 |  | Small-Scale Horn Processing (ILO - WEP, 1988, 104 p.) | ||
 |  | CHAPTER III. WORKING OF HORN | ||
|  | 1. The workbench | ||
| | 2. Drilling | ||
| | 3. Filing | ||
| | 4. Engraving and carving | ||
| | 5. Turning | ||
| | 6. Thread cutting | ||
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A wooden workbench is suitable for working horn. It should be equipped with a wooden vice, a fitter's vice and a bench clamp. The wooden vice is used for holding untreated horns. The fitter's steel vice has parallel jaws and is used for holding pieces of horn while they are being worked. The clamp is used to secure untreated or flattened horns firmly to the bench. It should have an eccentric grip to avoid splintering the horn.
A workbench with its fittings is shown in figure III.1.
Figure III.1: Workbench with
fittings
Twist drills used for drilling soft metals are suitable for working horn (figure III.2). A set of 25 drills ranging from 1 to 13 mm at 0.5 mm intervals (figure III.3) is usually sufficient. The drills can be used on a hand drill (figure III.4) or a low-powered 300 to 350 W portable electric drill (figure III.5) which can be clamped to a small bench stand, as shown in figure III.6. A small parallel-jaw vice (figure III.7) is very useful for securing pieces to be drilled to the bed plate.
Figure III.2: Twist drill
Figure III.3: Set of twist drills
Figure III.4: Hand drill
Figure III.5: Portable electric
drill
Filing is done with wood files. The three types shown in figure III.8, which are 200 mm long, are perfectly adequate in most cases. Two sets are necessary: one with large teeth for making the rough model and another with small teeth for finishing before polishing.
Figure III.6: Bench stand
Figure III.7: Parallel-jaw vice
Figure III.8: Wood
files
When a good deal of material has to be cut away in order to rough out an object in the solid part of the horn, artisans use a bill-hook, as illustrated in figure III.9.
Figure III.9: Bill-hook
Horn may be carved manually using chisels, mortises and gouges for wood carving, such as those presented in figure III.10. As it is not necessary in most cases to go much below the surface of the horn and as horn is relatively soft, light pressure is applied to the tool handle manually or the handle top is tapped with the heel of the hand or with a wooden mallet (figure III.11).
Figure III.10: Chisels, mortises and
gouges for wood carving
Figure III.11: Wooden mallet
In a semi-mechanised workshop, carving may be carried out using small milling cutters, such as those illustrated in figure III.12. These cutters are mounted on a small portable milling machine, as shown in figure III.13.
Figure III.12: Series of milling
cutters
On the milling machine, the electric motor (A) provides the power to rotate the cutter through a transmission cable in a flexible sheath (B). A milling spindle (C) enables the cutter to be held and directed manually during milling. The motor is switched on and off by means of a pedal (D). The horn should be firmly held by a vice or clamp during milling, but it may in some cases be held by hand when it is only the surface that needs to be worked. If no motor is available, the flexible shaft may be connected to an electric drill.
Figure III.13: Portable milling
machine
Horn may be worked on a wood or metal lathe. Cutting speeds, feed operations and cutting tools are similar to those used in working hard wood.
Horn may be turned using a loose head between stocks or by a combined method (mandrel on one side and tail-stock on the other), depending on the section to be worked and the type of turning operation required. In mounting a solid horn section only, the horn can be held safely by a mandrel, or between stocks or both. In mounting a hollow section, or in drilling, only a mandrel should be used.
In order to hold the piece tightly when using a mandrel, protective jaws previously milled to the shape of the horn should be used. If, however, a piece of both hollow and solid horn is to be worked, it may be held either with a mandrel or with mandrel and stocks, the solid section being held at its end by the tail-stock. Whenever a tail-stock is used, a central hole must be drilled (figure III.14) with a centre bit (figure III.15) at the end of the horn held by the tail-stock. Except in cases where short lengths are to be used, the horn must be heated and straightened before being mounted on the lathe. A brilliant finish can be obtained by polishing the horn on the lathe with oiled sandpaper.
Figure III.14: Drilling a central
hole
Figure III.15: Centre bit
The mounting shown in figure III.16 is easy to do and enables the outside of a whole horn to be turned on the lathe while being held between stocks. The drilled hardwood corner allows the horn to be fixed on the tip of the headstock. This type of mounting is particularly recommended for the rapid cleaning and polishing of untreated horn.
Figure III.16: Lathe work on a horn
held between
stocks
Screws and nuts can be made from horn, using taps (figure III.17) and dies (figure III.18) which are generally used for metal-thread cutting.
Figure III.17: Tap
Figure III.18: Die
A tap wrench (figure III.19) and a die stock (figure III.20) are essential for turning taps and dies by hand.
Figure III.19: Tap wrench
Figure III.20: Die stock
To make a screw, the external diameter of the horn, before threading, is taken to be equal to the diameter of the screw. It is different in the case of tapping: the diameter of the holes to be drilled before tapping is given in table III.l. The thread and screw dimensions given are those of the International Organization for Standardization (ISO).
Table III.1: Diameter of holes to be drilled before tapping (mm)
|
Screw diameter |
3 |
4 |
5 |
6 |
8 |
10 |
12 |
14 |
16 |
18 |
|
Screw thread |
50 |
70 |
80 |
100 |
125 |
150 |
175 |
200 |
200 |
250 |
|
Diameter of holes to be drilled before tapping |
2.4 |
3.2 |
4 |
4.8 |
6.5 |
8.2 |
10 |
11.6 |
13.6 |
15 |
 |
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