Seasoned oak turning question

[Steve Blackdog]

I have been having difficulties turning a bowl from a lump of seasoned oak.

There are a few knots in the oak and I'm finding it hard to stop the bowl gouge from bouncing.

Any tips? Should I change the speed - I'm taking it pretty slow.

Could it be my tool isn't kept sharp enough?

Should I be taking smaller cuts?

All thoughts welcome.

Cheers

Steve

 

[Paul Hannaby]

Hi Steve,
If you can increase the speed safely without causing undue vibration the yes, that should help prevent the tool bouncing.

I don't know if sharpness is also contributing to your problem but my approach when I find a piece of wood isn't cutting well is to sharpen the tool to see if that makes a difference before anything else.

The change in grain direction when you cut the knot can make life a little more difficult and a sharp tool, light cuts and the correct speed will all help.

 

[CHJ]

One aspect that can accentuate 'bounce' or propagate it is to press too hard on the bevel contact, especially at low speeds.

A good many times the 'bounce' is due to the slight give in your holding fingers, flesh is not rigid.

At slower speeds any tendency to reduce the depth of cut with a harder patch results in the tool lifting slightly away from the piece with the give in your fingers, as soon as it passes the hard portion your pressure dives it back into the wood.
This creates a 'bump', every rotation thereafter the 'bump' exaggerates.

Increasing the speed reduces the time the tool has to react against the spring in your fingers, a bit like driving a car over badly rutted roads, you speed up until the suspension does not have time to react and the ride smooths out.

So try highest speed that you feel safe with, sharp tools, and only enough bevel pressure to guide the tool, ** don't try to push it harder against the wood, that will be counter productive.

**All the forgoing has been covered by Paul, just my different wording.

 

[Steve Blackdog]

Chaz and Paul

Many thanks for your very helpful replies. Speeding up is counter intuitive when the piece starts to feel out of balance, but now you explain it so well, it all makes good sense.

Best wishes
Steve

 

[Jonzjob]

+1 for Chas' explanation. The higher speed the less chance for the gouge to bounce! Sharpe tools cut better too.. :mrgreen:

 

[nev]

without wishing to hijack the thread, but along similar lines -
if my tool gets quite warm when turning (oak) am i doing something wrong? too much pressure on the bevel? not sharp enough? (though i do try). i haven't noticed it happening with other woods :?

 

[CHJ]

without wishing to hijack the thread, but along similar lines -
if my tool gets quite warm when turning (oak) am i doing something wrong? too much pressure on the bevel? not sharp enough? (though i do try). i haven't noticed it happening with other woods :?

Although the sharper the tool the less heat you would expect to create from friction, in real life I doubt there is sufficient reduction to be able to tell the difference in regard to a blunt tool.

Yes turning tools do get hot, not unknown to be too hot to touch near the working end, even wood shavings leaving the tool can be too hot to stand when hitting the hand, therefore the tool itself must be similar in temperature.

Polishing (burnishing) the flutes of gouges can help with reducing the friction heat.

Am surprised it is only on Oak that you have noticed it.

 

[myturn]

Although as said above the sharpness itself is not likely to be the cause of generating additional heat the fact that the tool may be blunt will cause you to tend to push harder against the wood in an attempt to cut and that WILL cause more heat.

So will using too fast a speed.

Overheating the wood will cause it to distort unevenly and also develop stress cracks, some woods are more prone to this than others. Even the friction from hard sanding will cause yew to crack.