Slip Joint Springs

William Schrade

William Schrade

Joined
Jul 30, 2012
Messages
575
After making my first Slip Joint a few months ago I was wondering when is it best to load the spring. Before or after HT or doesn't it matter.
Thanks
 
Maybe I'm not understanding your question, but I never loaded a slip joint "spring".

It is just the spring tempered spine. The blade is fitted so the heel cams will snap it open and closed ( AKA - walk and talk). The tension needed isn't all that much, and is a product of how much steel you leave on the heel of the blade. When the heel is properly fitted on both sides the spine is flush with the liners and scales both open and closed.
 
After. You build your blade and spring, with the geometry like Stacy mentioned, with your spine fit a tiny bit proud of flush in all three positions. Then you heat treat. After HT, you get your spine 100% flush. Then when you build the liners, you offset the rear pin hole a bit to provide your spring tension. I don't ever "set" the spring itself. Usually 1/2 a 3/32 hole offset is a bit too much. Maybe 1/3, or a little less. Easier to show than to explain in words.
 
My springs are cut in such a way that they are "pre-loaded" by nature of their geometry. Because of that, I heat treat and spring temper before they are first pinned together under any tension.
 
Thanks for your replays. I disassembled an old knife and the spring appeared to be bent for more spring action. When I duplicated the spring there wasn't as much tension in it in the annealed state. Trial and error time.
 
Drew has a youtube video that helped me understand

P.S. Thanks Drew
 
William, steel in the annealed state has little or no "spring." Make it the shape that you want (bend, preload, etc.,) then harden and temper it. You will have to do some grinding after the backspring is installed.
 
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Drew's video is informative.
It's a lot easier just to bend the spring, then heat treat.
 
That was a very good video! I think I'll go through and watch all of them. I've recently started playing around with slipjoints in my spare time, be a while before I make any to sell though. I'm extremely picky about fit and finish, and haven't done anything I'm even remotely happy with yet..... But hey, the first fixed Blade I ever made 12-15 years ago looked like crap too
 
I load my spring also with the rear spring pin hole. No reason to bend a spring, which can twist it, and is a much less "exact" science. With the blade in place using a temp pin, and the front (middle) spring pin in place the same, I use a mechanical pencil to mark the profile of where the spring lays with the blade in the open position, on the liners (i.e. trace the outside of the spring to the liner), then I remove the blade, making note of where the spring was laying with the blade open, then lower the front of the spring, half the diameter of the pivot pin hole, by eye, simply spacing it from the tracing I made, then I clamp the spring in that position, and drill the rear spring hole through the liner.


That creates your "pre-load", then I do the final fit of the blade tang in each position. If for some reason I want more load later, I can drill another rear spring pin hole, on either side of the original, through the spring (I usually put an extra hole in the spring below the original one before I HT the springs, JIC I need it) and liner at whatever adjustment I need, and you'll never see the original hole, as it'll be covered by the scales, and won't be visible inside the knife as it's covered by the spring.


Personally, I HT before I ever adjust the spring or tang geometry. I like to do this all at once. I cut out blades and springs, and drill the pivot and spring holes, then HT. Afterwards I make liners, and do the above. This gives me a lot of latitude to make minor variations on the same pattern easily. I cut the springs a bit over sized, clean up the inside before I fit, and then remove excess material from the top usually.


Thing to consider about bending springs post HT, is that you're stressing them pretty heavily, it's difficult to bend them, and you usually need a softer spring, and/or it'll want to reset over time. I leave my springs around 50 RC, not easily bent at that hardness, and you're fighting the results of the HT you are trying to take advantage of. i.e.

I'm of the opinion that bending a spring post HT is something that is never optimal, but YMMV of course.
 
Great idea putting two holes in the butt end of the spring! That would have saved me quite a few sets of boogered up liners.
 
Jason Fry said:
Great idea putting two holes in the butt end of the spring! That would have saved me quite a few sets of boogered up liners.
Click to expand...


