How to replace a spring

The Symptom

If the PowerTool no longer provides its full 3000 mm tether extension, it is highly likely that the tether has been subjected to an uncontrolled release.

During an uncontrolled release, the spring-motor returns the tether at such a high speed that the silicone tube can not dissipate all of the kinetic energy of the spring-motor before the tether stops moving. In dissipating the remaining energy the spring will continue to move due to its angular inertia. The spring may then bend into a shape that will restrict future movement, or it may simply break.

This procedure describes how to repair a damaged or broken spring.

You'll need:

1. Screwdriver - 9 x 1.4 mm for current PowerTools, 9 x 1 mm for earlier units - for the spindle
2. 4-5 mm screwdriver for the spool pins
3. A second screwdriver the same as above or smaller to use as a lever if needed
4. #1 Pozidrive screwdriver (see below) for the spring motor cover
5. Smooth jaw snipe nose pliers to manipulate the spring
6. 2.5 mm hex key for the cover screws
7. Loctite 290

Dismantling The PowerTool

1. Remove the spring motor cover
   
2. Remove one spool pin 
   
3. The spool is likely to be held under tension, so to control its release,
   1. Undo the pin until it can be turned with the thumb and forefinger.
   2. Insert the 4mm screwdriver between the spring motor case (not the spool) and the block, to act as a brake.
   3. Undo the second spool pin and remove it.
   4. Then slowly remove the screwdriver.
   
   
4. Pull the tether to unwind the spool, taking care not to tangle the tether
   
5. Snag the tether between the angle sensor and the spool and lift out 100 - 200 mm
    
6. Use the loop of tether to unwind the spool (anticlockwise) until it is clear of the spindle thread and remove it
    
7. Using the 9 mm screwdriver (and ensuring that it fits snugly in the slot) unscrew the spindle - It could be very tight as it is locked in place with Loctite 290. 
8. There are three screws securing the spring cover, the heads of which are either Pozidrive (most likely) or Phillips. Pozidrive heads have a cross scored in the head 45 degrees to the slots, as in the left head in the image below. In the PowerTool, Pozidrive heads will be a bluish colour, while the Phillips heads will have a tinge of yellow. A Phillips head screwdriver will damage a Pozidrive head, but the opposite is less likely, so, if you are not sure which head yours has, use a #1 Pozidrive screwdriver. If you are sure you have a Phillips head, use a #2 Phillips head screwdriver.
   Remove the three screws
    
9. At this point, you should slip on a pair of safety glasses. If a spring is allowed to escape its confines uncontrolled, it will rapidly uncoil and could cause injury.
   So from this point, while working with the Spring Motor, take extreme care.
10. Remove the Spring Cover by gripping it with your fingernails and pushing on the spindle with your thumbs.
     
11. Take care, as you remove the cover to ensure that the spring outside tag is not drawn out of the Spring Housing with the cover. (Doing that would be difficult to repair) 
    
12. The last image above shows the absence of a bearing on the spindle. It has remained inside the cover.
    It is possible, however, that the bearing remained on the spindle, as shown in the image below. In this case, the Teflon washer in the cover will be damaged and must be replaced - later - and the bearing must be levered off of the spindle as shown below, using two flat screwdrivers.
    The process of removing the bearing will clean the hardened Loctite from the threads - a little.
    

The Repair Procedure for a Bent Spring
(see further below for a non-annealed spring repair)

1. The first image shows the likely damage. There is a loop of spring taking up valuable space. It shouldn't be there.
   The second shows what it looked like when new. Your mission (if you choose to accept it) is to make the first look like the second.
    
2. Remove the inside spring tang:-
   1. Hold the bulk of the spring with the thumb of your left hand. That is all that will save the spring from disaster!
      
   2. Grip the tang with the snipe nose pliers as shown
      
   3. Carefully draw out the tang from the spindle slot
      Don't let go of the spring until the tang is safely back in place
      
3. Repair the spring by flattening the kinks out with the pliers. It needs to be fairly smooth, but not perfect. Kinks take up space that limits the tether extension.
   
4. Install the tang temporarily:-
   1. Feed some of the free springs end back into the coil - use your judgement depending on the next step
   2. Lift the tang up and slot it into the spindle
   3. Push the tang fully into position
   
5. Reform the tang shape:-
   1. Grip the spring 0.5 - 1.0 mm from the spindle (this is where you will make a bend shortly, so don't lose your grip)
      
   2. Draw out the tang
      
   3. Using the index finger of your left hand, bend the tang back into a 'D' shape
   4. With the thumb and index finger of your right hand, increase that bend to 40 - 50˚ to fit the shaft
      
   5. Reinstall the tang into the spindle slot
      
6. Now you can let go of the spring
   

The Repair Procedure for a Broken Spring

1. If the spring, when subjected to uncontrolled releases, bends in the same place enough times it will harden and break at the inner tang as shown by the following image (if you look very carefully)
   
2. If there is a set screw in the spindle it must be removed to release the broken tang.
   A ball ended 2 mm Allen key will 'just' reach the screw, but once it has been wound out a few turns you may have to revert to the snipe nosed pliers to remove it completely.
   
