Thread: Best practice twice turned bowl

In simple terms you turn it over size. But having said that, much depends on the timber your turning and what it gets up to as it dries out, along with the way its cut out of the log. There is a plethora of ideas and methods available, but one size doesn't fit all.

In general terms you allow roughly 10% over size and thickness, this is a starting point. If in doubt leave as much as makes you happy, after all too much is better than too little. So a beefy tenon to the outside along with a liberal wall thickness, thick enough to allow you to turn a spigot/tenon to the inside. This will allow you a choice of which are to start on after drying.

My favourite drying method is to coat the outside with BLO after roughing out and place face down in a cool draught free place, for me thats on the floor at the back of the garage. If I have several roughed out then they all go in one cardboard box and then to the back of the garage.

I've tried various methods, and sometimes the timber itself determines the method.

Of late I have been turning green wood with an appreciable thickness of everything with regard to the size of the bowl. The 10% oversize as mentioned by Hughie is about where I'm at as well.

When returning to a dried green part turned blank, I use the generous tenon left on the bottom to grip and turn an expansion hold inside the bowl, I then flop it around and turn the whole of the exterior with the bowl being held by the inside of the bowl, leaving a minimal tenon on the bottom for grip.

This bowl which is finished at 195mm wide by 70mm high was done this way using Vicmarc 88mm shark jaws on a Vicmark 100 chuck.

VM90, VM100 Chuck Jaws: Shark Jaws

The same jaws are then used to hold the, in this case, quite small tenon. From there I finished off the interior with gentle cuts using sharp gouges with minimal scraper use to get the blend from bottom to the wall prior to sanding.

I've included a 5 cent piece to show the tenon, which is between 1.5mm to 2mm in depth. The jaws of the chuck are almost closed when full grip happens. Having the jaws almost closed, with approximately 1.5mm gaps left between the jaws as the jaws lock onto the tenon, ensures a near perfect and strong grip which leaves no jaw marks.

Not the only method, but one I am embracing quite a lot these days. It works well, but requires minimal to no catches as a considerable catch would likely move it in the jaws creating problems. Using larger tenons is obviously safer, but this shows what can be done.

Mick.

Chucking_001_IMG_20230613_180350_resized_20230613_060619251.jpgChucking_002_IMG_20230613_180356_resized_20230613_060617000.jpgChucking_003_IMG_20230613_180220_resized_20230613_060621174.jpg

But the real answer is keep collecting, building up the stock timber till you have a mix of dried, drying and green. I rarely turn green now due to the amount of dry timber I have on hand.

Originally Posted by hughie

But the real answer is keep collecting, building up the stock timber till you have a mix of dried, drying and green. I rarely turn green now due to the amount of dry timber I have on hand.

Yes. I much prefer the excitement of taking a blank to finished article in one sequence. The creative process seems disjointed and less satisfying when I have to set aside my vision for months before trying to capture it again. But that's probably not how others see it.

I have been working on some rough turned blanks at my Men’s Shed. Turned and in some cases cored by a member since deceased. I have been using the technique explained by Richard Raffan on his YouTube channel and described above. Use the existing tenon to hold the bowl while you turn a small temporary recess on the inside. This is done with a square scraper or skew. Then turn the bowl over the chuck and expand into the jaws into the recess. That gives complete access to the outside and allows you to true up the tenon.
There a a few problems such as getting the chuck key in while the bowl is in the way and that is helped by having shark jaws as mentioned above, which I don’t at the shed (note to self to take a better chuck tomorrow). You also need to be confident with a relatively shallow recess that can easily be removed when the inside is done.
One I did yesterday was too tight a fit over the chuck and there was no way I could get a chuck key in. I resorted to holding it between centers with the tail Centre holding against the flat section I had turned inside. It worked perfectly. It helps that these bowls are camphor laurel and easy to turn.
you can always use the between centers technique with a pad over the jaws of the chuck or something similar. In that case it helps a whole lot to leave a center mark in the middle of the tenon when you rough turn. A tiny mark with the point of a skew is perfect. I will take a couple of photos tomorrow if I remember.

