scraper. I start in the middle with the tip of the scraper. Then as I approach the steep side I slow down let the left side of the scraper make contact and then pull the scraper out. If you do it too quickly it will grab a lot of wood and can jerk the box out of the chuck.
Another possibility. Have you rounded over the left corner on your scraper. Many round nose scrapers come from the factory with a rather abrupt corner that goes straight into the side. Ideally you should grind this corner around and with some relief under the cutting edge. I usually go back about an inch.

 

[Greg Thomas]

one more idea

One little addition to all the good info already given. The area between wall and bottom is tricky and can be made more so if the tool rest is too far from the area to be cut. When scraping from the bottom up, a straight toolrest if close to the bottom will be too far from the transition area. Sometimes you have to make several moves to keep the tool rest at a good cutting distance. I'm thinking of getting a Robust j rest to help with that problem. Any feed back from those already using a j rest would be appreciated.

 

[john lucas]

Good info Greg. Of course the simplest solution is to design bowls with a nice flowing continuous curve from lip to bottom. Then it's very easy to cut.

 

[Patrick Miller]

Bret-
I suffered from much of the same early in my short turning career (2 years). The best thing I ever did was hook up (via AAW and the closest chapter) with a more experienced local turner who helped me out. An hour of one on one is valuable than any of the books, videos and forum advice (all very good and helpful) you are likely to encounter. I have since found turners to be a most helpful, supportive and mentoring bunch.
Have fun and don't leave before the miracle!

 

[Bret Hinz]

thank you so much, everyone, for the advice and encouragement!

after some expletives, I calmly set the scraper down and walked out to talk to the chickens. (I literally have chickens, which I went out and fed some bread ; not a weird figure of speech)

I've burned through a lot of cash in wood, but the problem is I have a TON of walnut that is free, I just needed a change of wood Got tired of cutting the same old thing.

the previous 2 bowls were asian satinwood, which for the most part, turned beautifully. Both bowls ended up being small plates.

The last was that stuff they had on sale at woodcraft last month (vigo something or another). $12 for a 2x6x6, plus 2-1/2 hours turning, down the drain :/ It was cutting beautifully, the nicest I had used thus far! Then the last few "touchups" with the scraper did it in.

I also picked up a chunk of paduk they had on sale, but think i better go back to the free walnut! or, guess i can go get a chunk of maple that should be nicely spalted by now.

you all have given valuable insight and it is appreciated more than you know. while some may not have given the exact right answer, i've got a lot to ponder.

i just found this article on catches. all the above information considered along with this article, and i think the problem may be too fast of rpms and cutting too low (below the 90-degree mark that is mentioned). I think i will also lay off with the scraper on the insides of bowls for a bit. see how the bowl gouge does instead. i was doing wonderfully using the edge of the bowl gouge to lightly scrape the inside of the bowl. don't know why i felt the need to grab that beast.

i'm not sure of the angle, pretty close to the same angle it came with. i've mimicked the angle every time sharpening the scraper, and have also ground the cutting edge around to the left side an inch or so (as someone mentioned above)

 

[MichaelMouse]

PLEASE do not use your gouge as shown in either of the first two illustrations. You want to cut inside as you see in the third, even though it's outside. There are several variations of this article around. At least this one is not the recipe for disaster that two others are. Figs. 3-4 here make me shudder. https://www.lylejamieson.com/instruction-classes/documents/5 Ways to Avoid a Catch-March1996.pdf

I also favor an absolute nose approach for entry on the rim, swinging to engage, then rolling to the "SAFE" he shows. The narrower you can enter a cut the less likely it will spit the tool back.

As to using the heel of the bevel, I'll let John tell you about the rediscovery (on another forum) of the first method to cope with the extended heel of the cylindrical gouges.

 

[Bill Boehme]

When you have a bowl with a flat bottom and a vertical side, the corner transition tends to concentrate stresses at that edge. Wood already has plenty of built-in stresses so it is a good idea to use shapes that help avoid that problem as much s we can. John Lucas recommended a smooth sweepng curve and I would like to say that I fully agree. I also think that making the bowl have a smooth continuous curve without any discernible transition points will result in a more pleasing form -- at least it does for me.

 

[john lucas]

Smooth arced bowls are also easier to clean. We jokingly call the straight sided bowls dog bowls. I know for a fact that it's harder to clean the juncture of the sides to bottom on my dog's dish that she eats out of every morning. They are stable which is why they make good dog bowls. Now let me say there's nothing wrong with that shape if it's what you want to turn. It just has more problems, catches being one of them.

