measuring the "strength "of the hammer spring using k constant

[UKairgunner]

Ok im thinking of changing the hammer spring and Ive seen lots of alternatives l, POWER..MAX POWER..etc. Now im a natural sceptic and wondered how you measure a spring...spoke to a Mech Eng friend and he advised Hookes Constant( as you do!)

A quick wiki about it and im  off

ive borrowed a power spring made by GMA and im comparing it to  the stock one supplied with the 2240

a few measurements taken first of the spring in the pistol .I measured the length out of the pistol,then when it was slightly compressed when it put in the tube and finally when its cocked .

for both spring its 50mm   38mm   25mm

then i rigged up a plastic tube  with a stop at one end and a plastic plunger at the other,i marked 25mm compression and pressed it against an accurate scale till it compressed to 25 mm and took readings of both springs at the same 25mm compression stage

they were 2.8kg  and 6 kg

when ive time im gonna work out the K constant which im assured by folks wiser than me is what Mec Eng types do

ill also take a pic of test rig when ive got time

[quickster47 †]

Good work.  Personally, I love doing stuff like this.

Anyway, you might want to try the hammer spring from a 1377 as I believe they are a little stronger.

Carl

[UKairgunner]

yes Carl,im interested in what"stronger" means. once ive taken the pics and crunched the figures i think this kinda thing can easily be used by anyone to compare any similar length spring used in air  pistols.

be back later with pics and even later with figures

[quickster47 †]

The 1377 hammer spring takes more force to compress to the same length as a 2240 spring.

In other words, it takes n pounds to compress the 1377 spring to a length of 1" and only .6n to compress the 2240 spring to a length of 1".

Carl

[UKairgunner]

thanks for that,im gonna get into the maths of what ive measured when i can gather enough brain cells in  one place at the same time

cheers

[CraigH]

Good stuff, this subject.  I measured the length and wire diameter of all the springs I have and have had a desire to build a little spring compressor to measure them, but much of my projects have been on hold for unrelated reason.

Looking forward to your results.    ( for whatever reasons, I cannot insert emoticons - 8^(  )

[UKairgunner]

ok here is the simple rig i made
the hollow tube has a stop end,the spring goes inside  and is followed by the plunger
the 3 marks on the plunger have been highlighted for the pic ,in reality they are fine lines
the first is to the actual legnth of the spring uncompressed .the second is at partial compression when loaded into the pistol
the third is to 25mm or 1 inch which is the final length when cocked

once loaded with spring and plunger i use a fishing scale/cooking scale to measure the force needed to compress to 25mm

[JMJinNC]

Nicely done! Great way to empirically derive/confirm the spring constant.

Free length, wire diameter, and coil count are also useful parameters to record since they determine working range from zero load to coil-stack (all coils touching). Stiffness of the wire then determines the "k" value (lb/in, kg/mm).

Also, you can have a spring that has a very long free length but it must be supported (externally or internally) or it will buckle. The upside is that the working length is so long that you can preload it a lot and have a very flat working load range.

FWIW, I'm a mechanical engineer so I do this stuff all the time.

JMJ

[UKairgunner]

thanks for that

Robert Hooke ...who first discovered hookes law of springs ,  was an early engineer who was a  son of a poor protestant preacher who was looked down on by his fellow scientists...but died wealthy(  he kept all his money in cash under his bed)

he would have understand every aspect of a 2240 except the plastic and co2( discovered a few years later)

dont suppose anyone would look at my results and calculate the k ...in metric please...

[UKairgunner]

so ive had a go

it seems the spring constant ,which is an accurate and standard indication of a springs stiffness and "strength", is 1100n/m for the standard 2240 spring and 2352 n/m for the hi-power GMA spring i tested

Probably a much better way to represent the results is to say it takes 6kg to cock a GMA power spring and 2.8kg to  do the same with the standard crosman spring

i wonder if crosman give any figures out ,,,,or would be prepared to?

also it should be said that a spring with almost twice the "power" will not give you twice the FPS/FDS....IT dont work like that

anyway im keeping the rig to test any other spring im offered

[UKairgunner]

So now I,ve chosen the spring i want to use but Im fed up with the fiddle sum screws and the stock  tube end. i want to fit a dogpoint grub screw into  a tapped hole made in the tube end  to enable me to change springs easily..but  the tube end has only a couple of mm thickness ,not suitable to tapping in a thread  .
i bought a GMA power adjuster ( which matched the stock look and has 7mm of metal thread) and cut down the the screw-in bolt  into a slotted end( measure twice cut once). I measured the original end position of the hammer spring and cut the thread  off so when the grub screw is flush with the tube end it replicates the original spring postion. I didnt want to adjust the hammer spring tension just change springs easily and it works a treat

[quickster47 †]

Very similar to the set up I use except I made my own.  Personally, I like being able to change the spring easily.

Carl