GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Topic started by: ray1377 on October 07, 2021, 01:04:54 AM
-
If this question is in the wrong place I do apologize. I didn't really know where it might belong.
For those who have the means and the ability to make their own break barrel custom parts I'm curious to know from you if when you make
a new spring guide how do you go about sizing it? I know a spring expands as its compressed so I'm guessing you want your new guide to be somewhat larger than the factory one you are replacing. The same would also apply to the tophat since they both fit down inside the spring.
Any info you fellows could provide on this would be greatly appreciated.
Thanks
Ray
P.S. Mrs.Liz, I'm sorry if this is in the wrong place.
-
Ray,
Great question and it might be moved to the Tuners gate. My understanding is that the optimum spring guide is slightly loose when the spring is compressed, but taught when the spring is released. IE. the spring "grabs the guide when it is released and absorbs most of the inherent vibration of the spring. So in a relaxed state the guide is hard to get onto the spring. Top hats may be slightly looser. Remember, the most important thing that the spring guide does is centers the spring as it it compressed. It wants to slant to one side or the other.
HTH?
-Y
-
The proper fit of the guide in the spring is determined by the intended use. For target shooting the guide would be a bit tighter than it would for hunting as the spring clamping back onto the guide after the gun is fired will tend to reduce the energy transferred to the piston. Its primary job is holding the spring centered. The top hat's job is to hold the end of the spring centered and help keep the spring from contacting the piston. It may or may not be used in conjunction with a piston sleeve.
-
Base line ...
Measure spring O.D. and write it down ...... Measure wire diameter and write it down ..... SUBTRACT wire diameter X2 from the spring O.D. and there is the @ spring I.D. ( actual guide size with be +/- pending application )
Generally when installing the guide it should be light to snug fit requiring some push to get it inside spring. Only trial and error ( AKA: Experience ) will get you the knowledge of whats just right.
* DEBURR the ends of coil so not to gall the guide when pushed on & smooth up the flat surfaces.
Have fun and good luck ...
-
On a Dutch forum I got the tip from some one who makes the guide better fit with a piece of an soda can.
Some where else I read some used a plastic from a soda bottle
-
Base line ...
Measure spring O.D. and write it down ...... Measure wire diameter and write it down ..... SUBTRACT wire diameter X2 from the spring O.D. and there is the @ spring I.D. ( actual guide size with be +/- pending application )
Generally when installing the guide it should be light to snug fit requiring some push to get it inside spring. Only trial and error ( AKA: Experience ) will get you the knowledge of whats just right.
* DEBURR the ends of coil so not to gall the guide when pushed on & smooth up the flat surfaces.
Have fun and good luck ...
Educate me if you would please, because while honestly not sure which of a half dozen forums I read it on, it was recommended
to set the spring before measuring and making guides. Is it something that should be or does it not matter if it's set or unset??
-
Educate me if you would please, because while honestly not sure which of a half dozen forums I read it on, it was recommended
to set the spring before measuring and making guides. Is it something that should be or does it not matter if it's set or unset??
Someone posted a video here yesterday in a different thread of a guy setting the spring before making the guides. He has a nice press to set them, and the ID increased after the set. If I can find the video I'll post it here.
-
My 2 cents linked here.
https://www.gatewaytoairguns.org/GTA/index.php?topic=190123.msg156196981#msg156196981 (https://www.gatewaytoairguns.org/GTA/index.php?topic=190123.msg156196981#msg156196981)
The proper fit IMO needs to have "some" friction at the PRELOAD spring Length/Diameter. Based on that fit I don't think it will make any difference if the spring is preset (scragged?) or not. I have NOT tried a direct scientifically based experiment to determine if there is any difference, just my opinion.
Made one a few weeks ago from a 1/2" x 8" hex bolt for one of my noisier Hatsan Mod85s. Liked the results so am making another one for another boingy Mod85. Plan to document that on the Turkish AirGun Gate in a week or two.
-
Thanks fellows for all the info so far. I'm learning more and more everyday on this particular subject. Does anyone know "from experience" just how much power "ie" FPS you loose by going to a larger diameter guide? Is there such a thing as too large? I know you have to at least get the spring around it and back in the gun but other than that there is a lot of trial and error I would think. And from the target vs. hunting application am I to assume that a tighter fitting guide will reduce power but aid in accuracy by having a smoother shooting gun?
