u/Fyvfyvfurry

Spring:

• 194.6mm relaxed
• 22 coils
• 20 working coils
• 25mm OD
• 21.4mm ID
• 1.7mm Wire diameter

Spring fit Limitations:

• 21.2 Min ID
• 27.8 max OD
• 52.6mm Compressed lenght
• 142mm Spring travel

Plunger tube:

• 44mm OD
• 40.5mm ID
• 151.1mm lenght

Barrel:

• 13.15mm ID
• 16.2mm OD
• 403mm lenght (i mismeasured it to 500 the first time)

Results of measuring may vary, if you know i mismeasured or didnt mention something - let me know.

Just made 3 aluminum plunger tubes for it.

You can make spring for most blasters at home.

Unless its some kind of funky shape spring, like in Nerf Sp-l, or maybe leihuiu lp-55, you are good with standart sized springs.

Most important - make it retain its shape after altering its shape.

Lets start - you can buy almost any size of industrial high carbon steel spring, only proiblem - some of these wont prime when cut to the lenght, required to fit the blaster. Obvious solution - make spring contain less coils per its lenght - stretch it until its good to go. Shape and force calculation will be explained in trhe next paragraphs. So, you stretch it, but, by doing so, you make spring lose its properties of retaining shape under repeated loads, so after installing it and serveral primings it will lose its lenght and any power.

For some industrial spring steels there is a way to make spring retain its newly acquired shape - heat treating, which is just soft tempering, just as its done in the production facilities after spring is cold-shaped and treated at 240c for 30 minutes, after which its left to slowly cool by ambient air.

After such treatment, if done correctly, spring may get bluish tint, and will acqure needed resistance to losing its shape. it works for GOST 9389-75 steel, and its pretty similar to steel that american industrial springs are made of.

Lets go by the basics of spring shaping

So most important limiting factors are:

• Maximum outer diameter, usually determined by plunger head shape, makes sure spring wont scratch plunger tube while in use
• Minimum inner diameter, usually determined by its place, for example, for kronos its 18.4mm, any less and it will hugthe plunger tightly and wont work properly.
• Spring relaxed lenght - lenght when not primed
• spring working lenght - lenght when blaster is primed and spring is squeezed.
• spring travel distance - key limiting factor, the reason why we stretch it, similar to priming handle travel distance (if there is no gearbox like in helios), slimilar to (=Spring relaxed lenght -spring working lenght)

So thats the limiting factors.

for the next steps, we must remember, that increace in spring force correlates with:

• Lesser the outer diameter of the spring - the stronger the spring
• Lesser the spring coils count per the same lenght - the stronger the spring ( stretching has its limits, and yoou better stretch it as little as possible to fit blaster, to increace power mainly change wire diameter).
• thicker the wire diameter - stronger the spring.

i wont go over spring characteristics such as coil count or mean diameter, not in this post.

Knowing all this, you can use the spring calculator ive made based on math behind helical spring and existing solutions ive used previously. Its made in an excel file with formulas and all you need to design decent sping for your blaster.

Lets dive in.

Summary of the sheet

First - input the desired force, relaxed and compressed lenght, outer diameter, and any spring diameter, sheet will help you decide what wire diameter to use

first step

Then see the minimal required wire diameter and change your diameter to what you have in your disposal and what is thicker than this. if you cant do that, thi is fine, but spring will definetly have shorter life, same for index - the further it is from the 7-10 range the worse, but its not that bad, as 4-12 is kinda ok, and its really broad range.

Second - see the resulted parameters at the bottom, be wary, thart coils count at the top is rounded and spring with such coil count will have "rounded" stiffness and force (bluish cells)

Second stage- calculated parameters.

So, we calculated our springs patrameters, but will it prime? Lets go top right and see, there are some insight on that

will it prime?

the more "will it prime" is, the more room you have for error when cutting spring to the needed coils count, in fact its a reserve of possible spring travel thats not used when spring is under its working load, it better be more than 2 wire diameters, that way its guaranteed you wont mess up the cutting part.

Now lets get to the steel parameters part

steel parameters

Maximum allowed stress is calculated by itself automatically, involves spring wire diameter and used in other calculations on the sheet

Rm is a tensile strenght, predetermined value, Steel modulus is also pre determined value, you need to find those for your steel for correct calculations.

Desired coefficient is the value that determines what loads will your spring endure in the future, 0,5 is good springs, andf 0.3 is impossible to satisfy with mild spring steel like GOST 9389-75 B2 steel, i dont recommend going higher with that coefficient on nerf blasters.

Calculator excel file is here

Importat things

220c when tempering is worse than 260c, 260 will temper it, 220 not really. 240 is ideal. Every temperingt decarbonizes your springs, but from experience, 2 or 3 temperings is still fine, you may use borax to avoid decarbonizing, be careful it turns into glass on the spring.

Cutting springs - bolt cutters are good, but it will destroy cutters pretty fast, angle grinder produces sharp microneeedles, avoid it or use good protective gear without gaps betveen shirt and gloves, learned it the itchy way. i use arc cutter, but it requires skil and can easily ruin spring by overheating it, and has potential; to slightly decarbonize its ends, borax is advised but its fine without it.

I need lenght, outer diameter and maybe internal diameter, and are there some parts that limit those, like catch on longshot limits internal diameter to 21mm minimum?

Thanks in advance!

I need a software for windows/android to calculate properties of compression springs made of GOST B-2 steel, as online calculator by dontochmash is currently stopped working. Any suggestions on software to use?

I need an E-bike, and due to being in Russia my choice is limited to chinese models. I consider Kugoo V3 Pro Max, but ive heard it needs to be waterproofed after purchase to avoid damage in the rain. Bike preferrably to be comfortable for commuting, it doesnt need to be super sporty thing.

Price, reliability, 50-70km range and weather resistance are top priority.

Any suggestions appreciated, thanks!

I have tried to make a better seal on my fury x by changing o-ring to a bigger one coupled with stronger spring, as a result first three shots were nearing 200 fps, and then it fell to 150-130. Then i disassembled it and noticed plunger is kinda loose, and old o ring didnt make seal at all.

Plunger tube, which is made of PTFE, stretched in diameter.

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So, i googled ptfe properties, and yes, it is easily stretchable and doesnt return to its original shape. I guess i have to accept it as a limiting factor in my future modding. I hope you find that info about PTFE(teflon) stretchimg properties useful. Next one to mod is xshot doomsday. Thank you for reading.