tailieunhanh - Engineering Drawing for Manufacture phần 7

Engineeringdrawing cho sản xuất đường kính là do thực tế rằng các thiết lập công cụ khác nhau để bán kính có thể được tách ra. Dấu vết Mỗi do đó đại diện cho dấu vết tròn xung quanh lỗ khoan mặt đất và hiển thị ra ofroundness, không phải là tuyệt đối | 96 Engineering drawing for manufacture Figure Example of a 20 00p go no-go gauge inspecting 10 shafts from a production line Fit systems Figure shows the three basic fit systems . The left-hand sketch shows a shaft which will always fit in the hole because the shaft maximum size is always smaller than the hole minimum size. This is called a clearance fit. These have been discussed above with respect to running and sliding fits as per Figure . In some functional performance situations an interference fit is required. In this case the shaft is always larger than the hole. This would be the case for the piston rings prior to their assembly within an engine bore or for a hub on a shaft. In some functional performance situations a transition fit may be required. Should the shaft and hole final diameters be an interference-clearance fit the clearances will be very small and the location would be very accurate. If it were an interferencetransition fit on assembly the shaft would shave the hole and thus the location would be very accurate. The shaft basis and the hole basis system of fits In all the examples given above the discussion has been concerning shafts and holes . It should be remembered that this does not necessarily apply to shafts and holes. These are just generic terms that mean anything that fits inside anything else. However whatever the case it is often the case that either the shaft or the hole is the easier to produce. For example if they are cylindrical the shaft will be the more easily produced in that one turning tool can produce an infinite number of shaft diameters. This is not the case with the cylindrical hole in that each hole size will be dependent on a single drill or reamer. Limits fits and geometrical tolerancing 97 Figure Typical clearance transition and interference fits for a shaft in a hole Clearance fit Transition fjtllnterference fitl Clearance fit Transition fit interference fit Shaft basis system of fits. .