Originally Posted by bruceward51

I have been working on some rough turned blanks at my Men’s Shed. Turned and in some cases cored by a member since deceased. I have been using the technique explained by Richard Raffan on his YouTube channel and described above. Use the existing tenon to hold the bowl while you turn a small temporary recess on the inside. This is done with a square scraper or skew. Then turn the bowl over the chuck and expand into the jaws into the recess. That gives complete access to the outside and allows you to true up the tenon.
There a a few problems such as getting the chuck key in while the bowl is in the way and that is helped by having shark jaws as mentioned above, which I don’t at the shed (note to self to take a better chuck tomorrow). You also need to be confident with a relatively shallow recess that can easily be removed when the inside is done.
One I did yesterday was too tight a fit over the chuck and there was no way I could get a chuck key in. I resorted to holding it between centers with the tail Centre holding against the flat section I had turned inside. It worked perfectly. It helps that these bowls are camphor laurel and easy to turn.
you can always use the between centers technique with a pad over the jaws of the chuck or something similar. In that case it helps a whole lot to leave a center mark in the middle of the tenon when you rough turn. A tiny mark with the point of a skew is perfect. I will take a couple of photos tomorrow if I remember.

Yes you will need long jaws of some sort or another. But consider this if the blank is dry, turn and finish the bowl on the outside with the foot turned to match your chuck jaws and if you are concerned for the strength of the foot run some CA around the foot where it joins the bowl and give ample time to dry and harden up. I generally wander inside for a cup of coffee, check the emails etc and back into it. I have been doing this for years and rarely have a miss hap. Also it can be a good idea depending on the bowl to support it with the steady.

Originally Posted by Gensol

Yes. I much prefer the excitement of taking a blank to finished article in one sequence. The creative process seems disjointed and less satisfying when I have to set aside my vision for months before trying to capture it again. But that's probably not how others see it.

depending on the timber , it only took me 6-8weeks for to finish the piece. Its handy if you have a moisture meter, these days they are not expensive on ebay etc. Alternately finish the outside and hold it by the foot to do the inside, see my other reply to Bruce

I'm not sure there is best practice when it comes to twice turned pieces, but here is what I currently do...

I put a tenon on the outside and a recess on the inside when I green turn.

At the 2nd turning, I remount the pre-turned piece by holding it by the inside recess. Sometimes that requires long jaws.

While 2nd turning the outside, I put a recess in the foot that will be used to hold the piece when 2nd turning the inside. I complete the outside through to and including the finish.

I remount the piece on the finished foot recess and complete the piece on the inside. I don't have to go back and do anything on the foot as that was completed when I finished the outside of the piece.

There are about as many methods of drying green turned blanks as there are turners! Try them all and see what works for you and the woods you turn.

I'm currently wrapping the pre-turned green pieces just as they are in heavy brown paper shopping bags, of which I have a supply. I periodically check and write the moisture % and the date of readings on the outside of the bags.

Photos from yesterday's session at the Geelong East Men's Shed. This is a blank that had been rough-turned by a now deceased member. In this case, the inside had been cored, but it must have been green, because it had distorted quite a lot.
I still didn't have any shark jaws and was working with 100 mm dovetail jaws on a Nova chuck.

1. I mounted the blank on the existing tenon and turned a recess at about 110 mm - the jaws I had would have been able to expand into that. If I was rough turning, I would probably have included a recess to suit jaws available.

IMG_7214.JPG

2. I turned the blank around, over the chuck. In this case, there was no way to get the normal chuck key in to expand the jaws, and the headstock was too close to allow me to get a normal hex key in as I normally would. So I just seated the chuck on the flat section of the recess and brought up the tail centre. The blank turned as true as could be expected and I had full access to finish the outside.

IMG_7215.JPG

3. Outside finished and tenon trued up ready to turn back around and finish the inside. Unfortunately I think this tenon is too small to be shaped as a foot for the bowl, to I will eventually have to turn it back around and remove this tenon. I have a few others set aside and will do them as a batch lot in a week or so, when I have completed this batch of blanks.

IMG_7216.JPG

The rest was nothing different to normal bowl work. It ended up a fairly thin wall (for me) about 8 mm. Nice piece of camphor laurel!

I have two Vicmarc chucks at home, and have a small set of shark jaws for the VM100. But I think that would be a bit small for a bowl this size, so I will probably get a larger set of shark jaws for my VM120. All I needed was a half good excuse!

This was the last pic I took, with the bowl ready for the inside work.
IMG_7217.JPG

looks like you got it well covered. This is what I use for some of my pieces Nova Long Nose Jaws - 75mm | Carbatec close its around 46-47mm so thats what I work to