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Thread: 3D Printed Piston Seal Mold

  1. #1
    Boolit Master
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    3D Printed Piston Seal Mold

    I finally got the time to draw up some preliminary CAD models of the Piston Seal Mold I mentioned in my last post.

    They are not to the right dimensions but I just wanted you to see what I had in mind. I'll have to dig out one of the old factory Piston Seals I have in my storage room to get all the right dimensions..

    I plan on first testing my 3D printed Piston Seal mold with plain silicone caulking. Then if it pans out I'll move to some Urethane caulking. The urethane caulking cures to a hardness level a bit softer than the factory piston seals so I'm thinking that if I apply some "Mold-Release" agent to the cavities of my mold and then dust the surface of the mold with some powdered graphite it will serve two purposes.

    The powdered graphite should impregnate all of the contact surfaces and act as a dry lubricant while at the same time harden the outer surfaces of the molded Piston Seal just a bit more. If I remember correctly the "Duro-Meter" hardness level of the factory seals is something like 85-95. I contacted the customer service department of the manufacturer of the Urethane caulking sold at my local Home Depot store and they told me that the Duro-Meter hardness level of their cured Urethane is about 65. I'm thinking and hoping that by adding the powdered Graphite to the surface of my home made piston seals it will bring my hardness level up to the 80-85 level. I think that level of hardness should work in a pinch.

    Some of you my remember some of my previous post where I tried turning my own Piston Seal replacements on my lathe with limited success. They worked but the material I made them out of was a bit to soft. That softness level cause my velocities to drop by a good 65-70 FPS. I've also mentioned at one point or another that I'd spent close to a combined hundred-buck on replacement piston seals over the years.

    If I can get this to work It should save me some money. I hope. Wish me luck. (these Seals should work on all the clone Umarex Octane air rifles as well)

  2. #2
    Boolit Buddy
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    Interesting project, I hope it works - I've just restored a sad old Walther LGR single stroke pneumatic target rifle. One of the problems I came up against was the piston seal. After a bit of searching I did find one but, although the outer diameter was correct the inner fitting was wrong. I ended up machining a new piston head and fitting an "o" ring that works perfectly.


  3. #3
    Boolit Master
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    That's a nice looking air rifle.

    Back when I was experimenting with different work arounds for the previous piston seals that had gone bad I too tried different lathe turned heads that I could mount different types of seals. One of those methods was a lathe turned metal head with dual slots turn around the circumference of the head in which I could put rubber O-rings. That method worked too but at the expense of velocity.

    I eventually gravitated back to the factory offerings and then I tried some of the aftermarket offerings I ordered from a seller in Australia. Those aftermarket seals were the best but they were more expensive than the factory piston seals. Those aftermarket seals were initially lathe turned on a CNC lathe out of proprietary materials that were said to be impregnated with graphite powder for added lubricity. The present Piston Seals being sold by this Australian vendor are now being molded instead of lathe turned.

    This is where I got the idea of trying to come up with a 3D printed mold for these Piston Seals.

    HollowPoint

  4. #4
    Boolit Master

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    I wish you luck Hollowpoint.
    I wonder if there is some kind of epoxy that might work for your seal.
    To lazy to chase arrows.
    Clodhopper

  5. #5
    Boolit Master
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    Quote Originally Posted by clodhopper View Post
    I wish you luck Hollowpoint.
    I wonder if there is some kind of epoxy that might work for your seal.
    I believe that there is such an epoxy kit you can buy and mix yourself that is sold in varying degrees of Duro-Meter harnesses. I'm trying to go at this on the cheap so if at first the Urethane Caulking doesn't pan out for me I know I can get some of the ingredients I need for mixing up the appropriate fixings to get me to where I need to be as far as the correct hardness levels. It's all a sort of financial benefit balancing act. If buying the epoxy kit costs more than just buying the already made Piston Seals then, what's the point?

