DIY breaking strain tester

[Volitan]

So I made my testing device today, and I’m pretty happy with it.

At least I made a prototype - I usually make a prototype of things before making the real thing just to get the bugs ironed out. 

This morning I bought a large, long-travel tension spring, which I reasoned would have more reliable performance then a small spring.

then welded up a few levers and brackets. Done. Simple and ugly but robust.

then took my old diving weights down to the friendly local postmaster to get them weighed to use for static testing.

then tested the device with the weights in static mode. Results were actually pretty awful between 0 and 2 kilos, then ok, then a strange blip of inaccuracy around 10-11 kilo. Then ok up to 15kg which is where I stopped.

So I figured the inaccuracy below 2kg was inherent and redesigned the device so that it actually kicked in at 2kg and marked that as 0kg on the scale. Then spent the rest of the afternoon refining it to remove any variation or play. Springs are strange, finicky little things to work with.

The result is pretty good - I don’t know how to express the accuracy mathematically, but 30mm on my scale represents one kilo, and the accuracy is within 0.5mm everywhere except around the 11 kg mark where it jumps up to 2mm, then down to 1 mm but in the other direction, then back to about 0.5 mm at the 13kg mark. I think that’s just a characteristic of the spring.

These measures don’t change no matter how many times I retest it so I suppose that’s conditional success.

i could be using the wrong term here, really it’s repeatability or reliability that I’m looking for not accuracy.

when I get access to a better workshop later in the week I’ll refine it a bit, replace the metal to metal joints with bearings, build the bollards (for wrapping line around) and put a slider on the scale so it preserves the maximum value after a test.

Cheers

 

[blaxland]

Hi my 2 cents worth 

1. Drag set to much less than line rating

2. litre of water = 1 kilo of weight

 so if testing knots try lifting that many litres 

I dont know what the "factory tolerance" is for knot tying or line manufacturing but it has to be at least 3% either way.

 

[ByeKatch]

I am obviously late to this thread - but thought the following link would be of interest to the thread author:

 

http://fishingbesthunting.com/fishing-knots-how-to-tie-the-six-strongest/

 

The American author used a force gauge to come up with his results.

[Volitan]

Thanks Andrew.

its interesting you should post this because I’ve just come inside from another session testing knots and leaders on my homemade testing rig.

I should publish today’s results.

cheers

V.

[kingie chaser]

On 11/17/2019 at 12:45 PM, Andrew from Port Stephens said:

I am obviously late to this thread - but thought the following link would be of interest to the thread author:

 

http://fishingbesthunting.com/fishing-knots-how-to-tie-the-six-strongest/

 

The American author used a force gauge to come up with his results.

Actually I like that bottom knot for its ease but that triline knot looks like a winner!

Edited November 20, 2019 by kingie chaser

[ByeKatch]

Hi V,

Your thread prompted me to become a member (after a long time casually reading).

 

The american link i posted did it rigorously. He bought over 2k of equipment. A chatillon ametek force gauge. And a frame. I think he fishes inland so his knot choices not so helpful (eg no FG vs PR knot)...

 

I don’t want to fork out big $ on a force gauge. I may not have to either...

 

I came across a great guy at this company:

https://www.test-measurement-australia.com.au/

 

Instead of buying a force gauge with lots of unnecessary features, he is putting together a simple system with approx 3 components that i can drill onto some marine ply and make a jig.

 

bottom line: 0.3% accuracy. 5-10% the cost. They will test the system, calibrate it then send it to me. To buy a force gauge with 0.3% accuracy would be thousands.

 

I’m glad you persisted. Saw some unhelpful comments through the thread...

 

 

[ByeKatch]

Hi Kingie chaser,

Fair bit here too:

https://web.archive.org/web/20160307173149/http://paulusjustfishing.com/4knotstested.htm

 

[Volitan]

My home made jig works very well and its accuracy is adequate but there are a couple of thoughts I’d like to pass on.

1. if you make a measuring system the most important thing is it has to be quick to do each test. While it’s common to see a tester state things like ‘this knot retains 90% of strength’ that is only an average. In reality the plot of knot strength will be a normal curve (actually a skewed normal curve) - so you need to do a lot of tests before you can be confident your average is valid. It gets old very quickly doing that with buckets of sand or water and a spring scale, especially when testing 20kg line and you have to lift 20+ kg of water, clean up and refill after every test.

2. the static line strength tests usually presented are not that useful. More important is to test:

- shock load (ever lost a fish trying to net it)

- durability (I stretch to 60% of break point 50 times, then test. This simulates a big fish giving your line hell)

- abrasion resistance (Salt strong shows a simple but brilliant jig for this)

3. And finally, line, knots and terminal tackle are a system. They all work together. Different knots work better with different lines. Some lines respond poorly to being tied to thinner metal fittings, others don’t care.

 

and yep, there were some unhelpful comments. If you do a search on my name you will see photos of a 27kg tuna I caught landbased in June. It was shortly after a period of intensive testing of knots and lines on my homemade test rig, which enabled me to greatly increase the reliability of my gear under stress. There is nothing like the feeling of hooking into a big fish and being entirely confident of your line and knots. I felt vindicated.

[Hoffies]

On 1/26/2019 at 3:33 PM, savit said:

@Volitan, Have a look at Paulusjustfishing website. A lot of line testing including knots:

https://web.archive.org/web/20160307173149/http://paulusjustfishing.com/4knotstested.htm

If Paulus does not explain somewhere on his website how he is testing breaking strain (equipment/technique etc) - just contact him.

Jfc man what a wild ride going down that rabbit hole for the past two hours was. 
 

I came here with a similar question to OP but after getting woke on breaking strength by reading my boy Paulus’ turbo autism I can tell you all right now you’re asking the wrong questions 

god I feel enlightened like the Buddha or something