Defective products are sent for two reasons:
  •  Employees don't know it is a bad product 
  • They felt some sort of pressure to move on without correcting the mistake 
It sounds simple, but it’s not. Let’s look into these further.
If the employee is truly unaware that a product is unacceptable, typically there are a few reasons why:
1.) They don’t know the standard. One common misconception (especially in todays unique employee pool) is the generational misconception of “common sense quality.” Owners commonly quip “He should know that’s unacceptable.” Instead, use printed standards, posted on machines and walls above machine centers. SHOW them what quality looks like, and what failure looks like. Hang examples above machines as a constant standard for whomever comes to work at that station. Send your employees emails with constant reminders of best quality practices and detailed photographs.
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2.) There isn’t an inspection process. If inspection isn't a part of each process, you will just plain and simple miss defects. Add inspection into every process, your're trading seconds for hours and time is money. 
Now, why would an employee intentionally ship an unacceptable piece of work? Internal pressures. The simple fact is this: for whatever reason, it’s sometimes easier to ignore the problem than deal with it. Humans are experts at finding these opportunities to save energy. Reverse that in your shop, make it harder to ignore than to deal with. Think of this example: I’m a guy running a rail end machine when a rail end blows out, and I know it. I’ve seen a few different types of phycology at play in these situations.
There are competing pressures in the shop environment that will persuade the employee that he needs to not take the time to correct the mistake, and to pass it on for someone else to find. Read the rest of the story on cabinet shop reworks here>>