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Thread: 3D Printed Piston Seal Mold

  1. #21
    Boolit Master
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    I printed up one last Piston Seal mold just to try to get a finished Seal-Geometry that fell between the shape of the factory Piston Seal and the aftermarket Piston Seal I bought from the Australian vendor I was dealing with a while back. One of the things I wanted to change also on one of the mold-halves is the vent-holes.

    On my initial 3D printed molds I had put three small vent-holes on the bottom half of the mold-set. This worked OK but I found that whenever I got a badly cast Piston Seal it was due to the fact that the casting resin was being sucked in and deformed in the areas of one or all three of these vent holes. I ended up eliminated two of those vent-hole and just going with one smaller hole.

    After several failed casts I got to where I'm getting good useable Piston Seals. It took that long to figure out the correct mixing procedure for the casting resin and when I tried mixing in some Powdered Graphite that procedure required a slight alteration to my mixing procedure.

    Right now I have eight Piston Seals that I've successfully cast and I plan on testing them in my first-gen Umarex Octane air rifle next week. I have a not-to-busy week next week so I plan on setting up my chronograph and re-testing the velocities of the existing factory replacement Piston Seal I presently have in my air rifle. I'll then swap it out for one of my new DIY home made Piston Seals with the Powdered Graphite mixed into the casting resin and then I'll test one of those same home made Piston Seals that I cast without the Powdered Graphite.

    The factory replacement Piston Seals appear to only be tinted to the various colors they come in, not really impregnated with Graphite or any other elements and it's those factory Seals that have generally given me the highest velocities. The Australian aftermarket Piston Seals gave me slightly slower velocities than any of the factory replacement Seals I've ever used and it's those aftermarket Piston Seals that were said to impregnated with Powdered Graphite. It will be interesting to see if adding that Powdered Graphite effects velocities at all. In my opinion, I think it has more to do with the geometry and fit of the finished Piston Seal rather than the inclusion or exclusion of Powered Graphite or any other additive to promote lubricity.

    The eight Home Made Piston Seals I've successfully cast represent about one-hundred dollars worth of replacement Piston Seals; that's if you include shipping from an online vendor. The aftermarket Piston Seals actually cost a bit more. Strangely enough, One hundred dollars is about the amount I've spent on replacement Piston Seals over the years I've owned my Umarex Octane break barrel air rifles.

    I have a few more closeup pics of my latest home made Piston Seals that I'll be posting as soon as I can get them shrunk down for uploading to the few online blogs I'm working with.

    At this point I want to remind the members of our Umarex Octane Users Group (AFTER I've Tested Them) that if you need a Piston Seal replacement please contact me and I'll send out one of these prototype home made Piston Seals. You will have to pay for postage but the Seal Is on me. The postage, when I send out trigger components is about two dollars and fifty cents worth of stamps and envelopes so I'm thinking that the postage for one of these little Seals will be about the same. ALSO; If you own a 3D printer and you'd like to try making your own Piston Seals as well, just contact me and I'll email you the STL files at NO COST.

    Please understand that you will have to process the STL file in your slicer software of choice to be printed on your particular 3D printer. The resolution on my printer was such that I had to lightly sand the surfaces of my prints to get a semi-smooth surface and then I opted to quickly pour and then allow to quickly drip off and dry some acetone on the surfaces of my mold-halves which gave me an even smoother surface in the areas of the mold cavities where the Piston Seals are actually formed.

    Your 3D printer may be a far better printer than mine and not need this kind of post-print work to get smooth surfaces. My printer isn't all that great but it's good enough to generally give me what I'm looking for, with a bit of work after the print.

    I'll be back with those photos later.

    HollowPoint
    Last edited by HollowPoint; 07-13-2019 at 09:00 PM.

  2. #22
    Boolit Master
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    This Project Is Nearing Completion

    Umarex Octane Home-Made Piston Seals.

    I cast up the last of my prototype Piston Seals this morning and it looks like they are going to work out well. I still have to test them but I can see no reason why they wouldn't work.

    Pictured in the photo are the eight finished Piston Seals I mentioned previously. The three black colored Seals are the ones that I mixed Powdered Graphite into the mix. The clear ones were just cast in the casting resin's natural color.

    I could have mixed in some coloring but since this is a DIY 3D printing project I didn't want to go overboard with these low budget home made Piston Seals. The Green and the Red Piston Seals are placed in the photo for comparison. The Green Seal is a factory made replacement Seal and the Red Piston Seal is an Australian made aftermarket Seal.

