Slipjoint spring tension

J

jamesbeat

Joined
Jul 26, 2009
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I know this may make some of you vomit in the aisles, but I have a bit of a thing for Rough Rider knives :D

More specifically, I like the sunfish knives.
Build quality is perfect on my two examples, and they seem to take and hold an edge well.

I mostly carry more 'serious' work knives rather than gentleman's folder type knives, but I like to slip a RR sunfish into my pocket too as the reaction from non knife folks is usually very positive, as they are just so darned cute.

I like the different scale materials available, and I think I'll end up collecting them all, as these little beauties are ridiculously inexpensive.

I currently have only one of these knives, as I have given the others away to non knife people in the hopes of turning them into knife people.

Anyway, I digress...

My one complaint about these knives is that the backspring is ridiculously stiff.
I have bent my nails back many times trying to open the large blade, and forget the small blade!
I sometimes have to use a screwdriver in the nail nick to even get it open.
All five of these knives that have passed through my hands have been the same.
Other RR knives I have had don't have this problem, and open about as easily as a SAK.

I've oiled and worked the blades back and forth, and left the blades half open for a week to try to take some of the tension out, but no luck.

Is there anything that can be done, short of dismantling the knife and grinding the spring thinner?
 
I hate "Nail Busters" too!
One of my all time Traditional Slipjoint pet peeves.

One day I want to write a long post on the topic & try to explain why, in my humble opinion, so many Factories still make 100+ year old errors!!! Just not quite sure where to post it......

Back to your knife.
It is easier to make a knife weaker than to make one stronger.
I would not recommend dis-assembly, you will probably need new pins to re-assemble the knife properly; & your chance of finding metric sized brass or Nickel Silver wire stock is slim to none.

The 2 weakening options you have:

1. Haft (sand off) the entire length of the back of the knife.
This will reduce the cross section of the spring beam.
Only sand in the direction of the blade back, cross scratches can create stress points.
Take off small amounts at a time & frequently check the force change.
You will be limited by the blade back if the knife is flush open, so you may need to haft blade back too.
Words of caution: don't attempt without a good grinder & a selection of several belt grits; do not overheat the spring; be prepared to throw the knife away if things go wrong - they probably will. :p

2. Reduce the deflection of the spring.
Probably the best initial approach, but tricky to do.
I recommend a small arbor press with a long (preferably hard) pin that is long enough to touch the inside finish of the spring just to the rear of the blade tang.
You will need to rig up a fixture base that supports the liners on the back of the knife while allowing the springs to be pushed past the point of travel during opening/closing. Again, push a little; check a lot!
The knife will probably need hafting afterward as the set spring seldom lays the same as it did before.
Words of caution: as this needs to be done with the blade(s) open, I highly suggest covering the sharpened edge with thick tape.
Arbor press force + sharp blades = potential epic accidents. :eek:
Be prepared to throw the knife away if things go wrong - they probably will. :D

Of course all of this will void whatever warranty you have.
Even if you succeed, the spring may start to loose force over time or break in the future! :o
A bad spring design is frequently terminal.
 
Phil's suggestion about thinning the backspring (by hafting/sanding) reminded me of something.

A while back, I bought a customized Buck 110 with fileworked blade & backspring. It's a nice knife, but the pull is very weak on it. I've always wondered if that had something to do with the extra 'meat' taken out of the backspring, for the filework. Seems much too weak.

Maybe having an experienced knifesmith putting on some minimal, but attractive, filework might be a creative way to 'fix' this.
 
Obsessed with Edges said:
Phil's suggestion about thinning the backspring (by hafting/sanding) reminded me of something.

A while back, I bought a customized Buck 110 with fileworked blade & backspring. It's a nice knife, but the pull is very weak on it. I've always wondered if that had something to do with the extra 'meat' taken out of the backspring, for the filework. Seems much too weak.

Maybe having an experienced knifesmith putting on some minimal, but attractive, filework might be a creative way to 'fix' this.
Click to expand...

Excellent point!
Although your 110 is a lock back & fileworking the lockbar would not affect the tension.

Deep fileworking of a pocket spring or pen spring will slightly reduce strength.

Although filework is perhaps a little expensive considering the knife in question. :D

If filework is to be that deep, it should be "added to" the profile of a good spring design.
 
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Phil Gibbs said:
Excellent point!
Although perhaps a little expensive considering the knife in question. :D

If filework is to be that deep, it should be "added to" the profile of a good spring design.
Click to expand...

Agreed. If the spring were designed & built with filework in mind, it should be fine. I'm leery of buying production knives anymore, with aftermarket filework on the spring.

I wonder how expensive a notch or two might be? Would the knife have to be disassembled to do it? On the one hand, it might be a bit much for an inexpensive knife. On the other, an inexpensive knife might be the best 'test subject' for such an experiment. I wouldn't want to test this on an expensive one.
 
Hmm, interesting suggestions.
I like the idea of trimming the whole back of the knife to reduce the spring, that idea hadn't occurred to me, although, like the best ideas it seems so obvious when it's pointed out :D

Unfortunately, I think it would ruin the shape of this particular knife, as the handle is symetrical.

I'm going to store the idea away for future stubborn knives though...

Maybe I should take it apart after all?
I'd only need to get to that one pin, so it should be relatively simple.
I'm from England, now living in the States, so it seems weird to me that metric rod would be difficult to obtain.
I'm building an AK at the moment, and trying to get hold of metric drill bits was frustrating!

