Tool marks when hollowing bowls

[David Wrate]

I turned some eucalyptus this afternoon. Completely green, cut from a log I picked up a few weeks ago.


I really struggled with a couple of things:
1) Even though it was green wood, it was really difficult to create the exterior shape. The wood just seemed really hard. This was the second blank from this log and the first one was easy to shape. Could the blank have dried enough in a week to make that much of a difference?
2) I had terrible tool marks on the inside. Some are still slightly visible. Seemed like I kept falling off the bevel so I'd have to go back and try to pick it up. Each time I left a minute trace of the original cut.
Definitely not an enjoyable experience. Though the aroma was very pleasant. So there's that.

 

[Monty Ivy]

You get those sometimes. I've had this happen to me. Change your attack. Switch from gouge to carbide, take smaller cuts, check tool rest height, and/or re-sharpen more frequently.

 

[Brian Gustin]

What Monty said, and invest in a negative rake bowl scraper - even a cheap one (I got a 2 piece pair on amazon, Hurricane brand I think.. 'cause I didn't have ANY decent scrapers , and ground the smaller one into negative rake, it worked wonders on a couple bowls that I couldn't get rid of tool marks otherwise.. after some practice with it, that is, and making a burnishing tool...)

 

[hockenbery]

had terrible tool marks on the inside. Some are still slightly visible. Seemed like I kept falling off the bevel so I'd have to go back and try to pick it up. Each time I left a minute trace of the original cut.

That slight undercut can be a daunting challenge. Hard to stay on the bevel through the curve.

I usually stair-step when hollowing bowls. This leaves lots of mass in the bottom making less vibration on the wall being cut.

When picking up a cut I try to start cutting just a little before the last cut ended. This cuts away any transition lines.

A negative rake scraper can work well at removing minor tearout made by coming off the bevel

 

[David Wrate]

Thanks for the feedback, it’s greatly appreciated. I’ll have a look around for a scraper set.

 

[Mike Johnson]

Every tool has a sweet spot, every piece of wood cuts a little different based on moisture, hardness, grain orientation, are you gripping the
tool handle with force or are you letting the cutting edge of the tool guide you through the cut? Certain wood species can quickly dull the
tool which requires resharpening the tool often or fighting your way through wood leaving tool marks. There are blind wood turners that
basically, use the feel of the tool cutting through the wood to guide the movement of the body and hand controlling the handle of the tool.

 

[robo hippy]

The marks that you are calling tool marks, look like tear out to me. This always happens when you are cutting up hill against the grain. Some times more, some times less, and that depends a lot on the wood. Of course sharp tools are a must for the finish cuts. For me, my final pass is almost always a shear scrape, and I prefer a burnished burr to the grinder burr. I have one video dedicated to that. As for scrapers, I NEVER use a scraper on the walls of a bowl, and this includes NRSs. They are fine for sweeping across the bottom of a bowl where the grain is flat, but when going up the walls and through the transition you still run into the uphill/downhill thing, and depending on the wood, that can make tear out more rather than less.

Some times, if you don't round off the heels of your inside bowl gouges, the bevel edge is rather sharp and that can bruise the wood. It seems that the bruising can be so bad that you can sand through to the outside of the bowl without getting rid of the rings. They are concentric and run the whole way around the bowl. Tear out is in quarters, so 1/4 tear out, 1/4 clear, 1/4 tear out, and 1/4 clear. This occurs in different quadrants on the outside than on the inside.

robo hippy

 

[David Wrate]

The marks that you are calling tool marks, look like tear out to me. This always happens when you are cutting up hill against the grain. Some times more, some times less, and that depends a lot on the wood. Of course sharp tools are a must for the finish cuts. For me, my final pass is almost always a shear scrape, and I prefer a burnished burr to the grinder burr. I have one video dedicated to that. As for scrapers, I NEVER use a scraper on the walls of a bowl, and this includes NRSs. They are fine for sweeping across the bottom of a bowl where the grain is flat, but when going up the walls and through the transition you still run into the uphill/downhill thing, and depending on the wood, that can make tear out more rather than less.

Some times, if you don't round off the heels of your inside bowl gouges, the bevel edge is rather sharp and that can bruise the wood. It seems that the bruising can be so bad that you can sand through to the outside of the bowl without getting rid of the rings. They are concentric and run the whole way around the bowl. Tear out is in quarters, so 1/4 tear out, 1/4 clear, 1/4 tear out, and 1/4 clear. This occurs in different quadrants on the outside than on the inside.

robo hippy

Thanks Reed, I was just watching this video. I'm not sure I understand as aren't you using a scraper on the wall of the bowl at 18 min:

View: https://youtu.be/ZM4ak8ygzS4

 

[robo hippy]

Yes, I am using a scraper, but I am not doing a scraping cut. Scraping cut is the tool flat on the tool rest and the cutting edge at 90 degrees to the rotation of the wood. For a shear scrape, I have the scraper up on edge so the cutting edge is engaging the wood at 45 or higher degrees. This 'shear' angle, or 'sheer' as in sheer face of a cliff according to Lyle Jamieson, is an age old principal used for cutting. I liken it to going over speed bumps in the parking lot. Hit them straight on, and it is a pretty big bump. Hit it at a 45 degree angle, and that bump is greatly reduced. The idea is that at a shear angle, the cutting edge is better able to get under the wood fibers and lift and cut as opposed to just scraping. This is used on hand planes, card scrapers, and even saw blades.

robo hippy

 

[David Wrate]

Yes, I am using a scraper, but I am not doing a scraping cut. Scraping cut is the tool flat on the tool rest and the cutting edge at 90 degrees to the rotation of the wood. For a shear scrape, I have the scraper up on edge so the cutting edge is engaging the wood at 45 or higher degrees. This 'shear' angle, or 'sheer' as in sheer face of a cliff according to Lyle Jamieson, is an age old principal used for cutting. I liken it to going over speed bumps in the parking lot. Hit them straight on, and it is a pretty big bump. Hit it at a 45 degree angle, and that bump is greatly reduced. The idea is that at a shear angle, the cutting edge is better able to get under the wood fibers and lift and cut as opposed to just scraping. This is used on hand planes, card scrapers, and even saw blades.

robo hippy

Ah that's super helpful Reed, appreciate the clarity.

