Bed Temperature

Discussion in 'BigBox General Chat' started by Julian64, Oct 3, 2016.

  1. Julian64

    Julian64 Active Member

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    So 60 deg for PLA. According to my big box and octoprint the bed is up to temperature in about two minutes and starts printing.

    According to a hand held thermal probe placed on the glass itself the bed is 40-45 degrees when printing starts. If I leave the bed stationary at 60deg according to octoprint the bed glass never gets beyond 48 deg no matter how long you leave it. If you alter the bed temperature to 80 deg the glass slowly gets up to 60 deg and not much higher.

    So question. Is there a calibration facility through octoprint or even on the rumba board itself?
     
  2. Ephemeris

    Ephemeris Well-Known Member

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    The glass is an insulator, the thermistor is down in the printed circuit board so the surface temperature is bound to be off by quite a bit. I suggest you just determine what works for the filament you've chosen and not worry too much :rolleyes:
     
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  3. Dr Jeep

    Dr Jeep Well-Known Member

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    Yeh the thermal gradient of glass means that when you heat the bottom of it the top will be at some point between ambient temp of the room and the temp you measured at the bottom. Then drafts etc will all have a further influence.

    It's possible to add an offset for these in the firmware but it's easier to just heat the bed to a temp that works and ignore what the real measured temp is.
     
  4. Alex Stevenson

    Alex Stevenson Well-Known Member

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    Now I'm curious. I've been thinking that if I have the temperature just right, then I should be able to print PLA reliably with just clean glass (no hairspray). However, I was (stupidly) assuming that the temperature was more accurate.

    Is my theory correct? Should I experiment more with the bed temperature, or perhaps is it not worth the extra effort?
     
  5. Jasons_BigBox

    Jasons_BigBox Well-Known Member

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    I use the UHU Stick recommended by E3D and it's very reliable. Easy cleanup with water and kitchen towels.

    The only problem I've had in months of printing was one that I had a problem removing (it had a large flat base). I've found razor blades going for getting under the edge of the print. If that isn't enough I have a collection of pallet knives/spatulas that I can slide under the razor and push further under the print. I think they're oil painting tools actually but very useful.
     
  6. Alex Stevenson

    Alex Stevenson Well-Known Member

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    Yeah, I've heard that works well. Hairspray for me works a treat, and depending on how much I use it just pops off when the bed has cooled down, so no issues removing it from the bed - never needed anything other than occasionally using a spudger. So, now I'm thinking that as I increase the bed temperature, I could respectively reduce the hairspray.

    Also wondering if the 60 degrees is recommended for the actual surface temperature, and if I have been unwittingly been setting mine a bit low anyway.
     
  7. Jasons_BigBox

    Jasons_BigBox Well-Known Member

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    I agree that the bed temp is lower than that read by the thermocouple. For me though, a setting of 60 works fine with PLA even if it is only 50 or so.

    The only adhesion problems I've had are with tall thin supports or ABS. I think I need higher temps with some ABS parts.
     
  8. Julian64

    Julian64 Active Member

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    I wacked mine up to 70 on octoprint, and that gives 55 on the top of the plate. Things is no matter how long I preheat for the temp doesn't go above 55 so I assume its a temp loss thing. Am using UHU but not had any corners lift since using the 70.
    Strange thing is it reverts to 60 after 2-3 mm of height so I assume it sets it every so often in the gcode.
    The temporary hike to 70 for the first couple of mm has been working very well for me though.
     
  9. GeckoBox3D

    GeckoBox3D Well-Known Member

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    I use printbite on my machine. This stuff is awesome. One surface for all materials, and I never have to recalibrate (I last recalibrated 3 months ago). Prints pop off reliably every time and have a nice shiny finish where they touched the bed. I print the first layer of PLA at 75, then 60 thereafter. ABS is done at 120/100. As long as I don't touch the bed, I don't even have to clean it that often (grease is a killer of first layers...)

    I've had success on it with ninja flex, PLA, pla/pha, abs, petg and nGen.
     
  10. Miasmictruth

    Miasmictruth Well-Known Member

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    Another good bed coating is 3d Eez, I have mostly only tried PLA and PETG and works great. I have heard good things about other materials too.
     
  11. Dr Jeep

    Dr Jeep Well-Known Member

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    I'll second that, not looked back since I installed it and even just upgraded my old printer before giving it to it's new owner as it really does take a lot of the pain away, particularly for people getting started. I've not really had a bed adhesion problem since fitting it (except for my ninja flex stuck a bit too well so I ended up printing that on blue tape)

    As you say if you keep your fingers off (I use a plastic scraper to remove any leftovers like perimeter prints) then it needs no attention between jobs.
     
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  12. dc42

    dc42 Well-Known Member

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    Yes, but good adhesion depends on the PLA filament and the glass. On one of my printers, I print PLA direct on to 3mm float glass with an indicated bed temperature of 65C. I took special measures when cleaning the glass initially, but I haven't cleaned it for about a year now. I wipe it with distilled malt vinegar before each print.