    Ideally I'd like to be able to do all of this with 3D print materials I have on hand and with materials I can get from my local Home Depot or other hardware store. Only time will tell if this will actually turn out to be the case for me. If so, I don't mind having to mix my own ingredients but, like I said, I want to first try to do in as cheaply as possible. This means just buying a tube of Urethane Caulking and running with that. I already have a couple of tubes of regular silicone caulking just laying around I can experiment with.

    Another thing that I want to test before I get to far into this is the chemical resistance of the print filaments I'll be working with. If some of the chemicals in the Silicone or Urethane Caulking tend to melt the material my mold is made of I'll have to search for a print filament that will resist that effect. I'm fairly certain that ABS or Carbon Fiber filament have the kind of chemical resistance I need to mold my Piston Seals but I have yet to test that theory.

    Thanks for the word of encouragement.

    HollowPoint

  6. #6
    Boolit Master
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    I was able to get both halves of this Piston Seal Mold 3D printed today. (2 hours and 20 minutes for each half) While I had the chance I went ahead and put some mold release in the cavities of the mold and squirted in some silicone caulking into the mold cavity.

    I thought I had three full tubes of silicone caulking in my storage room but it turns out that two of those tubes of caulking had been sitting for so long that they solidified on me. The third tube of grey colored caulking is one I had used just last week to seal some cracks on the side of my house with. I figured since I'd opened that tube earlier and let it sit for a while it too would be hardened in the tube as well.

    Fortunately it was still in it's liquid form so I used it. I'm hoping that the mold release I'm using will work well enough to release the silicone seal once it's cured. The "Mold-Release" is just some Johnson Paste Wax. I've used it as a mold release when I cast some 22 caliber hot melt bullets in one of my aluminum bullet molds a while back. It seemed to work pretty well for that application so I'm hoping it will work on this ABS plastic mold as well. I'm hoping the ABS plastic the mold is printed with has a chemical resistance to it.

    I don't know exactly how long it will take for my prototype Piston Seal to cure or solidify while encased in this 3D printed mold so I'm going to let it sit for a day or two just to make sure I don't open it back up and get a partially hardened band of mush.

    It looks like it might actually work. I don't see why it wouldn't. The one problem I did encounter was in the resolution -or lack thereof- of my 3D printer. The surface finish of my 3D printed mold wasn't as smooth as I'd like. This means that every imperfection on the inside walls of my Piston Seal Mold will transfer onto the surface of the silicone piston seal prototype I'm making.

    I still have some carbon fiber filament left over from my 3D printed rifle magazine project print. I was able to get some really nice surface finishes using that type of print filament. Once I've confirmed that this present ABS Plastic 3D printed mold is really going to work, if the surface finish on this first prototype Seal is terrible looking I'll go ahead and print a mold out of the carbon fiber. Right now this first attempt is just more or less as a proof of concept thing.

    I'll be back with updates once I've allowed the prototype silicone seal some time to fully cure.

    HollowPoint

  7. #7
    Boolit Grand Master

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    Wouldn't you be better off using a castable Urethane resin than silicone caulk?

  8. #8
    Boolit Master
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    Quote Originally Posted by longbow View Post
    Wouldn't you be better off using a castable Urethane resin than silicone caulk?
    Yes it would be better but since this is just the testing phase I thought it wise to test my 3D printed mold with some silicone caulking I had on hand first. If it pans out I'll then try some Urethane Caulking to see if it will cure to a useable hardness level for this application. If it does not, then I'll bite the bullet and order a small amount of castable Urethane resin.

    HollowPoint

  9. #9
    Boolit Master
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    It was just a bit over a day and a half of letting my first test cast of the Piston Seal sit clamped in a vice outside in the sun. I opened it up yesterday and found it still in it's liquified state. There's a day and a half of wasted time.

    I had just assumed it was silicone based caulking I was using. Turns out the type of caulking I used wasn't silicone caulking. It may have a small amount of silicone in it but it was not the relatively fast drying silicone I thought it was. Add to that the fact that it's encased in a semi-airtight mold and I guess it's no wonder it was still in it's liquid form when I opened the mold up yesterday.

