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Question Need to Start Sourcing Out Hammer O Rings forVM 68 - REPOST FROM MCB 2.0

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    Question Need to Start Sourcing Out Hammer O Rings forVM 68 - REPOST FROM MCB 2.0

    Post from 11/26/2015
    Well, its official. I think I was one of the last to have a lot of parts for the VM 68s. I kind of have to if I run a 250+ rental fleet and do custom VM-68s. If you are all wondering, I'm the guy who made up the "orange" VM ball detents and also had new springs made up, along with bolt rings. I've also made up other things for the VMs like venturi bolts, Thompson stocks, Vertical ASAs, custom brass barrels and so on. Most of this stuff was not openly sold and was used within the private fleet of VMs the MBoB uses. I'm not a business or a hacker, or a "store", or an Ebay seller. I'm just someone trying to keep one of the best and meanest markers ever made functional.

    And so... I have been using the last of the factory original manufactured parts for the past 10 years. I started out with just over 600+ VM-68 Hammer O rings. Over the past two years, it had began to show that the VMs we had were burping more and more. I would change out the o ring on the hammer and that would solve the issue for 500 rds or so and then back to burping. What I wasn't noticing was that the hard texture of the hammer o ring was turning to soft "taffy". In fact, the entire batch of rings that I had was doing this. We stored the parts and o rings in climate control - steady 60 F - in airtight bags in the dark. But urethane, as Drum has painfully pointed out, has a shelf life of 10-15 yrs tops. My original O rings from Sheridan/Crosman are from the mid to late 90s. It's now late 2015. Do the math

    Titus and I played around with the idea of making more hammer o rings. But since these hammer o rings aren't officially "o rings", but rather injection molded urethane "washers", we, or actually I had to pony up almost a $1000 to have a mold made. The reason I cringed about this, was that if the mold was "off", I wouldn't know until I was about a 1000 O rings made into the project. I just couldn't afford the financial risk at that time. And then there was needless drama between Titus and I, and I lost my good friend and this ultimately became a dead end.

    Anyhu, others have tried valiantly to make more of these VM 68 hammer o rings. Mader was the first. They worked and they were very affordable, BUT, they had horrendous issues. Mader's hammer o rings were made from stamped out of sheet urethane... I assume 70 durometer - Two problems in one. They were TOO SOFT and that made them elastic like rubber bands. The blowback exhaust would unseat this type of hammer o ring from Mader and push it against the body of the hammer, thus causing the o ring to act as a "bumper" that would prevent the hammer from striking the valve stem deep enough to create enough exhaust for blowback. The result was triple tapping burps and then decock.

    The other issue with Mader's hammer o rings was that they were stamped out. Stamping Urethane is much like stamping rubber. It "mushes" when pressed and the outer cut edges are not smooth. On Mader's hammer O rings, they were concave. This was bad because there was less contact service for the O ring to the internal diameter of the VM 68. If you have ever seen a stock factory made hammer o ring, you can see that the outer edges are rounded and perfect. That, and the fact that the factory hammer rings are at least a 90 durometer.

    Craig Palmer recently made a small batch of what looks like delrin made hammer o rings. I was able to get 3 of them to test. From what I understand, these a made by hand individually and the outer edge is rounded by hand also. This can lead to imperfections. Its simple human error and is in no way meant to be a dig on Craig and the Palmers. I personally commend his innovation and effort to help out us vm-68 knuckleheads. But sadly, only one out of three I obtained worked flawlessly. With the effort and cost put into making these, its not a feasible option for someone with more than the casual number of VM-68s to maintain.

    Injection molding as it has been pointed out to me through various avenues is the "only option" to achieve a perfect replica of the factory hammer ring. But this includes fabricating a mold, and doing the dance of test and hope that the first batch is the correctly made batch.

    So, is there anyone that can help me with this process without me paying an arm and a leg? I'm not trying to create a monopoly here. I just want to make an easily accessable part for folks that still use this marker and to also keep the ton of VMs I have working and taking names. And I'd like to do it right on the first try.

