• Beware of Counterfeit Woodturning Tools (click here for details)
  • Johnathan Silwones is starting a new AAW chapter, Southern Alleghenies Woodturners, in Johnstown, PA. (click here for details)
  • Congratulations to Paul May for "Checkerboard (ver 3.0)" being selected as Turning of the Week for March 25, 2024 (click here for details)
  • Welcome new registering member. Your username must be your real First and Last name (for example: John Doe). "Screen names" and "handles" are not allowed and your registration will be deleted if you don't use your real name. Also, do not use all caps nor all lower case.

Trouble finish turning bowls

Joined
Oct 5, 2019
Messages
2
Likes
0
Location
Round Hill, Virginia
Good afternoon all,

I've been turning on a Laguna 18/36 and have really started to struggle on finish turning the outside of bowls, particularly those I've rough turned months ago.

Whether I clean up an existing tenon or mortise or in the case of the photo, add a scrap piece as a tenon, as I turn the outside, the gouge will not smoothly cut into the wood. The photo is the most extreme example I've had, but the gouge will start vibrating badly and skipping on the surface of the wood. I've used both a 3/8 bowl gouge set at 45 degrees and a 1/2 bowl gouge set at 50 degrees. I use Raptor guides and a Wolverine jig to sharpen. Ultimately, I use either a carbide tool or scraper to fix it but that has it's own set of problems.

Thank you in advance!

20191002_111009.jpg
 

hockenbery

Forum MVP
Beta Tester
TOTW Team
Joined
Apr 27, 2004
Messages
8,591
Likes
4,886
Location
Lakeland, Florida
Website
www.hockenberywoodturning.com
Hard to trouble shoot not standing over your shoulder
The symptoms can come from a variety of causes.

Pressing too hard on the bevel,
Holding the tool too tightly
Not riding the bevel
Dull tool,
Cutting too fast
Too slow a lathe speed
Too fast a lathe speed

when truing the outside it is best done between centers so that you can
1. true the rim - this is most out of balanced weight
2. True the tenon
4. True the outside - I start truing at the bottom an work toward the rim in small steps
So that I am working from smooth to rough. The bevel rides nicely on the smooth part as you cut into the rough if the tool begins to bounce back up to the smooth and cut again. If the tool is bouncing It isn’t cutting a circle. The
4. Then put it in a chuck and retrieving the outside if necessary.

the second video in this thread on working with green wood is a video of how I mount and return a very warped bowl
http://www.aawforum.org/community/index.php?threads/working-with-green-wood.11626/
 
Last edited:
Joined
Aug 14, 2007
Messages
5,436
Likes
2,792
Location
Eugene, OR
To get that huge of an oscillating pattern, my first guess is either the lathe is wobbling from not being set flat on the ground, and/or your mounting method is loose. If you can grab onto the bowl blank and wiggle it at all, then your mount is loose. If you can grab onto your lathe bed and wiggle it all, then your 4 feet are not all under equal pressure/weight. Another possibility would be you have your lathe on a joist/wood floor base, and not concrete.

robo hippy
 
Joined
Aug 26, 2006
Messages
655
Likes
554
Location
Hampton Roads Virginia
The first thoughts I have when I see a pattern are harmonics, basically something is setting up a vibration. It could be the tool, the wood, the lathe or a combination. A long tool overhang will sometimes show up as a spiraled pattern. Ive chased those type of spirals down to a washer cut from a milk jug on the spindle, the guy said it was to keep the chuck from locking onto the spindle, problem was, it had too much flex and caused vibration. Another thing to check is the tenon, I see a slight gap at the shoulder in your pic. the tenon should not bottom out in the chuck, the shoulder of the tenon should rest on the top of the jaws. I undercut that shoulder ever so slightly just to make sure it's a tight fit to the shoulder. Tenons, even though not seen in the finished piece are excruciatingly important. Don't skimp. Cut a precision tenon. Your tenon should look so good that you could spray it with lacquer and set it on your mantle for all your friends to come over and admire....
Oops, I rambled... sorry...
c
 

john lucas

AAW Forum Expert
Joined
Apr 26, 2004
Messages
8,321
Likes
3,576
Location
Cookeville, TN
Most of it seems to be cutting in the wrong direction. Do you have the tailstock up. I start all bowls between centers. I place the bottom toward the tailstock so I can more easily turn from the foot out to the lip on a side grain bowl. Once I've roughed it out I still have the mark on the bottom from the live center. When it's dry I rough out the outside of twice turned bowls by putting a pad on my chuck, bring the tailstock up and true up the tenon and turn the outside. Then I can reverse it and hollow the inside always starting with the tailstock in place. When you get that vibration the tendency is to push harder on the bevel. That's the wrong thing to do. What you have to do is lighten up and try to just take the tops off the spirals. Several light passes and you should be able to get rid of the spirals. Then it should cut better.
 

