The primary objectives of this thesis investigation were: 1. To establish the maxima and minima values, within limits of the welding machine parameters: current and time, for 28 gauge, 24 gauge, 20 gauge, 18 gauge, and 16 gauge of SAE CR 1010 steel. 2. To implement and calibrate the instrumentation necessary to determine accurate values, within limits, of the variables under investigation. Also, to devise suitable controls for those fixed variables not investigated. 3. To correlate values of welding current and time with resulting tensile-shear strengths of the lapped welding joints. 4. To establish the combination of welding current and weld time which gives a maximum value of tensile strength for the metal gauges under investigation. A brief review of the more important literature on resistance spot welding variables was presented. The calibration process of determining voltage, resistance, and current was described. The mathematical prediction models (relationship between weld strength and weld time) were established for each heat control setting for different thicknesses under investigation, based on non-linear regression techniques. From the prediction models and the use of Calculus, the maximum tensile-shear strengths and corresponding maximum weld cycles were computed. The minimum weld strengths and weld cycles were determined by the welding conditions that just produced a weld of measurable strength. / Master of Science