    Just like the Ball Detents I made a few years back... I think I gave away the first 500 of them to folks that needed them. I want to do the same with the vm hammer rings if I can get help with making the injection mold and sourcing out a place that can make them and is reliable enough to produce them in a timely manner.

    Help?


    Warmly,

    Smiley

    #2
    Originally posted 11/26/2015

    Second half of my research:

    Quote:
    The hammer seal is a slight problem. You have a few choices to look at.


    1. Machine the seal groove to fit a standard -113 O-Ring so the seal is inexpensive and easy to get in several different materials. This may take some experimenting to get the groove diameter correct.

    2. Use a -015 O-Ring and a cap seal. The cap seal can be machined from several different materials depending on what material works the best. This will also take some experimenting to get the cap seal wall thickness correct. This will be middle of the road cost wise. We may be able to make a few cap seals from Hytrel.

    3. Machine or mold a special seal ring. This will be the most expensive to do and will require testing to make sure it works correctly. If the first mold is not correct a second one would have to be made. We are not set up to mold urethane only 80D Nitrile at this time.


    With any seal the lubricant you choose can affect how the seal material will age and work. Most material shrink when molded, many swell from the contact materials, some shrink from the contact materials, all change size with temperature and all will take a compression set with some being worse than others. Working pressure will have some effect on the compression set also.


    70 D Nitrile (NBR) is about the best for compression set with HNBR next, then urethane and Teflon is the poorest choice.

    Comment


      #3
      Post By Smiley on 11/26/2015


      This place make square rings by extruding the I.D. and O.D. then cutting them to width:

      Backup Ring, Back-up, O-Ring, Square, Quad, PTFE, Polyurethane

      "The tube is then machined into various cross-sectional configurations by using a precision grinder or lathe-type cutting machine. By using the process of extruding material, expensive molds are not required giving designers flexibility in sizing to their exact requirements."

      What about machining the groove in the bolt to take an "off the shelf" round urethane O-ring ?
      Other CO2 blowbacks function with round O-rings

      Have you tried backup rings with round O-rings ?
      The Purpose of the Back-up Ring is to stop O-Ring extrusion. Normally used in applications where pressure is 2500 PSI or higher.



      __________________
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      Last edited by Smiley; 11-26-2015 at 04:54 AM.

      Comment


        #4
        Posted on 12/6/2015 by Smiley:


        Quote:
        Originally Posted by Smiley
        This place make square rings by extruding the I.D. and O.D. then cutting them to width:

        Backup Ring, Back-up, O-Ring, Square, Quad, PTFE, Polyurethane

        "The tube is then machined into various cross-sectional configurations by using a precision grinder or lathe-type cutting machine. By using the process of extruding material, expensive molds are not required giving designers flexibility in sizing to their exact requirements."
        You can get square orings any size without a mold.
        they can extrude a tube with the correct dimensions and slice off the desired width.

        Comment


          #5
          Posted on 12/8/2015 by the Infamoussmiley


          Quote:
          Originally Posted by Smiley
          You can get square orings any size without a mold.
          they can extrude a tube with the correct dimensions and slice off the desired width.
          I did try that a while back experimenting with "homebrew" options. It was grossly problematic as the outer edge itself was rounded. And to duplicate that process 250+ times over, oh boy!

          Smiley

          Comment


            #6
            Posted on 12/16/2015 by Paintzapper:

            Quick question, I was messing around with one of the VM-68s I acquired recently and noticed some of my o-rings "kinda" fit but are just a little too thin.

            If the internal diameter of the o-ring seat were to be expanded slightly and one of my o-rings (don't know which one, just messed with them all) would then be wide enough make a seal, would that work?

            Maybe a flat rubbery ring that just sits inside of the o-ring seat and a commonly manufactured o-ring sits right on top of it of acceptable durometer creating the actual seal. The rubbery material would just be a spacer and is just slightly wider than the o-ring seating allowing the material to curl up at the edges and hold the o-ring in one spot better.

            I don't know if this would have an unreasonable amount of play but maybe it could work.

            Comment


              #7
              Posted on 12-27-2015 by the infamoussmiley:


              Quote:
              Originally Posted by paintzapper
              Quick question, I was messing around with one of the VM-68s I acquired recently and noticed some of my o-rings "kinda" fit but are just a little too thin.