Thanks
Ray
-
Base line ...
Measure spring O.D. and write it down ...... Measure wire diameter and write it down ..... SUBTRACT wire diameter X2 from the spring O.D. and there is the @ spring I.D. ( actual guide size with be +/- pending application )
Generally when installing the guide it should be light to snug fit requiring some push to get it inside spring. Only trial and error ( AKA: Experience ) will get you the knowledge of whats just right.
* DEBURR the ends of coil so not to gall the guide when pushed on & smooth up the flat surfaces.
Have fun and good luck ...
Educate me if you would please, because while honestly not sure which of a half dozen forums I read it on, it was recommended
to set the spring before measuring and making guides. Is it something that should be or does it not matter if it's set or unset??
Setting (scragging) the spring prior to installation is a topic that nearly begs for a new thread. I have scragged fresh springs from ARH, Vortek, etc... using the common method of the spring slipped over a length (@ 15") of all thread and the spring contained with a washer/hex nut at each end. Tighten the nut (s) and the spring compresses. It is possible to tighten and collapse the spring until it is absolutely coil bound (the spring will collapse no more).
Their are variants of the process of scragging a main spring. For example: the length of time the spring is compressed, how much is the spring compressed (completely coil bound or less than totally coil bound). And so on...
Suffice to say, if the spring you intend to use is already on the gun, it has been sufficiently scragged to take measurments for a new guide. Otherwise, with a new spring, simply make the guide "screw on tight", after a few rounds down range the spring to guide fit should be about right.
-
Thanks fellows for all the info so far. I'm learning more and more everyday on this particular subject. Does anyone know "from experience" just how much power "ie" FPS you loose by going to a larger diameter guide? Is there such a thing as too large? I know you have to at least get the spring around it and back in the gun but other than that there is a lot of trial and error I would think. And from the target vs. hunting application am I to assume that a tighter fitting guide will reduce power but aid in accuracy by having a smoother shooting gun?
Thanks
Ray
Great question Ray. The simple answer is yes, depending on the gun and the objective you are trying to reach, a guide can be too tight. If you are chasing fps for example. If you want more speed from a gun that is not a powerhouse, say an HW30, HW50s, rotary breech gun etc.. and want max fps, an over tight guide can cost significant fps.
-
I'm not going to get into specifics ... Being i am a professional tuner and manufacture custom guides near weekly for in house guns being tuned.
Yes if installing a NEW spring ... Set it first. No way to do that ? ... Easy Peezy ... Install New spring on the factory guide, cock gun and set it aside for 24 hours or so, uncock or fire a pellet ... take it back apart and you have a set spring 8) 8)
-
Subscribing.
-
Moving to the Machine Shop...
-
All good info fellows.
Motorhead, my spring is well used so I would consider it "set" for now :)
Not really looking for a powerhouse out of this gun, just want to smooth it out as much as possible and hopefully keep the power close to the same level.
Keep the tips and tricks coming. It's all appreciated.
Thanks
Ray
-
Someone posted a video here yesterday in a different thread of a guy setting the spring before making the guides. He has a nice press to set them, and the ID increased after the set. If I can find the video I'll post it here.
Paul Watts shows how much the ID of a spring opens up after the spring has taken a set. In other words, if you make a fitted spring guide, it needs to be for the spring ID after the spring has been set (by full compressing it to coil bind).
