Just snapped the CPM 154 lock back spring I made

JPSWorks

JPSWorks

Well-Known Member
Well crap,

I've been working making on a small lock back folder the last five days or so. The blade spring and rocker bar are all three CPM 154. I finished heat treating and tempering everything a couple of hours ago. I was test fitting everything and the spring needed to be a little bit tighter so I was going to bend it just a little and it snapped. I actually placed it on my workbench and tapped it with my hammer to attempt to bend it about 1/8 of an inch and it snapped the first time. I didn't even hit it very hard. I have bent and tapped spring steel before. The spring was definitely springy when I was depressing it while test fitting it.

The frustrating thing is, this is the second spring I made. After making the first one I tried to test fit everything before heat treating yesterday and realized the kick was too short so the spring didn't fit correctly between the blade and the rocker bar. I made another and though it wasn't very pretty it fit fine and I went ahead heat treated everything today. I know that the place where it broke was at the thin point, so the next one I will attempt to make it thicker throughout.

This is my heat treating method step by step using my Paragon unit.

1. Put the parts in the steel foil and double fold.
2. Placed in the room temp Paragon Furnace
3. Start program
4. Full speed ramp to 1400 deg
5. Hold for 15 min
6. Then full speed ramp to 1945 deg
7. Hold for 40 min
8. Plate quench between 1" aluminum plates with positive pressure and compressed air

Tempering
In my kitchen oven with an oven thermometer, the blade and rocker bar were tempered at 425 deg for 2 hours. Then repeated again at 425 for another 2 hours

Spring was put back into the Paragon furnace when it cooled back to under 1200 degrees. Then tempered at 1150 for 2 hours just one time. From all the reading I have done it appears that most people only temper the spring one time for 2 hours.

Should it be THAT brittle? Shouldn't it just over bend and not snap? Or was I just an idiot? Any advice is appreciated.

Thanks,

John

PS here are a couple of pics.




 
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Forgot to add this. Here is a pic of the spring where it broke. I super glued it back together to use as a template to make another, just not so thing at the breaking point. Also here is a video of the spring in action. Just click on the link or the small pic and it will load the video.


[video]http://vid45.photobucket.com/albums/f99/JPSWorks/Small%20Lockback%20Folder/TRIM_20140923_224118_zpsad68d925.mp4[/video]



 
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OK, just my opinion, but with the shape of your spring leaf, most all the load is in that thin waist. I was taught to start thick and taper all sides to the tip. This better spreads the load along the length of the spring leaf. Equal sided leaf, or uniformly round would be better than a leaf with a narrow waist, but tapered is best.
 
Just a question here, did I understand you're trying to "bend" the spring enough so it will take a different shape and it broke? I don't really think the spring steel will do that.... will it? I do agree with LRP about the shape - it should be thinner at end, tapering to a tad wider at other end. OR - at least same size all the way so the bending will be spread out from end to end rather than all at the same spot.

Good looking lock back.

Ken H>
 
I definitely need to make the spring fatter at the point it broke and then thin it out toward the end like you both mentioned.
 
I don't have the TTT table handy.
What was your target RC hardness with the 1150F temper?

I spent a lot time a long time ago trying to get a definitive answer on spring hardness. I found out there isn't one.

I did find most guys say 45RC but the range I read was from 40RC on a small gents slippy to nearly 50 on a big folder (with a thinner spring).


also I'm with LRB on the spring geometry.. thin to thick might be better.
 
BossDog said:
I don't have the TTT table handy.
What was your target RC hardness with the 1150F temper?

I spent a lot time a long time ago trying to get a definitive answer on spring hardness. I found out there isn't one.

I did find most guys say 45RC but the range I read was from 40RC on a small gents slippy to nearly 50 on a big folder (with a thinner spring).


also I'm with LRB on the spring geometry.. thin to thick might be better.
Click to expand...
I was shooting for around 45-48 but honestly don't really know what is best for this application. Just what I gathered from searching the internet.

Today I spent around six hours cutting out with a hacksaw and hand filing the shape of the new spring and new rocker arm. Hoping for better fitment of the opening and closing.
 
Be sure to post your results - temperature temper at, and photos of final shape.

Ken H>
 
KenH said:
Be sure to post your results - temperature temper at, and photos of final shape.

Ken H>
Click to expand...
Hello Ken,


I ended up making another one. Also had to make another rocker and two more blades before I got it all to line up correctly in both the open and closed positions. I will post up some pics soon.
 
What temperature did you temper at for the new backspring? Looking forward to pics.

Ken H>
 
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