MM I'm at a loss as to why you see something scary with Lyle's article. I think he covered it quite well. Maybe your reading something into what he says. I've talked to Lyle a bit and our turning styles are very similar, and safe. Could be it's simply hard to discuss in words what we mean.

 

[MichaelMouse]

MM I'm at a loss as to why you see something scary with Lyle's article. I think he covered it quite well. Maybe your reading something into what he says. I've talked to Lyle a bit and our turning styles are very similar, and safe. Could be it's simply hard to discuss in words what we mean.

The pictures. Look at the "grain" in figs. 3 and 4. That's an invitation to disaster. Especially when fig 4 implies cutting above center, nose into the rotation. Terrible illustrations. If people try to cut that way they're begging for a catch. If you look at fig. 2, and make the direction of the arrow the direction to be followed with the nose of the gouge, you're going to be cutting downhill. That is the way to work. Couple that with fig 5, which indicates the instability of the variable angle grind on a cylindrical gouge, and its potential to roll and catch, and you'll understand the advantage in keeping the belly of the gouge engaged if you can. Easily done with the old equal thickness gouge or after relieving the heel under center of a cylindrical. I prefer the former, though you've been discussing the latter over on WC. A rediscovery of the first method I saw in print designed to overcome the design weakness of the cylindricals. Second was the "Irish" grind, which started people standing the things on their ends to try and get what they were able to do on the old ones with full roll and depth control.

 

[robo hippy]

Well, several things here. I agree that the illustrations on Lyle's article are bad. It is very difficult to put turning, which is very 3 dimensional and in motion into 2 dimensional static format. Photography is far better, and video is better yet.

Figure 3 looks like the tool is pointing straight up into the wood. If you try that, if the bevel is rubbing, you can do some what of a controlled cut, but come off the bevel just a tiny bit, and you will have a spectacular catch. Figure 4 seems to show pretty much the same thing. I believe the tool is supposed to show the tool handle dropped about 45 degrees down, and at about 45 degrees away from the wood/coming away from the bowl rim.

There is control with bevel rubbing cuts, and I prefer them. You can also make the cuts without rubbing the bevel, and these are usually referred to as 'shear scrapes' which is a name that confuses me as it is not a scraping cut (scraper flat on the tool rest, cutting edge at 90 degrees to wood rotation) and when properly done is a nice shear or slicing/peeling cut as MM calls them. There is a point when going from a bevel rubbing cut to a shear cut, that if you just barely come off the bevel, it will dig in, like Lyle's 'risky' part of the cut in figure 4. This would be the same as pointing your finger into a spinning ceiling fan blade. There is also a point where if you are far enough off the bevel, it becomes a controlled scraping cut, like in figure 7 'safer' part. This is more like pointing your finger away from the spinning ceiling fan, and your finger will tick off the blades rather than digging in.

The 'shear scrape' cut is used by many turners for cleaning up the tool marks on our bowls, both inside, and outside the bowl, though it is a lot easier to do on the outside of the bowl. It is done with both gouges and scrapers. Most of the time, it is a clean up cut and only takes off little whispy shavings. MM is probably the only person I know who does this and actually removes stock with it. This is not readily clear in his videos as you can not see that he is not rubbing the bevel. It is a safe cut if you are working on the lower 1/3 of the blade, which keeps the part of the tool that is cutting directly over the tool rest, and the blade will not want to tip off balance, kind of like in figure 5. Note here, the blade MM uses has a flute profile like this: ).

Figure 5 is interesting. What is not shown is where is the bowl rim? I would expect it to be on the left of the gouges, which is the up hill side. Both cuts are fairly safe. Risky would be with the uphill side of the gouge coming into the wood. Big kaboom! This is a big problem if the flutes are straight up. I think this is what he is trying to show in figure 8.

robo hippy

 

[Ian Robertson]

We jokingly call the straight sided bowls dog bowls.

We call them "brake drums" in Australia.

 

[hockenbery]

Bret,
I agree with bill and John. Shape makes learning easier. shallow bowls up to Hemisphere shape is great practice.
Deep bowls or flat bottom are tough shapes for beginners and intermediates.

One common cause of catches on the inside is a tool rest too low.
If you cut or scrape below center the wood can and will drive down onto the tool.

I recommend using the gouge with the Handel level to the floor. Setting the rest so the cut is at center.
a sweeping Cut from rim to bottom center ends at the center with the tool always level and the top of the flute always pointing toward the bottom center of the bowl.
This is the only cut needed outside or inside a bowl. Once you master this on you can play with variations that yield more efficient cuts.

One improvement is after the entry at the rim, rotate the flute up to about 45 degrees which yields a Cleaner cut.
There is little tiny bit of wooden the dead center of the bottom.
Try to catch this little bit in the flute, this makes you to slow down and cut to center.

