Diagnostic help with turning results

[Gary]

I've posted 4 photos in the galary; they are closeups of a bowl (dish) that I turned. The pictures show grain damage. Is this a result of a problem with the wood or with tools that are not sharp; or with technique.

Any help or comments will be appreciated.

Thanks

Gary

 

[Ken Grunke]

I'd say it's grain tearout from using dull tools and/or a cut that's too heavy--did you use a gouge, or a scraper?
If a gouge, are you presenting the cutting edge at an angle to give a shearing action?
Looks like Elm, which doesn't "catch the edge" as easily as most other woods--it takes more force to get a cut started, in my experience.

Ken

 

[C Edward Moore]

Gary,
First, I applaud your willingness to ask the question. It's like a friend of mine who just had a serious tablesaw accident. He called last night and he wants me to come over so he can do an accident reconstruction. I agreed, provided me he doesn't show me the wound, just a diagram of it.

Second, I think that Ken is right. Sometimes it isn't just one thing and it may be a combination of the two suggestions, sharpness and presentation. What kind of tool were you using, how is it ground, how did you present it to the wood?

It looks as if the tool was presented so that the cutting edge was horizontal. or parallel to the tool rest. If it had been at a 45 degree (approximate) angle, then the tearout might have been reduced or eliminated.

 

[Mike Schwing]

Gary, if you have any familiarity with handplanes, this example may help you understand what is probably happening.

Run a handplane straight down the grain on a piece of flat lumber. If you're moving it with the grain, it'll cut nicely with no tearout or bruising. Think of that plane's iron as your gouge cutting edge. Now reverse that piece of lumber and go "up the grain", you may encounter some tearout, or it won't plane as smoothly. Next, skew that plane as to present the cutting edge of the iron at an angle to the wood, and run it straight down the workpiece. It'll shear those fibers off more cleanly rather than lift them up and tear them off. If you now move that concept over to the gouge and approach the workpiece with the cutting edge at a shearing angle, the results will be similar.

The more sharp your cutting edge, the less likely tearout will occur, but its nearly always, on good stable lumber, a result of tearing that grain out rather than cutting it cleanly. That can be caused by presentation angle, dull tools, or a combination of both. Most all lumber I've worked with can be cut cleanly with proper technique. The exception might be punky or spalted wood, and some woods are more prone to tearout than others. Butternut for example - difficult, so is willow.

Some say that faster spindle speeds are better, but I always, always, have better results with tearout issues with slow lathe speeds. My final shearing cuts are done at 100rpm or less normally.

You can also treat the tearout areas in some cases to stiffen the fibers up so they cut sharply. Sometimes an application of walnut oil will do the trick. Sometimes it takes sanding sealer. Even yellow glue will do the trick. I generally prefer a lacquer based sanding sealer as it dries quickly and doesn't get sucked into the work as deeply - which could give you troubles when applying a finish.

Hope this helps some.

 

[Steve Worcester]

I will tackle this from the angle of using a bowl gouge.
This tear out on the end grain is a very common problem. Even though the bowls orientation is side grain, (where the grain runs perpendicular to the lathe bed) , as it rotates the wood changes grain orientation. It goes from side to end to side to end, etc. That said, with the end grain you do not get the same support on the cut. As you cut it actually pulls up fibers of the wood and causes tear out.
You can minimize this tear out by making sure your tool is sharp and rubbing the bevel. If you were to engage the tool tip without the bevel, it will definately tear out.
An alternative to this is to take finishing cuts with a fingernail ground gouge, as David Ellsworth shows in his video on using the fingernail ground gouge. Essentially, the gouge is presented with the open portion of the flute facing up and a small portion of the front left part of the gouge makes a very fine shear cut. Mush easier to watch than explain.

 

[Gary]

Thankyou

Thank you all for the comments and suggestions.

I had used both a gouge and a scraper;

That bowl was turned at the lathes slowest speed (450 rpm) from a blank cut from a log that was about 3 months old; don't know what kind of wood it is
but is sure dulls a scraper fast.

I recently obtained a Wolverine sharpening jig and have viewed the oneway videos about using it. I'm getting the tools sharper than before I got the wolverine, but I'm still not satisfied. Think some web surfing for articles on sharpening is in order.