Maybe I could use my 'lathe' (cordless drill and a mill file :D) to turn down a pin to fit.

This all does seem like a lot of bother for an inexpensive knife, but really, I don't care how much these things cost.
It's such a satisfying little knife that I would happily have paid double for it.

I don't usually buy cheap knives, as I believe them to be a false economy, but Rough Rider knives were brought to my attention when I received a canoe knife as a gift.
Bone scales, nickel silver bolsters, flawless fit and finish, and a hair popping blade that sharpens easily and holds an edge well.
I don't know what the steel is, it says '440', so I guess it's probably 440a, but they must have got the heat treat just right.
I'd say that the blades on the RR knives I have owned have been on a par with a Victorinox SAK, which, while not the best blades in the world, are definitely serviceable.
I decided I needed more of this brand of knife, and was astonished when I did a bit of searching and found out how inexpensive they are.

The only thing stopping me getting one of each of the different scale materials is the stiff springs (and the fact that I keep giving them away...)
 
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Obsessed with Edges said:
Agreed. If the spring were designed & built with filework in mind, it should be fine. I'm leery of buying production knives anymore, with aftermarket filework on the spring.

I wonder how expensive a notch or two might be? Would the knife have to be disassembled to do it? On the one hand, it might be a bit much for an inexpensive knife. On the other, an inexpensive knife might be the best 'test subject' for such an experiment. I wouldn't want to test this on an expensive one.
Click to expand...

You posted while I was editing my post; posts with quotes on an iPhone are touchy! :o

Notching a spring to weaken it is probably a bad idea; stress concentration can cause surprising results. I have experienced first hand, large quantities of knives in boxes with their springs breaking like popcorn . :eek:
 
Maybe you should buy only what you can try as the only RR sunfish I had, did not have problem such you described.
Mike
 
Sorry, I forgot RR make two types of sunfish. My knife (and the others that I have owned) is the baby sunfish.
Is yours the large sunfish? I imagine the large one would be easier to open because of the longer blade.

I decided to go ahead and dismantle the knife.
The scales (faux abalone) have no pins visible, so I assumed they were glued on with epoxy and boiled the knife to remove them.
Unfortunately, it seems that the scales ARE epoxy (or something similar) and boiling them made them fall apart :(
The good news is that I was able to drill out the old pin and rotate the springs out of the liners.
I've also found a nail that is the right diameter to ise as a replacement pin.
The springs have a semicircular cutout which dictates how stiff they are, so I'm going to remove a little material from these areas with a grinding stone on my dremel.
If I do a little at a time and check with the pin, I should be able to fine tune the springs to be just how I want them.
 
Ok well I did it :)
It now operates like a swiss watch.
...well not quite, but it's infinitely better than it was.
I decided to err on the side of caution, and only removed just enough materiall from the spring to enable the blade to be opened with my thumbnail.
I could have made it easier to open, but I figured that if I made it too easy, it might loosen up too much with use.
I can open both blades with my thumbnail, and tension when open appears to be unaffected, or at least not noticably affected.

I used a steel nail for the replacement pin.
Being pointy, it acted as its own 'drift punch' so I was able to take it in and out easily as I removed material from the spring.
I had to remove a surprisingly small amount of metal to get the spring just right, so one pass with the dremel and then reassemble and check is definitely the way to go here.
Going slow also means the spring won't heat up too much and ruin its temper.
Once I had it just right, I left the nail in place.
I cut off the excess parts of the nail with a cutoff wheel on the dremel, dressed the ends with a file until they were just proud of the surface of the scales, and then tapped the ends with a ball pien hammer backed with a scrap piece of steel to form tiny rivet heads on each side.

The external cosmetics of the knife are (surprisingly) unaffected, and the springs are still perfectly flush with the liners.

The knife is perfect now, except for the fact that I now need to make some replacements for the scales I ruined :(
 
You should be able to get metric rod stock and drill bits from McMaster-Carr or MSC. Just for future reference. Going to be hard at the local hardware store, metric just never caught on.
 
serotina said:
You should be able to get metric rod stock and drill bits from McMaster-Carr or MSC. Just for future reference. Going to be hard at the local hardware store, metric just never caught on.
Click to expand...

Except in pretty much every industrialized nation other than America :D
I did actually end up getting then from McMaster Carr.
One of the most difficult things for me, having moved here from the UK has been the old fashioned methods of measuring things.
Fractional inches are a real pain, I can't understand why you guys still sitck with it!
While I'm sick of trying to think in inches, pounds, ounces, and farenheit, I still think absolutely everything else about the States is vastly superior to the UK, so I'll live with it :D

Funnily enough, although I measure in mm, I find it much more intuitive to estimate measurements in feet and inches.
I can look at something and say it's about 10", but I can't do the same in cm.
To me, inches and feet seem more intuitive than centimetres and metres, unless i'm trying to measure something smaller than an inch...
 
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jamesbeat said:
Funnily enough, although I measure in mm, I find it much more intuitive to estimate measurements in feet and inches.
I can look at something and say it's about 10", but I can't do the same in cm.
To me, inches and feet seem more intuitive than centimetres and metres, unless i'm trying to measure something smaller than an inch...
Click to expand...

I suspect that's why Imperial measurements have remained popular in the US. I've known Canadians who prefer them too, but that varies a bit more. One should be able to estimate in metric with practice, though base ten units are not as intuitive to most people and it will take concious effort.

I'm comfortable working with either, as the job requires. To me they're really just two systems, each with advantages and disadvantages.
 
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