If you make a tight spring guide based on a new unused spring's ID, the guide may be too loose after the spring has taken a set. A loose spring guide allows the spring to twang. Sticky grease should help for that, but setting the spring before sizing the guide would be the better approach:
https://www.youtube.com/watch?v=XCraLBDCTpw (https://www.youtube.com/watch?v=XCraLBDCTpw)
-
Well for starters the gun I wanted to make the new guides for has had a few thousand rounds put through it already so I'm thinking the spring is "set" as much as it's gonna set. I measured the ID of the spring at rest and it was .490 thousandths and the OD of the factory spring guide was .473 thousandths. Needless to say there was quite a bit of slack between the two. I ordered some delrin from McMaster & Carr and went to work on the lathe. I went slow and kept checking the fit between the new guide and the spring. It took a while but the final guide measurement that seemed to feel the best was right at .498 thousandths. It took a good firm push and twist to get it inside the spring but wasn't so tight I couldn't get the thing back out with some arm flexing effort. Its not gonna slide out by no means. It has to be removed if its coming out. I went ahead and cut two washers to put between the spring and the new guides. Polished everything up and made sure all was still de-burred and ready to put back together. Can go really sparingly on the lube at this point since there is now no metal to metal contact when dealing with the spring. I still have intentions to button or add glides to the piston especially to the rear to stop all wear if possible. After I got it all back together it cocks super smooth and the shot cycle has changed dramatically. No twang at all, and no buzz either. Its just a firm little nudge back into the shoulder and a slight thud. I'm pleased with the outcome and wish I had done this sooner. I'm going to shoot it for a day or so before I put it over the chrony. From the sound it makes I don't think I lost any FPS at all. Will update after that.
Thanks for all the information, tips and comments.
Ray
-
Seems like a satisfying outcome, Ray
I am surprised that so little interference still works when the spring is at rest under normal installed preload. It is as if the guide is wrapped in one layer of office paper. A useful data point.
-
Seems like a satisfying outcome, Ray
I am surprised that so little interference still works when the spring is at rest under normal installed preload. It is as if the guide is wrapped in one layer of office paper. A useful data point.
Yes, on paper it does seem like such a small amount, but the difference it made in the shot cycle is astounding. And as far as preload there is almost none to speak of. I can take the gun apart without a spring compressor. Just hold the compression chamber upright with one hand and push down on the edge of my work bench and use the other hand to push out the retaining pin. I shortened my spring to get as close to 12 ft/lbs as possible so that makes an added benefit when it comes time to take the gun apart :)
Ray
-
OK. A 0.008" guide to spring interference, after taking into account whatever preload there is sounds like a more specific data point. So, if a given nominal 1/2" ID spring had a 3" preload, then one needs to determine what the actual spring ID is at that ID and make the guide perhaps 0.008" larger in diameter...
How to determine spring ID under preload sounds challenging. Perhaps it can be inferred:
I can see a series of guide diameters being tried with a "long" spring, until the guide diameter is found that just calms the vibration at the longest preload likely to be used. Then the spring is cut shorter by an inch and the exercise repeated; until the spring installs with near zero preload. Then the "just calm" guide diameter is plotted against spring preload distance to define that mathematical function. Or at least get a good idea of what it looks like. I bet that pro-tuners have already put in the work to determine this valuable info.
-
Initially I used the tightness of the Delrin guide in a Maccari kit I bought decades ago that performed well in my .177 R10 as a "go by" when I first cut my own fitted guides and still use a similar guide fit.
Over the years my non-technical "ghetto tunes" it's become rather easy to fit a guide to a new spring. I have other guides in my parts bin that didn't kill vibrations sufficiently (harder to kill vibrations than twang) so I try different "discarded guides" till I find one that is a suitably tight fit into the spring that only be removed by twisting the guide counter to the spring wind and pulling. If the guide can be pulled without twisting the fit is too loose I'll measure the OD of the guide and cut a new larger guide (the discarded guide is saved for possible use in later springs).
Anywhoo......if the gun twangs or vibrates when testing the shot cycle the guide is also saved for a possible fit to a different spring in the future. It is possible to have a spring guide fit too tight in the spring so it takes too much force to "twist and pull" and it's removed and a couple thou is removed to loosen the fit a tad.
When the gun doesn't twang or vibrates without excess guide tightness and only a thin coat of Krytox on the spring (no thick grease), I consider the fit to be good........
(https://i.imgur.com/HkfVchn.jpg) (https://i.imgur.com/GXZl4Hh.jpg)
Bottom line (for me)...........
trying to calculate guide fit simply by measuring a spring is the fact that a spring ID can (will) vary over it's length, the coil ID is determined by the amount of spring preload, etc so I gauge the guide fit by tightness and then test the shot cycle after reassembling the gun.
Springs and guide material...........
(https://i.imgur.com/ipLkdUc.jpg) (https://i.imgur.com/veWEtV3.jpg) (https://i.imgur.com/nh5lB1b.jpg)
-
Thanks Ed;
So, you fit guides by how they feel coming out of the spring when you wind the guide in the direction that opens the coils; rather than a specific diameter interference. While your method sound more subjective, it takes into account the total friction between spring and guide. In other words the surface finish of a given spring is accounted for by feeling the friction, rather than insisting on a particular measured diameter interference.
