Finishing larger bowls turned with headstock rotated

[harvestbarn]

When you turn a bowl larger than the lathes bed capacity how is it best to finish the base?

I could make an oversize button jaw set out of plywood and is it likly to be suitable. I see Axminster sell 400mm jaws but they are fairly expensive for infrequent use.

 

[Dalboy]

Either that or a doughnut chuck which would be a safer option as it holds the piece much better

 

[selectortone]

The re-mounting jaws I made will only take bowls up to about 10". When I turn bowls larger than that I finish the foot while turning the outside of the bowl. I make an expansion recess and make it to the optimum diameter for my chuck's jaws (in my case Type "A" Axminster jaws expanding into a 100mm recess) and finish the foot completely before turning the inside. Provided the recess takes the jaws at their optimum expansion (so that maximum contact is made) and you don't go mad tightening them so that you seriously mark the inside of the recess, it works a treat. Any small marks can be sanded off by hand. I've done several bowls like this and am 100% happy with the result. (Not 100% happy with the my turning, just the method! )

Here's a 13-inch walnut bowl I did a while a go:

 

[nev]

As Selectortone says, Turn the base to fit your chuck, finish the bottom and even apply finish to the base or whole underside whilst the lump is mounted on the face plate. Then reverse and complete. If you want a 'no mounting visible' base then go for the donut chuck.
http://philroybal.com/MainPages/Article ... chuck.html

Tip: Mark concentric circles every few mill on your donut base, it makes centre-ing your bowl a lot quicker.

 

[Dalboy]

If you use a tenon or recess and leave it on the only people that will know or even frown upon it will be woodturners. Most of the bowls I sell are to none woodtuning people. Even though that is true I still like to loose the chucking points for my own satisfaction.
If you have larger jaws you can make a tenon which is only 1/8" deep and do so that you have a maximum grip on it so the jaws are gripping the complete circumfrence. once turned to do the inside as long as you take quite light cuts you should not have any problems.
The bowl below has a 3 1/2" foot which is a fraction under the 1/8" deep I held the bowl with that to turn the top and bowl section.

 

[duncanh]

I use a vacuum chuck. I also have a homemade donut chuck but I can't remember the last time I used it.

 

[KimG]

I use a large disc of ply wood that has a recess for mounting on expanding jaws, place some paper against the ply and the bowl against that and bring the tailstock up to support it, it is important when you make the initial base of the bowl to mark the centre somehow, I use a fine gouge and cut a tiny cone, the allows for easy centering of the tailstock when it comes to the plywood stage. turn the base off fairly slowly, sand and finish either on the lathe (at least the major part) or off, I take it off and use a morse taper chuck to hold a sanding disk and work through the grits then apply whatever finish is appropriate.

 

[harvestbarn]

Thanks all who responded that was very interesting.

I also have a similar method to that suggested by KimG a plywood disk was made with a mounting ring which fits into my chuck the front surface had a woven door mat glued to it and cut to suit. This works very well although not as versatile on bowls as a button chuck and cannot be used when the tailstock is not available.

 

[heronviewer]

I use a set of Cole jaws made to Alan Stratton's design, mounted in a Sorby Patriot chuck.

http://www.aswoodturns.com/2014/06/homemade-cole-jaws/

I used 9 ply birch ply and it works well. I use it for recutting the mounting of bowls that have been rough turned green and have distorted as well as for the finishing off of the bottom. Wedges help to get the bowl aligned and thin ply holds it all down. No tail stock possible or needed.

I know there have been comments on the safety of this and I don't stand in the line of the disc.

The photograph is of a distorted bowl before recutting the dovetail.

 

[CHJ]

I know there have been comments on the safety of this and I don't stand in the line of the disc.
...

I personally don't see a safety problem with your approach in your hands, you are aware of the risks and take suitable precautions and appropriate cutting loads.

There is always a risk that someone new to turning may do something stupid with similar setup, but like sticking fingers and abrasive into bored holes someone somewhere is going to do it once in a lifetime at least.

I'm afraid I don't bother to make neat clamping pieces anymore, I just rough cut and drill an odd piece of scrap to suit, anything deemed to be at risk of moving or flying off gets a quick dab of Hot Melt and the scraps get consigned to the trash can glue debris and all when finished.

 

[Deejay]

Afternoon Heronviewer.

Thanks for the link.

I like the plastic tubing idea. I use dowel wrapped with a turn of double sided tape at the moment. I'm just off to shorten the garden hose.

Cheers

Dave

 

[heronviewer]

I got a metre of ¾" ID reinforced polythene tubing from ebay for that part - it is smooth on the outside and is quite soft. Doesn't mark the bowl, even a finished one, so far. I suppose the shape of the rim of the bowl helps it to grip well. Not sure about the garden hose - won't it be rather hard ?

 

[Deejay]

Hello Robert

I only use the minimum possible pressure to hold a reversed bowl, so I don't think garden hose would be too hard.

However, the ID is about 12 mm so the walls of the 'pegs' would only be about 3 mm thick. I think a bigger hose would be better.

Cheers

Dave