Spring - Horikawa Gear Robot broken mainspring

[Action Robot]

I was inspired by Rhothgar's gear robot post to disassemble mine and see why it wouldn't wind. I confirmed that the mainspring seems to have snapped. It looks like it broke right where it connects on the inside, as I can see the one small piece that's bent to hold it into the winding shaft floating around loose.

It looks like in order to fix it, I'd have to completely disassemble the gearbox. It looks possible, but I'd like to know if there's any chance of success before I go too far.

Can I bend a new crimp in the end of the remaining spring, or will the metal just snap? Can I get and install a new mainspring? If so, where can I get one? Am I on a fool's errand?

thanks,

Dave

[Brian..]

Sounds like you can reuse the broken spring. Remove the small broken endpiece and examine the method of attachment to the spindle. You should be able to recreate this on the remaining piece of spring.

 It is possible to thread the renovated spring into the motor without dismantling anything. Attach the spring to the shaft, wind gently then slip the end of the spring into then slot in the engine casing. It's a tip that has served me well.

 

Springs can be worked on by heating them before bending. The shorter spring means you'll just lose a little running time.

 

[robothut]

Dave wrote, Can I bend a new crimp in the end of the remaining spring, or will the metal just snap? Can I get and install a new mainspring? If so, where can I get one? Am I on a fool's errand?

thanks,

Yes you can repair the broken end and yes you can replace the spring from a junker toy. As has been mentioned on a few posts in the past , the only way to make the sharp bend on the end of the spring where it attaches to the center hub is to first heat that end of the spring. You do not want to heat the entire spring only the end part that you want to bend. A lighter will do as the heat source. 

If you try to bend the spring with out heating first it will just snap, you need to UN temper the metal first.

[Martian Gil]

Dave, Brian is on top of it.   

Shorter running time, but the robot is back to good health.   I've fixed a few broken springs this way.

 

On the springs that I have fixed, I needed to take the gear boxes apart.

I can see where you might be able to perform the work without it, but I wasn't able - without fear of transferring too much heat to the gears themselves.  

 

I tried to pull the spring through the gearing itself, but the winding of the spring itself prevents success - and when I was closest to success with that method, I needed to unlock the "pig-tail" of the spring.  

I felt then that if I was able to get the heat and bend properly, that I would then be in a bad place trying to get the pig-tail of the spring back in place without breaking it.     The springs are incredibly rigid without heating.

Somewhat of a catch 22.  

 

If you do have to take the gear box apart, just take pics of the gear placement so that it's not a mystery puzzle putting it back together.  Even with pics, the reassembly will take a couple attempts - especially if your eyes are old like mine...

 

Also - my first 2 attempts at fixing both snapped again after the first test.  

At that point, I started quenching the hot metal to cool it after hardening to help avoid making it super brittle.    I don't know if it truly worked - or if it was just coincidence, but I haven snapped another repaired spring since then.

 

If you try this, here are some basic tools that I use in the process; 

• a basic multi purpose propane torch.   a garage torch or even a mini torch will do the trick.  

1. A pair of vice grip pliers - these serve a couple duties for me; it serves as a little heat sink, but primarily it locks the rest of the wound spring away from the process and makes isolating your work possible.

• a couple pairs of needle nose pliers - one to hold the spring where you want the bend, the other pair to bend.
• a bit of sheet metal for under or behind your work to prevent an unwanted fire.
• I used a hydraulic / gear fluid to quench - and a cheap brush to apply it after heating.  - again, I'm not swearing by this quenching process, just stating that since I started doing that, I didn't have any re-breaks.

Before you begin heating, reexamine the way that your broken spring pieces fit together, and then you know which way to make your bends.   If you do the opposite, the spring can come undone when winding.

 

It is possible - but it will test your patience.   That said - it's super satisfying to get your robot running again.

 

 

 

 

[Martian Gil]

Of course, John is on it too!    I think we were posting at the same time.

cheers!