    The small mountain of darker colored Piston Seals on the right are all of the failed casts I made before I figured out what I was doing. I left two of my latest Piston Seal casts partially in the molds just to show you what they look like when the 3D Printed mold-halves are separated. I also left the flashing on one of my latest finished Piston Seals to show that after they are removed from the mold the flashing has to be trimmed off.

    On the left, with the eight home made Piston Seals cast using my home made 3D printed Piston Seal mold you are looking at about One-Hundred dollars worth of Piston Seals if you figure that if purchased from an online vendor each one costs about twelve-bucks plus shipping. Just so I don't come off sounding cocky somehow, that small mountain of screwed up cast on the far right represents about 168 bucks worth of negative life experience. Some lessons are a bit more costly than others.

    I'll be back with one last post to show how they worked when I tested them over the chronograph in my Umarex Octane air rifle, then I'll call this project finished.

    I shall return.

    HollowPoint

  3. #23
    Boolit Master
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    Something Is Definately Wrong.

    Both of my Umarex Octane air rifles have been sitting unfired for a couple of months. I've mainly been shooting my Gauntlet PCP.

    When I wiped the dust off of my 1st-gen Octane and shot it over the chronograph it registered a velocity of only 806 fps. The second shot was 804 fps and the third shot was 801. From then on each following shot was a bit slower and a bit slower.

    I thought perhaps my Breech-Seal had flattened out from sitting so long and maybe that's why I was loosing power. I changed out the Breech-Seal and still got the same kinds of velocity loss results.

    I then thought maybe from sitting so long without being shot my existing Piston Seal had just settled and flattened out all round the circumference of the expansion chamber so I shot a few more shots hoping to get it to heat up the Seal and possibly allow it to expand to form a tighter seal. No such luck. I still got ever decreasing velocities.

    I then decided to swap out the existing Piston Seal (it was a factory replacement seal) for one of my Powdered-Graphite impregnated home made Seals. The first shot over the chronograph with one of my home made Piston Seals in place gave a velocity of 804 fps. From then on every following shot dipped lower and lower in velocity. Damn! This could only mean that my Gas-Spring was slowly giving up the ghost. These were tell tale signs of a Gas-Spring that is in the early stages of taking a dump on me.

    I went ahead and swapped out the Graphite impregnated home made Piston Seal for one of the DIY Piston Seals that I cast without the Graphite Powder. I got the same results but by then the velocities had dropped to the seven-hundred fps range. I stopped testing my home-made Piston Seals at that point cause if my Gas-Spring was dying there was no way I'd get good results.

    The one glimmer of hope I did see in all of this was the fact that I was getting the same types of velocities regardless if I had the factory Seals in place or my Home-Made Piston Seals in place. I'll be ordering another Gas-Spring in order to properly test these Home-Made Piston Seals that I cast using my 3D printed Piston Seal Mold. This time when I order that Gas-Spring I'll try to order the type of Gas-Spring that comes in the Umarex Octane Elite air rifle.

    My Octane Elite had also sat for months without being fired but when I tested it over the chronograph the first shot out of the gate was 888 fps with the same 14.3 grain Crossman Premier pellets. The following shots out of that air rifle leveled off at the 870-875 range where it had been before I let it sit for a few months.

    My 1st-Gen Octane normally yields repeatable velocities in the 860 fps range. This is why I knew something was wrong when I fired off that first test shot. I'll be back when I've taken delivery of the new Gas-Spring I'll be ordering. I'm hoping that if the Gas-Springs that come in the Octane Elite really are a bit more powerful than those that come in the 1st-Gen Octane, it may give me a slight boost in velocity regardless of which Piston Seals (Factory, Aftermarket or Home-Made) I install in my Octane air rifles.

    HollowPoint
    Last edited by HollowPoint; 07-16-2019 at 01:50 PM.

  4. #24
    Boolit Master
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    I'll Never Have To Buy Another Piston Seal

    Well, I figured out where my velocity went. I should say, I figured out the sources of my velocity loss.

    I was right about my Gas Spring going bad. I was also right about my Breech Seal having flattened out too. There was one other source of my velocity loss that I had completely forgotten about too. It had to do with the Pre-Load Shims I had installed on my 1st-Generation Octane back when I first bought it.

    Apparently those shims had fallen out when I disassembled my Octane initially to swap out the Gas Spring with the Gas Spring that came from the factory in my Octane Elite air rifle. Even with that swap I still had velocities in the mid to high 700 fps range. Something was still wrong at that point so I waited for my newly ordered Gas Spring to arrive before I did anything else.

