Turning

Subject:
Re: tool/work piece vibrations *PIC*

John K Jordan
>>>I am making some wooden mallets and have come across a vibration issue that leaves a series of helical "ruts" in the work piece...

Doug,

What tool are you using?
Is the head of the mallet towards the tailstock or towards the headstock?
What kind of wood?

I often see helical marks like that with a skew, making a bunch of ridges if close enough together. Once it starts it's difficult to make it go away since the bevel of the skew rides on the existing. The same thing can happen with a roughing gouge, spindle gouge, or other cutting tool. I'm suspecting bevel pressure is the problem.

If the heavy part of the mallet is towards the tailstock it can be worse because of flexing, but with 1.5" diameter handle that shouldn't be a problem.

If the wood grain is not straight down the axis it

Some woods seem to be worse than others.

I turn a lot of spindles and don't use a steady rest even for very thin spindles. I do use the "left hand steady rest", holding the tool in my right hand and supporting the work lightly just behind the cut. This works incredibly well.

However, I suspect your piece is sturdy enough that flexing is not the problem.

Too much pressure with the bevel can cause the problem. I try to back off of the bevel and take lighter cuts with just the edge touching the wood. Closeups of edges in action (e.g., in Mike Darlow's book) show just a tiny bit of the bevel touching, maybe 16" or less. Don't let the heel of the bevel press against the wood. It might help to round over the heel - I always do this on gouges and do it on skews too when I remember.

If I do get the helical spiral with the skew, I remove it with a pass cutting only with the very point of the short point, starting if possible a little be. This is generally a bad technique since it curls up the fibers but it will definitely take off the spiral.

Another technique I use for thin spindles is use a well-sharpened hand scraper with a flat edge, angled a bit so only a small part is touching the wood. Slow speed, sometimes in reverse.

I have used this method many times on thin spindles, often to control vibration on very long, thin spindles (for example, tapered from 1/2" to 1/16" over a couple of feet.) It will take out the ridges of the spirals too. For a diameter such as yours I might use a bigger scraper. A file would work too to get it round again, very slow speed!

Just for fun here's a larger spindle I turned that needed several techniques - a new handle from hickory for my favorite shuffle hoe!

JKJ

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