Bowl Gouge Bounce

[Joseph Maiorano]

Hi All,

Recently, I have been roughing a lot of green bowl blanks around 12 inches in diameter. I use a faceplate for bowls of this size, taking care that spot where the faceplate goes is as flat as possible. I start my roughing operation on the outside of the blank using a series of pullcuts going from the smaller diameter to the larger diameter. Once the bowl is mostly round, I switch to a pushcut. Here is where fun begins. The pushcut starts off fine. Then about an inch or so into the cut the gouge starts bouncing. The gouge has a sharp edge and I do not have a death grip on the gouge. I also try to minimize the pressure the bevel has on the wood. My question is how do I keep the gouge from bouncing out of the cut?

Any input would be appreciated. TIA for your help.

 

[hockenbery]

It is a lot easier for me to help someone when i’m Standing next to them.
You seem to have the right concepts but something is missing in the execution.

Lots of things can cause the “bounce”.
Almost all bounce is loosing bevel contact.

Causes are many - the ones I can think of
Too much bevel pressure- you said you had a light one
Tool rest too low - need to be cutting a bit above center
Cutting too fast
Cutting too deep
Dull tool - I know you said yours was sharp
Resin on the bevel
Not riding the bevel
Flute turned up too much 45 degrees is good.
Tool handle not against the body
Tool handle too low - I do this cut with the handle nearly parallel to the floor
Working too far over the tool rest 2” is a good limit to start with.

Probably a couple more someone will add

You might be interested in a thread I posted in tips and techniques - working with green wood.
Includes Two videos from the same demo. -roughing a green bowl and returning a dried bowl.
You can see how I rough a green bowl.

http://www.aawforum.org/community/index.php?threads/working-with-green-wood.11626/

 

[hockenbery]

I use a faceplate for bowls of this size, taking care that spot where the faceplate goes is as flat as possible.

I use faceplates for most of my hollow forms.
I start the pieces between centers and turn a slight concave for the faceplate.
This makes the rim of the faceplate have a solid contact.
While dead flat will work nearly as well as the concave, dead flat is nearly impossible to achieve and the concave works as well maybe better because it is easier to center the faceplate on the concave and holds in position as the first screw goes in.

Lyle jamieson has an excellent video that shows the shallow concave for the faceplate in his making a glueblock video. Same shallow concave works for bowls and hollowforms.

View: https://m.youtube.com/watch?v=y8b35iq4LTA

 

[Richard Coers]

Best reason to have a mentor or joining a club? 11 possible reasons given by hockenbery. Learning by yourself will require you to muddle through the 11 causes. Spending an hour with someone that can help, cuts the learning time dramatically!

 

[Clifton C]

Is this a new problem with this batch of bowls? When I hear or feel the "bounce" start I stop the forward motion of the gouge, back up a bit, and clean up the bounced surface, it never gets better on it's own. If you hear or feel it thru the tool it's on the surface, subtle as it might be. I started a word doc with Al's list (thanks Al) I hadn't thought about the resin. Hope others will help add to the list. At the first sign of a bounce I usually back up and try a lighter cut with less pressure on the bevel and a little extra downward pressure on the gouge into the tool rest. If that's not it, a trip to the grinder and try again. The downward pressure of the gouge on the tool rest might add some drag so dress and wax to keep it slick.

 

[Donovan Bailey]

I agree with Clifton...plus I find that it also helps my cut when I "slow down."

 

[Karl Loeblein]

Here's another likely culprit to add for the list.

Change in grain direction: Side grain forms spin between end grain & side grain which can cause a bounce especially as the walls get thinner allowing the piece to flex. Try lubricating the piece using a spray bottle of water or alcohol before making very light cuts with a freshly sharpened gouge. Also, try adding liquid dish washing soap to the water spray bottle for dry or soft woods prone to tear out like Box Elder or Hackberry. If a thin walled piece still flexes too much with lubrication & sharp tool then it might be time to pull out the 80 or 100 grit gouge.

 

[Odie]

Learning by yourself will require you to muddle through the 11 causes. Spending an hour with someone that can help, cuts the learning time dramatically!

Then again......if you do "muddle" through it by yourself.......you just might find new ways of doing things......it's how the "undiscovered country", gets discovered!

I have nothing against those who wish to have mentors, and instructors. Like we've all been told, these people can reduce the time one "muddles"......at the expense of all that personal effort you give up to arrive at the destination. I'm one who has "muddled" a lot in my learning experience.......but, I wouldn't trade what I've learned the hard way for going back and doing it with mentors and teachers. Bottom line here......is, there is something to be gained, and something to be lost......and, there is no going back over those bridges, once you cross.

