Still strugging with GetComponent and accessing other objects (C#)

I am still struggling with nulls when trying to access a script on one object from a script on a completely different one.

I had asked this before, but had to put this task down for a couple weeks - went to revisit it and still struggled with no luck for hours even with the previous help I am still missing something.

I did manage to clean up my code and concept though in the mean time - still won't work though.

ERROR=NullReferenceException: Object reference not set to an instance of an object Button.OnMouseUp () (at Assets/Standard Assets/Scripts/SimHub CSharp/Button.cs:31) UnityEngine.SendMouseEvents:DoSendMouseEvents()

Offending line: (Button.OnMouseUp())

        factoryLift1.GoToFloor(2); <-- something apparently null when we get here, why?

PUBLIC MACHINE factoryLift1 up top should hold a value - but it will not take, what is my error anyone? please?

 }

using UnityEngine; using System.Collections;

public class Button : MonoBehaviour {

 public bool pushed = false;
 public Machine factoryLift1;
       
 void Start() {
   
     GameObject tmp = GameObject.Find("Lift1");

     if (tmp != null)
     {
         Machine factoryLift1 = tmp.GetComponent<Machine>();
                     
     }
             

}

 void OnMouseEnter() {
     //renderer.material.SetColor("_OutlineColor", Color.blue); .//not important right now
 }

 void OnMouseExit() {
     //renderer.material.SetColor("_OutlineColor", Color.black); //not important right now
 }

 void OnMouseUp() {
     pushed = true;
     factoryLift1.GoToFloor(2);
           
 }

    
 void Done() {
     pushed = false;
 }
 

}

using UnityEngine; using System.Collections;

public class Machine : MonoBehaviour {

 public Transform target;
     
 private float floor1Height = 0F;
 private float floor2Height = 10F;
 
 private int floorNum;
 public Vector3 myDestination;
 private Vector3 velocity = Vector3.zero;
 public bool isActive = false;
 Vector3 floor1Destination; // start on ground
 Vector3 floor2Destination;
 
 // Use this for initialization
 void Start()
 {

     isActive = false;
     floor1Destination = target.transform.position; // original Vector3 Position - should be ground floor
     myDestination = floor1Destination; // set floor 1 = ground floor and starting position vector3

     Vector3 targetPosition = target.TransformPoint(new Vector3(0, 0, floor2Height)); // Calc new target vector3
     floor2Destination = targetPosition; // New Vector3 Position
 }
    
 void Update() {
     if(isActive)
     {
         MoveMe();
     }
 }

 void MoveMe()
 {
     // Move the elevator

     if (isActive == true)
     {
         float translation = Time.deltaTime * 2; // how smooth the motion is per update

         // Elevator Up
         target.Translate(Vector3.back * translation); //going up
         if (target.transform.position.y > myDestination.y)
              isActive = false; // Reached our floor
                   
     }
 }

 public void GoToFloor(int floorNum)
 {
     switch(floorNum)
     {
         case 1:
             myDestination = floor1Destination;
             break;
         case 2:
             myDestination = floor2Destination;
             break;
         default:
             myDestination = floor1Destination;
             break;
     }

     isActive = true;
 }

 void StopMe()
 {
     isActive = false;
 }

 void ResumeMe()
 {
     isActive = true;
 }

}