Chatter, tear out and have I really got a bowl gouge?

[LocalOak]

Hi

More questions I'm afraid, and I suspect they might be linked.

First off, I am getting some chatter and tear out on the inside of my bowls which I'm having a great deal of difficulty getting rid of. It is appearing on the inside of the bowls near the outer edge. If I understand correctly you need to use a bowl gouge to finish inside the bowl but can use a scraper nearer the middle. I have been trying to use nothing but the bowl gouge but I'm struggling with that and have resorted to the round nose scraper at times near the centre. However, I have tried both scraper and bowl gouge to eliminate the chatter and tear out, with no luck.

Here's a fairly poor photo of the problem.

[Edit, added another photo]

My next question is about the gouge I'm using. I inherited it and it is the most bowl gouge like tool in the kit but I'm not sure it is a true bowl gouge, having spent a bit of time surfing the slope. It is about 7mm across in total, with an almost square profile and a very very shallow flute. I have tried to photograph it but it's tricky, these are my best attempts.

and

and

and

I've ground it to an approximate fingernail with a shop made jig, which seems to work well, and I can cut with it. But it is tricky to control and digs in quite a lot. So my question is, is it really a bowl gouge, and if not, what is it?

I have my eye on a 3/8 superflute from Xmas, will that make my life easier?

Thanks in advance for any help.

Toby

ps. I've really got the turning bug now, and producing a bowl a night every time I get out to the shed.

 

[big soft moose]

that looks like a spindle gouge to me

 

[LocalOak]

Thanks BSM, so that means it's not going to be stable enough to prevent chatter when put over the rest and into the bowl? Makes sense to me.

Toby

 

[Bodrighy]

I go along with BSM and say it's a spindle gouge. A bowl gouge is a definite deep u shape flute. The one you have there is also fairly small dia. and once it goes past a certain distance off the rest it will vibrate which is fine for making pretty patterns but not for a smooth finish LOL. Different turners have different ways of finishing off the inside of a bowl, personally I rarely use a scraper but like to finish cutting from the rim down. Lots don't like this but I fidn that on soft wood especially it gets a really smooth finish just riding the bevel. The heavier the bowl gouge the better for me and I use a 5/8ths one on anything bigger than about 6" dia. bowls. Someone else will no doubt come along with their way of doing ti and it will work just as well for them. Try the different methods and see which works best for you. If it's a scraper fin but not with a thin spindle gouge. :lol:

Pete

 

[miles_hot]

The chatter looks like fairly significant vibration. How thin is the edge you're working on (i.e. could it be the wood vibrating - if so damp it with fingers held at the back surface). How far is the tool sticking out over the rest? I;d certainly go with Moose's view thats a spindle gouge - if that's all you've got I'd be tempted to use the scraper (which you can use anywhere on the bowl) - is there anyone near you who could lend you a bowl gouge to see if you get on better with it?

Miles

 

[CHJ]

Another for spindle gouge, but one of the problems you might be experiencing is lack of rigidity in the bowl when turning that thin, how are you hollowing, taking the full depth of the wood off in the centre? thus leaving a poorly supported rim.
As someone new to turning you may have better results only removing the central wood to 30-50 mm depth and finishing the inside surface, then take out the next 50mm and so in stages, that way the outer rim wood has maximum support.

Basically never go back to the outer rim once you have finished it, the wood will move out of round and cause all sorts of tool contact problems.

Way down the line with a lot more experience you will be able to tackle such distortion and learn when to leave well alone but for starters I would say use your abrasives to remove the chatter, as long as the finish looks good that's all that matters.

The next piece of wood may behave totally differently so there are no hard and fast rules on tool use, just some that are more likely to work in certain situations and you will find methods that you will become more comfortable using.

 

[woodturnerEric]

I have to agree with Chas,sounds like its where the bowl is thin and distorting under pressure from the gauge,also,it could be an old fashioned bowl gauge,not all bowl gauges have a deep flute,the long and strong ones look like a heavy duty spindle gauge,i have some of these myself.you do need to cut an inch or less at a time if your going thin,then finnish each section as you go,you need to make sure the bevel is rubbing to,that can cause breakout as well if it isn`t rubbing,as the gauge is at the wrong angle and only the cutting tip is touching causing loss of control and could cause a nice dig in to,I hope this might help,regards,

Eric.

 

[guyandzoe]

Those chatter marks are the result of the thin wood at the rim vibrating. The tool, or rather the pressure you exert on it makes the wood distort and spring back, a situation that gets worse and worse as the tool bevel passes over the previous poor cuts.

Sharpen the tool. Use your fingers (take CARE) to support the cut on the outside of the bowl. Using your thumb as a fulcrum for the tool on the rest and your fingers can support the bowl and (as has been said above) dampen the vibrations. Also change speed to eliminate the inherent harmonics you now produce as the bevel passes the chatter.

You'll sand for ever and not get rid of this type or marred surface. (Well, 60 grit will work but you'll end up with a smaller bowl as you watch the rim disappear).

 

[LocalOak]

Thanks very much for all the advice. The bowl vibrating makes perfect sense and I'll fiddle with my technique to avoid it. I'll also work at it in sections so not too much wood is left unsupported.

Very very helpful as always.

Thanks

Toby

 

[Oakbear]

That tool looks like a Machine Mart cheaper than cheap spindle gouge.
I have one and it's frankly dangerous!

I've kept mine until i find a use for it or a way to regrind it, but it's sat gathering dust for 2 years....

Get a reasonable bowl gouge, try again, and then see how your terchnique needs improving....

 

[robo hippy]

The chatter is the bowl rim vibrating when turning the inside. In really bad cases, this can cause your bowl to explode. You never get this vibration on the outside of the bowl as long as the inside hasn't been turned out.

I never use a scraper for finish cuts near the rim with it laying flat on the tool rest. If you have it up on its edge at a 45 degree or slightly steeper angle, it is a much more gentle cut. I do use my left hand very gently on the outside of the bowl as a steady rest, and the hand pressure must equal the tool pressure, again, very light and it will take a couple of passes to remove marks. Note here, ROUND OVER THE BOWL RIM! A sharp edge is like a razor saw and will slice you up in no time.

Another way to reduce the vibration is to turn thicker. This gives a bit more mass to dampen vibration. This does not totally solve the problem, but does help a bit.

Another way to reduce the vibration is to turn the inside in stages, especially if you are turning bigger pieces. Finish turn down an inch or so, then go down another inch or so. You will have to blend in the start of the next stage with the previous stage as wood moves/adjusts when bulk is removed, even if the wood is dry.

robo hippy