Some adivce

[colinhart]

Jolly Good evening to all turners more experienced that I (thank is likely to be everyone)

I have a query and wounder if anyone would be able to shed any light on my frustration..

I am new to turning (since December), and have be working trying to perfect the bowl. My query is as follows:

I rough turn the bowl, turn the outside and sand / finish (this bit I am ok with).
I then start to turn the inside, and all starts off fine. As I continue to hollow the bow and make the walls thinner, it goes from cutting evenly to a loud "screeching" noise and seams to have lost its shape, I seem to never to be able to recover it.

I am hoping this is a newbie issue that simple advice can overcome?

Thank you for reading, thank you even more if you can give me some direction?

Kinds regards

Colin.

 

[finneyb]

Colin

Try going to Cambridge Woodturners meeting http://www.cambridge-woodturners.co.uk/profile.htm .
Next meeting is 2 July - Brains Trust
I don't know Cambridge Woodturners, but suspect you will get lots of help with this problem and many others in the future.

HTH

Brian

 

[colinhart]

Cheers Brian,

As it happens I am going along already...

Regards

Colin.

 

[Castanea]

Hi Colin,
Others may correct me - I'm a more experienced turner, but not by much!
I think the screeching noise you are hearing is vibration - mostly of the tool.
There a number of possible causes. The further the tool stretches over the toolrest the more it will vibrate so try to get the tool rest to reach as close to the cutting edge as is practicable and safe. The narrower the tool is the more it will vibrate (hence the massively chunky bowl gouges and scrapers you sometims see) so is your bowl gouge hefty enough for what you're trying to do? A blunt tool is more likely to vibrate (instead of cutting cleanly) than a sharp tool and (closely related to that point) if you are pushing too hard that can also cause vibration. If you are not turning the tool in the most efficient angle to cut that can also cause it to vibrate because it's being pushed against the wood and isn't cutting into it properly. Finally if you try to get the wall of the bowl too thin it may start to flex and wobble and everything will start to vibrate!
I'd suggesting looking up Lyle Jamieson on YouTube - his bowl turning is second to none (although he can be a bit oppinionated at times - his way is good but it's not the only way!) I do like his down to earth explanation of how the tool is cutting and whenever something isn't working for me I tend to turn the lathe off and try to analyse what the tiny part of the tool I'm trying to cut with is actually doing and why that's not coming up with the goods.
There's nothing better than having someone show you, watch you and guide you though so a trip to Cambridge Woodturners might be your best bet. It might be worth taking the tool you are using along too - sharpenning is often half the battle with turning so if people can help to get that side sorted the rest tends to fall into place much more easily!

 

[Random Orbital Bob]

Jolly Good evening to all turners more experienced that I (thank is likely to be everyone)

I have a query and wounder if anyone would be able to shed any light on my frustration..

I am new to turning (since December), and have be working trying to perfect the bowl. My query is as follows:

I rough turn the bowl, turn the outside and sand / finish (this bit I am ok with).
I then start to turn the inside, and all starts off fine. As I continue to hollow the bow and make the walls thinner, it goes from cutting evenly to a loud "screeching" noise and seams to have lost its shape, I seem to never to be able to recover it.

I am hoping this is a newbie issue that simple advice can overcome?

Thank you for reading, thank you even more if you can give me some direction?

Kinds regards

Colin.

Where in the bowl is the tool when the screeching noise is heard? Is it near the rim or closer to the transition between wall and base?
What size gouge and what type of grind are we talking about?
I'm assuming the bowls are being turned green by the sounds of the shape change, is this true?
Typically how deep are the bowls?
Where is your toolrest positioned when its happening?
How are you sharpening your gouge and I'm assuming it's a deep fluted gouge, is this correct?
How thin are the walls when the sound first appears?
What speed is the lathe running at (roughly) and whats the diameter of the typical bowl?

 

[colinhart]

Thank you all for your replies, I'll take some photo's and try to explain as best I can.

Sadly time to go to work, suite and wood laithe not the best combination.

Regards

Colin

 

[paulm]

As others have mentioned/asked, there could be a number of things going on and some more information would help figure out how to help

In the meantime I would suggest completing the inside wall of the bowl an inch or so at a time and trying not to go back to that completed area again with the tools. What I suspect is happening is that the wall thickness is being reduced too much and you are still going back over it with the gouge, or scaper, when thin, causing the bowl wall to flex out of shape slightly and/or vibratein the process, which will make the horrible screeching noise and also create the out of round effect with uneven thickness of wall.

That can also be worsened by blunt tools, excessive overhang over the rest, too much pressure, green timber, some kinds of timber that flex naturally even if seasoned like willow, etc.

So sharp tools, light cuts as you get near finished thickness, and reduce the inside of the wall in stages down to the bottom so that the rest of the bowl provides support to the thinner areas and they don't flex/vibrate so much would be things to try next ?

Cheers, Paul

 

[Paul Hannaby]

The usual cause for the screeching is too much pressure of the tool against the wood as the bowl gets thinner. The only pressure you should be applying to the tool is downwards against the rest. What most people do initially is to tense up in an attempt to prevent the problem and that usually makes the problem worse so try to relax and let the tool cut without pushing it against the wood.

It goes without saying that the tool should be as sharp as you can make it.