Looking at Involuted/Inside Out Turning

Looking at Involuted/Inside Out Turning:
Richard Findley takes a look at involuted turning for the first time.

Involuted turning, or inside-out turning as it is otherwise known, is an interesting two-stage turning technique, which produces a turned design with a hollowed out centre and an opening in the side of the item. Internet searches bring up a huge amount of examples of candle sticks, lamps, fun Christmas tree decorations, artistic pieces and even furniture with involuted legs.
As with all of my articles in this series I’m exploring a technique that is new to me so my first step is a little research into the subject. While the examples I see on the internet are fascinating, nothing really jumps out at me. I flick through some of my books and in Mike Darlow’s Woodturning Methods, I spot an apple with an apple-shaped cut out on its side. This immediately appeals to me as turned fruit is something I am often commissioned to make and regularly demonstrate to clubs. The example in Mike’s book is on a pedestal, but I decide to focus purely on the apple. The book also gives detailed explanations and pictures of the technique, which is a great help to a first-timer like myself. With Mike’s kind permission I decide to give it a try.

The plan
My intention is to turn an apple, roughly life-sized with an apple shaped cut out, or window, in the side. On my way through the project, I will take my guidance of the techniques from Mike’s book and, as usual, use my own woodturning experiences to help fill in any gaps. 

The theory
Involuting involves starting with four equal sized sections of timber that make up quadrants of the final piece. They are temporarily fastened together while the inner portion of the design is turned. The quadrants are then rotated and refastened together, this time permanently, for the outer shape to be turned revealing a negative space formed in the first turning operation. In my case the inner shape is
a stylised silhouette of an apple with the outer shape also being that of an apple. I have some pretty comprehensive instructions and photographs to follow from Mike’s book so it should be pretty straightforward, but we shall see!

Timber selection
Apples are a great way of showing off exotic or interesting timbers, being only relatively small but of a shape that really presents the timber well, but even relatively plain timbers will look good turned as apples and displayed in a wooden bowl with a selection of other turned wooden fruit. Because this is involuted, the section of timber I need is actually smaller than that needed for a normal apple, as it’s made up of four sections or quadrants, rather than a single blank. I had a look through my various timber piles and found a piece of American black walnut which would fit the bill. I selected walnut for several reasons, firstly I love it; its deep chocolate brown colour is just beautiful under oil. Secondly, the darker material should hide the glue lines that are inevitable in an involuted project and thirdly, it is an off cut from another job and I like to put offcuts to a good use.

Preparation
My research suggests that careful preparation is going to be key to the success of this project. My first job is to rip the timber into a strip and plane it square and accurately to size on my planer-thicknesser. The 40mm walnut has finished at 34mm square, which will give me a 68mm apple, slightly smaller than I usually make, but still within the realms of a realistic apple size. I usually make my apples around 5mm shorter in height than the diameter so I need 63mm for the apple plus a good bit of waste at each end to allow for my temporary fixings that I will use for the first stage of turning. I decide that around 75mm at each end would be enough plus the material I need for the apple so I cut my quadrants into 220mm lengths.
I closely study the timber and chose the best faces. Both for the interesting figure and for a grain pattern that looks like it will work as a finished item and appear as natural as possible. As all of the quadrants are from the same board this isn’t too difficult, but it is surprising how much variation you can get over a metre or so of timber. To make sure I can easily identify which way round the quadrants should be positioned, I make some marks on the ends. Initially I drew a square around the joining corners, which will be the final position of the timber. I then rotate each piece by 180° and drew a circle on the joining corners, which is the position for the first turning process. 

