Discussion in 'Piston & Spring' started by Buffalo, Nov 26, 2017.
Much more refined, Nick.
Those were my thoughts , When My Brother (A gas turbine engineer) looked at it he said such a huge reduction in acceleration would be a lot softer, it was , but it actually gave more sight picture movement, and I didnt like the shot cycle
The two grades that I compared are both 'valve' grade wire. Both are considered much less fatigue sensitive when compared to 'standard' grade low alloy spring materials. Valve grades have higher standards of steel cleanliness, meaning that the propensity of non-metallic inclusions affecting fatigue cracking sensitivity is greatly reduced. In general, airgun springs are low cycle service applications. When you compare to the dynamic loading of car engine valve springs for example, which are being compressed hundreds of times per minute.
To answer your question... I wouldn't class airgun springs as 'fatigue' sensitive. failures are generally related to high impact/high loading and of course inappropriate heating cycles applied when attempting to shorten springs.
High performance motorbikes can be hundreds of times per second!
One of my favourite videos below. Shows what springs can really do
Thanks for that... my point exactly! Valve springs are highly dynamic and would be prone to high cycle fatigue. Hence why 'valve spring' quality wire is used.
A certain person on here used to drop spanners in works race engines... the valve springs were an off the shelf publicly available spares part used by the same engines on the road. Service interval on the road was 12000 miles... service interval on the track was about 120 minutes. Or something like that... dunno he mumbles a lot
I would assume there is a fundamental difference in the stresses on a car valve spring and the way an airgun spring does it's job. Not many car valve springs break when compared to how many airgun springs break. A cars valve spring is very controlled in it's compression and extension cycles where an airgun spring is compressed pretty much to the max and then let fly only to be hammered by piston bounce at the end. I've had many, (more than 5 less than 10), airgun springs break over the last 250,000 shots and not one car valve spring break in at least a million miles of driving in my cars and trucks over the last 42 years.
Engine valve springs V airgun springs..?
You're quite right, but the point being made was that the spring steels being used are 'valve quality' grade springs....or at least they are pitched as such in their sales description! Greater control of steel cleanliness and the amount of de-carburisation around the wire circumference, makes the wire much less susceptible to fatigue type failure.
It would make perfect sense for 'valve quality' Silicon Chrome or Silicon Chrome Vanadium springs to be used in airguns, irrespective of these grades being used in high cycle fatigue applications such as engine valve springs. These grades are also particularly suited to high impact, shock loading ..... just the service conditions that you describe!
I hope that addresses your pertinent point..?
I reluctantly opened my target gun up to see how it has been fairing as it's lasted so long!, I have the same guide in this as Brians first guide ie 2 piece : ally washer with Steel guide, mine has a delrin pre load washer , this washer has worn a very small recess into the ally in the region of .005" so not a lot.The spring has no preload , and no real evidence of the spring jumping. What has happened is the bore of the washer has worn suggesting that there may be a little run out in the piston rod , in my case I think this is why the guide has survived , to explain why: the rear of the guide locates radially in the trigger block recess ( don't know why but on this one I have a very short shoulder) and with the guide now clear in the ally washer it's working like a universal joint , effectively allowing for any run out or out of square in the trigger block. In the standard TX there is room for a big clearance in the guide bore , and the rear of the guide has a very loose location radially, This must be deliberate on AA's part as I do know that most of the standard piston rods I have come across have been bent to a greater or lesser extent, (I have made my own rods to eliminate this ), in my reduced tube tune (21 mm), my guide walls are in the region of 1mm thick because of the available room and spring dimension, so tightening all the sizes up and trying to make it all more rigid has possibly gone against me .
So I have taken a page from Colin Chapmans book and got rid of the guide ! Well more like make one component do two jobs , I have lined the piston rod with a delrin sleeve so it now acts as the spring guide ( it's effectively solid so shouldn't break) and at the trigger block end I have a recessed steel bush to locate the od of the spring , so a reverse guide if you like , I have built his all into Nick2's Tx along with the vortek spring and a revised stroke which allows 20mm of pre load.I have built my own gun using the same spec only I have a nylon guide to test ( to see if it's flexible enough to work) so a two pronged approach.
Zero pre load in my own gun( the one that has survived )
View attachment 26910
Sloppy rear guide (universal joint?)
