Edit post

Edit your reply below.

Post Body
Enter your post below.
I think slack might be called a necessary evil.  I don't believe that slack was provided for the purpose of starting a train one car at a time, however, it was put to that use.  As has been mentioned, couplers require a bit of slack to allow the knuckle lock to slide into position.  The coupler parts are cast without machining, so they have a considerable dimensional tolerance.  To allow for that tolerance, and for the fact that they are not lubricated, the parts must fit rather loosely.  The accumulation of that looseness adds up to the coupler slack.  Link and pin couplers had much more slack generally because there were a lot of manufacturers making the parts, which were not exactly and not always interchangeable.  So they had more looseness to accommodate the greater variation of parts. 
Tags (Optional)
Tags are keywords that get attached to your post. They are used to categorize your submission and make it easier to search for. To add tags to your post type a tag into the box below and click the "Add Tag" button.
Add Tag