Bill Boehme

Administrator
Staff member
Beta Tester
TOTW Team
Joined
Jan 27, 2005
Messages
12,886
Likes
5,169
Location
Dalworthington Gardens, TX
Website
pbase.com
To get that huge of an oscillating pattern, my first guess is either the lathe is wobbling from not being set flat on the ground, and/or your mounting method is loose. If you can grab onto the bowl blank and wiggle it at all, then your mount is loose. If you can grab onto your lathe bed and wiggle it all, then your 4 feet are not all under equal pressure/weight. Another possibility would be you have your lathe on a joist/wood floor base, and not concrete.

robo hippy

I agree with your assessment that something is loose. Additionally, there might also be issues with tool sharpness and technique. Here are some things that I see in the picture:

newbie-mistake.jpg
  • I see a big gap between the top of the jaws and the shoulder of the tenon. This is a serious issue when it comes to getting a solid grip on the piece. As it is pictured, the piece is free to wobble no matter how much the jaws are tightened. The cause is probably due to one of the following reasons:
    • The tenon might be too long and is bottoming out before the shoulder makes contact with the top of the jaws
    • There might not be a a crisp corner between the tenon and shoulder
    • The tenon might be smaller at the end than it is at the shoulder. For the Oneway profiled jaws the tenon should be either perfectly straight or (preferably in my opinion) have a slight dovetail so that it is slightly smaller at the shoulder than it is at the end
  • I'll call it a glue block that you have between the chuck and the rough turned bowl. The main problem is gluing end grain to side grain ... that type of glue joint is very weak. If you need a glue block then use a side grain piece of wood with the direction of the grain aligned with the grain direction of the bowl blank.
  • I see a lot of grain tear out that has already been mentioned by others. My guess is that the bowl gouge is being used as a scraper so that there is no bevel contact to support the cutting edge and the tool might also be scraping above centerline so that the wood is pushing the tool back as you are pushing the tool into the wood.
  • The rough scraping marks along with the grain pecking (little bits a grain tear out) also hints that the tool is probably dull and seems to have a very rough edge. Based on my own self-taught learning experience fifteen years ago I would guess that you are holding the tool very tightly and unconsciously pushing very hard to make the tool cut. With a little more experience, you will find that you can hold the bowl gouge with your thumb and forefinger of each hand and let the lathe do all the work.
Nothing beats one-on-one instruction. There is an AAW chapter near you, the Catocin Area Turners in Leesburg. Their next meeting is on October 17 at 6:30 PM. The location is at the Leesburg Volunteer Fire Department, 215 W Loudoun St SW.
 
Joined
Oct 5, 2019
Messages
2
Likes
0
Location
Round Hill, Virginia
Thank you all for your analysis! So many good suggestions, I will put much more focus on my tenons, mounting the bowl and truing from the bottom to rim. Thanks again!
 
Joined
May 4, 2010
Messages
2,432
Likes
1,850
Location
Bozeman, MT
Eric,
You've had really good responses so far and I would encourage you to consider all of the suggestions. Al Hockenberry's list of things that can cause the bounce is spot on. Bill's visual observations are remarkably astute and his photo very clear.

This type of problem was really common for me for a while, so I know where you are. If I'm not mistaken, that looks like ash, a wood that is very prone to this problem, as are many of the harder woods. You won't get this problem with aspen or poplar.

When you've got sharp tools, properly applied, with a slow rate of advancing, when the bouncing starts, the key thing is NOT to try harder to control the tool. First, you can't do it. Second, trying will make it worse.

For now, do whatever you must to get rid of the ripples and start with a smooth surface. Then, at the first inkling that bounce is starting, stop what you're doing. Leave the tool in place, take a deep breath, relax your hands, back up just a tad to where the surface is smooth and there is no bounce, and resume at a slower speed of advance and a shallower cut without pushing the tool into the wood. Or resharpen your tool and do this.

