Cause of banding on insides of bowls?

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wabbitpoo

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My biggest current problem at the moment is getting a smooth finish on the inside of bowls. What I get a lot of is a series of ridges (or furrows, actually) created as my bowl gouge traverses to the centre. Once I have them the gouge tends to then follow them on the next pass. Am I pushing too hard? I do recall reading somewhere some time ago that easing the bevel can help. Advice please! Its driving me nuts!
 
This is due to the length of the bevel and the curvature you are following. You can improve the situation by shortening the bevel or grinding the heal off the gouge. I have 2 or 3 gouges where the heal is ground away to reduce the bevel length to 3 or 4mm
 
Make sure you aren't too far over the rest as well as that can cause bounce and chatter. OK if you want a pretty design but not good for smooth surfaces.

Pete
 
Once you have the shape you want on the inside ,

you can then use a round nose scraper to tidy the inside if the bowl ready for sanding
 
You could try a spindle gouge if the bowl isn't too deep. There are lots of turorials on youtube for bowl making.
 
Two things may be going on.I'm not sure which from your description.

Firstly as has been said you may be having trouble with your bevel lifting off. This will give series humps and bumps in the bottom of the bowl as you try to get a flat without bevel support. The humps and bumps will be irregular interuptions in the curve you are seeking. Recutting while pressing harder will make the tool follow and accentuate these ridges. Relax your backhand, seek bevel control and cut through the ridges and over the dips.

Secondly you may be experiencing what I might describe as a 'resonance' as the tool bounces over end and side grain. As you get to the bottom of the bowl your tool is more and more presented in direct opposition to end grain. This can cause a sort of chatter which results in spirals at the base and centre of the bowl. Again relax the back hand and try to cut through. If that fails lower the lathe speed so you dont hit that same resonant screw cutting effect and go again. If that fails try speeding up the lathe to seek the same effect.

This might also be tool chatter but I think you'd soon recognise that and be able to counter it quite easily.
 
gnu":2nnv4d5l said:
You could try a spindle gouge if the bowl isn't too deep. There are lots of turorials on youtube for bowl making.

True ..... but

It sounds like the OP is finding their way with turning. I would caution against trying this for a couple of reasons:

Unless the bowl is v.shallow it is asking a lot of a spindle gouge, esp given the OP has an issue with bowl gouge results so the additional lack of rigidity could compound the issue.

Spindle gouge primary grinds tend to be shallower than bowl gouges making a much more aggressive tool - again perhaps not welcome for the OP.

I don't mean to dismiss your suggestion out of hand but the OP may wish to go down this route with a little caution given the current problems.


BRgds
S
 
These are a selection of bowl gouge profiles,
to give you food for thought. Deep flute, acute bevel will make it much easier.
You try it.



John. B
 
I use the 'E' profile for everything, perhaps a bit steeper bevel and ground with a slight hamster cheek rather than very steep sides to give a variable bevel angle around the gouge to make life easier inside deep bowls when you need a back-cut to help you out.
 
Profile d is ideal for the bottoms of bowls as you can run the bevel along the bottom getting a good finish with less chance of a catch. Using a fingernail on the bottom can be prone to nasty ones IME

Pete
 
Pete how do you shape your bevels with a long grind? I ask because I have never had a catch in the bottom of a bowl with a long ground gouge. Indeed the idea of the long grind is to avoid catches; the wings are ground out of the way for this reason.

I know some turners grind the long grind bevel very steeply around the corner and this can cause trouble with control - one goes from safe with good bevel control to an 'instant' situation where the gouge is full of wood all along the wing - BANG!!

If one grinds with a good hamster cheek this will not happen.

I have not yet found a situation where I would need a gouge with a short steep bevel. And I make hundreds of bowls of all shapes and sizes each year. I know they are recommended by many but I always end up asking 'Why?'.
 
I have two bowl gouges that I use mainly, one is ground back with a long cutting edge like the E profile though maybe steeper (going to have a go with Glenn's double bevel for this one), this, if presented to cut down the side of the bowl and not turned as you go round the corner of the bottom presents a very aggressive cutting edge that can catch dramatically rendering a thinner bowl necessary :lol: I use this for the sides down to the turn in the bottom then transfer to a gouge that is ground at about 60 degrees sand can keep the bevel all along the bottom. I use it for platters as well. I know some use scrapers and shear cut but I seldom do.

Pete
 
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