Five Hollow Forms archive

Wednesday 13 July 2011

Mark Baker creates five hollow forms from five different timbers

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Hollow forms are somewhat daunting when you first start out, but the result can be quite spectacular. The problem for many is how to present a tool in a restricted opening in order to hollow it out. You are, in effect, cutting blind, with tools that you might not use for any other purpose. For these projects I use scraper-tipped tools: some straight, and some are swan-necked to reach further round curves, but some of the tools sporting cutting tips can be articulated. Scraper-type hollowing tools are a good place to start, not necessarily leaving the best finish or the quickest at removing wood, but they are relatively low cost and are a good starting point for creating hollow forms. They can also be used on wet, dry, end or side-grained timber varieties.

There are five projects in total, each getting progressively more difficult as you go along. These can be tackled as your skill and confidence levels increase. Sizes are shown, but of course, are scalable to suit your lathe.

Tools used:

2mm (5/64in) parting tool, 10mm (3/8in) swept-back, bowl gouge, 10mm (3/8in) beading/parting tool, 10mn (3/8in) spindle gouge, 13mm (1/2in) Swan-neck, hollowing tool, 20mm (3/4in) spindle, spindle roughing gouge, 10mm (3/8in) straight shaft articulated tip and a hollowing tool

Teardrop vase in sycamore

Sycamore is a great timber to practice with and this shape allows you to work with a straight hollowing tool. The teardrop shape allows you to easily pull out the shaving without having to resort to a vacuum extractor to remove them. This shape evolved from a teardrop drawing, but it has also been likened to a pear form.

This end-grain project is first mounted between centres, shaped to the approximate form, and a spigot is then created in order to mount it in a chuck. Once chucked, the external shape is refined and a hole drilled or turned in the middle. Drilling with a bit held in a Jacob's chuck, held in the tailstock spindle, is fast and easy, but turning it out takes a little longer.

The hollowing is carried out in stages, working about 30mm (1 1/4in) deep and making sure the wall thickness is correct and blended in with the previous cut area before moving to a lower section. Continue until you have the internal shape and wall thickness you require.

Refine the outside shape further if required, then sand the piece inside and out to a smooth finish. You may require an abrasive on a stick to get to the bottom of the inside - it is not advisable to stick fingers in hollow forms.

Once sanded, mark a gentle slope and, with a saw, cut away the waste. I use a drum sander held in a drill to shape the edge and create the rolled over rim effect. After creating the rim and finish sanding, the item needs to be parted off, the underside sanded to shape, and the piece finally finished.

Onion form in ash

This hollow form is turned from one piece, but in two parts to ensure the grain aligns when the piece is finished. The timber is initially shaped and mounted as per the previous project. The neck section is kept parallel at the widest size possible, and a drill is used to make a hole down the neck section, this is then refined with a spindle gouge. Use a fine parting tool to create a taper and part the neck section off. The taper created on the neck will have a corresponding taper in the base.

Hollow the base using a tip scraper, working through the large hole. Once complete, refine the taper to allow the neck to be fitted precisely. Remove the base form, mount the tapered end of the neck section in a chuck, but ensure you do not grip or damage the taper. Grip on the parallel section and drill the centre of the bottom area so the central hole is all the way through the neck piece, and gently blend the hole in with a curve. Re-mount the base piece, making sure it is running true. Apply PVA glue to the tapers, align the grain and fit the neck into the body. Use the tailstock to centralise the neck and clamp it in place while the glue sets. Refine the body and neck to the shape required. Now, with the corner of the thin parting tool, cut a small 'V' on the join line to disguise the join. To confuse the eye further, place a 'V' cut either side of the one already marked. If the joint and grain alignment is good, you will be hard pressed to see which one is the join. Sand to a fine finish - satin lacquer was used to finish the piece.

Hollow form in spalted birch

This is another end-grain piece and is the largest of all the projects featured here. The spalted wood adds a nice visual element that complements the overall shape. The choice of timber and/or colour has a major impact on the overall effect and appearance.

This piece is turned in two parts: there is a stepped rebate onto which the lid section is fitted and glued. The piece is mounted and shaped in the same way as the sycamore vessel. However, prior to parting off the lid section, a 10mm (3/8in) hole is drilled in the centre. Once drilled it is parted off and put to one side while the inside is hollowed out. Make the step in the rim as per the drawing and then create the wall thickness required for the rest of the piece. Sand the inside and remove the base section from the lathe.

Mount a scrap piece of MDF or ply on the lathe and turn a 10mm (3/8in) wide tenon about 6mm (1/4in) deep. The hole in the lid locates onto this tenon and is held in place with double-sided tape or hot melt glue. Now face off the underside of the lid and cut the shoulder. You then are left with a clean-cut edge to the size required for a tight fit. Offer the base form up to check for fit, and once you are happy, part off or prise off. Remember you are working with fragile end-grain, you do not want it to split at this stage. Glue it into the base form, remembering to match up the grain.

