Thread: Chucks

It seems to depend on a bunch of factors. Direction of grain, propensity of the wood to split, how heavy handed you are with the gouge etc.

I usually use a recess around 3-4mm deep. If you grip it around the outside it seems to work better though - turn a foot about 3mm high the right diameter for one of your jaw sets (you should get multiple sets larger than standard and/or a stepped set) and don't turn a recess at all. More wood for the chuck to grip.

One of the main factors for the chuck not gripping is that the recess or spigot youare using is not dovetailed. If you look at your chuck jaws you will notice the are dovetailed so if you create a dove tail for them to fit into you will create a better grip for the chuck. Another reason is that if you look at the chuck jaws when they are closed they form a near circle , as you open the jaws this circle becomes a square. For the best use of the jaws you only open them 5-10mm and you will still have a fair amount of the chuck jaw getting good purchase on the timber. Some have the idea that because you can expand the jaws to the full extremes of the chuck that is where they they make the foot but you are courting danger as all you need is a slight catch and off it goes cartwheeling across the floor. If you need to make a larger foot buy a larger set of jaws . You will not regret it. On most bowls and platters I prefer to work on a spigot as this is getting a better grip on the wood and less chance of the wood splitting from over tightening .

antman

I've had bowls fly off the chuck when I used to use jaws internally, much the same as you did.

Since using spigots I've yet to suffer that terrible feeling of 'it was almost finished'.

GC

Thanks everyone for their replies. I went and had a good look at the recess (what was left of it) and while I did have a dovetail cut as Jim mentioned the material inside the recess was getting in the way of the chuck jaws and they couldn't actually grip the entire edge. This would explain the side of the recess breaking away.

I also noted that the jaws were not expanded more than about 5mm. This wasn't for the reason Jim explained, it was so I could get as much as I could out of the blank. But I knew there was a real reason

For my next project I will try a spigot. Do people remove the spigot when finished? If so how do you do it and grip the job?

Thanks
Anthony

To remove the spigot and depending on the shape of the top of your bowl you can use the cole jaws {nova} or bowl jaws {vicmarc} to hold the bowl by either removing the complete spigot or reshaping the spigot to create a foot to stand on.
If this is not an option then you have to form a jam fit chuck on mdf and fit the bowl to this with the added support of your tailstock and and ease the spigot of or reshape .
Remember that the bowl is almost finished so take care and do not be in a hurry .

Anthony, if you are using a Vicmarc chuck you might want to invest in a set of step jaws ( about $50) , these will allow you to have a spigot which can be left as a foot. The foot can be decorated and finished, then used to grip the bowl with to finish the inside. If you are accurate with the measurement of the foot these jaws will not leave marks. The jaws were designed by Richard Raffan for making boxes.
Cheers
Barry

Antman

This doesn't answer any of the issues you raised, but it's an interesting story about chucks. Like some of the respondents to this post, I have had bowls fly off the chuck, but usually with no real harm done. But it doesn't always happen that way!

Recently I was doing a fruit bowl at the request of a friend. I hade made it out of maple and had finished it. It was about 45cm diameter and 25cm deep made out of a well figured piece of maple. Wall thickness was about 3mm on the sides with a base about double that.

I was polishing it on the lathe and had a recess turned into the bottom. It was held in a bonham chuck in expansion mode.

I kept getting some dull streaks in the polish and couldn't quite get it right. It was probably at a standard that I could have stopped then, but I wanted to get a perfect finish. So I decided to speed the lathe up and see if I could polish out the streaks.

I changed the belts to 2000 rpm and, as is my practice, stood to the side as I turned the lathe on. The results were spectacular. Pretty much as soon as the lathe reached top speed (about half a second) the bowl disappeared with a BOOM! Literally...it just disappeared before my eyes. I figured out later that the bowl had left the lathe and hit the edghe of the bed smashing it into about twenty pieces and flinging pieces to the walls and ceiling in all directions along the plane of rotation.

Just imagine trying to smash a wooden bowl (of any dimensions) into twenty pieces with a single blow of a hammer. It starts to give you some idea of the forces created in woodturning.

It also gives you an idea of the importance of safely chucking the work!

Regards

Jacko

This is an example of why a spigot works better as you can apply more pressure on the foot and not worry about it flying of. With the recess you may have had some of your finish in the recess and with the extra speed it has skidded in the chuck and the next result is 20 peices of scrap. Another consideration is that you are going just a bit too fast for the timber, some will let you get away with fast speed and some dont. Each peice is different.

Thanks Jim. You're right about each piece being different. The trick is to know the foibles of the piece on the lathe at the moment and that comes with experience. You don't know where I can buy a batch do you?