Stoppered Hollow Form
Monday 23 November 2009
Mark Sanger turns this striking spalted beech hollow form complete with its own anjan stopper
Tools used: Swan-neck hollowing tool, straight hollowing tool, 12mm (1/2in) spindle gouge, 6mm (1/4in) parting tool, 38mm (1 1/2in) spindle roughing gouge, 10mm (3/8in) spindle gouge and 20mm (3/4in) skew chisel
Turning a hollow form through a small hole is not without its problems, but there are alternative ways of making them,
all of which give great results and allow a little more access for the hollowing procedure.
One alternative involves turning a spigot at the top of the form one third of the diameter, to a desired length to suit the design. This is then parted off and the form hollowed through a hole slightly smaller than the diameter of the spigot. Once complete, it is glued back into a shoulder with the grain aligned. This spigot is then turned and blended to produce the neck of the hollow form.
If you try this design be mindful that different woods and materials have different rates of expansion and contraction, so ensure to use well-seasoned wood.
For this project take a piece of 100 x 100mm (4 x 4in) diameter x 200mm (8in) long, stock turned end-grain spalted beech, turned with the grain running parallel to the spindle axis, with a piece of anjan for the hollow form stopper.
Mount the blank in the middle of the two centres and rough to the round using a 38mm (1 1/2in) spindle roughing gouge with the spindle speed at around 500rpm
On the blank mark the main points of the form using a ruler and pencil. First mark 20mm (3/4in) up from the base - this gives a waste area away from the chuck for safety when turning down the base. Next, mark two-thirds the distance from the base line to the top and a further 20mm (3/4in) along from this line. This is a general guide as to where the curve of the shoulder will start and then join the neck of the form. After having made a few forms these markings can be dispensed with as it will become instinctive as to where to form the shoulder and neck
Using a 6mm (1/4in) parting tool and callipers set to just over a third of the diameter of the roughed blank, part down to size. You want to eventually make the top of the neck around a third of the diameter as this will keep proportion in the form. Once the first diameter is formed, part along to the same diameter up to the top line nearest the tailstock end - this is where the neck is parted off
Using a 13mm (1/2in) spindle gouge blend the shoulder down towards the neck - this allows for more room when parting off the neck. Blend from the first line of the shoulder to the neck/second line stopping slightly short of the neck material. The neck is parted off to allow a small amount of waste to be left - this will act as an indicator for a recess and for final blending after being glued back into the shoulder. Continue using the spindle gouge to form the rest of the profile. Blend the shoulder into the base, leaving some extra material on the lower part of the form to give strength during hollowing. This extra thickness will be turned away before parting off
Mark the neck and the shoulder with a pencil to allow the grain to be re-aligned when glued back in place. Use a 3mm (1/8in) parting tool to part off the neck to leave a small amount of the spigot material behind
Use a 25mm (1in) Forstner bit to drill out the form in a 300mm (11 1/2in) extension. Measure the length of the form and mark this measurement on the shaft of the drill/extension, minus 20mm (3/4in) with the lathe running at around 200rpm. Drill in a short distance and withdraw the tool to remove the shavings and to prevent the tool from binding
Using a 20mm (3/4in) skew chisel held horizontally on the toolrest, turn a recess approximately 5-8mm deep into the shoulder. Open out the recess taking fine cuts until you near the wood/diameter left when parting off the neck. Make sure that the recess is cut parallel or the neck may not fit positively. Continue taking fine cuts, regularly checking the fit of the neck into the shoulder. Aim for a light pressure fit
Hollow out the inside to a wall thickness of around 6mm (1/4in) Start hollowing from the shoulder working down to the base, regularly removing the shavings to stop the tool from binding. Use callipers to check the wall thickness and aim for an even thickness of around 6mm (1/4in)
Glue the neck back into the recess using Cyanoacrylate glue. Due to the open and absorbent structure of spalted beech, it is best to use low viscosity glue. High viscosity (thin) will soak into the wood before it glues the neck. Align the grain using the previously made pencil marks. Due to the spalting in this project, it was easy to align the grain, and the pencil markings will help greatly. With the neck glued in place, drill out the neck using a 10mm (3/8in) drill with the lathe set at around 200rpm. Use a 6mm (1/4in) spindle gouge to open out the inside entrance of the neck, producing a convex curve that will mirror the outside profile of the neck once the outside is profiled
