GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rkr on January 11, 2021, 02:02:02 AM
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I've been thinking of making a lightweight delrin or nylon hammer for my Evanix, mainly to reduce friction but I'm also interested in other benefits it may provide. To my understanding it provides faster shot cycle and faster valve opening but dwell is reduced. How does it go in practice, say if I cut the hammer weight in half do I need more hammer spring force to keep the power level in max. power configuration (.257 Evanix at 160 fpe)? What are the real pros and cons of a light weight hammer, is it for air efficient pellet shooters or is it also useful for higher power bullet guns?
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In larger caliber and high power guns .... likely not going to work well unless combined with the use of a balanced valve configuration.
Here on the GTA i was one of the first major contributor to the R&D that took place what was in the time HEAVY HAMMER use and looked at what a Lighter & faster hammer would take to get equal result in power while reducing air use by actually reducing dwell when it was excessive.
This lead to gains in air efficiency that in that time was pretty ground breaking.
The original post goes back 8+ years and can be viewed here ...
See: https://www.gatewaytoairguns.org/GTA/index.php?topic=38088.msg354519#msg354519 (https://www.gatewaytoairguns.org/GTA/index.php?topic=38088.msg354519#msg354519)
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You're going to need enough hammer energy to crack the valve open, regardless. You can trim the weight of the hammer some, and that may still work for your tune with the current hammer spring. There comes a point of dimensioning returns with hammer weights before needing more hammer spring for the same tune.
It's true, the lighter the hammer the faster the valve dwell. I use some MDS hammers, but with my higher powered tunes I have hammered in a JSB 34gr or two to up the MDS hammer weight on those tunes to avoid the need for a higher rated hammer spring. In other words, it's a balancing act to get the hammer weight as light as possible without too much heavy hammer spring for a particular tune with a particular weight projectile.
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A pure MDS nylon / Delrin / PEEK hammer will not be a good match for a 160fpe rig unless, as Scott says, it gets paired with a balanced valve.
For a conventional valve, you could go with an in-between approach…a hybrid hammer paired with a PEEK poppet. By hybrid I mean a plastic hammer with a metal core or slug of some kind to bring up the weight. The PEEK poppet will make the valve noticeably easier to knock open relative to a more common Delrin poppet, so more of the hammer’s energy is conserved (in the form of momentum) for the purpose of providing dwell.
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If your current tune is wasting air from too much dwell, then a lighter hammer can improve efficiency with no power loss.... If you are already tuned so that increasing hammer spring preload gives more power, then installing a lighter hammer will very likely reduce power, and require even more spring to get back to where you were....
This means that without a balanced valve, if you are trying for more power, typical for a Big Bore, fitting a lighter hammer will likely make the gun even harder to cock, and in fact going heavier on the hammer may be advantageous.... Since there are very few balanced valves available in the aftermarket, or used in factory PCPs, fitting a balanced valve so that you can use a lighter hammer in a Big Bore will generally mean making it yourself.... The exception is the Cothran Powerhouse, which drastically reduces the hammer strike required.... but it cannot be easily tuned for a bell-curve, so is best fitting in a regulated PCP.... again, not often the reality in a Big Bore....
Bob
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Thank you for your comments. I think I'll make a delrin or nylon hammer and see what happens. I need to make a steel face for it anyway and I can always add weight if needed. In Evanix the sear drags against the hammer belly and there's wear marks at hammer skirt as it rubs against the aluminium frame so softer self lubricating material should reduce the drag and help in shot-to-shot consistency.
As for the balanced valve, I made one for my .45 sniper and while it allowed much reduced hammer strike it also tends to start leaking after few shots - so I decided to keep this gun simple with traditional valve as I need reliability and tight fps spread.
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Following
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One more question, do I want Delrin/POM, Nylon or PTFE as the material for the hammer body? The face where sear engages will be steel but the hammer will be pulled back from a slot in the hammer body by a 3mm steel stud in a sidelever system. The hammer sides will be only 1.5mm thick.
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Probably not PTFE due to its softness. MDS nylon (molybdenum disulfide impregnated, Nylatron is a trade name) Delrin, or PEEK would be better choices. I don’t think any of the 3 is distinctly superior for the job you have planned. All are tough and have high self-lubricity.
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If the cocking pin only engages in a 1.5mm wall made of plastic, you may have a strength issue....
Bob
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If the hammer sidewall is only 1.5mm thick, that means most of its weight is at the business end of the hammer?
If so I’m picturing a sandwich hammer assembly. The thin back portion with the cocking slot in steel, a slug of plastic on that, followed by a steel disc on the face to support the sear.
The plastic portion could be through-drilled and the whole thing assembled with a screw from the front end. Crudely, picture a slotted flat head screw with a fender washer going through the plastic slug and threading into the back end of the hammer.
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When I had my Gen 1 rainstorm with a regulator, was very successful using a 100% Aluminum hammer made from 7075 grade.