 

[Dean Center]

David,
Regarding the outside shape. It's not real clear what you've got from the pictures posted, but I can suggest one general thing to which to attend.

The outside shape is determined by how you move your trunk as you turn. If you want a curve, you have to move yourself in a curve. (Dance Move #3) You rotate your trunk slowly and shift your weight from one foot to the other, in order to move in a curve. (when you watch a video of a good turner, don't watch the wood, the chips, or the tool--watch where they put their feet and how they move themselves)

Doing that presumes that you are following the A-B-Cs and are anchoring your gouge on the tool rest near the cutting end, and against your side with your hand at the other end of the tool. (Depending on your height, the lathe height, and whether the tool is horizontal or angled, the anchor point on you could be from your under arm to your hip)

Ideally, the inside shape would be created in the same manner, and if you have a lathe that allows you to turn off the end of the lathe, you actually can. Most turners end up having to reach their right hand across the lathe bed to start the inside cut, and you can't really do that with your hand against your hip. This awkward position is exactly where the torn grain happens, perhaps partly for that reason.

The other reason it happens at that spot is the undercut upper part of the inside. To get the cleanest cut on the inside of a bowl, we cut from big to small--that is, from the rim to the bottom. EXCEPT that under the rim, the widest, or Big, part is not at the rim, but just below. In order to get a clean, downhill/with supported fibers cut in that area, we would have to cut the wood from the widest dimension, back and up towards the rim! Not something you can do with a regular bowl gouge. You can do it with a Hunter carbide tool, though.

Most of us, I think, cut it going towards the bottom of the bowl and do the best we can, then try to clean it up. To do the best we can, the last few passes have to be very shallow, the tool has to be very sharp (right off the grinder), and we either have to leave a lot of mass in the bottom of the bowl, cutting just the first 2+ cm or we have to apply stabilizing pressure against the outside of the bowl with out left index finger, or both. (If you look at a recent picture Odie posted of his lathe with a bowl in progress, you can see he stabilizes the side of the bowl with a bowl steady, which is similar to using your finger, but requires fewer bandaids and curse words)

The good news is that you've gotten your dog bowl out of the way and now you can start making aesthetic bowls.

 

[David Wrate]

David,
Regarding the outside shape. It's not real clear what you've got from the pictures posted, but I can suggest one general thing to which to attend.

The outside shape is determined by how you move your trunk as you turn. If you want a curve, you have to move yourself in a curve. (Dance Move #3) You rotate your trunk slowly and shift your weight from one foot to the other, in order to move in a curve. (when you watch a video of a good turner, don't watch the wood, the chips, or the tool--watch where they put their feet and how they move themselves)

Doing that presumes that you are following the A-B-Cs and are anchoring your gouge on the tool rest near the cutting end, and against your side with your hand at the other end of the tool. (Depending on your height, the lathe height, and whether the tool is horizontal or angled, the anchor point on you could be from your under arm to your hip)

Ideally, the inside shape would be created in the same manner, and if you have a lathe that allows you to turn off the end of the lathe, you actually can. Most turners end up having to reach their right hand across the lathe bed to start the inside cut, and you can't really do that with your hand against your hip. This awkward position is exactly where the torn grain happens, perhaps partly for that reason.

The other reason it happens at that spot is the undercut upper part of the inside. To get the cleanest cut on the inside of a bowl, we cut from big to small--that is, from the rim to the bottom. EXCEPT that under the rim, the widest, or Big, part is not at the rim, but just below. In order to get a clean, downhill/with supported fibers cut in that area, we would have to cut the wood from the widest dimension, back and up towards the rim! Not something you can do with a regular bowl gouge. You can do it with a Hunter carbide tool, though.

Most of us, I think, cut it going towards the bottom of the bowl and do the best we can, then try to clean it up. To do the best we can, the last few passes have to be very shallow, the tool has to be very sharp (right off the grinder), and we either have to leave a lot of mass in the bottom of the bowl, cutting just the first 2+ cm or we have to apply stabilizing pressure against the outside of the bowl with out left index finger, or both. (If you look at a recent picture Odie posted of his lathe with a bowl in progress, you can see he stabilizes the side of the bowl with a bowl steady, which is similar to using your finger, but requires fewer bandaids and curse words)

The good news is that you've gotten your dog bowl out of the way and now you can start making aesthetic bowls.

Thanks Dean, appreciate the tips!

 

[robo hippy]

David, if you ever swing down Oregon way, let me know. I love play dates. Oregon Woodturning Symposium in mid March this year in Albany, OR, about 45 miles north of me.

robo hippy

 

[David Wrate]

David, if you ever swing down Oregon way, let me know. I love play dates. Oregon Woodturning Symposium in mid March this year in Albany, OR, about 45 miles north of me.

robo hippy

Gosh, that would be fantastic Reed! We do like to take our bike out for road trips

 

[David Wrate]

David, if you ever swing down Oregon way, let me know. I love play dates. Oregon Woodturning Symposium in mid March this year in Albany, OR, about 45 miles north of me.

robo hippy

I'm going to make plans to attend the Symposium

 

[robo hippy]

Cool! See you there!

robo hippy