Three designs are being considered for a worm gear set to pr

Three designs are being considered for a worm gear set to produce a velocity ratio of 20 when the worm gear rotates at 90 rpm. All three have a diametric pitch of 12, a worm pitch diameter of 1.000 in, a gear face width of 0.500 in, and a normal pressure angle of 14.5degree. One has a single-thread worm and 20 worm gear teeth; the second has a double-thread worm and 40 worm gear teeth; the third has a four-thread worm and 80 worm gear teeth. For each design, compute the rated output torque, considering both strength and pitting resistance. The worms are hardened steel, and the worm gears are chilled bronze.

Solution

Decide on the potential factors to be used in the design; assign names and establish the number of levels of each that are necessary or feasible or that naturally exist. If you expect that the response will be a nonlinear function of the factors, at least 3 levels per factor must be used. If a Central Composite or Mixture design is being considered, the designs available depend on the number of levels.

Is this design and analysis intended to get information about the process response(s) or about response variation or both? If about variation, should a Subsidiary design be used? If not, what kind of replication should be used?

Are all the Factors now being controlled or are they all considered essential, that is , all Main Factors?

Are some Factors not now being controlled but could be controlled for the experiment? Should they also be considered as Main Factors or they be grouped as Subsidiary Factors?

Are there some Factors that cannot be controlled but may be measured during the experiment? They should be included as Casual Factors.

Are the Factors quantitative or qualitative? Can or should qualitative factors be converted to be quantitative? Qualitative factors may not be used in any form of response surface or nonlinear model.

How might the factors interact? Include any prior experience, intuition or technical judgment! Factors that interact must all be Main factors. Resolution 3 Screening designs may be used to show lack of significance but factor significance may be masked by interactions. Use Resolution 4 designs as a minimum if at all possible.

What and how are the Responses to be measured? Responses must be quantitative even if they are based on subjective evaluations.