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  1. #31
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    Yep, you are spot on with that. Definitely wouldn't worry about heat transfer on small diameters on the corners. Heat shields, you'd be amazed, Just a piece of crinkled foil will remove all the radiated heat load from the bottom plate. Still have environment heat though... but this is normal. A good long print will make the normal plate pretty darn warm too. That is the radiated heat mixing with the convection from the fans. That heat shield on the print head is effective as it too has a reflective coating to deal with the same issue. Still damn hot!

    I did not know that about Borosilicate glass. I know PLA will stick to it but with CubeGlue slurry'd on the plate, it is excellent, even cool. And the glue remains with the glass no less. Yes, you probably got the same glass from eBay. Not all glass is this flat!

    24V is a great choice in that you can run lighter lead-wires, or better yet, heavy lead-wires with less loss. Thanks for the reminder on out-gassing!
    I'll get back to this project at some point. Really interested in the flexi-buildplate... Have you tried cooking any LokBuild on your plate yet?

    Am I to understand you will make your own heater element with NiChrome wire? That will be interesting. I was thinking to do that with a thin sheet of alumina I have on hand That alumina sheet could easily be bonded to glass for a light weight hot bed. Any reason to shun the circuit board heaters?

    - - - - - - - - - -

    And please fess up here... what am I looking at in the grayscale rainbow print picture?

  2. #32
    Administrator bolsoncerrado's Avatar
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    Welcome to the forum!

    Dont you have a video of the 10 cubes working at the same time!?!? THat would be glorious ahhahaha


    Nice work on the heated beds indeed!

  3. #33
    Administrator bolsoncerrado's Avatar
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    Quote Originally Posted by TommyDee View Post
    And please fess up here... what am I looking at in the grayscale rainbow print picture?
    Railway / connector system?

  4. #34
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    Thank you. There seems to be two distinct activitites. Tinkering with the printer or designing parts and printing. I enjoy either but not at the same time. But then I combine the two activities anyway to get a sense of forward motion. I had carefully avoided the heated build plate a few years with pla, clever abs work arounds, preheating the build plate and boxing the heat in. I wanted to build all that abs track and accessories to supplement the meager amount provided for a friend to have a satisfying experience with this set:

    https://www.amazon.com/gp/product/B07BK6M2WC/

    It was impossible to avoid a heated build plate any longer. I had thought about this a long time previously but could never overcome a few issues and thought if I did, the cube would probably meltdown.

    They did a great job on the cube 3 but they just did not finish it. However I believe there is one major design flaw and another major deficiency. All the other irregularities could have been fixed along the way in a product's life. I am not sure how they thought that multiple bend Bowden snake choice could ever work and then they were committed to that approach. It would have been interesting to be in those engineering meetings. But I also feel all the 3d printing is not ready for the general public or one in every home. The other major weakness is the nozzle carriage mount.

    WP_20190205_02_23_06_Pro.jpgWP_20190129_05_21_55_Pro.jpg

    They must have iterated themselves into a corner there. The amount of plastic gripped by the screws is a bit frightening. It is tight quarters in there and they kept chipping away at the plastic. After much wrestling, I wiggled out of there like this and managed to increase the integrity. That is a dollar store piece of good quality non-magnetic 0.025inch stainless steel off a chopper/scraper to sandwich the plastic mount and move it only the 0.025inch forward. The next weak link is how the heater block mounts to the white plastic. A stainless steel spacer from the rear stainless steel plate to the heater block with a long screw is next.

    WP_20190206_05_50_24_Pro.jpgWP_20190207_00_14_16_Pro.jpg

    Now there is some needed strength there in balance with the rest of their design. All the machines seem to fail there eventually and I wanted to also reinforce that point from heat. Look how they have some of the hot air flow vented on that plastic from the heater block through the holes in the black plastic shroud directly on the mount.

    I had a video of five or six cubes pumping out classroom pla. It did get me to the "nine women and a baby a month" island.

    answering more above... The four support spacers are hot to the touch but also your finger will cool them before it hurts. I agree, stainless would lower even more that heat migration now that I got the height established. It could use some polish there. Less heat is always better there.

    and the heating element... For electrical heating, I think we want a large resistance discrepancy with the source leads or those leads will heat too. And the thicker lead wire will also get hot by heat conduction too. Then nichrome just seems to be the hard to beat but not the only material of choice. There is just that problem of reliably connecting to it over temperature and time. Upon dissection, the first pad eventually gave out at that connection. That is why it would be nice to just make your own to adjust it there. I would cover the thinner aluminum with Kapton and then a 3m heat adhesive sheet. A pattern for the heater wire could be 3d printed to place the nichrome on the adhesive and then removed. Topped off with another layer of Kapton. Really the bigger challenge is the mechanical connection and support of the source wires. I probably would increase the aluminum in the front with a tab balcony to support the connection. Then there is the issue of where and how to monitor the heat. After all that track printing, I can say, once it was successfully printing it was rather difficult to get it to fail by rocking the boat.

    About the surfaces... I agree, it seems the cube 3 confined quarters printing and sidewalks were beneficially heating the build platform. I would add bamboo curtains to the front and back to trap more heat. I now am really enjoying the ease of bare glass with these large base short parts and they slide off. Now eight years ago (ugh), my last post about 3d printing: http://makerbot.wikidot.com/forum/t-286617 I guess nothing is the better answer for these parts. Now I use the heat to hold off the shrink until after the print is completed and not interfere with the abs natural ability to stick.

    sorry about the lengthiness
    Last edited by Kame808; 02-12-2019 at 04:50 PM.

