Exterior surface roughness is reflective part surface index of a of error of microcosmic geometry appearance main technique, it is to examine the main basis of quality of spare parts surface; What it chooses is reasonable, matter to the quality of the product, service life and manufacturing cost directly. The selection method of surface roughness of surface of mechanical spare parts has 3 kinds, namely law of numeration, trial and analogy law. In work of design of mechanical spare parts, applying prevailing is analogy law, this way is handy, rapid, efficient. Applied analogy law needs to have enough reference material, all sorts of existing mechanical design offerred more overall data and document in manual. The most commonly used is the exterior surface roughness that suits with photograph of tolerancepublic errand grade. Connecting general reason condition to fall, demand of public errand of dimension of mechanical spare parts is less, the exterior surface roughness of mechanical spare parts is worth smaller also, but between them nonexistent fixed function concerns. For example the got-up surface of the certain and mechanical spare parts on machinery of the handle on a few machines, instrument, handwheel and sanitary equipment, food, their surface asks to be machined very glossily namely demand of exterior surface roughness is very high, but demand of its dimension public errand is very low however. Be in usually, have the part that dimension public errand asks, there still is particular corresponding concern between grade of its public errand and numerical value of exterior surface roughness. In monograph is being made with machinery in design manual of a few mechanical spare partses, the experience that to the dimension of the exterior surface roughness of mechanical spare parts and mechanical spare parts tolerancepublic errand concerns and computational formula have a lot of introductions, paratactic watch offers a reader to choose, but as long as attentive read come, with respect to meeting discovery, although adopt identical experience computation formula, but the numerical value in place list is endless also and same, some still has very big difference. This was brought to the person that is not familiar with this respect circumstance puzzle. What exterior surface roughness chooses in also increasing them to work in mechanical spare parts at the same time is difficult. In real work, to the machine of different type, its spare parts falls in the condition of same size public errand, it is discriminating to the requirement of exterior surface roughness. This is the stability issue that coordinate. In design and making a process of mechanical spare parts, to the machine of different type, the cooperates stability and interchangeability requirement of its spare parts is different. In design manual of existing mechanical spare parts, of report basically have the following 3 sort: The 1st kind basically is used at accurate machinery, very tall to assorted stability demand, requirement spare parts is in use process or classics after be being assembled for many times, the wear limit of its spare parts does not exceed 10% what public errand of spare parts dimension is worth, the face that this basically uses in accurate instrument, appearance, narrow measure, ponderosity wants the attrition range of the spare parts, be like cylinder inside the main shaft neck of boring machine of the main shaft neck of the surface, accurate machine tool, coordinate. The 2nd kind basically is used at average accurate machine, taller to assorted stability demand, the wear limit of requirement spare parts does not exceed 25% what public errand of spare parts dimension is worth, the requirement has very good the interface that join closely, its basically apply in sell aperture like the machine tool, tool, surface that cooperates with scroll bearing, awl, the working face of cooperates the surface, gear teeth of a cogwheel that still the interface with opposite motion higher rate is like sliding bearing. The 3rd kind basically is used at current mechanism, ask the wear limit of mechanical spare parts does not exceed 50% what dimension public errand is worth, without the spare parts interface of opposite motion, be like box top, sleeve, the working face of the surface with clingy requirement, key and keyway; The interface with opposite motion not high rate, if the bracket aperture, lining, job that takes axle aperture expresses face, reducer,wait a moment. Here we are worth to the of all kinds watch in mechanical design manual undertake statistic is analysed, standard of will old country of exterior surface roughness (GB1031, the 1983 new country standard that 68) changeover uses international standard ISO to promulgate to consult (GB1031, 83) , use preferential chosen assess parameter, namely average deviation is worth outline arithmetic Ra ＝ (Dx of ｜ of Y of ｜ of 1)/(l) ∫ L0. Use Ra preferential a series of chosen numerical value, derivation gives exterior surface roughness the concerned relation between Ra and IT of dimension public errand is the 1st kind: Ra ≥ 1. 6Ra ≤ 0.