3. Remove the broken tang
   
4. Retrieve the end:-
   1. Hold the bulk of the spring with the thumb of your left hand
   2. Retrieve the broken end of the spring with snipe nose pliers
   3. Draw the end out 20 - 30 mm
      Don't let go of the bulk of the spring until the tang is reformed and safely back in place
   
5. Grip the spring 4 - 5 mm from the end with snipe nose pliers so that the 'upstream' side is square.
   
6. Bend the end as shown below
   
7. With the thumb and index finger of your right hand, increase that bend to 40 - 50˚ to fit the shaft
   
8. Temporarily fit the tang back onto the shaft
   
9. Reform the tang:-
   1. Grip the spring 0.5 - 1.0 mm from the spindle (this is where you will make a bend shortly, so don't lose your grip)
      
   2. Draw out the tang
      
   3. Using the index finger of your left hand, bend the tang back into a 'Z' shape
   4. With the thumb and index finger of your right hand, increase that bend to 40 - 50˚ to fit the shaft
      
   5. Reinstall the tang into the spindle slot
      

Reassembling The PowerTool

A word of warning.
If you feel the need to test the spring motor before installing the spring cover, be very careful to contain the spring with your thumb. As the spindle is rotated to compress the spring it will no longer be contained by the spindle and will attempt to break its bounds.

(You have been warned)

1. If the Teflon washer in the spring cover was damaged during dismantling:-
   1. Re-insert the bearing (levered from the shaft) into the cover. It should touch the inside of the encoder disc. Take care not to damage the encoder surface.
      
   2. Partially remove the adhesive protection from the Teflon washer
      
   3. 1. Align the washer concentrically with the bearing
      2. partially fix
      3. remove the remaining protection
      4. press firmly
      
2. Slip the spring cover back over the spring holder to the spindle, taking care to keep the outer spring tang inside the cover
   
3. Press the cover (and its bearing) over the spindle with your fingers behind the spring holder and thumbs pressing adjacent to the bearing as shown below.
   (If you do not press over the bearing, the encoder disk may be unseated by the stationary bearing)
   
4. Align the spring cover screw holes and install the screws. Taking care to engage the existing threads and not over-tighten (or the threads may be stripped)
5. Clean the spindle threads of any hardened Loctite.
6. Insert the spindle thread into the PowerTool block, taking care to engage the threads correctly. Cross-threading is NOT an option.
7. Using the correct 9 mm screwdriver, screw the spindle home and tighten ~ 1/8th of a turn. Stripping the thread is also NOT an option.
   
8. Feed the spool onto the spindle and engage the threads
9. Using 100 - 200 mm of tether, lead the spool clockwise (like you did at the beginning but in the other direction) until the top of the spindle is flush with the top of the spool.
10. Continue rotating the spool until the bottom of the thread well is in alignment with the angle tube.
11. Pull the tether through the angle tube until it's outside of the PowerTool block.
    
    It will now be obvious if the alignment was achieved above. If not:-
    1. snag the tether between the spool and angle tube
    2. lift some out
    3. turn the spool until alignment is achieved
    4. Pull the tether through as before
12. Wind the spool down into the block. This will draw the tether in and wind it onto the spool.
    
13. If the spool pulls all of the tethers in before it bottoms out on the spring case:-
    
    1. snag the tether between the spool and angle tube
       
    2. lift some out and take a turn off of the spool, being careful not to drop tether below the spool.
       
    3. Tighten the tether and use the spool to pull it back in
    4. Repeat until the spool bottoms out and the tether remains slack
       
14. Slowly rotate the spool anticlockwise until the pin threads can be seen at the base of the spool pinholes. This should take less than a turn.
15. Carefully install the spool pins. Do not over-tighten then. Less than 1/8th of a turn once bottomed is more than enough.
16. Reel out the tether to its full extent. The top of the spool needs to finish level or just below the top of the spool pins.
    
17. If the top of the spool is too low:-
    1. Hold the top of the spool from returning with your left index finger
       
    2. Snag enough tether from the spool side of the angle sensor to loop anticlockwise around the spool.
       You'll have to change grip to pass the tether under your fingers.
       Don't release it!
       
    3. Pull the tether tight, check the height and repeat as needed.
       Don't let the top of the spool move above the spool pins.
       Ideally, you will have added 2 - 4 turns when done.
18. Return the tether to find it stopping with some tension on the silicone tube
    
19. Replace the spring motor cover
    
20. Remove the battery cover
    
21. Remove the sponge packing
    
22. Remove the battery, but don't unplug it
    
23. Place a drop of Loctite 290 on the end of the spindle
    
24. Clean up any excess Loctite
25. Replace the battery
26. Install the sponge packing making sure that it reaches or rises above the block surface
27. Replace the battery cover, taking care to capture the mini-USB connector
28. Install the four screws - they need to be firm, not excessively tight