              If the internal diameter of the o-ring seat were to be expanded slightly and one of my o-rings (don't know which one, just messed with them all) would then be wide enough make a seal, would that work?

              Maybe a flat rubbery ring that just sits inside of the o-ring seat and a commonly manufactured o-ring sits right on top of it of acceptable durometer creating the actual seal. The rubbery material would just be a spacer and is just slightly wider than the o-ring seating allowing the material to curl up at the edges and hold the o-ring in one spot better.

              I don't know if this would have an unreasonable amount of play but maybe it could work.

              In responding to this post and another's -


              Quote:
              As far as the Hammer O rings go, why not talk to a machinist to see if we could get the O-ring channel opened up to a more standard size. I thin we have enough hammers lying around that we could spar a couple for experimentation.
              I did do this a while back when I started playing around with machinist. I even reached out to Tom Vanderbilt (I think I spelled his name correctly) about the Hammer O Rings. IF we were to machine out the hammer to make an "O ring grooved slot", the O ring itself would need to be such a high durometer just to make sure it does not nick when cycling. That's not that bad of an idea, BUT the depth of the hammer ring slot is already deeper than it should to have this done. What that means is that we would have to machine out a brand new hammer. (ick! and expensive ) Or, use dental floss to build up the slot to make the o ring to sit high enough.


              Ironically, the famous Chinese S4 had that O ring slot instead of the traditional hammer "washer" ring of the VM 68. It's problematic and after all of these years, I have not found a 100% complete fix for this. And this is 80% of the cycling problems that the marker has.


              Another idea is to take the bolt O ring and shave the sides down and try to see if it will work... I misread Paintzapper's message initially and that's what I thought he meant.



              -Smiley

              Comment


                #8
                Posted on 2/15/2016 by HTRN

                Have you guys thought about water jetting them out of a sheet? The biggest issue is the somewhat sloppy tolerances of the waterjet. McMaster Carr sells neoprene sheet in a variety of thicknesses..

                Comment


                  #9
                  Posted on 2-16-2017 by the infamoussmiley:

                  Quote:
                  Originally Posted by HTRN
                  Have you guys thought about water jetting them out of a sheet? The biggest issue is the somewhat sloppy tolerances of the waterjet. McMaster Carr sells neoprene sheet in a variety of thicknesses..
                  Would we be able to create a round outer edge on the ring?

                  -Smiley

                  Comment


                    #10
                    Posted on 3-31-2016 by Giuseppe:

                    Does anybody have a good set of calipers and an unused hammer O-ring? If so, would you please post the dimensions for me? I need inner diameter, outer diameter, and thickness. Thanks!

                    Comment


                      #11
                      Posted on 4-1-2016 by the Infamoussmiley:

                      I have the measuements. Do they sound right?

                      0.070" Thick
                      0.706" OD
                      0.497" ID
                      90 Shure Urethane

                      Does that sound right?

                      I don't have anymore unused samples. What I have were sent off to various places for estimates.

                      Smiley

                      Comment


                        #12
                        Posted on 4-1-2016 by Giuseppe:

                        Thanks, Smiley! Off the top of my head, that looks pretty close. I'll double-check when I get back home in a couple of days. In the meantime, my brother is going to look into 3D printing options. There are some very cool new flexible printing materials out there, so who knows...

                        Comment


                          #13
                          Posted on 4-3-2016 by Giuseppe:
                          Hmmmm...

                          Comment


                            #14
                            Posted on 4-7-2016 by infamoussmiley:


                            Quote:
                            Originally Posted by Giuseppe
                            Hmmmm...

                            https://photos.smugmug.com/photos/i-...-96TRV6Q-L.jpg
                            Hi,

                            Your outer edge on the ring is flat. It NEEDS to be round. The flat and concave do not work.

                            What is the material you are playing with?

                            Smiley

                            Comment


                              #15
                              Posted on 5-17-2017 by infamoussmiley:

                              Things have shifted to this thread.

                              Smiley

                              VM-68 Delrin Hammer Mod?

                              Comment

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