IIRC had inserted a short round slug of tungsten carbide to be the strike surface while adding a bit of weight.
Good polish and gentle radius on the sear to hammers holding edge and across the top where dragging all was well and no wear was present.
Had done this 5-6 years ago and Sadly don't have any pictures ... BUT DID FIND the original post ... post #17 talks about the hammer.
See: https://www.gatewaytoairguns.org/GTA/index.php?topic=67566.msg643145#msg643145 (https://www.gatewaytoairguns.org/GTA/index.php?topic=67566.msg643145#msg643145)
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I am surprised the following link wasn't yet shared. Good stuff courtesy of rsterne on the subject.
https://www.gatewaytoairguns.org/GTA/index.php?topic=99949.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=99949.0)
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All of the previous responses are giving you great input. I followed Scott's light/ultralight hammer posts and applied the concept to many of my guns.
Early in the process I made a peek hammer for my P15. The OEM p15 hammer weighs in around 18 grams. My all peek hammer weighed a whopping 3 grams. it didn't work so well, obviously.
(https://i.imgur.com/SDHeiGR.jpg)
I use a 17gram hammer on a 90fpe .30 pellet shooter. It is in freeflight, and very easy to cock, however it is opening a Cothran valve.
I have a 60fpe .25 QB build that is opened by a 17gram all peek hammer. But mods were performed giving that hammer a pretty good running start.....
Running the same 17 gram hammer in my Gauntlet required excessive cocking effort to get sufficient dwell from the small plenum. Ultimately settled for a 26gram hammer.
In my .457 Extreme I reduced hammer weight by 40 grams and delivered a tighter string at higher fpe.
In my Bulldogs, when equipped with conventional valves and unregulated, reducing hammer weight is not helpful at all.
Even with a balanced valve we may need more hammer mass to facilitate adequate valve dwell.
All of my .257 testing has pointed towards needing dwell to build power. Heavy hammers provide dwell.
There is no perfect answer, every gun and application is different. 160fpe out of an Evanix is indeed a unique application.
Some of us have to physically see something fail to learn from it. My all peek p15 hammer is a good example of this.
Best of luck, whatever you do please share the the story and results.
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I started making a delrin body with steel bolt through it as the face of the hammer. Skirt of the hammer ended up at 1.7mm and it doesn't look too flimsy. Weight is 22 grams vs. 37 grams of the original hammer. I need to set up my lathe for milling next and the gun needs some other mods before I can put it together so testing won't happen anytime soon. I will report how it works when I get to testing phase.
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Some results in the gun related thread https://www.gatewaytoairguns.org/GTA/index.php?topic=147066.msg156086756#msg156086756 (https://www.gatewaytoairguns.org/GTA/index.php?topic=147066.msg156086756#msg156086756)
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Hi All, Another thought on hammer speed, is having a vent hole in the tube for the hammer. So that the hammer isn't compressing air going forward, It can make a big difference in hammer speed. hth
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That’s a good reminder. Note the same can apply to a vacuum behind the hammer. For example, the old BAM B50 platform is susceptible. It tends to cause wild velocity fluctuations.
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That is a good point, James. I drilled for venting in all of my hammers. Venting the hammers will also improve the ES.
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I had addressed hammer venting issues many years ago and still keep aware of this issue with some designs. Indeed compression on the forward side and vacuum on the back side can really screw with ES stability.
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Another aspect of hammer is the strike length. I have an opportunity (having two stock hammers) to shorten the nose of one by 3-4mm, in Evanixes the hammer nose is about that much in front of sear engagement point. If I understand it correctly that should increase the hammer velocity and thus energy (with spring pushing against it all the way) causing higher valve lift with shorter dwell? Is 3-4mm worth it or am I just wasting my time and ruining a good hammer?
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You are correct about the effect on lift and dwell. Whether or not it would be beneficial, I’m not sure. Generally it is helpful with low to medium energy tunes, and less so with power tunes and long barrels where long dwell is necessary.
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Longer hammer travel, with the same spring pushing it (under pressure all the way).... will cause the (same) hammer to hit the valve travelling faster.... This means more energy (lift) and more momentum (dwell).... The valve will open faster, further, and stay open longer.... It has the same effect as increasing the spring rate, but without the same increase in cocking force....
Shortening the nose of the hammer (or the valve stem) is a useful mod. to open the valve more without increasing the maximum cocking force.... Just make sure the hammer can't run into anything other than the valve stem, or it can damage things.... or cause you to lose power instead....
Bob
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Yes, increasing the stroke length by shortening the hammer will produce more hammer energy. This can be compared to swinging a hammer in a confined space to being able to swing a hammer in a less confined space.
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Hi Bob, is the increase in momentum (dwell) an absolute or a generally speaking?
It's been a while but I recall running some calculations on a scenario where the momentum worked out to something a bit less. We recognize that momentum is a simple product of mass and velocity:
p = mv
So it's true that momentum will increase as long as the increase in velocity exceeds the drop in weight.