-----odie-----

 

[Odie]

Al has covered quite a few possibilities.....and, he's correct.

I do have a thought to add.......and, that is the most likely culprit, is a tool that isn't as sharp as it could be. You see, in bowl turning, you deal with "bringing to round", and resistance over end grain, vs long grain. If the tool isn't sharp (and many turners only believe their tool is sharp), then it requires pressure to cut. The less sharp it is, and the more variance of resistance there is.......the more tendency for the tool to oscillate with the resistance. When this starts, it compounds itself, making things worse. This usually results in those harmonic spiral grooves. The solution is to stop the cut, re-sharpen, and start over. A sharp(er) tool, with less pressure......will always result in a cleaner cut. Those spiral grooves will act similarly to an "out of round" condition, and should be dealt with as if it were. Don't think your bevel rubbing on the spiral grooves will be productive......it won't.

-----odie-----

 

[Joseph Maiorano]

Thanks for the replies. After reading through hochenbery's check list and watching his video, I was able to pick out a few things to change up. For starters I was dropping the handle too much, the tool rest was too low and I was opening the flute too much. From the video I noticed the arm on the tool rest was more rigid with a locked elbow and the initial cuts are more of an arc through the blank. I mounted another blank, this time between centers, and had more success. The only issue I had was that a spiral bump formed about two thirds through the blank towards the edge of the bowl. I ended up switching to a scraper to clean it up.

I would agree that finding a local club is the way to go. Unfortunately, around here the nearest club is not local.

Thanks again.

 

[hockenbery]

Good that you are getting better results. Each bowl you do should be better.

the video I noticed the arm on the tool rest was more rigid with a locked elbow and the initial cuts are more of an arc through the blank

This is true for the initial roughing cuts. Up to about the 8 minute mark in the roughing video.

The “A” frame formed by the straight forward arm and tool handle at the top of the thigh maintains the cutting position of the gouge edge and bevel so that I make a bevel riding cut through the interupeted edge of the newly mounted blank when roughing is started. No bounce on the toughest part of the roughing.

After the initial roughing
the forward arm is not straight and the elbow is close to the body most of the time.
The job of the forward hand is to keep the tool on the tool rest with a tiny downward pressure. I often use just the thumb and forefinger to guide the tool rather than grip it.
Everything should be relaxed letting the wood come to the tool. The tool sort of feeds itself.
The tool with a well positioned cutting edge and bevel knows what to do so just follow it through the cut. The grip should be just firm enough to keep the tool from falling on the floor when it comes out of the wood after the cut.

 

[Joseph Maiorano]

Clifton, this is more a new to me problem. I upgraded from a mini lathe to a full size lathe last year so I just started turning larger bowls from green wood. Prior to the upgrade, I didn't do very many bowls. I turned mainly small trinkets from dried wood. I'll try backing out and restarting the cut the next time the bounce starts.

Odie, I do find myself going to the grinder more often. The difference in the cut is amazing.

 

[Richard Coers]

Al has covered quite a few possibilities.....and, he's correct.

I do have a thought to add.......and, that is the most likely culprit, is a tool that isn't as sharp as it could be. You see, in bowl turning, you deal with "bringing to round", and resistance over end grain, vs long grain. If the tool isn't sharp (and many turners only believe their tool is sharp), then it requires pressure to cut. The less sharp it is, and the more variance of resistance there is.......the more tendency for the tool to oscillate with the resistance. When this starts, it compounds itself, making things worse. This usually results in those harmonic spiral grooves. The solution is to stop the cut, re-sharpen, and start over. A sharp(er) tool, with less pressure......will always result in a cleaner cut. Those spiral grooves will act similarly to an "out of round" condition, and should be dealt with as if it were. Don't think your bevel rubbing on the spiral grooves will be productive......it won't.

-----odie-----

Why the advice Odie, isn't he supposed to learn by himself?

 

[Dean Center]

I'll try backing out and restarting the cut the next time the bounce starts.

You've had really good advice.

One more thought. If you have had some bounce and produced a variable surface, when you go to recut, you sometimes/oftentimes have to take a little deeper cut than you think. If you try just to cut the tops off the bumps, you will likely find you start bumping up and down again. If you take a slightly deeper cut, the bevel will be riding on new wood, with no waves or bumps in it, and you can get a level cut.

 

[hockenbery]

if you have a chance to get a quality class or a workshop - take it.