First fixing
Now I have identified how the walnut quadrants will be positioned I need to join them together ready for the first turning. There’s a few options available to me here, Mike uses nuts and bolts in his book, which are effective, but I am not comfortable with chunks of metal sticking out of the wood while it spins at high speed. I have seen various other methods used in books and on the internet, all of which have their pros and cons, but I decide that the best option is to use screws to fasten it all together while I turn the first part of the job.
To ensure everything is perfectly lined up and ready for the screws to be fitted I use G-cramps to hold the timber securely in place before pilot boring and driving in eight 50mm, No.10 screws. Having three hands would have made this operation a lot more straightforward, but after much fiddling and adjusting, the cramps were fitted and with the timber held in just the right position so I could then drive the screws in. Now that the screws are securely in place, the cramps can be removed.   

Turning the inside 
This is the part that holds the most mystery to me. I know the shape I need, but how deep do I need to cut to achieve the effect I want? The one thing that is clear from the pictures in Mike’s book is the inside needs
to be turned down to a full circle with no flats. To help me visualise this properly I decided to make a full-sized drawing. This immediately helps me to see the size of the cut out and to position it compared to the apple, although the final position isn’t set until I turn the outside of the apple. 

First fixing options – pros and cons
Nuts and bolts
Pros – Secure fixing with some small amount of adjustment
Cons – Large chunks of metal spinning at high speed are nerve racking at best, dangerous at worst
Glue and paper joint
Pros – Tried and tested method, both secure and easy to separate
Cons – Potentially difficult to line joins up accurately. Need to allow glue to dry overnight
Cable ties
Pros – Easy to do
Cons – Possibility of  timber slipping
Screws
Pros – Secure, easy and safe
Cons – Fiddly to fix initially

I decide to cut out the small apple and use this as a template to mark its shape on my walnut blank. I am unsure if this will be much help because as I draw the shape onto the wood, I suspect that I will need to cut much deeper than this. 

Finally, I can get the wood onto the lathe, mounted between centres and begin to form the apple-shaped cut out. Being unsure as to exactly how this should look, my only option is to stop the lathe frequently and keep checking the progress of my cuts. The cut out in my paper template is a real help in achieving the ideal shape and, once I get it all fully round, it is just a case of gradually forming the negative curve of the apple shape. The trickiest part is the undercut, which forms the top curve of the apple cut out, but I manage to cut the curve without incident. With the shape turned to my liking I can sand. Despite only needing to sand for a few minutes, I manage to bang my fingers on the spinning corners several times so I can’t emphasise enough the need for caution here. This makes me glad I didn’t choose to use nuts and bolts as the damage they can cause to fingers doesn’t bear thinking about!
Before moving on to the next phase I lay my square against the edge of the timber to check how the cut out looks. I am happy with it, although I still find it hard to visualise if it will look exactly how I would like it to in the final piece.

Glue-up
The first stage fixing needs to be reversible so the screws were ideal, but the second stage needs to be permanent so this time I use glue. To get everything perfectly lined up I once again use G-cramps to pinch the timbers together while I pilot drill new holes and drive in screws to hold it while the glue dries. As soon as the screws are in, the cramps can be removed. Initially I just glue up two pairs of the quadrants then pass my sharp hand plane over them to make sure they are flat and true before gluing, cramping and screwing the two halves together to form the complete block. I wipe the excess glue squeeze-out away with a wet cloth as best I can, despite my care in spreading the glue, some still manages to get where I don’t really want it! I leave the block to one side to fully dry over night, pleased with how the apple shaped cut out looks.

The outside
With the glue dry the screws have done their job and can be removed. I mount the blank between centres and get it roughed to round, keen to see how the cut out looks in the round. I am pleased to see the join lines are all good, tight and the apple shape, although clearly stylised, is easily recognisable as an apple. It occurs to me that, although I usually aim for realism with the shape of my apples, I’m not going to be able to fully achieve this with this apple because of the open space in the centre. I’m going to do my best to get it as realistic as possible with the restrictions that the cut out gives me, but it is likely to end up slightly stylised like the apple in the cut out.
One of the restrictions that the cut out puts upon me is that I can’t use a screw chuck as I normally would, partly because the screw is likely to protrude into the opening and partly because the screw is likely to put undue pressure on the joint and could ruin the whole job so I decide to form a spigot at the base end and work from there.