    The good news here is that the Johnson Paste Wax I used as a mold release kept me from having to scrap the mold and print a new one. I was able to just wipe the residual caulking out of the mold and try it again with some real silicone caulking. I'll let this one set over the weekend. Hopefully that will be enough time for the silicone to cure.

    If or when I try to mold my Piston Seal out of Urethane caulking, I know for a fact that it is formulated to cure in 15 minutes but this is if it's exposed to the air. It may take a bit longer since it will be encased within my mold. I may have to open up the four little ports where I squirt the goop into the mold. This way although they're still relatively small holes, it will give the urethane maximum exposure to the air to facilitate the curing time.

    I shall return.

    HollowPoint

  10. #10
    Boolit Grand Master

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    Not sure about Urethane caulk but I am pretty sure silicone caulk is a moisture cure so needs to be exposed to the atmosphere or it will take a very long time to set up.

    That's the reason I suggested urethane resin... like two part epoxy it will set due to chemical reaction of the two parts rather than needing moisture. That and it is available in a variety of final hardnesses from something like Shore 60A to Shore 85D.

    Any solvent based (requires evaporation) or moisture cure "stuff" needs to release or absorb so in a closed mould not the best. If you are just proving in principle I'd think any epoxy would provide a reasonable casting to check dimensions. Might be kinda hard so not usable as a seal but good enough to measure.

  11. #11
    Boolit Master
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    Yea I'm having to re-learn some of this stuff all over again. I did make my own Piston Seals a while back by turning them on my lathe and during that time I had researched the subject of casting them from polyurethane resins. If I remember correctly the correct hardness level of the polyurethane resin that I needed to use was something like 90 or 95 Shore-A stuff.

    Right now I just want to test this mold with whatever I can get to cure in a reasonable amount of time. Even if the dimensions are off a bit it doesn't really matter. If I really want to go whole-hogg into this casting stuff I'd just as soon make a silicone mold that will mold multiple samples at once rather than one at a time. I'm just trying it with this 3D printed mold just to see if it will work for me.

    If it does it will suit me just fine cause I'm not shooting my break barrel air rifles as much as I used to now that I have a PCP. This means that my existing Piston Seals should last a fairly long time. I'm wanting to try to get this DIY home printed mold to work for some of the guys in my Umarex Octane shooters group who may be interested in making their own Piston Seals rather than having to order replacements periodically.

    HollowPoint

  12. #12
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    I would guess that anything in a tube won’t cure in a mold since it would not be exposed to air, just like when it was in the tube! You probably need something that is mixed with a catalyst so it hardens or cures via a chemical reaction.

  13. #13
    Boolit Master
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    Quote Originally Posted by garandsrus View Post
    I would guess that anything in a tube won’t cure in a mold since it would not be exposed to air, just like when it was in the tube! You probably need something that is mixed with a catalyst so it hardens or cures via a chemical reaction.
    You're probably right. I'm working off of my assumptions of what I've experienced with the two solidified unopened tubes of silicone I mentioned in one of my previous posts. This is why I was considering enlarging the four small ports on the backside of my mold to give the goop just a bit more exposure to the air.

    I checked out the mold today as it sat and the four little 1/8" strings of silicone that leaked out when I clamped the mold-halves together have completely solidified. They are only thin strands and they're exposed to direct air but it does give me some hope that the rest of the silicone will cure a bit sooner than my previous attempt. We shall see.

    HollowPoint

  14. #14
    Boolit Master
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    Nearing The End Of This Project

    Umarex Octane 3D printed Piston-Seal Mold

    I'm nearing the completion of my 3D printed Piston-Seal mold project. It was slow going at first but I think I have all of the kinks worked out of it. My initial 3D printed molds were too far out of spec but I went ahead and cast some Piston-Seals using plain silicone caulking. Those first attempts turned out like absolute KaKa; mainly because of the surface finish on my molds and because the mold release agent I was using was not really intended for this purpose. At first I used some Johnson's Paste Wax and then I tried some Pam Kitchen spray on grease. As you guys in the know may have surmised, this stuff was the only thing I had on hand to use as a mold release agent at the time. It really wasn't intended for this application.

