Bowl Saving archive

Wednesday 30 September 2009

Tracy Owen looks at a number of different systems designed for coring out bowl blanks

Gallery

This month I am going to be discussing different ways of coring out the middles of bowl blanks, as well as looking at the range of dedicated bowl saving and regular tools that are available to you. All the systems shown are capable of multiple saves, including working with natural edges. Hopefully you will find some useful tips in this article, which have worked well for me over the last 12 years or so. Coring out the middle of a bowl blank not only saves the wood from being wasted, thus saving you money, but it is also quicker and easier than gouging it out, as well as being suitable for use on either dry or wet wood. I have used mainly freshly-felled timber, simply because wet wood is much easier to work with, especially when you are making deep plunging cuts. The bulk of my bowl production, including a range of bowl saving or coring, uses mainly timber native to the UK.

Coring with a parting tool

1. This is a diamond section parting tool from Robert Sorby. The profile of this tool reduces the risk of binding in the cut and the wide section in the middle of the blade is the only part rubbing against the wood. This reduces the amount of friction and heat build up and makes it a good tool for coring out the middles of small bowl blanks

2. One of the simplest ways to save the middle of a bowl blank is to mount the blank on a small faceplate and use a parting tool or slicer blade to cone out from the back; this is a plunging cut into the middle. Only a straight-sided cone can be saved this way but it is a good, easy and cheap way of saving the middle of a bowl blank instead of making shavings on the floor. I shape the outside of the wet bowl blank first, bringing up the tailstock for extra security. You can also core out the bowl by turning the blank round and holding onto the pre-cut dovetail. Usually when I use this method, I cut a large dovetail or straight tenon and use gripper jaws to give a much stronger hold and reduce the chance of it being broken off, using the tailstock once again to help keep things in place. A diamond parting tool is a good one for small jobs as there is less friction with the tool against the wood due to the diamond section. You might be able to part down in one go, releasing the shavings as you go. You may also have to make two passes to get the alignment correct

3. Ensure that you stop short of going all the way to the centre with this parting cut. Pull the tailstock out of the way and break away the outer bowl from the bowl save

4. Here is a small bowl save still fixed onto the original small faceplate. This could be used in one of two ways: either turned to a finished bowl whilst mounted on the faceplate, or you could turn a new spigot or dovetail, turn it round and core out some of the middle to leave a thick wall. This could then be put on one side to dry and then re-turned when dry

Coring with a Robert Sorby slicer

1. Here is the Robert Sorby slicer blade being used from the front. Here I decided to make two bowl saves, leaving me with three bowls in total. This blade can only be used to produce a cone shape. I would normally use this at a fairly low speed, somewhere between 500-700rpm. This slicer blade can be used with an arm brace or a pistol grip handle, but I always use the side handle for extra support. Again, clearance cuts may be necessary to ensure the correct angle of cut to prevent binding

2. Next, remount the roughed out bowl blanks (or any bowl blanks that have had the middles cored out). I keep a range of dome-shaped discs which have a dovetail cut on them to fit into the chuck, then just select the one which is of a similar shape to the inside of the bowl. Place the bowl over the dome and hold into place using the tailstock. This bowl can now be held very firmly and the outside turned to a finish

Coring with a Kel McNaughton system

1. The McNaughton Bowl Centre Saving System is available with four different sets of slicing blades; a handle and toolpost comes with the set of blades you choose. The sizes of the blades used are dependent on the size of the bowl blank you wish to core out. There is a mini-set for blanks of 100-255mm (4-10in) diameter, a standard set for 200-355mm (8-14in) diameter, and a large set for 255-480mm (10-18in) diameter. A combined set is available of the standard and large blades, each with a straight slicer included for cutting straight-sided cones. The toolpost is essential for guiding the slicing blades through the blank, and the small pillars on top of the post keep the slicing blades vertical. The T-shaped bar at the rear prevents the blade from kicking upwards and comes in different sizes to fit different lathe banjos. With the smaller sets of blades, this system will work on the smaller lathes available, but for the largest of the slicer blades you will need a big, heavy machine with plenty of power

2. Here is the McNaughton system all constructed and ready to go

3. This is the McNaughton system in use. Having shaped the outside of the bowl blank, grip onto a 93mm (3 5/8in) tenon with gripper jaws. I intend to cut away only one bowl save out of the middle using the coring system. This blank measures 200 x 150mm (8 x 6in) leaving the larger bowl with about 25mm (1in) wall thickness. This will leave a bowl save of about 125mm (5in) by the time I have lost the thickness of cut

4. Here is the bowl blank with the middle cored. From here on I make a single cut with a bowl gouge on the inside of the larger bowl to clean up the surface – the smaller one will be put back on a screw chuck. Cut a new dovetail on it at the bottom, then cut out the inside of the smaller one leaving a similar wall thickness of about 25mm (1in)

5. When roughing out in warm weather, I recommend covering the whole of the outside and the rim of the blank with PVA glue. This slows down the drying process and helps to reduce the chance of the bowls splitting. You could just do the end-grain, but I find it best to do the whole bowl

Coring with a Woodcut system

1. This is the Woodcut system all set up and ready to go. The Woodcut has two curved blades, one large and one small, that can be re-sharpened. Both cutters are loaded into the saver for setting up purposes but only one cutter is used at any one time. The handle and clamping block bolts are slackened and this frees up the slicing blades to allow the one of your choice to be put in the appropriate side. It is easy to change, taking only a few moments and can be used on bowls with an outside diameter of 150-405mm (6-16in)

2. Here is the Woodcut bowl saver in use on a 255 x 114mm (10 x 4 1/2in) bowl blank leaving a 32mm (1 1/4in) wall thickness. The centre save will be 180 x 75mm (7 x 3in). Once the centre core is popped out this, like the previous one, is mounted back on a screw chuck to cut a new dovetail on the back, turned round, and some of the middle removed to leave a 25mm (1in) wall thickness. This is then set to dry as a set of two bowls. With this system it is possible to do more than one centre save from the same log

Coring with a Oneway system

1. The Oneway Easy-Core Coring System will fit any lathe with flat bars. You need a base set, which includes the handle to suit the size of your lathe. This clamps onto the bed of the lathe and comes in sizes of 405, 510, 610 and 680mm (16, 20, 24 and 26in)

2. In addition, there are four knife sets available to fit the handle, these come in sizes 230, 280, 330 and 405mm (9, 11, 13 and 16in). Each knife set includes a support, knife and cutter

3. Here is the coring system in action. This bowl blank is big enough to do two centre saves.


Woodworkers Institute

Tagged In:

turning , Tracy Owen , Bowls , blanks , saving

Glossary Rollover a term to view its definition

Bowl Gouge , Faceplate , Centre , Lathe , End Grain , Bowl turning attachment

Top Tips

A few things to think about when you are coring out the middles/centres of bowls:
If the bowls are being cored out and left to dry, rather than the bowl being turned straight away, extra wall thickness should be allowed for the bowls drying out as otherwise they will end up being misshapen
Write the date on the rim of the bowl when roughed out. You will then have an idea of how long each one has been drying
When bowl saving it is best to work at a fairly slow speed, somewhere between 500-800rpm, depending on the size of the wood used
When using a dovetail or tenon into a chuck when coring out, it is a good idea to ensure that it is a suitable size to be strong enough to withstand the deep plunging cuts from the slicer blades
When using any of these systems the parting tool or slicer blades all need to have a good sharp edge so that they will work well
It is a good idea to retract the blade when making these parting cuts to clear any shavings and to reduce any binding in the cut