≤ of 008 × IT Ra 0.
8Ra ≤ 0.
010 × IT the 2nd kind: Ra ≥ 1.
6Ra ≤ 0.
≤ of 021 × IT Ra 0.
8Ra ≤ 0.
018 × IT the 3rd kind: Ra ≤ 0.
042 × IT list of afore-mentioned 3 kinds of relation, if express 1, watch 2, the watch is shown 3 times. Express grade of 1 public errand and exterior surface roughness to be worth (use at accurate machinery) tolerancepublic errand grade is basic dimension (500 surfaces of ～ of 400>400 of ～ of 315>315 of ～ of 250>250 of ～ of 180>180 of ～ of 120>120 of ～ of 80>80 of ～ of 50>50 of ～ of 30>30 of ～ of 18>18 of ～ of 10>10 of ～ of 6>6 of ～ of Mm) ～ 3>3 surface roughness numerical value.
10.
20.
4IT70.
10.
20.
40.
8IT80.
20.
40.
8IT90.
20.
40.
81.
6IT100.
40.
81.
63.
2IT110.
81.
63.
26.
3IT120.
81.
63.
26.
3 watches surface roughness of grade of 2 public errand and surface is worth (use at common and accurate machinery) tolerancepublic errand grade is basic dimension (500 surfaces surface roughness counts ～ of 400>400 of ～ of 315>315 of ～ of 250>250 of ～ of 180>180 of ～ of 120>120 of ～ of 80>80 of ～ of 50>50 of ～ of 30>30 of ～ of 18>18 of ～ of 10>10 of ～ of 6>6 of ～ of Mm) ～ 3>3.
20.
40.
8IT70.
20.
40.
81.
6IT80.
40.
81.
63.
2IT90.
81.
63.
26.
3IT101.
63.
26.
312.
5IT111.
63.
26.
312.
5IT120.
46.
312.
5 watches grade of 3 public errand and exterior surface roughness are worth (use at current mechanism) tolerancepublic errand grade is basic dimension (500 surfaces of ～ of 400>400 of ～ of 315>315 of ～ of 250>250 of ～ of 180>180 of ～ of 120>120 of ～ of 80>80 of ～ of 50>50 of ～ of 30>30 of ～ of 18>18 of ～ of 10>10 of ～ of 6>6 of ～ of Mm) ～ 3>3 surface roughness numerical value.
81.
63.
2IT80.
81.
63.
26.
3IT91.
63.
26.
312.
5IT103.
26.
312.
5IT116.
312.
525IT126.
312.
525 in work of design of mechanical spare parts, when choosing numerical value of exterior surface roughness by dimension public errand, ought to the machine according to different type, choose corresponding watch value. Those who need a specification is, the Ra in the watch uses value of the 1st series, and the limiting value of old GB Ra is worth for the 2nd series, the meeting when conversion encounters numerical value to go up to lean and leave the question that lean. We are used in value of the watch in the watch on lean, because this is helpful for improving product quality, specific value uses next relying on. The content of the tolerancepublic errand grade of old GB and the watch with exterior corresponding surface roughness and form are more complex, section of same to grade of same public errand size is same and main dimension, the exterior surface roughness of aperture and axis is worth not identical, different cooperate phyletic numerical value not identical also, as a result of,this is old public errand and coordinate a standard (GB159, the tolerancepublic errand numerical value of 59) is concerned with afore-mentioned elements. Active new GB noncombatant duty and cooperate (GB1800, it is identical that each standard public errand of basic measure inside section of same to grade of same public errand size is worth 79) , make the corresponding watch of tolerancepublic errand grade and exterior surface roughness simplifies greatly so, more scientific also reasonable. In designing the job, the choice in the final analysis of exterior surface roughness or must from set out actually, measure the exterior function of the spare parts and craft economy in the round, ability makes logical choice. The tolerancepublic errand grade that gives out in the watch and exterior surface roughness are worth the reference when can offerring a design. CNC Milling