Weekend Projects – Offcentre Bowl

Monday 9 July 2018

I have made offcentre bowls for many years. This design is just one of many variations that are possible by offsetting. This design requires offsetting in one direction only and a small amount of offset, so is a good one to start with. Think about offsetting at two points or more; this will require accurate marking out to maintain symmetry. The possibilities are endless; it's down to imagination and the time you want to spend on making the bowl.

The size of bowl blank will depend on three factors: the swing over your lathe bed; the amount of offset – a 200mm bowl blank with an offset of 10mm dictates that the bowl is now equivalent to a bowl of 220mm diameter – and finally, the size and weight of your lathe. The bowl will be running out-of-balance part of the time, which will place extra strain on the lathe bearings and can cause the lathe to vibrate and rock if a high speed is used, so keep your speed slow when turning in offcentre mode. You should take a clean cut across the top face while it is running true; this will mean you don't have to work on the top while it's running offcentre. Start with a small offset for your first offcentre bowl and then increase the amount of offset for further bowls. There are ways to overcome the out-of-balance problem using counter weights on the opposite side to the offset; this will bring the bowl blank back into balance. I am using a faceplate on this piece as it is easier to move centres than to turn two spigots and hold in a chuck. Imagine turning on five centres using spigots. Make sure the screws are holding the faceplate firm and are the correct length: too long and you will lose more timber when turning the base away to remove the screw holes; too short and you run the risk of the piece coming loose and detaching from the faceplate. I used spalted beech (Fagus sylvatica) here and the finish used is sanding sealant and wax. This piece is not too figured as I feel this would distract from the form. Check for any splits or faults – as with any turning you have to think about centrifugal force.


Find the centre of the blank using a cardboard disc. I have many different ones for various diameter bowl blanks. These have a hole in the centre which allows you to mark the centre with the tip of a pencil or rule. Now you have the centre you can set the pair of compasses to the radius of your faceplate and draw a circle


Fix the faceplate to the bowl blank by lining up with the circle drawn previously. If you only have long screws available, you can use a spacer to reduce the depth the screws penetrate the disc. Make sure it fits flush with the bowl blank


Using the bowl gouge, you are now ready to true up the outer edge of the bowl blank; this will allow you to bring the piece into balance. The bevel angle should be 50° on the gouge. While turning, try to keep the bevel in contact for good tool control. As the gap between the bowl blank and the toolrest opens up, stop the lathe and move the toolrest closer to the piece


You now need to clean up the base so you can mark on the dimensions. Use a pull cut from the centre towards the outside, with the flutes around 30° from vertical facing the direction of cut. Mark the centre of the bowl with a pencil; you can see the centre easier while the lathe is running


Now you can mark the base diameter. You can see this is 50mm from the centre, which will give you a base of 100mm; this is because the faceplate is 80mm and with a 10mm offset, the faceplate will still sit on the full base. Any less and you may find the faceplate overhangs the base


Using a pair of compasses still set at the radius of the faceplate, place the point on the 10mm offset mark and draw a circle. As you can see, this circle is still within the base diameter


Use the bowl gouge to start shaping the outside of the bowl. This is a simple curve; you don't want to distract from the features of the offset bowl. Always start at the base and work towards the rim with the flutes facing the direction of cut. You can clearly see the mark for the base


Use a sharp bowl gouge to achieve a clean cut; this will minimise sanding later. Keep the bevel in contact with the bowl, which will control the cut, with the flutes facing the rim. Here you can see that I have created a step for the base; part of this will be removed later when finishing the base. Use the long point of the skew chisel to mark the centre for realignment later


Start sanding the outside of the bowl, starting with 120 and working through the grits up to 400. Stop the lathe and check you have no tool or sanding marks remaining. If you do, you will need to re-sand through the various grades until you achieve an acceptable finish. Use a cellulose sanding sealant to finish the bowl and once dry, rub back with a Nyweb pad; this will denib any raised grain


Remove the faceplate from the top face, fix to the centre of the base and then turn the top flat with the bowl gouge. The bowl will still be running concentric so is easier to turn at this stage


Sand through the grades until you achieve a fine finish. You don't want to leave any tool or sanding marks. Now use the sanding sealant and denib when dry


Remove the faceplate, place on the offcentre circle and fix firmly. Remember that this will now be running offcentre so check your lathe speed before reattaching the bowl to the lathe. Place on a slow speed or at your lathe's lowest speed setting


After attaching the faceplate onto the lathe spindle, move the toolrest assembly towards the bowl, leave a small gap and lock firmly. Rotate the piece by hand several times; this will ensure that the bowl will not catch the toolrest


Make a pencil line on the blank around 30mm from the narrowest edge. Rotate the blank by hand. The position can be varied depending on your chosen design and how thin you want the edge to be


The outer bowl will now be running offcentre, which can cause a light lathe to rock backwards and forwards – this is why it's set at a low speed. Use the bowl gouge to start removing the inner bowl; this is just like turning a standard bowl. Keep enlarging the bowl in width and depth


Stop the lathe and check the progress. Remember that the wall thickness will be uneven due to the outer and inner bowls not running concentric. You can always take more out, but you can't put it back, so be careful and take your time


Use a sharp bowl gouge to take a fine finishing cut. As you can see in the photo, the shaving is coming off in a curl; this indicates a sharp tool and correct tool presentation. With the lathe turned off check the curve with your fingers and feel for any lumps for and bumps. If any are found then turn them away


Use a French-curve scraper to take a fine cut; this will remove any tool marks from the bowl gouge. Shavings should come off the scraper. If this turns to more dust then your scraper needs sharpening. Work from the rim to the centre


Remove the toolrest and sand through the grades to a fine finish, then seal. The only part that needs finishing is the bowl you have just turned. Be careful of the outer rim, which is running eccentric


Cut a plywood disc, drill a recess in the back for the chuck to expand into and cover it with anti-slip mat. You can then fix it to the faceplate. I often use this very useful piece of kit for re-turning the bases of bowls


Line up the revolving centre with the hole which you placed with the point of the skew chisel. Wind the revolving centre into this hole; this will give you enough support while you finish the base of the bowl. Just apply sufficient pressure to hold the bowl against the wooden faceplate


Use the bowl gouge to remove the waste from the centre; this will remove the screw holes left from the faceplate and will allow you to finish the underside of the foot. Leave around 8mm in the centre for the revolving centre – any less and the timber around the revolving centre may split. If in any doubt about the thickness of the bottom of the bowl, stop the lathe and check


Clean any marks away with the scraper, but be careful when near the revolving centre. As you can see, all the screw holes are gone, and all evidence that a faceplate was ever used. Remove the toolrest, sand through the grades and seal with sanding sealant


Place the bowl on the bench with anti-slip matting underneath; this will protect the top surface. Use the skew chisel to remove the pip left from turning, and once removed, sand through the grades and apply sanding sealant to the centre


Use a three-part buffing system to finish the bowl; this will give a very good finish. Hold the bowl at the bottom corner of the buffing wheel as in the photo – hold firmly and use on all parts of the bowl. The wax used is Carnauba, which will give a good finish


The completed offcentre bowl in beech should look something like this