A good class can replace years of trial and error struggles.
I’ve seen hundreds if students leave classes able to turn a 220 surface on much of a bowl surface so they sand with 120, 220, 320 and they are done.

They aren’t done learning and improving but they have a good skill level in surface achievement which allows them to concentrate on form and finer surface.

There are lots of good turners in Vermont
One who teaches is Johannes Michelson is in Manchester. He has a 3 day hat class. a cowboy hat is just a bowl turned thin with the rim bent. If you can turn a hat your bowls won’t need much sanding.

 

[Odie]

Why the advice Odie, isn't he supposed to learn by himself?

I'm not a mentor, or an instructor......so, whatever insight I give, is worth exactly what you paid for it!

-----odie-----

 

[Bill Boehme]

Why the advice Odie, isn't he supposed to learn by himself?

Let's play nice. The sandbox is big enough for everybody.

 

[Emiliano Achaval]

if you have a chance to get a quality class or a workshop - take it.

A good class can replace years of trial and error struggles.
I’ve seen hundreds if students leave classes able to turn a 220 surface on much of a bowl surface so they sand with 120, 220, 320 and they ware done.

They aren’t done learning and improving but they have a good skill level in surface achievement which allows them to concentrate on form and finer surface.

There are lots of good turners in Vermont
One who teaches is Johannes Michelson is in Manchester. He has a 3 day hat class. a cowboy hat is just a bowl turned thin with the rim bent. If you can turn a hat your bowls won’t need much sanding.

I wish I had taken classes my first few years turning. I only had Del Stubbs guiding me along, LOL. I agree with Al, even if you have to travel, take some classes...

 

[john lucas]

ONe thing I haven't seen mentioned unless I missed it. Quite often just rotating the flute a few degrees one way or the other will stop bounce. If you have already created a ripple from the bounce back up and start that cut over. Then if it starts feeling rough rotate the handle one way or the other slightly to see if you can get it to cut better. Most of the time that takes care of the problem for me.

 

[Lamar Wright]

Quite often just rotating the flute a few degrees one way or the other will stop bounce

...John, your quote really helped me when learning how to use the bowl gouge...also being more patient

 

[Joseph Maiorano]

Taking a class with JoHannes Michelsen has been on my radar for a while. Now that I'm doing a lot of bowls, I will be looking into it.

Below are some pics from my second attempt since starting this thread. I started with a cherry blank 12 inches in diameter and ended up with a 10 inch bowl and a 7.5 inch bowl. I am pleased with the results and did not have to break out the scraper. This time I kept the wood wet, sharpened the tool a couple of extra times, backed out and started the cut over once the bounce started. I think the real key was to be patient with the cut, letting the wood come to the tool.



Thanks again for all your help.

 

[hockenbery]

Taking a class with JoHannes Michelsen has been on my radar for a while. Now that I'm doing a lot of bowls, I will be looking into it.

He is a good Good instructor and quite an innovative guy.
While the class project is a hat.
What you learn is how to turn thin with a surface that needs little sanding.

 

[Bill Boehme]

I agree with Al. Johannes has demonstrated turning a hat a couple times at SWAT ... once in the vendor area where it was more up close and people could talk to him while he was working.

 

[Dean Center]

Isn't Al Stirt also in Vermont? I haven't been to a class by either of them, so others may have comments about the pros and cons of the two teachers.

 

[hockenbery]

Al Stirt is an excellent teacher too. He is in Northern Vermont Enosburg Falls.
I have had the pleasure of being Als gofor and helper in classes at Maryland hall and in my shop here in florida.

http://www.alstirt.com/Pages/StudioTeaching.html

Londonderry to Enosburg Falls is a 3 hour drive
Londonderry to Manchester is 20 minutes

 

[john lucas]

Al.stirt is fantastic. He will be a featured demonstrator at the Tennessee demonstrator this January.

 

[Dean Center]

Londonderry to Enosburg Falls is a 3 hour drive
Londonderry to Manchester is 20 minutes

How could anyplace in Vermont be 3 hours? Vermont is just barely larger than our county.
For perspective, from Alzada, Montana to Yaak, Montana is farther than it is from Chicago to Washington, DC. Of course, Odie's the only one who knows where Yaak is--do you know where Alzada is, Odie? (hint: it's a suburb of Sturgis)

 

[robo hippy]

There is always some bounce in bowl/side grain orientation. It comes from cutting through end grain, then side grain, and repeat every revolution. You could also say you cut up hill, then down hill and repeat. Funny thing is that the tighter you clamp down on your tool, the worse the bounce gets. The light touch greatly reduces the bounce.

robo hippy

 

[hockenbery]

There is always some bounce in bowl/side grain orientation.