Allow the glue to set, re-mount the form and create the top face of the lid and opening. Sand and apply your finish.

Heart-shaped vessel in lignum vitae

This project is not an end-grain project. Instead, the grain runs side to side like a standard bowl. Lignum vitae was chosen for its stunning colours and, because it is dense, I find it surprisingly easy to work with.

Based on a cartoon-type heart shape, it is one of the most difficult shapes to make in as much as you have a lot of changing to do in order to cut with the grain and still ensure a nice even form. It is open enough for people to feel all the way round the internal form and, as such, any errors will be detected. The piece was initially mounted on a screw chuck, a tenon cut, the back shaped, and then mounted in the chuck in order to cut the opening and hollow it out.

A swan-neck tool is required to reach under the inner section of the top; a straight tool can be used thereafter. The wider the opening, the more area you can work with the straight tool.

It is a simple case of following the same hollowing procedures as before with you working one section to completion before moving onto the next.

Sanding lignum can be a problem: it is naturally oily and readily clogs abrasive. You will need either plenty of abrasive or a bronze brush to unclog the abrasive, rather than throwing it away. The finer the grit, the more polished the surface. The natural oils form a very fine finish that may not require any further treatment. I did however, put oil on this one.

Classic vessel in cherry

This classic Roman/Greek form in cherry is a wonderful shape to experiment with. You have two options with this piece: one is the make the item in two parts as per the previous project, and have the join under the flared upstanding lower neck section, or hollow through a smaller hole than you have before. This was hollowed through the smaller hole and took about three times longer than the last piece. This was due to the shavings needing to be regularly cleared out with a wire and vacuum extractor. As with the onion form previously, this shape could be hollowed through a wider hole in the base. A stepped recess is cut in the base and then a plug is fitted.

Again, this is an end-grain project which starts off being mounted and shaped in the same way as the first project. I used a 10mm (3/8in) spindle gouge with the wings swept back. The outside should create no problem as far as shaping is concerned, just remember to cut with the grain - that is from the widest diameter to the smallest - downhill for a fine finish.

The inside requires a swan-necked tool in order to reach the inside of the curved shoulders. The straight tool with articulated tip can help a lot, but it just cannot reach those difficult areas.

As with the first project, work down in stages ensuring the wall thickness is correct/blended in with the previous section's cut before moving on to a new area.

Once the hollowing is complete, abrasive held in forceps should be used in order to sand the inside. If you can touch it and see it, sand it. The piece is then finished with lacquer and wax.

Woodworkers Institute

Tagged In:

Mark Baker , Hollow forms , timbers

Handy Hints

1. The slanted neck adds an interesting element to the piece that can be enhanced further by carving the neck area to mimic the angle of the slant shown
2. Alternatively, the eye can be drawn to the sloping neck by applying a contrasting colour to its rim, but it is advisable to only try this with light coloured woods
3. Remember to undercut the base when parting off to prevent the pieces from wobbling around freely
4. The two-part turning method for hollow forms will help you create shapes that would otherwise be impossible or take too long to turn. The smaller the hole, the more difficult the piece is to hollow out, and the more time is spent removing shavings that clog up the inside, thus preventing cutting
5. The shape of the onion form form also lends itself well to being hollowed from the base. This is done by inserting a plug into the bottom of the piece
6. For the hollow form in spated birch it is advisable to only use CA (cyanoacrylate glue) to glue the lid to the base. If you do not do this, the cyanoacrylate glue can creep into the grain and will stain the wood. Be careful, as this will require covering the whole piece in the glue in order to match the staining.
7. When you are hollowing end-grain it is easier to drill a hole down to the centre and hollow from the hole to the edge
8. Lignum vitae is a timber that is prone to heat checking: be careful not to generate too much heat when sanding. Wet sanding with water or oil is a good option if no sapwood is present. If there is any present the sanding slurry from the darker heartwood will contaminate the cream-coloured sapwood
9. Also consider slowing the lathe speed down when sanding so that less heat is produced by friction. This also reduces the chances
of heat checks occurring in the piece
10. When using swan-neck tools, it is important to ensure that only the straight part of the shaft of the tool is supported by the toolrest. You may need to place the toolrest further away from the workpiece to ensure this is the case. If the swan-neck part of the tool sits on the toolrest, the cutting edge of the tool will not be supported and the tool will twist downwards
11. Shavings could be removed from the inside using compressed air if you have it in the workshop, but be sure to wear eye protection at all times

Diagrams Click an image to enlarge