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4.1.12. Milling reference datum This term refers to a special milling ®xture technique, which is required when milling a compound-angle in a workpiece. The measurement is extremely dif®cult if you take the workpiece out of the ®xture. The technique here is to set up a datum which is theoretically in the same plane as the matching surface. When the cutter approaches the datum, a very thin layer, usually a sheet of thin foil or paper, will be cut off. Then, the machining is completed.
4.1.13. Additional support The term is for those supports beyond the regular locating points, which can prevent the workpiece from deformation due to cutting forces. These supports need to be applied carefully in order to avoid interference with the locating points. It can be made from regular screws, as well as any ®xture element.
4.1.14. Slot-to-slot distance This term refers to UMJFS elements, especially to the base elements. The adjacent T-slots on the base elements are always 60mm apart. So, the distance
Towards the design and development of modular jigs and ®xtures 385
between slots are multiples of 60mm. For example, 180mm is the distance between ®rst and fourth slots.
4.2. Naming conventions
A naming convention is established for UMJFS to facilitate communication. Particularly we establish a convention for names of workpieces, which will actually be mounted on ®xtures of machining. For example, a workpiece called ``work table'' is well known as a major component for a product. Another naming convention we need is for UMJFS elements. There has been a well established convention available, one name matches a particular element. However, a quite amount of work still needs to be done in order to ®t our needs.
4.2.1. Base The name refers to the base elements. As mentioned earlier, the basic unit for the dimension of UMJFS element is 60mm. Then, one basic unit is 60mm, two basic units are 120mm, and so forth. The thickness of the base element is always one basic unit. This convention is especially designed for naming the base elements. There are T-slots equally spaced horizontally and vertically on the working surface of the base and the slot-to-slot distance is always one basic unit, 60mm. By counting the slot number, one can tell the exact size of the base element. For example, 263 means the base size should be 120mm6 180mm660mm.
4.2.2. Support elements There are lots of varieties of support elements. Three basic cross-sections are available. They are
Table 1.
Cross-Section Height of support elements (mm)
45660 10 15 20 30 60 90 ... 60660 10 15 20 30 60 90 120 90660 10 15 20 30 60 90 120
Table 2.
45660 60660 90660
10mm T-slots, two sides T-slots, two sides T-slots, four sides 15mm T-slots, two sides T-slots, two sides T-slots, four sides 20mm T-slots, two sides T-slots, four sides T-slots, four sides 30mm T-slots, 2 sides vertical T-slots, 2 sides vertical T-slots, 2 sides vertical 60mm T-slots, 1 sides vertical T-slots, 1 side horiz. T-slots, 2 sides vertical T-slots, 2 sides horiz. T-slots, 2 sides vertical T-slots, 2 sides horiz. 90mm T-slots, 1 sides vertical T-slots, 1 side horiz. T-slots, 2 sides vertical T-slots, 2 sides horiz. T-slots, 2 sides vertical T-slots, 2 sides horiz. 120mm ÐÐÐÐ T-slots, 2 sides vertical T-slots, 2 sides horiz. T-slots, 2 sides vertical T-slots, 2 sides horiz.
Table 3.
Cross section Angle in Degrees
60mm660mm Ð Ð Ð 7.5 15 30 45 90mm660mm 0.75 2 5 7.5 15 30 45
386 Kakish, Zhang and Zeid
45mm660mm660mm, and 90mm660mm. There has been a series for the height of support elements to meet the high demand in ®xture assemblies. Table 1 lists available element heights: The different slot arrangements of the support elements provide ¯exibility for assembling different ®xtures. Existing arrangements are shown in Table 2. Another group of support elements is the angle support, which has been designed with an angled surface relative to the datum surface. A series of elements representing different angle con®gurations are shown in Table 3. A series of hollow supports may be designed to meet the need of a large light structure, while maintaining the structure's strength. They only have key ways on both ends, but no T-slots on any other surface at all. Table 4 shows the basic con®guration. Other support elements are stretch plates with single T-slots and a width of 45mm, 60mm and 90mm, and also right/left L-shape supports.