    Although I was able get those initial casting attempts to come out at all, I found that the silicone caulking tended to shrink as it cured so I tried casting with Urethane Caulking instead. The Urethane Caulking was a little better and it more closely adhered to it's intended dimensions but my mold release agent tended to not want to release my newly cast Piston-Seals as easily as I would have liked.

    I finally switch to some Hornady Imperial Case Lube and it worked perfectly as a mold release agent. Now I'll move forward with this project and try to cast some Piston-Seals using some actual casting resin. I'm thinking it's going to work out well. At the very least it should be interesting.

    This casting resin is said to generate about 170 degrees of heat as it's curing. I was concerned that this heat might melt my ABS plastic mold but the filament I printed the molds out of takes about 200 degrees Celcius to melt so I think I'm good. On a positive note; this casting resin generates it's own heat so the hardening time is about three or four minutes and the "Fully Cured" time is about an hour and a half and that's with the resin enclosed in the mold. I guess I'll find out when the time comes.

    I had to let the silicone caulking sit in my mold for a whole week and even then, when I opened up the mold it was still tacky. The Urethane Caulking took only about three days till I could safely pull it from the mold and in both cases I still had to let them set for a day or so before I could really handle them without inadverdantly distorting them.

    Wish me luck.

    HollowPoint

  15. #15
    Boolit Master Forrest r's Avatar
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    sort of makes you wonder how "plastic dip" would do. Or a combination of a o-ring (think rebar) in the center and then a urethane/rubber product.

  16. #16
    Boolit Master
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    Quote Originally Posted by Forrest r View Post
    sort of makes you wonder how "plastic dip" would do. Or a combination of a o-ring (think rebar) in the center and then a urethane/rubber product.
    This isn't my first go around with trying to make my own Piston Seals. The first time around I actually tried the "O-Ring" thing and although it did work, I was not able to maitain the pellet velocities I was getting with the factory Piston Seals. I also tried turning my own Piston Seals on the lathe. Those lathe turned pistons seals also caused a substantial drop in velocities. I'm pretty sure it was because in both cases the materials I was using was to soft; and I wasn't exactly sure what the correct material for this application was. If in the end it required some kind of specialty casting resin and I couldn't get my Piston Seal mold to work I figured I'll just mix the whole sha-bang in one shot and mold it into a cylinder and then I'd have the right material to turn on my lathe.

    I pictured both my lathe turned Piston Seals and the O-Ring Piston Seal (because they were so soft) grabbing the inside walls of the pressure chamber under load as they expanded outward; kind of like the old school expanding brake shoes would do on the inside of the brake drum when one hit the brakes.

    I'm hoping to get a decent serviceable Piston Seal when all is said and done. I own and shoot a PCP now so my break barrels don't get as much use as they once did. The Piston Seals I have in them now should last for quite a while but, I still remember all the times I had to buy replacement Piston Seals. Over time I'm pretty sure I've bought close to eighty or ninety bucks worth of replacement Piston Seals.

    This project is mainly for the guys in our Umarex Octane Shooters group. Once I get this to work reliably I'll turn the 3D print files over to any one of them who would like to print their own Piston Seal mold in order to cast their own. When it comes to this kind of stuff there really isn't alot of Do-It-Yourselfers who would try this but there are some. Those are the guys who can benefit from making their own; just like bullet casters benefit from making their own bullets. The initial upfront time and cost may be enough by itself to put some people off but just like in bullet casting, if you shoot your guns alot then it pays for itself fairly quickly.

    HollowPoint

  17. #17
    Boolit Master
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    My mixing ingredients showed up for casting the Piston Seals out of my 3D printed mold. I didn't have the right kind of mixing cups but I couldn't wait so I mixed some up in a shot glass.

    Remember I mentioned before that it took my silicone caulking seals over the weekend to cure and even after that it took a couple of days more to fully dry? Well, this urethane casting resin takes only about an hour and a half to get decent results. My first Seal looked good superficially but I could see a bunch of tiny air bubbles had developed from when I mixed the two ingredients together. There was also one big air bubble that I can't explain but at least now I know what I'm up against.