Reed I have to agree there is always some vibration and some bounce.

But there does not need to be detectable bounce.
I get smooth cuts foot to rim on face grain bowls using a gouge.
The idea is to make all cross cuts so that there is no cut into the endgrain.
That said the nature of the gouge is to cut 90% toward the head stock (cross cut) and 5% towards the ways ( rip cut). This is why the back side of the endgrain almost always has some tiny ( hopefully microscopic) hard to see tear out with a good cut.

Cutting foot to rim, I get no bounce when using a sharp tool with a clean bevel, cutting in the right direction with a good flute oriention, and a modest depth of cut using a good feed rate and lathe speed.

When doing a pull cut above the low rim on a natural edge bowl I do get the slightest sensation that could be called a bounce however the tool is not bouncing. Cutting air and wood is like the rapid sensation of a buzzer the gouge moves smoothly but you feel the wood contact between the air interruptions.
The cutting edge engaging the wood then air is a smooth process with a tiny rapid flutter.

 

[robo hippy]

.... But there does not need to be detectable bounce.
I get smooth cuts foot to rim on face grain bowls using a gouge.
The idea is to make all cross cuts so that there is no cut into the endgrain.

Al, not getting this at all.... Maybe have to see it. End grain comes around twice every revolution, with grain and against grain twice every revolution.

This part as well:

... That said the nature of the gouge is to cut 90% toward the head stock (cross cut) and 5% towards the ways ( rip cut). This is why the back side of the endgrain almost always has some tiny ( hopefully microscopic) hard to see tear out with a good cut....

"90% toward the headstock? 5% to the ways"?

I am guessing this is about what I call 'presentation' which is how the sharp edge is presented to the wood. Scraping cut is cutting edge at 90 degrees to the spin of the wood, and a shear cut is the cutting edge at a higher angle. Most of the time a gouge is cutting at about 45 degrees to the rotation. Using the wing of a swept back gouge with the handle dropped is one way to get a higher shear cutting angle. I hold my gouges mostly level, and prefer a more round nose shape with a more blunt nose profile, like ), which when rolled over on the side can give a really high shear angle. The more conventional 45/45 or 45/60 sweep, have a smaller sweet spot on the nose and longer sweet spot on the wing. The higher the shear angle, and the sharper the tool is, the less tear out you get, but you always get some when you are cutting up hill. I guess also included in reducing the tear out is feed rate, or how much and how fast you are trying to remove wood... Too fast and too heavy a cut = more tear out.

The only way I have found to almost totally eliminate any run out on any bowl I have ever done is to shear scrape. Since you are not rubbing the bevel, you are just taking off the high spots. I can get an almost complete pencil line around a bowl this way compared to half a circle with just the gouge...

robo hippy

 

[hockenbery]

@robo hippy Here are a couple of pictures.
The idea is to try to never cut toward endgrain.
Unfortunately the the gouge does not cut 100% in the correct direction on spinning wood.
A small part of the cut goes in the wrong direction. It actually cut over anout 90 degrees with
Most of the cut going i the right direction.

Cutting from foot to rim is a cross cut and never cuts endgrain it is always cutting a fiber with a longer fiber behind it. supported fibers cut cleanly because they cannot bend.

Because of the curvature of the gouge edge and the rotation of the wood a not all of the cut is toward the rim.
Tiny parts of the cut are tangential to the bowl where you are cutting. This cutting component does cut into endgrain. Fibers on the back side of the endgrain ar not supported by fiber and tend to break off instead of cut.

Below shows most of the cut cutting fibers in the desired direction x red arrow. But some of the fibers are cut in the wrong direction by a tiny bit of the cutting force - yellow arrow.

 

[robo hippy]

Ummmmmm, What??? Maybe we need a play date.... Only part that makes sense to me is that the nose of the gouge is doing a shear cut, and the wings are doing more of a scraping cut, which is more of a presentation issue to me, shear vs scrape. When you are cutting down hill, you have supporting fiber, when you cut up hill, yes there is fiber behind the cut, but you are still going up against the grain and it is not supporting the cut fiber, it is resisting... Or some thing like that.

robo hippy

 

[Bill Boehme]

I agree with Reed. I don't understand your rationale for what the 90% and 5% are supposed to be representing, but for certain they don't proportionally represent the effect that either force or direction has on cutting end grain.

