Workholding

5 Work-Holding

5.1 General Conditions

For chucking blanks, and pieces completely oval turned on one side, onto the ovalturning lathe there is a variety of holding and chucking devices, among them chucks which are used for normal (circular) turning. But, take note, the screw chuck used for holding circular facework is strictly forbidden when oval turning as it does not hold the blank safely in its position. The blank can twist, and this is extremely dangerous. Any movement of the workpiece from its starting position must be absolutely avoided.

When circular turning one can rotate the workpiece within loose chuck jaws, with an oval workpiece this is not possible. The workpiece must remain in the chuck in the same position from the very beginning. The new ovalturning lathes allow the chucked workpiece to be rotated together with the chuck or the faceplate.

Work-holding devices should be as light as possible due to the unbalance forces when ovalturning. Wooden parts are prefered. One should choose the lightest types of steel chucks.

The workpiece should be held as close to the faceplate as possible. Overhanging workpieces cause vibrations and consequently no cleanly cut surfaces.

5.2 Screwing on

Figure4201

The faceplate of the Ovalturning Lathe ODM30 has a series of through holes and M8 thread holes for screwing workpieces and work-holding devices to faceplate

A cut oval blank – for instance for bowl turning – can be screwed directly onto the faceplate from the rear using strong hexagon headed wood screws.

Figure 4202

Figure 4203

To protect the faceplate a cardboard disc is placed between it and the workpiece allowing cuts to be made up to the rim of the bowl.

Figure 4204

Hardwood disks for recesses or spigots are likewise screwed from the rear onto the faceplate.

Figure 4205 The shallow ebony bowl, with the outside completed, is jam fitted into a recess in a hardwood disc screwed onto the faceplate. Note the slots for levering the bowl out after ovalturning and sanding the inside.

Figure 4206

For workpieces hanging over the faceplate a board is screwed onto the faceplate using M8 countersunk screws. The workpiece is fixed onto the board from the rear using hexagon head woodscrews.

Figure 4207

Flat light blanks to be turned completely from the front, as with shallow bowls, are glued with paper onto a board which is then screwed from the rear onto the faceplate.

5.3 Chucks

Figure 4301

The claw chuck consists of a hard plywood board about 27mm thick and 4 claws made from 2mm steel sheet. Their prongs are hammered into the blank. The claws are screwed onto the board using M6 screws. On the rear of the board there are in-line holes with captive nuts beneath.
(Workshop J. Volmer)

Figure 4302

WThe wedge chuck is used for workpieces with parallel edges, e.g. rectangular picture frames. It is simple to build, but has a small chucking range.
Wedge chuck for the Ovalturning Lathe ODM15. (Workshop J. Volmer)

Figure 4303

Two-jaw chuck for workpieces with parallel edges, screwed on the faceplate of the ODM15. Chucking range 9mm to 102mm, plywood body, mass 0,39 kg (Workshop J. Volmer).

Figure 4304

Two-jaw chuck for workpieces with parallel edges, screwed on the faceplate of the ODM30. Chucking range 94mm to 240mm, plywood body, mass 1,5 kg. (Workshop J. Volmer).

Figure 4305

Two-jaw chuck with 4 sharp-edged screw heads for chucking internally or externally oval turned pieces, e.g. bowls.

Figure 4306

VICMARC Four-Jaw-Chuck VM90 screwed on a short flange (instead of the faceplate) of the ODM30, with two sets of jaws fitting circular grooves in oval sawed blanks.

Figure 4307

Drills, made of steel sheet, for drilling circular grooves fitting the steel jaws SC45 and SC67 of the VICMARC Four-Jaw-Chuck VM90 (Workshop J. Volmer).

Figure 4308

VICMARC Four-Jaw-Chuck VM90 with hardwood jaws, screwed on by deep-set countersunk-head screws, jaws pressed together for turning an elliptical spigot fitting the recess of the workpiece. Best chucking if the ellipse axes coincide with the jaw edges.

Bild 4309

VICMARC Four-Jaw-Chuck VM90 with hardwood jaws, pressed together with wooden spacers for turning an elliptical recess fitting the spigot of the workpiece. The ellipse axes coincide with the jaw edges

Figure 4310

Small bowl with spigot, outside shape turned, chucked by the hardwood jaws for ovalturning the inside

Figure 4311

Screw chuck with ring of prongs as anti-twist device for ovalturning long grain pieces using the tailstock (ELLPIN)(Workshop J. Volmer)