    When my new Gas Spring arrived and I installed it, shooting over the Chronograph was still giving me velocities in the mid to high 700 fps range so I re-checked my Breech Seal. I found that the tiny shim that fits directly below my Breech Seal had vanished. This left my Seal sitting in the circular channel at the breech in an uneven manner. The bottom of the Breech Seal sat higher above the face of the breech and the top of the Breech Seal sat flush with the face of the breech so I made another shim out of milk-jug plastic.

    It wasn't that difficult to do and when I got that taken care of I was then getting velocities in the high 700 to low 800 fps range. That was a good sign but I was still off from my previous velocities of around the 860 fps range. It left me scratching my head wondering. At that point I hadn't yet discovered that I'd lost my Pre-Load Shims somewhere along the way.

    As luck would have it; and it being summer time here in Arizona I was fiddling around in the shop bare-footed. I stepped on something that caused me to have to reach deep down into my repressed bucket of foul language. It was a sort of involuntary response kind of thing. When I looked down to see what I'd stepped on it turned out to be one of the two Pre-Load Shims that I mentioned above. It was an "A-Ha" moment. I got on my hands and knees to find the second shim and I was back in business.

    Those two Pre-Load Shims are nothing more than a couple of dimes that I pressed into a cone shape to fit inside the receiver plug of my 1st-Gen Umarex Octane air rifle. Stacking one on top of another gave me on average an added 35 to 45 fps extra velocity when installed. I believe that those two shims also accounted for the shortened life span of the two previous Gas Springs I've had to replace. I've owned this 1st-Gen Octane since about 2009 and in that time I've had to replace my Gas-Spring twice. I know of other guys who have owned and shot their 1st-Gen Octane air rifles just as long and their Gas Springs are still going strong. That must make me one of those Velocity-Whores who is willing to pay for just a little bit more for velocity in the form of having to buy new Gas Springs more often than most.

    I lubed up and reassembled my Octane for what I though would be the last time. First shot over the chrono gave me a reading of 1032 fps. I guess I used a little to much lube cause the following shots read, 845-851-856-842-851. It never went above 856 fps and it never went below 842 fps. OH, and I almost forgot to mention that this was with one of my Home-Made Powdered Graphite infused Piston Seals in place.

    I can live with that; although I would always rather have more velocity if I can still retain good accuracy. Since I don't shoot either of my Octane air rifles as much as I used to I opted to take it apart one more time. I figured that I'd go ahead and remove the Pre-Load shims and shoot it without those Pre-Load Shims instead. Even though the time span between Gas Spring replacement is more than a couple of years, it still sucks to have to shell out for new ones each time. The price seems to have gone up on those replacement Gas Springs each time I bought one. If I could figure out how to make my own Gas Springs; or refurbish the ones I have, that would be awesome.

    As for my Home Made Piston Seal project that I've made using my 3D Printed Mold; I'm happy to report that I'll never have to spend a dime on another Piston Seal for the life of either of my Octane air rifles.

    I took some more photos but I still have to shrink them down or I won't be able to upload them for you all to see. I'll be back with those photos later.

    HollowPoint

  5. #25
    Boolit Master
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    Here are a few of those pics I mentioned in my Previous post. They should be self-explanatory. If you have any questions please feel free to ask.

    As of now I consider this 3D Printed Piston Seal Mold project a success. I've tested random samples of my Home Made Seals in both my 1st-Gen Octane and my Octane Elite and found them to give velocities close enough to the velocities I was getting with factory replacement Piston Seals and aftermarket Piston Seals that I feel confident in proclaiming my success.

    The 3D Printed Mold performed admirably. I even broke down and printed two more so that I wasn't just casting one at a time. Any more than that and my Urethane mixing routine would be rendered compromised.

    The mix begins to harden within three minutes so that gives me just enough time to be able to pour that mix of ingredients into my molds before it gets to hard to pour and then quickly clamp the mold-halves together.

    If you look closely at the small hill of Home Made cast Piston Seals you can see that the surface finishes on them isn't any where near as smooth as the surface finish of the factory replacement Seals or the aftermarket Seal in the photo. No matter. They still work; and when they're installed no one sees the surface finish anyway.

    I was going to include photos of the chronograph readouts too but time got away from me. I haven't yet deleted those velocities from my chronograph so for those here who are hard to convince, if need be I can photograph those too if I have to.

    HollowPoint

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check