  5. Thanks TommyDee, bolsoncerrado thanked for this post
  6. #35
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    No, I meant the geometric pattern that that image is showing.

    - - - - - - - - - -

    Excellent. Yes, those are the weak links. There is also one on the flanges that hold the black plastic to the white one. A flange crew goes a long ways to firming that up.

    Definitely like the stiffener. That whole alignment solution is bogus. They really did struggle with making two nozzles exactly parallel. Kind of hard to do when all your nozzles are off just a touch too much in themselves.

    So what dollar tree part was that? It seems made for it!

    - - - - - - - - - -

    As to terminating the heater wire, why not screw a barrier block or connector to the aluminum plate?

  7. #36
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    I agree, the leveling scheme looks like it had been an afterthought. Like, "oh yeah, we need that". I am not sure how they wanted it to be used. The plastic can not be stressed like that. I assumed the mount would be loose and adjusted on the set screws. But then there is not much access to tight it down. Maybe the measurement was made in a jig and transeferred to the set screws so that the adjustment was not made under tension. However, I saw many cubes with the set screw ledge cracked off. The belt notches were also often snapped off and the plastic against the slide cracked too.

    It all is a shame because most all of the rest of the design is good and just has normal problems that occur. I guess that is the attraction for finding and correcting them.

    A terminal block is okay. The pad that failed was open at the connection. It might be best to not bend the wire tightly there or score it. Being able to service it is good.

    WP_20190103_10_17_07_Pro.jpg

    It just was a way to conveniently get the metal for a buck. Some assembly required

    WP_20190131_04_11_07_Pro.jpg
    Last edited by Kame808; 02-13-2019 at 03:49 PM.

  8. #37
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    Oh! LOL! I was thinking you found the "perfect" piece at the dollar store. Yes, a buck for the scraper? Nice!

    I went through adjusting mine and forgot all about that 3rd screw. The plastic is just creamy enough to ignore it, but those little set screws... yea, junk. This too was a hole they designed themselves into.
    Last edited by TommyDee; 02-13-2019 at 06:09 PM.

  9. #38
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    On rereading this all again, I should clarify that I currently use a 12v rated silicone heating pad but often run it over voltage to 18v from the 24v modified power supply. hmmm... The failure mode could be the wire running hotter and damaging the insulating materials or connections. This is all not as easy as the purchase options would suggest. I mean, how can they know the wattage or nichrome wire you will need for your application to get it and the print bottom to 120'c? It would be helpful if the nichrome wire would operate at 120'c only to keep it all safe. But in reality it is much hotter to get the platform to 120'c overcoming the losses in the insulating materials. Running that nichrome wire hotter may damage the wire, connections and insulating materials. Be careful. For example, an incandescent lamp in a block of ice can still burn out on over voltage. But if I keep that filament cool, it can run with more current. I believe it is best to build your own heating pad and will try that next. It seems we need as much nichrome wire as possible to overcome the coupling losses of heat to the platform.

    By the way, I was using one of the eBay mosfet boards and it failed after a while. Unfortunately I had to dive into their design. It was not too robust. The mosfet gate likes 10v but will operate to 5v and maybe 4v typically. Since the stated power supply is 12v or 24v they just put a voltage divider on the gate drive. That is "kinda" sloppy. It is better to clip the voltage at 10v. Once I modified the circuit the mosfet is always cool to the touch as it should be. I learned to not take these eBay circuits for granted. ugh.

  10. #39
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    I come from a world of power supply design. You are absolutely right in that a lot of things have gotten "sloppy" in these DIY -proclamations-.
    But yes, by "overclocking" your 12V pad, it basically causes accelerated degradation all too common with significant heat rise from ambient.

    Our buddy Don once posted up a mod where he used power resistors to generate the heat. Somewhat spotty for distribution, but I can see a more intense effort could benefit from having a entire bed of Dale aluminum housing power resistors bolted to the plate. The heat transfer is near optimal compared to nearly everything else! The weight, not sure... thermal distribution from the bottom of the plate to the top will give you a good idea of how wide apart you can space the resistors. But if you manage the wattage according to the resistor's ratings, you got a nice sealed heating element similar to that frozen light bulb where no oxygen can get to the business end of the heater. Give it the right amount of energy, and it should last forever according to its design specification.

    As to NiChrome... same thing, you can do the math since it is a resistance wire. Or you can simply measure it and backtrack the requirements. I'd probably opt to run a couple in parallel. The beauty of NiChrome is that it tolerates oxidation very well. But as in most examples of how it is used, you will see high temperature insulators managing the structure. Once you come into contact with things like Kapton, where you might stress some of the adhesive or the film itself, you can develop hot spots that essentially become thermal run-away issues, and not necessarily a specification problem of even an insufficient margin error.

    I really haven't looked into the heated bed too much. I have a 24V pad... I have glass plate... I even have a 1mm thick alumina plate if I need an insulator. You'd think that I'd have this done by now But like you are seeing, it is never that easy. These systems demand a lot of design margin to remain reliable.

    Mosfets... Yea, cool devices but they do fail... and if they fail closed, bad stuff happens! Every RC hobbyist probably has a horror story or two. I have scars

    But since we are just passing ideas...

    Alumina is impervious the the temperatures we are trying to achieve. I've seen alumina tubes on eBay for reasonable costs. What about coiling the NiChrome wire and protecting it inside a thin walled alumina tube... square if you can find it... and using a ceramic cement (high temp adhesive that also aids in heat transfer)... to attach it to the build plate. Now you are starting look a lot more like a bonafide heater element ready for some serious cooking.
    Last edited by TommyDee; 02-20-2019 at 11:38 PM.

 

 

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