It is the right level of friction that damps axial spring vibration. Almost any level of actual guide contact should stabilize the spring to prevent sideways spring vibration.
If one argues that greasing the guide reduces the friction, and thus the axial damping comes from somewhere else, then perhaps the act of slightly opening the free coils near the end of the guide as they bounce back onto the guide takes out that unwanted energy. In any event, if it takes force to move the spring coils against the guide, unwanted energy is being taken out of the system.
It looks like you taper or round the free end of the guide to help the coils find their way on. That seems to make a lot of sense.
-
It wont matter if you press your guide at all to install, it doesnt take much compression to expand the spring. Ive made some that were snug to fit and had to compress the spring to get them out, the amount I needed to compress was less than the amount compressed to reassemble.
I also use a piston liner and havent had any problems so far. The most trouble Ive had was fitting a top hat because total compression to lock was already pretty close to the springs limit.
-
"Almost any level of actual guide contact should stabilize the spring to prevent sideways spring vibration."
My personal opinion isn't that twang is "sideways spring vibration" but spring coil oscillation along the spring guide after the piston comes to a stop (or perhaps rebounds on the high pressure air just before the pellet pops the leade.)
I personally believe that the reason a factory HW95 twangs and vibrates so much is the fact that the factory guides a a loose fit to the spring even after the piston comes to a stop. The piston comes to a rather abrupt halt at the end of the stroke and the loose fitting spring coils are free to bounce back and forth along the guide till they stop moving. IMHO, a properly fitted guide grips the spring coils when the piston is at maximum extension. When the spring is compressed by cocking the spring ID increases which released the guide by cocking. With the shot the piston surges forward so the spring ID is reduced allowing the coils to grip the fitted guide once more. Since the coils of the expanded spring are once more gripping the tight fitting guide the individual coils aren't free to oscillate like they would on a loose fitting guide.
It does seem that HW has increased the spring guide OD when I compared an old factory guide that came with the R9 and the Factory guide that came with my HW95 a few years later, however once the spring & guide are preloaded during installation there was considerable twang/vibration with an ARH spring wound with a nominal .515 ID before setting..........
(https://i.imgur.com/cYHcotm.jpg) (https://i.imgur.com/ezK0Mul.jpg)
-
I agree with Ed on all counts. I have no preload on my spring so it doesn't increase in diameter after installing it in the gun. And I fit my guides to just be tight with a twisting back and forth motion to install and remove them. The factory guide would just fall out of the gun by itself it was so undersized. Same goes for the top hat so I made a new one of them out of the same delrin also.So far it seems to work great and was well worth the time and effort.
Thanks
Ray
-
It does seem that HW has increased the spring guide OD when I compared an old factory guide that came with the R9 and the Factory guide that came with my HW95 a few years later...
Good to see Weihrauch has improve their product. My .177 R9 purchased in 1998 has the worst twang of any of my springers, while my .22 HW95 bought recently has no twang. So I may have got a combination of factory parts that produced the worst and best results with respect to twang. This HW95 shoots as smoothly as my R7, except that the R7 is quieter. Both are unmodified.
It makes sense that the twang is mostly axial vibration of the spring, along the length of the guide. That is the direction of travel of the piston and spring with the most significant energy transfer to it.
-
Keeping things simple for the novice, first ensure spring ends are free of burrs or you will be getting a a good shove fit on burrs and not the mainspring itself, leaving it loose further up inside the spring.
Suitably flat on its base and de-burred (i use a small half moon riffler file as a small slip with a dremel can nick the spring) …we then go for Ed and Motorheads nice push fit….no arguments from me on that one.
Im now using PTFE as a lube, bowing to Eds better experience…
Initial testing looks promising as it does not seem to have the temp sensitivity of Moly, particularly here on cold days….perhaps not so much of a problem for you stateside.
-
first ensure spring ends are free of burrs or you will be getting a a good shove fit on burrs and not the mainspring itself, leaving it loose further up inside the spring.
A very good point that may seem obvious, but should be mentioned.