What causes the tool marks in bowl turning, specifically in the end grain part of a bowl: the parts that come around twice each rotation. To be clear the face grain is perpendicular to axis of lathe. The tools cause it I know, but ways to avoid? Final Cut is a push cut with a 5/8 bowl gouge, plenty sharp I think but could be wrong.
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Tool marks on end grain
- Thread starter Paul Durden
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Practice, practice, and more practice is pretty much the solution - You're most likely getting burnishing tool marks which are caused by actually rubbing the bevel as you cut - In reality, one should FLOAT the bevel (Bevel barely touches wood, so softly that the wood doesn't know it) and achieving that does take rather a bit of practice (as well as sharp tools - If you can't start and continue a cut without pushing edge into wood, the tool ain't sharp enough.... should be able to rotate wood by hand and touch edge to wood with other hand, following bevel, and it should slice cleanly with little to no effort involved - that kind of sharp...)
I’ve ran into something similar to this, but I use carbide tools.
The speed you use and the “touch” you have seems to make all the difference!
The speed you use and the “touch” you have seems to make all the difference!
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I assume you are referring to the back side of the endgrain
This is tearout from a tiny bit of unsupported cut fibers.
Sharp tools, high shear angle, light cuts all help to reduce this.
As the end grain comes around the first 1/2 has long fibers behind supporting a clean cut.
The next part of the endgrain has shorter fibers behind making the area prone to tearout
This may help to show what I described
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A very sharp, smaller bowl gouge will help. I use a 3/8" Ellsworth grind for finishing cuts. Sometimes a 1/2", but almost never with my 5/8".
A freshly sharpened bowl gouge and a push cut from the rim to the bottom kissing the bevel. As soon as you lift the bevel off you get tear out. For me size of gouge doesn’t matter.
I had a mentoring day with one of our guild members yesterday. It is indeed tear out from endgrain. it can be resolved with a sharp, really sharp bowl gouge. My bowl gouge was only sharp until I compared it to his. Better if resolved before sanding.
I usually use my bowl gouges straight off a 180 grit CBN wheel, but if I'm having trouble with a clean finish cut, I've found that honing the edge can help. I use a small superfine diamond/ceramic hone from Eze-Lap (model CD4).
Any time you are cutting against/into unsupported end grain, like on the bowl, you will get tear out. Some woods are better at having less, mostly denser woods, and some woods, mostly softer ones, are horrible like cotton wood. Some times polishing/stropping the flutes after sharpening helps, some times a higher grit CBN wheel helps, some times you just have to resort to the 80 grit gouge/abrasives. I have not yet taken one of my tools and sharpened them to the level of my bench chisels or plane irons. Some day....
robo hippy
robo hippy
Yup ,its kinda horses for courses. Lol, I often suggest that beginners use Pinus Radiata to learn. The promise is if you master this pine you will be a master of not only technique but also of sharpening.
Dave Landers
Beta Tester
The other thing I do is try different gouges and/or different presentation of a gouge. Sometimes, a piece will respond well to a shear cut, other times not. Sometimes it wants a push cut. Sometimes it's a 40º gouge. Sometimes a negative rake scraper. But always light cuts with a sharp tool.
I will go over a problem area with light experimental cuts until I find the gouge/presentation that yields a surface I'm happy with. And especially with problem wood, it's not always the same for the entire piece.
In the meean time, while you work on your “no tool marks” skills, shear scraping with a scraper or long wing bowl gouge can clean them up. Try shear scraping moving in both directions and observe which direction works best for the current wood. Also, hand cabinet scrapers (lathe off) can do a nice cleanup as well.