New set up ( reverse guide )
Apologies for the drawn out post but its snowing and I can,t go shooting, oh and this new format is great Rob very easy to do the images .
Zero pre load picture
Looking forward to getting it back Nick.
See i have not had 1 spring break, no guides break now for a long long time also, some lads shoot 500 a month some are shooting 500+ a week, i have Diana and TX all down at 22mm now, multiple FT shooters bringing feedback not only in the UK to me.
21mm probably has to high pressure, reduced dia port will up that pressure even more, if the spring resonates it will break and break guides.. I watched my 52 spring resonate down at 20mm, its not nice to watch, the pressure at 20mm is over 2000psi we think at sub 1mm from plug face, however i cured it, that gun is now utterly superb running 11fpe with express and what many would feel a 6fpe spring. However 20mm is hard...so im sticking 22mm.
I gave up chasing the lowest recoil and fastest locktime, i prefer things that last and people have some confidence in, what i do may not be the best there is but it seems to be lasting a hell of a lot longer.
What a wise approach Tony.
They 've gotta be reliable .
Ahhh no going to have to stop reading this article I'm starting to get curious.....
'tis a slippery slope
welcome to it
My problem is I am like a dog with a bone , and I am hooked on the 21mm firing cycle . having said that Nick 2 now has his power plant back, and I am now working on A 22mm hw 97, I have an idea to get it skirtless with the standard rod and trigger sear, I have one at 23mm with a tx style rod and sear , but the weak link is the adapted sear so trying to avoid that , if not it will have to be skirted .
Nick, honestly you are chasing the near recoilless dream at the expense of robustness. I had to lend Brian the the power plant from my hunter carbine to prove not all the kits break, he posted on Lost Volume that they do which mean't i was being tarred with the same brush by many, as small = weak in peoples minds. He has since bought that kit from me and supplied a new comp tube so I can now remake the HC power plant.
Soon as you chatted to loki at the bash I thought here he goes again trying to get the minimum movement from his gun, you will note i did not have mine tested, i have lost interest in chasing that dream. My guns are way better than a stock one, much easier to cock, mine have less input energy so less strain on the springs, a huge reduction in recoil and near no surge plus i stayed with the mk3 spring so the guides have some meat to them also, and now i have moved to steel nose with POM guides and a bespoke seal that I supply so spares are easy to come by also. lads in Malta and Portugal are stocking up on seals and bearings from the get go, i doubt the originals will wear fast but they have all they need to enjoy their shooting.
97 rods need a key way slot milled in the top to use the stock sear, so as you push that rod back on cocking the rod aligns right via a pin in the trigger block...already thought of that one
You may have thought of an idea for the 97 rod , but have you tried it yet?, I have something similar in mind but will use a bog standard rod .
I know the 22mm tunes are more reliable i have built several of them ,and tried others , your own gun included , I am not keen on the firing cycle of the skirtless set up with the long piston nose , to my mind the only advantage over a good 25mm tune , is the easier cocking. I prefer the longer spring room afforded by the full piston , but then of course i am limiting my choice of spring, I have a semi skirt idea on the go at the moment that gives me the spring room and allows me to utilise the mark 3 spring, using the seal you sold me at the last springer bash , not had it in a gun yet , I hope i like the cycle . If not I will keep trying different ideas till i get what I want .
The re-vamped 21mm worked well on its first comp on Sunday, I finished with a 53, 2 points behind the open pcp winner, so I am well pleased with it. I know its early days yet, & only time will tell if Nicks modifications prove reliable. There's just something about the way it shoots, that like Nick ,I dont want to give up on it either.
Nick, i dont run long noses, where do you get that from? 20mm at 21.5mm od, if i use a 95 spring 200 to 205mm long, if i run a Mk3 spring 220mm or so long, if i run one of the special i had done 215mm long...stock OEM springs are 225 to 230mm long and run way more preload than i do.
The piston flies straight, the bearings are there to support it as you cock it, not when it fires. I tested a seal on a top hat mounted on the end of the rod with a steel inset guide also, so no body at all, shot just fine...but to fast for me, and i decided some support is better than no support BUT i bet longevity testing would have shown it lasted well.
Regards the rod nope not tested, will do though, been testing stroke on the 77 and i hit what i need so slow steady progress.