Best thing is some hands on tutoring or watching.

Have fun work safe,
Al

 

[Bret Hinz]

thanks, guys! I appreciate all the help!

I've been working with shallower pieces of wood, so was trying to make the most of the bowls by making them flatter bottomed.

think that's another tip i'll take and run with- lay off the flat-bottomed bowls for a while.

 

[MichaelMouse]

It is a safe cut if you are working on the lower 1/3 of the blade, which keeps the part of the tool that is cutting directly over the tool rest, and the blade will not want to tip off balance, kind of like in figure 5. Note here, the blade MM uses has a flute profile like this: ).

The great thing about using the broad sweep gouge is that you have a sweet spot all the way across. The nose is an arc of a circle, the flute an arc of a circle, so all points are equivalent. Not so with parabolas. The blade doesn't tip because it can't, it's supported parallel to the edge as it cuts progressively deeper. It's not heel to toe, but side to side on the ride. I've been posting these forever, but we'll try them again.

The "cove" and how it's produced are most obvious in outside pictures.
http://i35.photobucket.com/albums/d160/GoodOnesGone/BroadOutProgressive.jpg

But the same is also done inside.
http://i35.photobucket.com/albums/d160/GoodOnesGone/BroadInStaging.jpg

I think it's good illustration because if you look up at 11:30 - 12:00 you'll see some progressive cuts involving only the side grain, then a step back to round, and then back to the entry. The curve made by the gouge is obvious in the stages.

Here's a cutaway or three.
http://i35.photobucket.com/albums/d160/GoodOnesGone/5-Cut-Shapes.jpg
http://i35.photobucket.com/albums/d160/GoodOnesGone/6-Surface-Out.jpg
http://i35.photobucket.com/albums/d160/GoodOnesGone/7-Surface-In.jpg

As you can see by the curved leading edges, the stock is being removed not by taking a big sideways bite, but by cutting progressively deeper. Those who use a curved scraper will recognize the principle. The point of initial engagement removes a thin bit of material, and the following, broadening curve continues to deepen it. With the gouge, there's not only the curve of the nose, but the curve of the flute to help make the cut progressively deeper as the tool is advanced on the rest. It's not, as Hippy implies, My technique. It's the way things were done until the 60's when the machine shops presented us with that mixed blessing the cylindrical gouge.

You can safely take off a lot of thickness by rotating the gouge or using a broader one.
http://i35.photobucket.com/albums/d160/GoodOnesGone/GreenStart.jpg

Or tilt more toward the vertical and take less.
http://i35.photobucket.com/albums/d160/GoodOnesGone/GreenProgress.jpg

There's the gouge, supported side to side, taking various bites down the inside, and producing virtually continuous shavings on green wood.
http://i35.photobucket.com/albums/d160/GoodOnesGone/GreenRoundOut.jpg
http://i35.photobucket.com/albums/d160/GoodOnesGone/ShavingLesson.jpg

As old Frank Pain said, the wood will teach you how it wishes to be cut. This type of shearing/slicing gives almost no tug on your hand.

Bret, here's what you can do when you don't have a corner to turn.
http://s108.photobucket.com/albums/n28/MichaelMouse/?action=view&current=CherryPeelIn.mp4

Same old 1/2" gouge that came with my Monkey Wards lathe. Still a pleasure to use.

 

[Richard Coers]

Another tip that may help you with your original design, is to use a narrower scraper. You will have less edge into the wood, and it will be easier to control. Don't use a thinner scraper though, and thinner will be easier to get into a resonance and cause a different problem. An aggresive burr on a wide scraper is very difficult to control on the straight sides of a bowl. It will have a tendency to self feed (catch) into the long grain.

 

[robo hippy]

The scraping cut, tool flat on the tool rest will generate more stress on the wood as you cut, just the nature of the tool, and size matters little. This is fine for roughing: your surface is rather rough! Hello there, it is a ROUGHING CUT!. For finish cuts, never use the scraper flat on the tool rest. Main problem with self feeding, and this never happens on the outside of a bowl when you are roughing, and the inside has not been turned away/out, is the walls will start to vibrate, and the vibrations can be extreme to the point where you hit and miss on the wood for a bit, then one big hit, and it explodes. To keep this from happening, you roll the scraper up on its side, and do a shear cut (why aren't scrapers sold with the bottom edges rounded over?). The shear cut will slice the wood, and there is minimal pressure on the wood as it cuts.

A negative rake scraper will lesson the pressure of the cut, but it is still a scraping cut, and will not leave as clean of a surface as a shear cut.

robo hippy