Weekend Projects - Simple plywood bowl archive

Friday 2 October 2015

Dennis Keeling presents a simple project for the beginner turner and shows you how to create this simple plywood bowl

Gallery

Plywood is an excellent medium for constructing bowls. When finished it can look very attractive, as long as a few golden rules are applied to construction and turning. The layered laminar construction of plywood can become a beautiful feature of the bowl. There are many different grades of plywood from cheap and knotty construction quality, all the way through to expensive and dense marine ply. The sort of plywood sold at DIY supermarkets is slightly better than the worst construction quality, but still not ideally suited for bowl construction. The ideal plywood for bowl turning is a birch (Betula pendula) plywood, grade A or B. Grade A is knot free and the finest quality; Grade B has a few knots and slight imperfections - the knots may have been plugged - but it is still good quality board. It's usually available in 2,440 x 1,220mm sheets, sometimes cut into 1,220 x 1,220mm or 1,220 x 610mm. These types of plywood are usually only available from timber suppliers.

Tools used:

Bowl gouge

Spindle gouge

Diamond shaped parting tool

Tungsten-tipped tool - optional

Teardrop shear scraper

Square-end negative-rake scraper

Rotary sander

Circular saw or bandsaw

Large button jaws

Design

We are using a 6-layer design developed in Woodturner Studio using its excellent Bezier curve facility to create a beautiful shape. You need Grade B birch 18mm 12 ply for this project. Cut a strip of 1,220mm plywood to 200mm wide and then into 200mm squares

STEP 1

The first step for this project is to cut a 1,220mm length of plywood to a 200mm strip and then cut the strip into five individual 200mm squares. Care should be taken while cutting to ensure the saw blade does not breakout through the back of the plywood. A sharp cross cut blade is ideal here; not a rip-cut blade

STEP 2

The next step is to mark the inner diameter of the bowl to be cut on the squares before the assembly process begins. Now you can mount the squares on the lathe using large button jaws. Using a diamond-shaped parting tool, cut out part-way through the inside of the second level

STEP 3

To avoid breakout of the plywood when cutting out the centres, it's best to only cut half-way through and then turn the plywood square round on the jaws and cut the remainder from the other side

STEP 4

When the centres of all of the levels have been cut out the corners can be removed using a bandsaw or by hand using a tenon saw

STEP 5

Dry fit the levels together to ensure that the cut-outs line up. The sections should look something like this

STEP 6

You will be using a wooden faceplate to fix to the first bowl level. The faceplate must be flat before the gluing stage - flatten the surface with a bowl gouge and check for flatness with a steel rule

STEP 7

The first level is now glued to the wooden faceplate with a glued paper joint. Glossy magazine paper works best using quick setting PVA glue. Centre the first level on the tailstock and apply an even pressure to the glued joint. Leave under pressure for an hour to stop the paper from bubbling

STEP 8

You can now glue up the plywood squares using a quick setting PVA glue. Centre them on the tailstock - I use a round MDF disc with concentric circles drawn on it to centre the levels. The glue sets within 10 minutes and the next level can be glued in an hour

STEP 9

It's important to ensure that the face grain direction of each plywood level is at right angles to the previous level. It's easier to draw an arrow on the side of each level to show the grain direction. Glue up the remaining levels leaving an hour between each gluing

STEP 10

The finished composite should look something like this. I left mine overnight for all the glue to dry out completely before the next turning stage

STEP 11

Mount the wooden faceplate in your chuck and start by cleaning off the rough edges using a bowl gouge. The glue in the plywood quickly takes the edge off the bowl gouge so be prepared to keep sharpening the gouge when it becomes difficult to cut with

STEP 12

Start to establish the rough shape of the bowl. I found it easier to use the bowl gouge in shear-scraping mode rather than bevel rubbing mode. This is a pull cut and allows a smooth contour to be established

STEP 13

Once the rough outside shape has been established, the inside can be turned. The bowl gouge burns very quickly on the inside because of the glue. I used a tungsten-tipped shear-scraper to establish the inside contour on the bowl

STEP 14

The final shape of the inside is established using a teardrop scraper in shear-scraping mode - 45° to the toolrest. The scraper needs to have a flat 90° bevel ground on a coarse grinding wheel. It quickly loses its edge so constant sharpening is needed. Don't forget your work is only as good as your last cut - so make sure the last cut is with a sharpened tool

STEP 15

Since you will next be removing the bowl from its wooden faceplate base, you have to sand the inside now as you won't be able to get back to it on the lathe later. The dust from plywood is pretty awful and not good for you, so ensure that you have good dust extraction working. Start at 100 grit and work up to 320 before the first coat of sealer. Then when the sealer has dried, take it up to 400 grit

STEP 16

The wooden faceplate can now be removed from the base of the bowl. A knife blade positioned on the paper joint quickly separates with a sharp tap from a hammer

STEP 17

Mount the bowl on an MDF cone jam chuck and centre the base on the tailstock with a small steb centre. Position the toolrest at the side and slowly revolve the bowl to ensure it is revolving centrally

STEP 18

The base of the bowl can now be turned down to shape using the bowl gouge in shear-scraping mode as before. Take long, light sweeping cuts to establish a smooth continuous contour shape

STEP 19

Check the bowl thickness throughout using callipers. Try for 3mm wall thickness. The bowl will not be too heavy - yet still strong enough to give it body

STEP 20

Clean up the outside shape with a square-end negative-rake scraper. Take fine slivers to give a mirror-like finish

STEP 21

Clean up the base with a spindle gouge in shear-scraping mode. Try not to cut through the base lamination if possible - the feathering between laminations on a flat surface is not very pretty. The pip under the steb centre can be removed with a flat woodworking chisel later and sanded

STEP 22

The outside can now be sanded. I used an old rubber disc that had previously broken away from its rotary mount. Start at 100 grit and work up to 320 grit before applying the first coat of sanding sealer. After the sanding sealer has dried it can be sanded up to 400 grit

STEP 23

It's now time to apply your preferred finish. Since my wife has an art gallery my pieces for sale get handled a lot so I prefer to use a silk finish acrylic lacquer. Three light coats of spray lacquer - leaving to dry for at least an hour between coats - and then denibbing with either Webrax or wire wool between coats

STEP 24

The finished bowl should look something like this - a bowl to be proud of


Briony Darnley

Tagged In:

Dennis Keeling , Weekend Projects


Handy Hints

1. Be careful when cutting the plywood to ensure you do not let it break-out on the back face. Sharp tools make all the difference
2. The grain direction of the plywood layers must always be at 90° to each other to give a pleasing laminar
3. Plywood sawdust can be dangerous - always use dust extraction
4. Apply an intermediate coat of sanding sealer before using the finer grits of sandpaper to raise the grain and fill the voids
5. Your work is only as good as your last cut - so make sure you use a sharpened tool
6. Use shiny magazine paper for the paper/glue joint - it works better than newspaper
7. Reverse the lathe for sanding - this will ensure that the dust is sent away from you

Diagrams Click an image to enlarge