Q.   What is a good number for rework in the initial machining and cut-up operations?
 
A.  This is an interesting question and the answer will vary by species and by the definition of a defect.  A good target value that I saw at one facility I visited (and I think it is reasonable) was 3%.  That is, 3% of the pieces needed reman work during manufacturing.  
 
This company was trying to avoid sending any defective pieces to the next manufacturing step; being perfect is likely too expensive. So, they are prepared to give a next processor or customer a credit for a few defects.  Note, however, that the cost of the defect at this point is much higher than if it had been caught and corrected earlier.
 
 
 
 

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Gene Wengert, aka The Wood Doctor, troubleshoots wood related problems, and explores lumber and veneer qualities and performance, species by species, in Wood Explorer, inside FDMC's Knowledge Center.


So, here is the key that many people miss:  Careful inspection and then removing a defective piece from production is noteworthy.  But we want to do more than eliminating the defective piece.  We need to identify and then correct the cause, if at all technically and financially possible.
 
Some defect is too expensive to eliminate...that is why we use putty!
 
A good follow-up question is “Why do we have defects?”  Here is a short answer.  Some species have spiral or twisted grain (pine and hard maple are especially troublesome).  Varying moistures can be an issue.  Knife and machine set-up is critical.  Over-drying, which is easy to prevent, increases defects.
 
It is therefore very profitable to continually monitor and determine the cause of any defects (there are a lot of wives' tales about some defects, so oftentimes technical, knowledgable assistance is required to avoid solutions that do not work) and try to correct the cause.  

 

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