Please consider us for your next engineering design project! Specimens were held for testing as shown in Fig. Determination of the Lower Tolerance Limits A normality assumption for a data set must be shown to make reliable tolerance analyses before calculating tolerance limits. Therefore, LTL values dowel diameter tolerance analysis white oak specimens were calculated using the expressionanaalysis those of red oak specimens were calculated using binomial probability. Standard dowel pin sizes coming soon!

For this purpose, T-shaped edgewise dowel joints were constructed to determine their ultimate failure load capacity levels. Therefore, sample sizes were determined using a modified Faulkenberry-Week method for a univariate normally distributed data set created for a pilot study, which had 30 specimens. Accordingly, specimens were constructed. The results of the study indicated that the LTL method provides a sound design value estimate for dowel joints used in furniture frames.

The mechanical properties of wood member and joint strength play a vital role in determining the strength of the furniture frames Derikvand and Ebrahimi To produce durable furniture that is able to withstand usage loads, it is necessary to have rational estimates of the joint capacity used in its construction. Joints are the weakest part of the furniture structure and significantly influence its overall reliability.

Accordingly, failures are typically due to loose or failed joints rather than fractured legs or rails Eckelman et al. Thus, when designing furniture, it is essential to have reliable estimates of the load carrying capacities and the variability of capacity of the joints used in construction Eckelman Dowel joints are widely used in chairs and tables because of their favorable cost and production characteristics, and numerous studies have been conducted to determine their load capacity levels Zhang and Eckelman ; Eckelman et al.

However, reasonable design values for dowel joints used in the furniture frames have not been established. In engineering design, it is vital to manage data Dowel Diameter Tolerance variability due to material properties. Identical samples may not provide similar test results due to inherent variation caused by inconsistency in the creation, location, and propagation of dislocation and cracks Lee et al.

When large-scale production begins, property variation and the potential for structural failure are expected to increase due to the variability in material used, design errors, and manufacturing errors. Determining the acceptable level of design values should measurably increase the reliability and safety of structures Wencheng Therefore, furniture joints must resist external loads by utilizing such design values. At this point, a source of difficulty for designers and engineers lies in estimating the failure probability for structures and making appropriate reliability analyses Echard et al.

In a previous paper Eckelman et al. The results of the study indicated that this is a useful approach that provides information needed to rationally determine design values.

Of particular interest, the study allows designers to relate the fraction of the average value with the degree of confidence used for design purposes. Therefore, the question arises whether a statistical lower tolerance limit approach could also be used to determine reasonable design values for two-pin moment-resisting dowel joints. The aim of this study was to examine the estimation of reasonable design values for two-pin moment-resisting dowel joints by using the lower tolerance limits LTLs method.

The construction of the specimens used in this study is shown in Fig. The red oak Quercus rubra and white oak Quercus alba materials used in specimen construction were obtained from a local sawmill. A single meter-long board was cut from the end of each full-length board obtained for the study.

Blanks, The defect-free rails and posts were then randomly selected from this pool of material. Plain red oak dowels Quercus rubra , averaging 9.

Holes were drilled in the rails and posts to a depth of The tolerances were 0. The coated end of each dowel was then inserted into the accompanying rail hole to a depth of After the rail components cured for 8 h, the post holes and the exposed dowel surfaces were coated with adhesive. The dowels were then inserted into the holes at the edge of the posts, and the resulting assembly was clamped together for 8 hours.

Specimens were held for testing as shown in Fig. The vertical rate of load head movement was Loads were applied to the rail at a point 0. Tests were continued until a non-recoverable drop-off in the load occurred Erdil et al. The following expressions were used to calculate bending stresses, shear stresses, and axial stresses of the joints Eckelman ; Hibbeler :.

Where is normal stress due to bending MPa , F 4 is bending moment capacity N. The parameters d 1 and d 2 are distances between the rail center and the centerlines of the dowels loaded in tension and compression mm , respectively, and y 1 and y 2 are distances between the dowel centerlines loaded in tension and compression, respectively, and the outside of the dowel loaded in compression mm. Where is normal stress due to dowel withdrawal MPa , F 2 is axial force on dowel in tension N , and d 3 is the distance between dowels in compression and the outside compression rail edge mm.

A normality assumption for a data set must be shown to make reliable tolerance analyses before calculating tolerance limits. If a distributional assumption were not made, tolerance analysis would be damaged. Otherwise, occasionally, data may not be close to normal. In this case, researcher may not wish to make any distributional assumption and non-parametric tolerance intervals can provide an answer to obtain lower tolerance limits Young For design purposes, statistical lower tolerance limits for normal distribution enable a designer Dowel Diameter Tolerance Light to apply test results to the performance one can expect from similar joints in practice—with a specified degree of confidence.

These limits are defined by the expression,. A secondary question of importance involves the sample size needed to establish the data base on which the selected level is based.

Sample size determination for univariate normal distribution, based on specified tolerance intervals, was developed by Faulkenberry and Weeks Young et al. In the case of non-normal distributed data sets, non-parametric tolerance limits are calculated by means of the following binominal probability expression Young ,. In the pilot study, according to Dowel Diameter Tolerance 10 Central Limit Theorem CLT , 30 T-shaped edgewise two pin moment-resisting dowel joints, constructed of red oak and white oak, were used as reference data to determine sample sizes using the modified Faulkenberry-Weeks method.

The results of these data sets are shown in Table 1. In order to check normality of the data sets, Shapiro-Wilks tests were done for both sample groups. The Shapiro-Wilks normality test shows that p-values for joints constructed of red oak and white oak are 0. Both p-values are greater than 0.

Identical sample sizes were obtained for both data sets. Results for the joint specimens constructed of red oak are illustrated in Fig. The average ultimate load capacity was The highest and the lowest load capacity levels were Results of the joint specimens constructed of white oak are illustrated Fig. The highest and lowest load capacities were The normality assumption may be violated due to data set outliers Fig.

Therefore, LTL values of white oak specimens were calculated using the expression , whereas those of red oak specimens were calculated using binomial probability. Boxplots and histogram graphs for a: specimens constructed of white oak b: specimens constructed of red oak.

The parameters indicated in Eqs. In respect to the calculations in these equation, results of the LTL values of joints corresponding to bending, shear, and axial stresses are given in Table 4. According to the results, the LTL value of joints constructed of white oak for bending stress were Those of shear stress and axial stress were 2. On the other hand, those of red oak are Fixed fastener calculations will show minimal interference between dowel pins and slip fit holes. Dowel pins should be installed into press fit holes after finishing processes and not removed there after.

After the mating components are assembled the first time, one should note assembly orientation for repeat assembly of mating dowel pins. It is optimal to design for one configuration assembly fool - proof.

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