    I'm going to the store tomorrow to pick up some of those little condiment cups and some mixing sticks like maybe some popsicle sticks or something like that. This first time around I was just using that shot glass and eye-balling the amounts then stirring them with a plastic spoon.

    I also bought a small tube of powdered graphite so I can impregnate the contact surfaces of the piston seals for what I hope will be better lubricity I want to cast a couple more clear urethane seals first to try to eliminate as many air bubble as I can before adding the graphite. With the graphite in place I'm afraid that it may mask any larger imperfections. I don't really know for sure. I've never cast anything like this before.

    I'll be taking photos of my progression and post them when I get far enough along.

    I'll be back.

    HollowPoint

  18. #18
    Boolit Master
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    It Works! I've made some useable DIY Piston Seals

    It took me several tries to figure out the right mixing procedure for this Urethane Casting Resin. I'm still not getting perfect results but I'm now getting what I think are good useable Piston Seals.

    At first I tied casting some Seals with just plain semi-transparent Casing Resin. The finished seals had a ton of tiny air bubbles in them. It's hard to see the bubbles in the photos but they're there. I then tried just dusting the mold cavities with Powdered Graphite so that just the contact surfaces of the Piston Seals had this Powdered Graphite lubricant at surface level of the Piston Seal. I thought I'd done a good job of dusting those mold-cavity surfaces pretty evenly but when I took my cast Piston Seals out of the mold there were large void on different parts of the surface of the finished Seal.

    I then tried actually mixing some Powdered Graphite into the two-part Urethane mix (Resin and Hardener) but that too was giving me some finished Seals with voids in various places. A second attempt with the Powdered Graphite gave me some much needed success. I only used a very small amount of Graphite Powder on that second attempt and that seemed to be the pathway to getting some useable home made Piston Seals.

    The Urethane Casting Resin and the Hardener both came in 23oz. bottles. I also bought some mold release agent which also came in the same size bottle. Each individual Piston Seals takes only about 1 1/4 teaspoons of each ingredient to make. I suck at math but I'm thinking I could make a whole lot of mistakes and still have enough Urethane casting resin to make a ****-load of Home Made Piston Seals.

    After looking at the outcome of my more successful attempts at casting these Piston Seals I may do one more tweak on my 3D printed Piston Seal mold so as to get some finished Piston Seals that more closely resemble the factory Piston Seal.

    I've been having trouble uploading photos to our group site again so if my photos don't come through I'll also have them up on my Instagram page as well. If any of you guys have some experience with Urethane Casting Resins perhaps you can give me some pointers that will yield better results. As for now, I think I have enough Home Made Piston Seals to start testing them in my Umarex Octane air rifles.

    I'll be back with those results as time permits.

    HollowPoint
    Last edited by HollowPoint; 07-07-2019 at 09:30 PM.

  19. #19
    Boolit Master

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    Good deal. Glad you are posting your experiments, failures and successes.
    To lazy to chase arrows.
    Clodhopper

  20. #20
    Boolit Master
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    Initially I thought about just milling a Piston Seal mold out of aluminum. I'm confident I could have done it on my hobby mill but not everyone has a hobby mill or a mill of any kind.

    Some of the guys in our Umarex Octane air rifle group do have 3D printers so I thought I'd try making my mold out of ABS plastic so that anyone who might be interested in printing a mold of their own could use the same STL files to do so. If you already have a 3D printer all you would have to do is set up the files in your particular slicer software for printing on your printer.

    I decided to print one last iteration of my mold to try to get the overall shape of my Piston Seals somewhere between the shape of the aftermarket Seal and the Factory replacement Seal. I noticed when I ran the aftermarket Piston Seals over the chronograph that my velocities were a bit slower than the velocities I was getting with the plain-Jane factory Piston Seal replacements so I thought maybe by configuring the outside geometry somewhere in between the two different Seals I might reach a happy medium.

    I think it's going to work out real well. Even with all the mistakes and failures I've experienced with this project I'm still going to come out ahead.

    HollowPoint

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