Regardless of having a hole there already Jason, buy 140 degree Notched Tip Straight Flute carbide drills in the size you use for the spring pins, it will drill a very concentric hole through hardened springs without any trouble. The only the to be careful of is the really shitty chip clearance of the straight flute drill combined with the flakey chips of hardened steel. 1/16 drills need to be run super fast (like 8k if you can swing it), and peck quickly on a good base. The higher speed will blow the chips out better, and they need high speed on a pretty tight drill to avoid breaking the cutters. If you can make that happen, you'll get holes that are nearly as nice as cut and reamed on unhardened stock.

I use them all the time now, especially when I'm "freehanding" a new design. I'll cut a basic oversized spring and a square ended blade following the dimensions of one of my other patterns for the tang end, and then cut spring holes after I get the profile figured out.
 
MA Ford twister hiroc drills are my usual choice for drilling hard steel. I'll use them if I change my mind and decide on using bigger pins. About the only thing that will successfully ream out holes in a hardened tang. They are expensive (a single 1/8" drill is about $20) but they are very good. I've drilled through files and taps with them before.
That said I'd still be inclined to drill all the holes before HT. If the holes Shrinking after HT becomes an issue, a set of plus and minus reamers (thou over and thou under of each size) can prevent that easily enough
 
Bill DeShivs said:
Why are you drilling hardened springs?
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Bill, as I explained, sometimes it's easier when I build something a certain way. I usually don't.

Regardless, those drills will put holes in hardened springs with ease if necessary.

I explained it to Jason, for the situation he mentioned, where he needed a new rear spring hole to adjust pre-load without new liners.

I'm definitely not trying to suggest that you should drill your spring holes hard, just offering a solution should a situation arise where it's necessary. ;)
 
Geoff Flato said:
MA Ford twister hiroc drills are my usual choice for drilling hard steel. I'll use them if I change my mind and decide on using bigger pins. About the only thing that will successfully ream out holes in a hardened tang. They are expensive (a single 1/8" drill is about $20) but they are very good. I've drilled through files and taps with them before.
That said I'd still be inclined to drill all the holes before HT. If the holes Shrinking after HT becomes an issue, a set of plus and minus reamers (thou over and thou under of each size) can prevent that easily enough
Click to expand...


The reason I mentioned the straight flute notched tip drills specifically is because they leave much more round holes that any twist drill I've seem, carbide or otherwise, especially for new holes. Otherwise, most good quality solid carbide drills I've tried will drill hard steel fine, but reaming even with carbide reamers can be tricky if the hole ends up sloppy in my experience.

FWIW I like BestCarbide AlTiN coated cutters, I've been using them for a few years and they've performed as well or better than any of the more ubiquitous brands I've tried, and they offer all sizes of this type of drill.
 
I understood. Sometimes you make a set of liners, get the back pin hole wrong and lose your spring tension. Previously I just made a new set of liners. Javan's talking about adding a pin hole to the spring and re-drilling the liners. It's a fairly limited use situation.
 
javand said:
The reason I mentioned the straight flute notched tip drills specifically is because they leave much more round holes that any twist drill I've seem, carbide or otherwise, especially for new holes. Otherwise, most good quality solid carbide drills I've tried will drill hard steel fine, but reaming even with carbide reamers can be tricky if the hole ends up sloppy in my experience.

FWIW I like BestCarbide AlTiN coated cutters, I've been using them for a few years and they've performed as well or better than any of the more ubiquitous brands I've tried, and they offer all sizes of this type of drill.
Click to expand...
I'll give them a try sometime! I've always used the hirocs as they are what the supplier I usually deal with sells, and most of my tooling is either kennametal or MA Ford.

The square die drills sold by KBC are even more expensive, but supposedly even better. I've got a 1" coming my way for a totally unrelated to knifemaking project. It hurts just thinking about how much that thing cost.....
 
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