    On the other printer I print on to PEI. I have never found printing on to glue stick or hairspray very satisfactory. I think any high end printer should include a bed with a PEI, PrintBite, Filaprint or similar good printing surface.
     
  13. Dr Jeep

    Dr Jeep Well-Known Member

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    Yeh agree with that, I had pretty good results at first on the BB printing PLA to glass, but then you move to something like Edge and need UHU, which then means you have a pretty annoying cleanup job to get back to clear glass again. It's just too hard for my liking. Hairspray has never worked for me. Experimented in the past with kapton and blue tape, both worked but they aren't that long lived so again it's just hassle.

    Just as a warning, the printbite instructions say that it's not recommended to stick it to borosilicate glass as it has a different expansion rate and can fracture the glass...so far I've not had this happen to me in 30 or so prints since I fitted printbite but obviously if you shatter the glass then both the glass bed and the printbite would need to be replaced which gets a little expensive.
     
  14. GeckoBox3D

    GeckoBox3D Well-Known Member

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    I've been using printbite on toughened glass now for months with no issues. May be a good alternative. You could also use aluminium sheet or tooling plate which will be my next upgrade.
     
  15. Dr Jeep

    Dr Jeep Well-Known Member

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    Toughened is probably best though borosilicate like on the BB shards real easy in comparison
     
  16. GeckoBox3D

    GeckoBox3D Well-Known Member

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    It is possible to remove printbite from a surface apparently, just takes a bit of effort so if it does crack, just remove glass and get some new adhesive sheets. From what I've heard, the likelihood of the glass breaking is very low. If you have a good piece of glass with no defects I doubt it will ever become a problem.

    Most glass breaking stories from 3D printing I've heard have come from defects caused by ripping ABS prints off the glass and taking chunks with it, or cooling glass too quickly after heating.
     
  17. Julian64

    Julian64 Active Member

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    I just started, and am having some success with printing onto the glass. After the post above I stop using the UHU for PLA and just started to print. Total disaster. I then lowered the head to make it much closer to the glass so the first run round gets pushed onto the bed. This seems to have immediately worked for me.
    Only doing small jobs but the PLS glass finish is much better then UHU. Obviously I might have a problem when I come to do PLA as mentioned above, but currently very happy with printing straight onto glass.
     
  18. gonzalo

    gonzalo Well-Known Member

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    This thread shifted from bed temps to print surface options...
    Adding my 2 cents;
    In my other machine I have used the hi temp gecko surface with great success, also the one for nylon is fantastic.
    The zebra plate, now printinZ is very good too and one side is white and the other is black which is very cool too so you can have contrast and see what is going on. But at the end I put away all that stuff and kept using a 4mm thick PEI sheet. It worked wonders. The thing is, the bed size of the other printer is only 14 by 14 cm. So holding the PEI to the alu bed with clips was good enough. IMG_6204.JPG IMG_6061.JPG IMG_6140.JPG IMG_6021.JPG
    Above you can see some 10+ hour prints done on my new PEI bed.

    For the BB you must have something flat and rigid that won't bow under temp, so I covered my glass bed with a 1mm thick PEI sheet (the one that Lulzbot Taz sells for their machines) and it works wonders. No cleaning necessary, I just scrub the surface with my spatula, sand with 400 grit sandpaper and clean with alcohol. The prints come off with a beautiful mat finish on the contact surface. 60c for PLA/PLA blends and 80c to 100c for ABS/ABS blends.
    My struggle is not with either bed temp nor surface type... it's the Z height. I can not make the nozzle start 2 prints at the same height to save my life!
     
  19. dc42

    dc42 Well-Known Member

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    To get the IR sensor working well with thin PEI sheet, you need to paint the underside of the PEI black. Clean the PEI with isopropanol and spray it with several light coats of matt black barbecue/stove paint. The paint needs to be cured with heat so I baked it in an electric domestic fan oven at 170C. After that, use heat resistant adhesive (e.g 8153LE or 468MP) to attach the painted side to a glass plate or other flat surface. Preferably use ordinary float glass, not borosilicate, so that there is less difference in the thermal expansion of the glass and the PEI (although as the BigBox has no heat spreader between the bed heater and the glass, float glass might not be such a good idea in this case).

    The reason for doing this is that PEI is transparent to IR. About 8% of the light from the sensor is reflected by the top surface of the PEI, and this is plenty for the sensor to work with. But if you don't paint the underside of the PEI black, there is a stronger and non-uniform reflection from the adhesive layer underneath the PEI. This interferes with the surface reflection which causes the trigger height to be less uniform.

    The bed of my Delta printer is done like this and it works brilliantly. The PEI sheet had one glossy side and one dull side, and I painted the dull side. I didn't sand or otherwise prepare the top surface of the PEI, I just spray a little isopropanol on it and wipe it with a paper towel occasionally. PLA sticks to it so well that I usually have to wait for the bed to cool down and tap the sides of the print with a small hammer to release it.
     
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  20. gonzalo

    gonzalo Well-Known Member

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    Great info, but, my IR sensor is under the bed looking at the black acrylic frame painted mat black, not at the PEI sheet... o_O
     

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