However a typical hammer is nose heavy, owing to being bored out in the back for the spring. Shortening its nose removes a proportionally large amount of weight reative to how much it has been shortened, making it possible that the bump in velocity does not offset the weight loss. Maybe?
Meanwhile the increase in energy (lift) is more intuitive. Shortening the hammer gives it a longer runway to achieve a higher velocity, and since energy increases by the square of velocity, higher energy is pretty well assured.
KE = 0.5mv^2
For example, let's imagine a hammer that's 10cm long...kind of a long hammer but it makes the thought exercise easier with a nice round number. Let's say 7.5cm of it is bored out almost entirely for the spring pocket, leaving 2.5cm of full thickness at the nose. Very nose heavy. I want to lighten it up so I take 2cm off the nose. Because the rest of the hammer has such a thin wall, I've cut the hammer's weight in half. Therefore to get more momentum than before, the modified hammer needs to achieve a velocity over 2x greater than the original hammer. Is that what happens?
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Oh, I just re-read your reply and see you made a distinction for an unmodified hammer...
....will cause the (same) hammer to hit the valve traveling faster
I think that addresses my question.
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I was responding to the increase in hammer travel, independent of any other variables.... If you have a very unusual hammer (per your example), where shortening it lightens it a LOT, I supposed the momentum may stay the same or decrease.... You could, of course, increase the hammer travel by shortening the valve stem, or drilling a hole in the front of the hammer, causing almost no weight change, and what I stated would still apply.... Alternately, you could machine off most of the (heavy) front of the hammer in your example, leaving a thin stub of the original length, in which case the travel would be the same, and the momentum would decrease, because all you are changing is the mass....
It reminds me of a George Bernard Shaw quote.... "All generalizations are false - probably including this one".... ::)
Bob
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FWIW and offering no further constructive input ..... as MUCH hammer fiddling as I've done on many many PCP and VALVE configurations i still time to time get surprised when a small change in weight or stroke gets altered and the power output changes drastically.
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Yep... in simple terms...
Consider the difference in impact downrange between a light pellet and a heavy pellet leaving the barrel with the same force.
The light pellet will arrive faster but the heavy pellet will carry more 'punch' when it arrives.
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Hi Scott, I did an experiment once where I made up a number of spacers in .005 increments, that I placed on the back of a valve to see what different dwell times would do. On this valve using a .070 spacer I got a noticeably higher velocity, than with a .005 thicker or thinner spacer. It was a sweet spot for velocity. I was surprised by how narrow the spot was. Maybe you were hitting it with your minor hammer stroke and weight changes?
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Hi Scott, I did an experiment once where I made up a number of spacers in .005 increments, that I placed on the back of a valve to see what different dwell times would do. On this valve using a .070 spacer I got a noticeably higher velocity, than with a .005 thicker or thinner spacer. It was a sweet spot for velocity. I was surprised by how narrow the spot was. Maybe you were hitting it with your minor hammer stroke and weight changes?
Absolutely and my comment was based upon this knowledge without a free fall down the rabbit hole as to why ?
If a tune is "TEETERING" on the edge of more so or less so making a difference .... these minimal changes are EYE OPENING examples where you get an in your face WHOA I had no idea that what ever "Tune parameter" or shift you made was so close that such a dramatic cause and effect happened you needed to understand .. or try and understand.
Some what as we commonly say is a BELL CURVE peak .... this name sake can be applied in more than one place in the operation of a PCP or many other type systems where the EBB and TIDE break direction and WHERE this shift happens has relativity.
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James, if shimming the back of the valve changed the velocity, then the hammer must obviously have been coming close to the back of the valve.... Most PCP valves only open a fraction of the available mechanical travel.... For example, a Disco valve stem protrudes about 0.31" from the back of the valve, and the valve spring goes coil bound when it is still 0.060" from flush.... In other words, the valve only has 0.250" of travel available.... I have measured the actual valve lift (using an O-ring sliding on a lightweight, captive spring guide), however, and it varies between 0.060" at 2000 psi and 0.125" at 1000 psi.... In other words, the lift has nothing to do with the hammer hitting the back of the valve (or bottoming out the valve spring), it is a balance between the hammer energy opposed by the closing force on the poppet....
Having said that, I have had valves that WERE lift limited because they had a very short stem.... In some of those, if you increased hammer strike (eg. preload) the velocity would gradually increase (as expected), but if you went too far, the hammer would bounce off the back of the valve (shortening the dwell), and the velocity would drop.... That was the only situation where I found that there was insufficient mechanical valve lift available, and a longer valve stem would have produced an increase in velocity (at that pressure).... If you have mechanical valve lift sufficient to allow the poppet to lift 1/2 of the valve throat diameter, you have enough for any EFFICIENT tune.... In fact, the flow through the valve will not increase after the lift is greater than 1/4 the throat diameter.... That is where the curtain area (under the seat) equals the throat area....
Bob