 |  | Small-Scale Horn Processing (ILO - WEP, 1988, 104 p.) | ||
 |  | CHAPTER VII. ASSEMBLY METHODS | ||
|  | 1. Bonding | ||
| | 2. Joining | ||
| | 3. Pinning | ||
| | 4. Screw and nut assembly | ||
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Bonding is the easiest way of assembly. Most strong adhesives are suitable. Artisans in Madagascar prefer to use modern epoxy resin adhesives. The technique for bonding horn is the same as that used for bonding wood or iron. The pieces are first cleaned carefully with fine sandpaper. Then a very fine film of adhesive is applied to the two surfaces to be bonded. Finally, the two parts are pressed together until the adhesive has hardened. This process may take 24 hours. The parts may be held together by placing heavy objects on top of them, or they may be held in a vice or bench clamp. A well-equipped workshop should possess manually operated vices such as those shown in figures VII.1 and VII.2. The vice in figure VII.3 may be fixed to a table or shelf during the drying process. The vice in figure VII.1 may be replaced by a hardwood model, manufactured by a joiner, or even by a horn vice.
Figure VII.1: Manual vice
Figure VII.2: Manual vice
Figure VII.3: Bench
clamp
This method of assembly is commonly used by artisans, for example to mount a leaf on a branch (see figure VII.4).
Figure VII.4: Assembling a leaf
In order to make a joint, a cylindrical hole must be drilled in the support piece and the male end of the part to be mounted must be filed to the same nominal diameter. In the example given in figure VII.5, it is a leaf stalk. Parts may be assembled with a tight or loose fit. If a tight fit is required, the diameter of the male part should be slightly larger than that of the hole. The pieces must be forced together in order to obtain a rigid assembly. If the diameter of the male part is slightly smaller than that of the hole, the assembly will be loose. It may be made rigid by placing a small quantity of adhesive in the hole before assembling the parts.
Figure VII.5: Example of
joining
Pinning, known as pegging or dowelling in woodworking, allows rigid but dismountable joints to be made. Pinning is a form of joining as it consists of placing a pin or peg in a Pin, cylindrical hole drilled through the two parts to be assembled, which are joined together as shown in figure VII.6. The pin may be of horn, hardwood or metal. The nominal diameter "d" of the pin depends on the nominal diameter "D" of the male part.
Figure VII.6: Example of pinning
|
D |
6 |
8 |
10 |
12 |
14 |
16 |
18 |
20 |
|
d |
1,5 |
2 |
2,5 |
3 |
3,5 |
4 |
4,5 |
5 |
It is possible to dismount the assembly by removing the pin with the aid of a pin-punch, such as that shown in figure VII.7.
Figure VII.7:
Pin-punch
We have seen in Chapter III that screws and nuts may be made from horn. The following paragraphs describe three particular techniques of threaded assembly, which can be very useful to horners.
Threading a screw is an easy task. The same screw will therefore be used in the three cases examined. The original feature of the method lies in the technique used for nut threading.
Figure VII.8 shows a screw-tipped rod which could, for example, be a lamp support screwing into a tap-threaded base. Figure VII.9 shows the two parts before they are screwed together. It will be seen that the base (the nut) is tapped through. This is usual when the nut component is not very thick. In this case, nut threading presents no problems.
Figure VII.8: Threaded screw
Figure VII.9: Parts before assembly
When the nut component is thicker, it need not be threaded through, but only to a depth sufficient to accommodate the screw. As it is difficult to thread to a precise depth, it is preferable to thread the nut component to a depth slightly greater than the length of the screw. Before threading the nut component is, in any case, drilled through (figure VII.10).
Figure VII.10: Nut threading
Figure VII.11 illustrates the depth of screw cutting recommended for this type of assembly (in mm).
Figure VII.11: Parts before they are
assembled
|
Ø D |
3 |
4 |
5 |
6 |
8 |
10 |
12 |
14 |
16 |
18 |
|
L |
5 |
6 |
8 |
9 |
12 |
15 |
18 |
21 |
24 |
27 |
|
H |
L+2 |
L+3 |
L+3 |
L+4 |
L+5 |
L+6 |
L+7 |
L+8 |
L+8 |
L+10 |
In figure VII.12, the hole is neither drilled nor threaded completely through. This is known as recessed threading. It is used especially when the surface of the nut component opposite the surface which receives the screw must be, for aesthetic reasons, free of drilled or threaded holes. This technique is also used when the nut component is too thick to be completely drilled through.
Figure VII.12: Recessed threading
Figure VII.13, which shows the parts before they are mounted, indicates the recommended depths of drilling and threading according to the screw diameter.
Figure VII.13: Parts before they are
mounted
|
Ø D |
3 |
4 |
5 |
6 |
8 |
10 |
12 |
14 |
16 |
18 |
|
L |
5 |
6 |
8 |
9 |
12 |
15 |
18 |
21 |
24 |
27 |
|
H |
L+2 |
L+3 |
L+3 |
L+4 |
L+5 |
L+6 |
L+7 |
L+8 |
L+8 |
L+10 |
|
P |
L+5 |
L+6 |
L+8 |
L+10 |
L+12 |
L+14 |
L+16 |
L+18 |
L+20 |
L+22 |
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