Weekend Projects - Blockwork bowl archive

Friday 31 July 2015

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Dennis Keeling creates a segmented blockwork bowl from various woods which is perfect for those turners new to segmented turning

There may be many of you wanting to try segmented turning but you feel that you do not have the right equipment to try it. This is a simple project using 45° angles and standard spindle blanks. The idea for this article is to show you how to make a segmented bowl without any machining. Blockwork is the basis of segmented turning and the technique goes back hundreds of years. It is simple and straightforward to make a bowl with this technique - it even accommodates any errors that you may make along the way. For this project I have selected three different 40mm square spindle blanks. The woods used are mahogany (Khaya ivorensis), sycamore (Acer pseudoplatanus) and cherry (Prunus spp) - but any hardwoods could be used. This project is perfect for the beginner segmented turner.

Tools used:

20mm bowl gouge

Teardrop shear scraper

Small round-nosed scraper

Fingernail spindle gouge

Mitre block or mitre saw - optional

Disc sander - optional

Mahogany, sycamore, cherry or any close grained hardwood. See cutting list

Design

The design uses a 45° mitre joint which is easy to cut on a variety of jigs. If 40 x 40mm material is not available then any size square section can be used - the width of the next level will be two-thirds of the thickness of the wood larger than the previous level. For a 30mm square with a 80mm wide first level - the second level will be 80 x 30 x 2/3mm - 100mm wide. This 40mm square section design only uses four levels but five levels or more could be used with thinner square section

STEP 1

Prepare the timber for cutting. The only requirement is that one face is planed flat. If the square section does not have a flat surface then one face should be planed flat by hand

STEP 2

Cut the two base lengths - in this case 80mm long. In order for them to fit on the lathe the ends should be square and the lengths equal. Glue them together with yellow aliphatic glue - Titebond Classic - and clamp them flat for 30 minutes

STEP 3

Fit the square section into wide jaws on your chuck. For my first prototype, I used a wooden faceplate with a paper glue joint, but that proved not to be strong enough when initially shaping the sharp edges later

STEP 4

Clean up the face of the base using a bowl gouge in shear scraping mode. Clean up the sharp edges at the same time

STEP 5

Make sure the base is level by testing with a metal rule. In order to get tight joints it is important that this surface is level

STEP 6

You can either cut the segments with a mitre block by hand at 45° or by using a bandsaw or mitre saw, if you have them. A hand cut 45° joint is perfectly acceptable. The planed face should be at the bottom; it will be the face to be glued to the previous level

STEP 7

If you have a mitre saw you need to make sure that it is cutting accurately by initially using some scrap wood to make sure that, when assembled, the four segments close up correctly

STEP 8

To ensure that the joints come together accurately when glued it is worth cleaning up the faces with a disc sander. They not only have to be cut at 45° but the cut faces also have to be vertical. It's not a problem if you do not have a disc sander, but you may have to hand sand one segment to make them fit accurately together as a ring

STEP 9

I used a simple string framing clamp to hold the segments together but six clamps could have been used. Make sure the segments come together without any light between them by dry fitting them first

STEP 10

In order to glue the four segments together and accurately glue them to the first level, you need to conduct the whole process in one operation. The string clamp holds the four segments together and the tailstock puts pressure on the two levels. Use yellow glue as before and ensure that the framed level is positioned centrally and brickwork-fashion with the first level

STEP 11

When the glue has cured - after about four hours - use the bowl gouge in shear scraping mode to clean up the slight undulations ready for gluing the next level

STEP 12

You now need to glue up the third level as before. Ensure that the segments are central and positioned at 45° to the previous level. Use a piece of foam between an MDF disc mounted on the tailstock; this will give an even pressure when gluing

STEP 13

Make sure the third level has been cleaned up with the bowl gouge first to ensure it is flat. The top - fourth level - can now be assembled and glued up as before. The string clamp needs to be very tight to ensure the segments do not creep apart under the pressure from the tailstock

STEP 14

You are now nearly ready for turning. The sharp corners need to be removed with a hand saw as the wood has a habit of splitting on sharp edges

STEP 15

You can now turn the outside down to shape. Be careful not to remove any of the main body at this stage - just level off the segment layers. The bowl gouge works well on the outside but the glue joints will soon dull the blade so you may have to re-sharpen your gouge a few times

STEP 16

Once the outside shape has been established you can hollow out the inside. Initially use the bowl gouge to start the inside profile. Start with the bowl gouge bevel at 90° to the top of the bowl or it will skate across your bowl. Once the bevel is rubbing, then the bowl gouge can be turned to cut the inside to shape

STEP 17

The bowl gouge tip soon gets burnt on the glue joints. Optionally, a better tool for hollowing the inside is a hollowing tool with a limiter to stop it cutting away too much

STEP 18

Establish the contour of the inside with a teardrop scraper. I also used a small half-round end scraper to clean up the bottom of the bowl where the hollowing tool was ineffective. Once the inside contour has been established, check the wall thickness with callipers. Plan for 3mm wall thickness, then sand the inside, starting at 120 grit and working up to 320 grit

STEP 19

Now, turn the bowl round on the lathe and support the top of the bowl on the headstock via an MDF cone, which will not mark the bowl. Now you need to centre the tailstock on the base for support; this will also allow you to clean up the outside and the base of the bowl

STEP 20

Use the bowl gouge in normal bevel rubbing mode to bring the base of the bowl down to shape. With segmented structures it is better to work from the top of the bowl to the base

STEP 21

Finally, clean up the outside with the bowl gouge in shear-scraping mode. This is a pull cut taking fine whiskers of wood away to give a very smooth finish

STEP 22

Clean up the base with a fingernail spindle gouge leaving a small pip in the centre. Make sure the centre is undercut so that the outside edge sits well on a flat surface. Now you can sand the outside of the bowl as before

STEP 23

Remove the bowl from the lathe and cut away the pip on the base. I usually place it on some router matting and carefully carve away the pip with a wood chisel. Next, sand the base to remove any tool marks

STEP 24

The bowl can be finished with your favourite finish - oil, lacquer or melamine. I gave my bowl four coats of high gloss acrylic lacquer, rubbing down with Webrax between each coat. The finished bowl should look like this


Briony Darnley

Tagged In:

Dennis Keeling , Weekend Projects


Diagrams Click an image to enlarge

Handy Hints

1. The success of this bowl will depend on the accuracy of the joints. Time spent making them fit before gluing makes all the difference
2. Ensure all wood used is very dry - you cannot afford any movement in the segments
3. Carefully choose which woods you are going to use. I decided to use three different contrasting woods, all of similar density, but the choice is up to you