Ultra-Z-Geek Question: What is the purpose of the spring in the wiper linkage gear?

[240260280z]

I just re-assembled one for a friend. The spring was there but the 90 degree spring end that fits in the slot was long gone.

 

I now wonder. What does the spring do?

 

It was interesting that the spring in this 73 had a plastic ring around it.

 

Here is what I am talking about sans ring

 

Edited May 16, 2015 by Blue

[Mark Maras]

I didn't fully disassemble my linkage on my Sept 73 260. The spring in mine(if there is one) must be broken too. I assume, since it is a clock spring, it puts tension on the arm to hold it in the resting position. Now I'm going fully disassemble my linkage to see if the spring is there.

[siteunseen]

Blue and his pictures strike again! I've done tons of stuff after looking at his pics.

LaBatts!

[Namerow]

My guess (and that's all it is) is that the spring keeps the entire linkage lightly loaded during the load cycle that the motor and linkage experience as they go about their business. By far, the principal load on the system comes from the friction load created by the wipers sweeping over the glass.  That friction load goes through a 'pause' and then reversal when the wiper blades reach the end of their sweep.  The clock spring in the motor output link would inhibit a 'click' in the system during the load transition event.

[Mark Maras]

Makes sense to me. The spring had a purpose. I haven't looked at mine yet, but I think one could bend a new end on the spring using heat(very small & focused). It has worked for me in the past, The trick is in the cooling. If the spring is quenched too fast the steel becomes brittle, If you don't cool it fast enough it will lose it's springiness. I have found that a rapid quenching & then a slight reheating 350-400 degrees seems to work quite well. This a basic tempering technique used for knives & other tools.

[Patcon]

oil quench or water?

[Mark Maras]

I normally use old engine oil. It actually will transfer some carbon from the oil to the surface of the steel hardening it in the process. Are you going to go for it?

[Patcon]

Maybe at some point. Way down the list though...just getting educated.

[Captain Obvious]

There are quite a few different compositions of tool steel designed to be hardenable. Some are designed for an oil quench and some are designed for an air quench.

 

Steel hardening is a complex science. Not easily done right in the home shop. I've done some and have had "reasonable" results.

 

The most difficult hurdle I've had is oxidation while hot. Unless you're using an inert atmosphere or coating the parts with a compound designed for heat treat, the parts get an oxidized scale of material on the outside. If the part is very thin (like a small spring), by the time you oxidize that outer portion, there isn't much left.

 

Most of what I've done has been using O-1 (oil quench 1), but next time the need arises, I'm going to try A-2 (air quench 2) because I believe it machines easier. I'm not sure if either of those grades are suitable for spring making.

[Mark Maras]

I agree, scale is a PITA. Concerning this spring, I wouldn't heat it enough to form scale, just enough to keep it from breaking.

Air quench HMMM, I'll have to try that.

[Captain Obvious]

Oh, and I forgot about the water hardening series as well. Here's a page from McMaster with a little info on some of the more common grades of tool steel:

 

http://www.mcmaster.com/#tool-steel/=x8iikp

 

And I still have no idea if any of those grades are commonly used for spring applications. I don't do much of that and what I do-do (doodoo?) usually starts with an existing spring with modifications to something that already exists.

 

And one more thing... I purchased some anti-scale coating compound after the last time I did some home hardening. I haven't use it yet as the need hasn't come up, but the next time I'm going to give it a shot. I have a jar of this stuff sitting on the shelf:

 

http://www.brownells.com/gunsmith-tools-supplies/metal-prep-coloring/heat-treating-accessories/non-scaling-compound-prod1122.aspx

 

Edited May 18, 2015 by Captain Obvious