The stalk is an area that I can’t quite make up my mind about. Normally I turn a stalk, which looks quite natural, but I wonder if a stylised stalk that better matches the one in the cut out would work better here so I give it a go, aware that if I don’t like it I can cut it off and go with one of my usual stalks. I begin shaping the upper curve of the apple and the stylised stalk trying to keep the balance between them as the shapes develop. Just as I begin taking the stalk to somewhere near the thickness it needs to be, the decision is taken out of my hands and it snaps off! Annoying, but not the end of the world, back to plan A, or was it plan B?
One feature I especially like to accentuate on my turned apples is the way the top curve continues deep into the heart of an apple. I feel this really distinguishes my apples from many others I see. Unfortunately, because of the cut out, I can’t take this curve anywhere near as deep as I normally would so I take it as deep as I dare, bearing in mind I now also need to drill a hole and glue in a turned stalk. 

Wooden apples and fruit
I make a lot of turned fruit. My aim is for realism, although I’m aware that to make the fruit instantly recognisable I am making something of a caricature, emphasising those areas that immediately stand out as an apple or pear. I usually make apples from 75mm square stock and cut them around 5mm shorter in length than their width, so 70mm for 75mm wide apples. They are initially held in a chuck while I turn the base, which is drilled and reversed onto a screw chuck to allow finishing off the top. The screw hole is filled with a clove and a turned stalk is glued in to the top of the apple at a slight angle to give a more natural look to groups of apples. I usually finish with a gloss lacquer, sprayed on, but some woods such as walnut can look better under oil.   

The bottom
Usually I hold an apple on a screw chuck to finish the top and fill the hole with a clove, which closely resembles the blossom in the base of a real apple. As I’m not working in my usual way I need to come up with an alternative. I’m reminded of a comment made to me at a demo once where a chap told me he usually uses a pyrography iron to burn a blossom type pattern into the base of his apples. This wouldn’t work for me normally, but here it could be perfect. I develop the lower curve of the apple cutting as far back up into the apple in an undercut as I can, which unfortunately isn’t that far and sand the apple while there is still enough wood between the apple  and the waste block. Having had one breakage already, I don’t intend to get another!

Once I’m comfortable that I’ve done all that I can, I part the apple from the waste block. The small nib left on the apple is tidied up with a carving gouge then I heat up my old, cheap and nasty pyro kit. I bought it years ago and every now and again it comes in handy, but it isn’t great. It’s one of those soldering iron-come-pyro burner things, but all I need to do is put a little burned texture on the bottom of the apple so I’m sure it will
be within its capabilities. I simply burn dots onto the area of blossom on the apple and I think the effect
works quite well. 

Stalk
My usual method of turning stalks is to use beech (Fagus sylvatica) off cuts, roughly 10 x 10 x 60mm, with an angle cut at one end. I hold these in my chuck fitted with engineer-type jaws and simply turn a long flat cove shape, then form a stem to match a drilled hole in the apple, usually 3.5mm. I then stain it with a ‘tudor oak’ stain; this gives a green-brown colour, which I think suits the job perfectly. I drill a hole in the top of the apple at an angle, which adds character and realism, and glue it in once the apple is finished.

Finishing
I usually spray lacquer my apples, but I feel walnut looks best under oil and with the added complication of the cut out, I think oil will be easier to apply. I use three coats of hard wax oil, glue the stalk into place and the involuted apple is finished.   

Conclusion
This has been an interesting experiment. I think the end result is largely a success. If I were to do it again there are things I would change and improve such as using a larger section of timber to give me a larger apple. With perhaps a slightly smaller cut out so I could get more curve into the top and bottom of the apple. I can see this working with other fruit as well as in other areas. The stylised tree shown in Mike’s book is certainly food for thought. Careful planning and timber selection is, as ever, the key to success in this fascinating area of turning.