Once the inside of the neck is complete, place the form between centres and shape the neck using the spindle gouge, working from the largest diameter in. Approach the curve from both sides working downwards to the base of the curve, using the same procedure as if you were making a cove. Blend the shoulder into the neck, aiming to produce a flowing curve
Uing the toe/ long point of a 20mm (3/4in) skew chisel horizontally on the toolrest, turn three concentric grooves to hide the join, with the middle of the three covering the join itself. Use the skew in a slight trailing position with the handle slightly raised to prevent the tip from digging into the shoulder. Alternatively, you could use a small beading tool or spindle gouge
It is now time to blend the lower half of the form into the base using a 10mm (3/8in) spindle gouge. Aim to blend the base to a third of the diameter of the form as this adds balance to the form by tying the diameter of the base and the neck together
Using a 50mm (2in) hook-and-loop arbor in a drill, sand the main body with 120-400 grit. Do the same covering the inside of the shoulder and outside of the neck, but do this by hand on these areas. Keep the abrasive moving over the surface, and once completed, dampen the surface with tap water on kitchen towel. When dry, cut back with 600 grit. Cover the surface with sanding sealer - in this instance I used cellulose sanding sealer. Allow to dry then cut back with 600 grit abrasive, if required, then buff with the lathe at around 2000rpm with safety cloth or paper towel. Once the surface has been buffed you can apply a wax finish of your preference, but make sure that the wax finish is compatible with the sanding sealer you have chosen to use
Using a 3mm (1/8in) parting tool, part off the form down to around 20mm (3/4in). Using a fine saw, remove the form from the waste wood, then remove the small spigot from the base using a sharp chisel or reciprocating carver. Always ensure to work away from your body/hands when using sharp tools. Finally, finish the base with abrasive and seal with sanding sealer, as before, then apply a layer of wax finish
Rough down between centres a 30mm (1 1/8in) diameter x 70mm (2 3/4in) length of anjan/contrasting wood using a spindle roughing gouge. Use a 6mm (1/4in) parting tool to part down a 10 x 25mm (3/8 x 1in) spigot. The diameter is turned to 10mm (3/8in) to allow it to fit into the neck of the form
Use a 10mm (3/8in) spindle gouge to shape the stopper - the shape is produced in the same way as the main form. The base of the stopper at the widest point to the base is a third of the height of the stopper. The form is blended back in from this point to the tip. Try to produce a teardrop shape of one continuous flowing curve, but leave some waste material at the drive centre end to be blended later. Finish the stopper using 120-600 grit abrasive, as before. Use a black spirit stain for the stopper to darken the wood, complementing the spalting. The whole form is then tied together in both shape and colour
Once the stopper is stained, dry the surface and buff with kitchen towel. Carnauba wax is then applied with the lathe spindle speed at around 2000rpm. Working at this speed causes the wax to melt and gives an even high shine to the surface
Using a Jacobs chuck in the headstock of the lathe, reverse the stopper and tighten in the chuck while using gentle pressure from the running centre. Leave 15mm (5/8in) of the stopper spigot protruding to allow for the final parting. If you do not have a Jacobs chuck that will accept over 10mm (3/8in) diameter, you could use a waste piece of material in the lathe chuck jaws and drill a 10mm (3/8in) hole in the centre to a depth of 10-15mm and press the spigot into this hole as with a jam chuck. Using a 20mm (3/4in) skew chisel, continue the curve of the stopper, taking fine cuts until the waste material is parted off
Starting at 320 grit, gently blend the tip of the stopper with abrasive. The tip then requires staining and waxing, as before. It is not an issue that the rest of the stopper has already been waxed prior to the stain being applied, as the sanding procedure will cut this back, allowing the stain to take. Using a 3mm (1⁄8in) parting tool, part the stopper from the chuck with the lathe speed at around 500rpm
Here is a variation of the hollow form. I decided to produce a contrasting body made of spalted horse chestnut complete with an anjan neck