Experienced turners leave this problem behind as they have good muscle memory and are far more relaxed in their turning than learners. Over time, you'll learn to be more sensitive to the beginning of the bounce and be able to do the counter-intuitive, Zen thing before the ripples develop. Eventually, you won't have to think about it. It just takes observation and practice.
 

Emiliano Achaval

Administrator
Staff member
Beta Tester
TOTW Team
Joined
Dec 14, 2015
Messages
3,307
Likes
4,226
Location
Maui, Hawaii
Website
hawaiiankoaturner.com
Thank you all for your analysis! So many good suggestions, I will put much more focus on my tenons, mounting the bowl and truing from the bottom to rim. Thanks again!

I would like to second to join a AAW club, go to their meetings, find a mentor, have fun!!
 
Joined
Jan 24, 2010
Messages
3,058
Likes
900
Location
Cleveland, Tennessee
Interesting question and answers. I am working up to doing some bowls with the my stash of wood...enough to build Abe a small log cabin.
Dean, my muscle memory is good. It's the rest of my memory that is lacking.:p
 

odie

TOTW Team
Joined
Dec 22, 2006
Messages
7,075
Likes
9,482
Location
Panning for Montana gold, with Betsy, the mule!
The very instant your tool begins to the "in and out" motion, you should know it's not working for you.....time to quit the cut, and evaluate. Pressing harder will not solve this.....and sometimes the problem is you were taking too aggressive a cut in the first place. The most common reason is the tool needs to be sharper, given that the tool choice and technique is good.

Note: In Bill's photo in post #7, the tearout is the result of moving the cut towards the corner. This will always cause tearout at the very edge of the corner, particularly at the end grain. This is a technique impropriety. Always start the cut at the very edge of the corner and move the cut away from the corner.....never towards it. ;)

There are times when you want to move the cut towards a corner, but the proper way to handle this is to stop the cut just short of the corner, and then resume the cut at the very edge of the corner from the opposite direction, moving the cut away from the corner......:D

-----odie-----
 
Joined
May 30, 2019
Messages
3
Likes
0
Location
Wadsworth, Ohio
I want to impress that Emiliano has very good information for you. I can relate to the many problems that I experienced over the last year. Find an AAW club and ask someone to be your mentor. I’ve found that most turners are more than eager to help you along. I was lucky enough to find a turner at the NCWT group, and have become very good friends. Also, I’ve found that learning to sharpen tools correctly is a must. Probably, the most important thing to learn is SAFETY. Hang in there, everyone started at the beginning. Don’t stop asking questions.
 
Joined
Jan 8, 2020
Messages
189
Likes
52
Location
Bloomfield, New Jersey
Look at the Stuart Batty demo video from Mid-Maryland Wood Turners (https://hooktube.com/watch?v=N7BjRcSDurM - Hooktube's a proxy for youtube. Use hooktube and say good bye to the ads). At about 26 minutes he shows how bowls end up with that wave pattern. He explains that it's riding the bevel that causes the wave pattern. If you watch the tip of the gouge closely and listen to the chirping start you'll see he's right.

I re-ground a gouge to his 40/40 idea and the turning experience was the difference between night and day. I've never gotten a better finish.

YMMV. It's worth a try, though.
 

Roger Wiegand

Beta Tester
Joined
Nov 27, 2018
Messages
789
Likes
914
Location
Wayland, MA
Website
www.carouselorgan.com
I've gotten that kind of pattern. If you rule out the kinds of problems with something loose that others have discussed I found that the solution for me was to shift how I was applying pressure to the gouge. I was pressing the bevel into the wood, which allowed it to set up a harmonic chatter as the tool bounced from relatively hard end grain to softer side grain as the piece rotated. I was coached to instead hold the tool down firmly to the toolrest and float it over the surface with vey little pressure on the bevel. Pushing down on the toolrest rather than into the cut with the gouge was an instant cure for me. Riding the bevel excessively is not your friend in this situation.

Haven't tried the Batty technique yet, but it's consistent with my experience.
 

hockenbery

Forum MVP
Beta Tester
TOTW Team
Joined
Apr 27, 2004
Messages
8,591
Likes
4,886
Location
Lakeland, Florida
Website
www.hockenberywoodturning.com
hold the tool down firmly to the toolrest and float it over the surface with vey little pressure on the bevel. Pushing down on the toolrest rather than into the cut with the gouge was an instant cure for me. Riding the bevel excessively is not your friend in this situation.

excellenf description! The tool is eager and able do all the work If we gently put it in position to succeed.
 
Back
Top