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Tuning FX Impact M3 modified plenum front part remedy for slow initial shots

mubhaur

Member
Nov 8, 2015
1,460
58
Karachi, Pakistan
    Dear Friends, 

    Finally I got made the front part of the M3 plenum on the pattern of Impact MK1 style.

    So now the O ring is not just dropped into the cavity but it's held into a groove and a retaining screw with a peek plug of 3mm ID is made.

    The set up cost me a bit high but worth a try. 

    Shall share the results after reasonable testing. 

    Bhaur

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    mubhaur

    Member
    Nov 8, 2015
    1,460
    58
    Karachi, Pakistan
      In fact with low reg pressure while using 18.13 grain pellets at around 870 fps, M3 is not consistent for around 4 shots taken first time in the morning. 

      Means it settles gradually after a few shots.

      Seeker found a solution for it that worked for him perfectly but it worked for me partially. He used peek disc to avoid the O ring from protruding. 

      Hence I went back to MK1 system of O ring sealing the valve rod in the plenum.

      MK1 didn't have the problem that MK2 PP and M3 have.

      Very few people notice it.

      But for those who notice it, it's very irritating. 

      Hence for more for consistency and for using various weight of pellets at various fps without much adjustment of reg pressure I understand that the new setup will work. Just like mk1 worked for all this.

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      Seeker

      Member
      Jan 23, 2022
      314
      12
      Europe, Poland
        Bhaur, would you please explain the purpose of this? Thanks,

        Mike

        Just get familiar with this topic: https://www.airgunnation.com/topic/fx-impact-mk2-slower-first-shot-no-reg-creep/

        @mubhaur, that is a better solution trchnically than a peek disk. However, it is more expensive and difficult to do.

        Anyway, the best solution would be to place an oring groove on the rod. Thanks to that every shot would cancel any potential oring extrusion instead of exaggerating it. But it requires a different design and a thicker valve rod which implies other difficulties.

        I found a peek disk approach working nicely. However, it is critical to make a gap between the rod and peek disk as small as possible but not too small. Proper balance of the dimensions is a key factor determining the outcome of this approach. On the other hand, the same dimensions are also important in mubhaur's vision. 
         

        mubhaur

        Member
        Nov 8, 2015
        1,460
        58
        Karachi, Pakistan
          Hello Friends, 

          The modified front part of M3 plenum is working fine.

          In fact I understand that there are two factors.

          One is better arrangement of O ring placement. This matter has been solved with the new plenum part even with PU90 O ring.

          Although the O ring doesn't protude or extrude now but the stickines of O ring is still there.

          Hence if I do not tune the way I have found best the first shot may be 20fps low. But the 2nd shot is always perfect. 

          In order to overcome the first shot issue due to the stickiness of O ring , I tune it in the following way;

          In case I need to achieve 900fps with a certain projectile, I take the power up to around 980fps by tightening the hammer spring.

          Now I start closing the valve to the extent that I get the required 900fps. 

          In this kind of tuning, since the hammer spring has enough power to produce 980fps the powerful hit of hammer nicely overpowers the stickiness issue of O ring and I get the desired 900fps in the very first short. For the 2nd shot although the hammer hit is high but as I have already adjusted the valve to such limit that it cannot produce more than 900fps the 2nd shot is also consistent. 

          So with the mod in combination of this kind of tuning, the 1st shot and all the next shots remain in single digit spread.

          Hope it helps.

          Bhaur
           

          bigHUN

          Member
          Jan 16, 2020
          1,936
          84
          Canada
            Mubhaur I like your idea making a new end-cap, way better then dropping the 2 orings (in sandwich) against the peek puck inside cavity.

            I would do pretty much the same for my MK2, but I shoot BR so the first 4-5 shots I can just dispose.

            >>> But this is not a lathe work - this is a CNC mill work (including cutting the thread) and the machine must have a good spindle break.

            Second, the threaded end cap I would do deeper pocket so the metal doesn't even touch the NBR90.

            Could even happen that the new=separate oring pocket not compressing the PUR90 and can work now stand alone....worth to test it.

            Edit:

            To make this same piece on CNC Mill, 3 side setup, total cutting time less then 6 minutes.

            or the option #2

            On a traditional=manual lathe a "offset diameter" separate into two pieces, and the smaller OD seal + lock in the same way as the Valve House titanium body. Only need an extra oring...
             

            mubhaur

            Member
            Nov 8, 2015
            1,460
            58
            Karachi, Pakistan
              Mubhaur I like your idea making a new end-cap, way better then dropping the 2 orings (in sandwich) against the peek puck inside cavity.

              I would do pretty much the same for my MK2, but I shoot BR so the first 4-5 shots I can just dispose.

              >>> But this is not a lathe work - this is a CNC mill work (including cutting the thread) and the machine must have a good spindle break.

              Second, the threaded end cap I would do deeper pocket so the metal doesn't even touch the NBR90.

              Could even happen that the new=separate oring pocket not compressing the PUR90 and can work now stand alone....worth to test it.

              Edit:

              To make this same piece on CNC Mill, 3 side setup, total cutting time less then 6 minutes.

              or the option #2

              On a traditional=manual lathe a "offset diameter" separate into two pieces, and the smaller OD seal + lock in the same way as the Valve House titanium body. Only need an extra oring...

              People using Impact in competition in my country also complain.

              The reason being that after the sighter shots there is 10 minutes gap in actual starting of competition and even in so short tome the 1st shot goes South sometimes. 

              Bhaur
               

              bigHUN

              Member
              Jan 16, 2020
              1,936
              84
              Canada

                People using Impact in competition in my country also complain..........Bhaur

                Bhaur, you have a great opportunity here, but the part need to be cut on CNC Mill with auto tool changer.

                About a full 8 hrs of CNC programming - with some coffee brakes + you need two jigs, and these can give you roughly about 6 minutes total cutting time per piece. Translated to your local currency still makes a business case. A manual lathe is a no-no unless you do it on your own time.

                It must be cheaper then the OEM part: https://www.europeairguns.com/en/fabricantes-2/fx-airguns/FX10338
                 
                Mubhaur I like your idea making a new end-cap, way better then dropping the 2 orings (in sandwich) against the peek puck inside cavity.

                I would do pretty much the same for my MK2, but I shoot BR so the first 4-5 shots I can just dispose.

                >>> But this is not a lathe work - this is a CNC mill work (including cutting the thread) and the machine must have a good spindle break.

                Second, the threaded end cap I would do deeper pocket so the metal doesn't even touch the NBR90.

                Could even happen that the new=separate oring pocket not compressing the PUR90 and can work now stand alone....worth to test it.

                Edit:

                To make this same piece on CNC Mill, 3 side setup, total cutting time less then 6 minutes.

                or the option #2

                On a traditional=manual lathe a "offset diameter" separate into two pieces, and the smaller OD seal + lock in the same way as the Valve House titanium body. Only need an extra oring...

                Mill-turn lathe would drop it complete. 
                possibly a a larger swiss lathe would fit the bill too.