What am I doing wrong

[Waka]

Hi Guys

I have been turning off and on for a few years but a problem has been bugging me for quite a while.
While turning a bowl I can get the outside really nice and smooth with the tools resulting in less sanding. But when it comes to the inside I seem to have a series of tool marks that I can't seem to remove even with the scrappers.

All help will be welcome.

 

[mumble]

How big/deep a bowl are you turning? As you go inside a bowl your tool extends further over the tool rest and you are more likely to get vibration.

For bowls I tend to use a Sorby "S" shaped tool rest.

I am sure others will be along to explain this better.

 

[woodbloke66]

Hi Guys

I have been turning off and on for a few years but a problem has been bugging me for quite a while.
While turning a bowl I can get the outside really nice and smooth with the tools resulting in less sanding. But when it comes to the inside I seem to have a series of tool marks that I can't seem to remove even with the scrappers.

All help will be welcome.

Flexipads are your friend; start by cutting out your own discs from Abranet sheets, beginning with 80 and finishing with 400g. I use mine with the Kirjes system which includes the motor and flexible drive. Good extraction mandatory though! - Rob

 

[CHJ]

Waka, are you trying to use Bowl Gouges with the same Front Bevel that you use on the outside on the inside?

It is often necessary to have a steeper front bevel to go across the bottom and when transiting from side to bottom to get adequate support.

Also be prepared to have a gouge with relieved bevel length so that you can maintain support without the heel of the bevel bruising the wood.

 

[Chris152]

In addition to the advice above -
I was getting marks inside and out recently and found this link helpful:
https://www.youtube.com/watch?v=qnym1IyOPgE
The bottom line for me was to keep the tool sharp and wait for it to do the cutting - don't hurry it. After watching that, I stopped using the scraper too, and find sanding out any turning lines easier than sanding out the tearout that scrapers can cause sometimes.
I should add that sheer scraping (which Jamieson talks about) can lead to catches if you're not very careful.

 

[Waka]

Guys
Thanks for the replies, my bowl was only about 3" in depth and I was using the Sorby "S" rest, but the light has come on for me. Watching the tube video has brought it all into perspective, I've been going from the inside out instead of the other way.
I have found it easier perhaps because I'm left handed, tomorrow I will tackle another bowl and see how I get on. It's true when they say a picture is worth a thousand word.
can someone answer me why you can't use a scraper going from rim to inside of the bowl?

 

[CHJ]

...
can someone answer me why you can't use a scraper going from rim to inside of the bowl?

You can, but think about it and what is happening.

If you push a round nosed scraper from the rim inwards you are presenting maximum area of cutting edge and probably going against the grain, if it is tending to catch it will only dig deeper and compound the problem.
If you drag it from the centre to the outer then you are likely to have a smaller cutting edge in contact and flowing with the grain and less likely to dig in.

If your lathe can reverse try using it in reverse for internal scraper use, it's how I do most of my undercutting internals on such as the last few pieces on my Gallery. You are not leaning over to see and can hold the scraper handle against your body for better control.
If the scraper has a fresh sharp edge and you provide adequate hand support and control, tending to use it in a trailing (negative rake) orientation you should be able to sweep it inward or outwards.

Don't use a wide edge, try with a 1/2" round nose and blend with that rather than trying to do blends with a wide curved scraper until you get better results.

If you are getting vibration or tear-out try soaking the wood in sealer or water and increase your physical control of the tool to 'shave' the cutting so that you have see-through ribbons coming off.

 

[Waka]

Thanks Chas

I'm afraid I don't have reverse on my present lathe, maybe the next one. I understand what you are saying, I've now got to put it into practice.
I'm sure I'll get there in the end.
Thanks for your help.

 

[peter-harrison]

My understanding of the reasons why it is better to cut from the outside to the middle is that the wood is travelling faster as you go out. Therefore, if you are going inwards, the wood is continually decelerating and is less likely to snatch. I think that how much you take off is more affected by the shape of the tool, and how you present it to the work.

 

[Maurizio]

An underlying difference can also be the thickness of the wood. On the outside you have the core supporting your cuts, so there is less vibration and you can be more aggressive with your tool. On the inside, any extra pressure can cause some distortion when your wall gets thin! I was down to 3mm on a nice tulip bowl last night, and took 'one more cut' with a now blunt tool and had the damn rim explode. Not a pleasant way to finish a session! Light and sharp is my new motto :lol:

 

[CHJ]

…. I was down to 3mm on a nice tulip bowl last night, and took 'one more cut' with a now blunt tool and had the damn rim explode.

You know that you should NEVER take that 'one last cut'
If going that thin I resort to working from the rim internally and finishing as far as possible as I go, removing as little of the core support as possible on each short section.
Not the best for 'perfect off the tool' finish but I don't like wrecking something and nobody knows I have had to finish the internals with a little more sanding than a purist would have you striving for.

 

[Maurizio]

You're completely right!

I'm still a complete beginner, so I'm exploring different methods for really thing turnings - I'll try your suggestion next. I'm aiming for 'purist status' but at this stage, I think I'd like more complete turnings to show people! :|

 

[CHJ]

One trick for that fine even thickness edge, as soon as you have finished shaping the outer form and faced off the front face.
Is to cut your rim profile to required thickness and a few mm deep with a parting tool.

This then gives you a visually even rim thickness regardless as to how the wood moves as your hollowing progresses, it also then provides you with a bevel reference to avoid the risk of the gouge skating outwards across the edge surface before you can get it cutting cleanly.

Does not really matter if the wall thickness is not consistent due to things going oval as you proceed with internal material removal as to a future viewer your rim is a perfectly even thickness.