reverse engineering – recent advances and applications - OpenLibra

A Systematic Approach for Geometrical and Dimensional Tolerancing in Reverse Engineering
Δh_max = max{(maxRdM_h – minRdM_h), maxRFh, (60·meanRRah), Uh},
Δs_max = max{(maxRdM_s - minRdM_s), maxRFs, (60·meanRRas), Us}
In this step, the analysis is directed on the assignment of either ISO 286-1 clearance fits or
ISO 2768 general tolerances through the validation of the condition,
137
Δh_max + Δs_max + |a| ≥ maxRdM_h – minRdM_s (1)
where |a| is the absolute value of the maximum ISO 286 clearance Fundamental Deviation
(FD) for the relevant nominal sizes range (the latter is approximated by the mean value of RdM_h,
RdM_s sets). If the above condition is not satisfied the analysis is exclusively directed on ISO
2768 general tolerances. Otherwise, the following two cases are distinguished, (i) Δmax ≤ IT
11 and (ii) IT 11< Δmax ≤ IT 18. In the first case the analysis aims only on ISO 286 fits, whereas
in the second case, both ISO 286 and ISO 2768 RE tolerances are pursued.
3.2 Sets of candidate IT grades, fundamental deviations and nominal sizes
The starting point for the Step (b) of the analysis is the production of the Candidate tolerance
grades sets, ITCAN_h, ITCAN_s, for the hole and shaft features respectively. It is achieved by
filtering the initial Candidate IT grades set, ITCAN_INIT, which includes all standardized IT
grades from IT01 to IT18, by the following conditions (applied for both the h and s indexes),
ITCAN ≥ maxRF , ITCAN ≥ maxRdM - minRdM
ITCAN ≤ 60·meanRRa , ITCAN ≥ U
Moreover, in case when estimated maximum and minimum functional clearance limits are
available (maxCL, minCL), candidate IT grades are qualified by the validation of,
ITCAN < maxCL
ITCAN < maxCL – minCL
The above constraints are applied separately for the hole and shaft and qualify the members
of the ITCAN_h, ITCAN_s sets. Likewise, the set of initial Candidate Fundamental Deviations,
FDCAN_INIT, that contains all the FDs applicable to clearance fits i.e. FDCAN_INIT = {a, b, c, cd, d,
e, f, fg, g, h}, is filtered by the constraints,
FDCAN ≤ minRdM_h – maxRdM_s
FDCAN ≥ minCL
(5)
FDCAN < maxCL – (min ITCAN_h + minITCAN_s)
The latter constraints, (5), apparently only apply in case of maxCL and/or minCL
availability. All qualified FDs are included in the common set of Candidate Fundamental
Deviations, FDCAN. In the final stage of this step, the Candidate Nominal Sizes Sets, NSCAN_h,
NSCAN_s, are initially formulated for the hole and shaft respectively. Their first members are
obtained from the integral part of the following equations,
NSCAN_h_1 = int [ minRdM_h – max FDCAN - maxITCAN_h]
NSCAN_s_1 = int [ maxRdM_s + max FDCAN + maxITCAN_s]
(2)
(3)
(4)
(6)