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Another 3D printing conundrum with a segway into casting bronze

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  • Another 3D printing conundrum with a segway into casting bronze

    I’m only posting this because there seems to be quite a few members with 3D printers on the forum that might have had days like this.

    After I set my printer (Ender 3V2) up it ran great for about two days. Small items like calibration cubes printed perfectly. After that I tried to print a guide arm for the filament to give it a better angle into the extruder and that’s when Merde hit the ventilour. So back to the drawing board, I search around the net for helpful videos and found a couple by CHEP. The first was a better way to tram the bed and the second was a pattern that can be printed out to fine tune the tram. Both worked fine. Then I calibrated the extruder and adjusted the flow rate of the filament. The X and Y axis travel was very good from the factory. So everything should be good right. Not so much. I tried the guide, with a raft and about half way through it the raft started to peel off and eventually popped off of the bed. Next I tried with just a brim figuring that the thickness of the raft while cooling might contribute to the lift. The brim popped off before it was even finished printing. So while rummaging around the kitchen for a knife to gut myself I decided to give the World Wide Spy system another try. I found a guy that clearly explained the problem. The usual bed temp. for PLA is 60C and that is fine for stock beds or the better thin flexible beds BUT it is no good for glass which I have. Glass doesn’t disperse the heat as well so the bed temp. needs to be at 70C to work. I tried and he was right. I have been happily printing like a mad fool for the last few days.

    Now for the machining content. One of the things I want to do is lost PLA casting. It is like lost wax casting but instead of making a model, then a RTV mould and finally cast a wax pattern that can be invested in some refractory material, with PLA, you just print it, invest it and then burn it out and cast the part. I printed out a part from my next project. It is the front trunnion from a ½ scale model of a 1906 Maxim machine gun. This is a tricky part to machine but casting will make it easier. The printing of the 3D part failed 4 times at approximately the same spot. A bit perplexing and the only thing different from other prints is the infill rate was lowered to 5%. I watch some videos on this and that appears to be the standard infill since there is less to burn out. I tried it for the fifth time at 20% infill and the print was good???????????????????????????
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

    Southwestern Ontario. Canada

  • #2
    that does sound strange, can you show a pic of the part and where it failed?

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    • #3
      Yep, and we need to hear exactly how it failed? Error fail, or the part didn't print right etc.

      Comment


      • #4
        Dunno much about 3D printing, but I do know that: Everyone I have seen doing last PLA is using at least 10% infill regardless what brand of system they have.
        25 miles north of Buffalo NY, USA

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        • #5
          5% might not have been enough of a support structure to support the part surfaces being printed. Any particular way these failed?

          I still have not tried lost PLA casting, but want to.

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          • #6
            A certain amount of infill is needed on most parts to give the top skin some support to print on, without the infill is there if you have something like a flat top you'll end up printing in air. You might be able to increase the number of top layers and get it to work, but at that point you probably won't be saving any plastic over just using a 15% infill
            on the gladd beds, the glass takes longer for the heat to equalize, and the normal preheat time most printers have isn't long enough for the top of the glass to hit the right temperature. Set the print bed temp manually to 60c about 5 minutes before you start printing to let it preheat, then start the print. Works every time

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            • #7
              The filament would get chewed up by the extruder and break at approximately the same place. The only thing I can think of is that the lack of infill was buggering up the retraction and it was just moving the filament back and forth in the same place. Basically it didn't know what to do. Eventually the machine was "printing" without filament. I increased the infill and it is OK. Just thought it might be an interesting fault.
              The shortest distance between two points is a circle of infinite diameter.

              Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

              Southwestern Ontario. Canada

              Comment


              • #8
                I’ve been playing with lost PLA casting in AL. Not sure about bronze but with Al I’ve been printing at %102 size to make up for the metal shrinking.

                Comment


                • #9
                  Originally posted by loose nut View Post
                  The filament would get chewed up by the extruder and break at approximately the same place. The only thing I can think of is that the lack of infill was buggering up the retraction and it was just moving the filament back and forth in the same place. Basically it didn't know what to do. Eventually the machine was "printing" without filament. I increased the infill and it is OK. Just thought it might be an interesting fault.
                  That is an interesting one, and i think youre right, too much retraction in one spot just wore out the filament. Cura should have a setting to limit how much retraction you can have in a certain amount of filament, think its called maximum retraction count. Might try lowering that, assuming you wanted to print at 5% infill still

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                  • #10
                    Cura does have a setting for that but I will leave the infill at 20%. Sometimes it will do that anyway, not very often but there doesn't seem to be any reason., 5 or 10 times it prints OK and then it doesn't and with the same settings. It must be part of the learning curve.

                    no 704 how does it turn out???
                    The shortest distance between two points is a circle of infinite diameter.

                    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                    Southwestern Ontario. Canada

                    Comment


                    • #11
                      ive also played around with lost PLA. Im using an old pottery kiln to do the burn out and just regular plaster of paris for the mold. i start low, about 150*F for a couple hours, then up to 300*F for another 2 hours and then start bumping it up 100*F an hour until I hit 900*. Then straight out and into a bucket of sand and i pour the aluminum in.

                      I havent put much effort into refining things, but i got ok results on simpler parts. I put the mold in the kiln upside down, and when a lot fo the PLA melted out onto a tray, i would take the tray out. Im not sure if its the PLA, PoP or something else remaining in the kiln, but it smells really bad and makes my eyes water when the temp gets higher. I think its the acid in the PLA, but couldnt stand it, so I havent done much more since.

                      Plaster of paris also gets fairly brittle at those high temps, so I wasnt getting very consistent results with small details that i was playing with. I tried making some model engine blocks with water cooling, and the passages would fill with plaster, but the plaster would break and move around inside the molten aluminum and wreck the part.

                      thats all thats coming to mind right this minute. If i think of any other details i will add them later.

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                      • #12
                        Looks like you have a typical subtractive machining problem, to fast or to much doesn't work, to slow or to little doesn't work either. The answer is likely somewhere in the middle (-:

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                        • #13
                          The couple of casts I have made using lost PLA turned out great. You can see my finger prints where I pressed in wax for vents. Using commercial investment can’t rember the Brand but it’s about $40 for 30# on eBay. Along with a SS flask and spru cap. I pull a vacuum on the investment after pouring it then fire it in a potters kiln. Actually installing a ramp/soak controller on the kiln tomorrow. Then pull a vacuum on the flask as the metal is poured.

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                          • #14
                            [QUOTE=loose nut;n1953335]Sometimes it will do that anyway, not very often but there doesn't seem to be any reason., 5 or 10 times it prints OK and then it doesn't and with the same settings. It must be part of the learning curve./QUOTE]

                            Well youve got me curious now. After the print fails, what do you do before starting the next print? How far along in the failed print do you get, time-wise? Do you get the same failure mode every time, with the extruder grinding the filament? Have you tightened the nozzle on the print heat while the extruder is at operating temperature?

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                            • #15
                              I had a print fail last night, nothing special or difficult. I was using the standard Cura PLA profile BUT I changed the infill pattern to triangles. When the infill started printing it didn't look very good, I don't know why and then failed in the same manner. I reset it to print again but with the grid infill and it printed fine. Apparently some types of infills don't like to play nice with some shapes. That is my guess anyway.
                              The shortest distance between two points is a circle of infinite diameter.

                              Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                              Southwestern Ontario. Canada

                              Comment

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