 

[hockenbery]

Ummmmmm, What??? Maybe we need a play date.... Only part that makes sense to me is that the nose of the gouge is doing a shear cut, and the wings are doing more of a scraping cut, which is more of a presentation issue to me, shear vs scrape. When you are cutting down hill, you have supporting fiber, when you cut up hill, yes there is fiber behind the cut, but you are still going up against the grain and it is not supporting the cut fiber, it is resisting... Or some thing like that.

robo hippy

This is the fundamental way gouges work.
The nose and leading edge of the lower wing do the cutting. With the bevel riding this is a very clean cut.

1. The cut is made in the direction of the big arrow and most of the cutting force is in that’s direction all making a crosscut. The endgrain reallynis no issue.

2. A small amount of the same cut does take place in the other directions including straight up I. The direction of the ways ( worst cut) this tiny bit of cut causes tiny, tiny tear out on the back side of the endgrain.

With the handle dropped slightly and too rolled to 45 degrees the cut is extremely clean because the shear angle makes less cut in the wrong direction.

 

[hockenbery]

don't proportionally represent the effect that either force or direction has on cutting end grain.

That is what I hoped to represent. If the cutting-edge were vertical all of the cut would be toward the headstock. But we cannot get a vertical cutting edge to work.

Since it is slanted some of the cutting components are distributed toward the ways of the lathe.
This is what creates the rougher surface in the back side of the endgrain.
With a sharp tool good shear angle, and light cuts the back side of the end grain becomes acceptable

The red component does all cross cuts

The yellow component does a cut in the totally wrong direction and into the endgrain

The idea with cutting is to reduce the yellow component to acceptable.

 

[Joseph Maiorano]

A bit of an update on my progress. I''m getting better at controlling the gouge through the cut and I am able to go from foot to rim in one pass especially fresh off the grinder. The gouge is cutting just above center, flute at 45 degrees or less, handle is parallel to the floor. For the most part, the gouge almost self-feeds through the cut.

I did notice that the more balanced the blank is at the start, the easier it is to control the bounce.

I have another half a tree to practice on.

Vermont - ya just can't get there from here.

Thanks again for all your help.

 

[robo hippy]

If the end grain wasn't an issue, then there would be no tear out at all... I frequently cut with the nose at a 70 to 80 degree angle for the high shear cut, though if I went to 90 degrees, it would still cut but it would be like trying to get smooth cuts with a parting tool edge. Yea, all cutting for bowls goes from base to rim. When cutting end grain/hollow form or box form orientation, if you always cut with the grain, you can get zero tear out because the grain supports the cut. You can still get tear out if you go against the grain, or try to take off too much too fast, and more so with a dull tool... Red arrow cutting still hits the end grain twice each revolution...

robo hippy

 

[hockenbery]

Red arrow cutting still hits the end grain twice each revolution..

The red arrow does not hit the the end grain it cuts the fibers.
Lay a small board on your bench. An 1/8” from one end make a cut toward the end.
Makes a clean cut.


A view of the top of the board below
If we spin the table as we cut most of the cut goes in the red direction but a small component of the cut goes in the yellow direction. On the backside of the endgrain the fibers are unsupported. This is what happens in turning our correct direction cut has a small component cutting in the wrong direction. It is this tiny component of the cut that hits the endgrain.
Fortunately a sharp tool at the correct angle makes the bad component insignificant.

 

[robo hippy]

Still scratching my head... I can easily see how the top drawing applies to spindle turning/pencil sharpening, and as near as I can tell, same with the bottom one. Cutting into unsupported fiber/uphill/against the end grain still happens twice each revolution. How significant the tear out is depends on the wood, the sharpness of the tool, the shear angle, and your tool feed rate: too fast you get more tear out, just right it can become 'insignificant', well, depending on what species of wood you are turning and how solid/punky it is. The red arrow makes sense to me, the yellow does not, unless you are doing a scraping cut.... Maybe I will have to come to the Florida Woodturning Symposium...

robo hippy

 

[hockenbery]

Cutting into unsupported fiber/uphill/against the end grain still happens twice each revolution.

The whole trick is to not cut into that unsupported fiber very much.
I your cut is toward the headstock only a tiny portion of the cutting component is toward the unsupported fiber.

The fibers on the backside of the end grain have support toward the headstock (rim) and no support perpendicular to the ways.

Maybe I will have to come to the Florida Woodturning Symposium...

. It should be a great time. Weather is often iffy then but the symposium is indoors.
Great facility.