I've never seen a method for calculating the traditional Cp and Cpk for product attribute data. One book I have says that you take the average output (yield) and compare with "management expectations". It goes on state that "if the level is unacceptable, further analysis and action must be directed toward the process itself (management responsibility)." Their parentheses, not mine. Now that I've stopped rolling on the floor laughing and wiped the tears from my eyes, I'll continue. If you subscribe to the theory that SPC is a means to end, a tool by which to improve processes and capabilities, putting up the control chart, tracking yields and responding to the out of controls is probably adequate to accomplish your goal. If you have to have a Cpk number, why not reverse engineer it? After all, the Cpk value is only telling you what the expected yield of the process is. As an example, a process capability of 1.00 means that you have an expected defect level of 1,350 ppm on a one-sided specification (which is applicable to a yield attribute). Thus if your attribute control chart showed you had an average yield of 99.865%, your Cpk would be 1.00. ---------- From: Hinners Hans CIV WRALC/LYPME [SMTP:[log in to unmask]] Sent: Thursday, September 09, 1999 2:55 PM To: [log in to unmask] Subject: Re: [TN] Process capability Eric and all, How about tracking the yield through the process/machine over time - per shift, daily, weekly, whatever makes sense? Example, I have 95% yield so I know for every 100 scheduled/produced I can expect, on average, to get 95 good ones to go to the next step. I can't tell you which ones are good until I measure/inspect something. I think of process capability (or the index), Cp or Cpk, as a means to compare the ability of a process/machine to produce something within tolerance. It tells me whether I will go broke trying to make something. Hans ~~~~~~~~ Hans M. Hinners WR-ALC/LYPME Bldg. 640 Materials Engineer 380 Second Street, Suite 104 Manufacturing Eng. Sec. Robins AFB GA 31098-1638 912-926-1970 (Voice) 468 - 1970 (DSN) 912-926-7974 (Fax) [log in to unmask] > > What is the best way to determine the process capability of a machine in > terms of defective units produced? How can I say that a certain machine is > capable only of producing a certain no of good units everytime it is being > run? Any inputs will be highly appreciated. > > Eric > FAAI ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ############################################################## ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################