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I got a Wanhao Duplicator 6 printer branded as a Monoprice Ultimate about a year an and a half ago, 6 months after I got it I decided I hated the buildplate (I had to use a gluestick on every print to get it to stay down) so I removed the original fake buildtak, and got a piece of borosilicate glass and a sheet of PEI that I attached to it.

Glass buildplate on top of aluminum bed, covered with PEI

After about 8 months I started noticing issues with my bed being weird and never really being level no matter how much time I spent leveling it. (I level my buildplate by printing giant concentric circles, comparing the thickness based on the color in different portions, and turning knobs based on that.) Today after an hour of trying to level my bed I decided to just print the model I was going to print anyways (a pyramid model) and discovered why it never seemed level.

A single printed layer of gold silk PLA from tty3d

It seems that different portions of my buildplate are at significantly different heights. Is there something I did wrong to cause this to happen, does it just happen over time, and is there anything I can do to fix it? My current plan is just to buy another sheet of the PEI and stick it directly to the aluminum buildplate installed on the printer. It would result in MUCH better thermal transfer between the heater and the PEI anyways, which is important because the whole point of PEI is that it sticks to PLA extremely well at high temperatures, and not very well at low temps.

If nobody knows what might cause this I'm just going to go ahead and get an new sheet of PEI and omit the glass (it was a bad idea anyways). Thanks for reading.

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    $\begingroup$ Get a thicker piece of glass (1/4 inch). Only attached it to the existing bed on one side, and let the other side be free. $\endgroup$
    – user77232
    Commented Nov 1, 2019 at 20:23
  • $\begingroup$ Possible duplicate of Will a glass bed warp as it is heated? $\endgroup$
    – Trish
    Commented Nov 1, 2019 at 21:02
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    $\begingroup$ I've been successfully printing with the WhamBam system. A magnet is stuck to the AL bed. Then a sheet of PEX material stick on a piece of flex-steel is used as the print surface. The magnet holds it in place. When a print is done, the flex-steel is removed, let it cool 30 seconds or so, give it a little flex and the printed parts pops right off. Every several prints (10, 12?), give it a wipe with some isopropyl alchohol and you're ready to go again. We used blue tape for a while, and after fighting pieces off the AL, we went the WhamBam route and couldn't be happier. whambam3d.com $\endgroup$
    – CrossRoads
    Commented Nov 4, 2019 at 18:52
  • $\begingroup$ How thick is your glass? $\endgroup$
    – Technophile
    Commented Nov 5, 2019 at 15:49
  • $\begingroup$ your build surface looks really scratched up. did you ever clean it? check youtube.com/watch?v=ShFaJ027pFs and youtube.com/watch?v=DzaPFlEKP10 $\endgroup$
    – Trish
    Commented Jan 19, 2020 at 9:04

3 Answers 3

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Looking at the picture, the first thing that came to mind was, "are you sure it's the bed?".

The height variance looks very regular, and while I'm unfamiliar with this printer's specific mechanics, my thought process trended to the Ender 3 and other v-wheel extruder mounts. If the extruder and gantry carriages are mounted to the gantry spars on V-wheels instead of sleeve bushings or other linear guides, and you've spent a lot of time printing small objects where those wheels are going back and forth over a relatively small travel distance for the entire print, you have been unevenly wearing the wheels so they've become eccentric around their rotational center, and this will cause the extruder to vary its height over the glass in a very regular pattern tied to the circumference of these carriage wheels. This happens especially quickly if you over-tighten the bearings against the gantry spars in an attempt to make the printer more precise.

If the printer uses sleeve bushings, the worn sleeve won't rotate, and any wear on the spar will be very localized to the areas in which you print, but if the printer has spent most of its life printing a grid of small objects (tokens, sets of small figurines), you can still get this regular wear pattern as the printer will spend more time over those areas of the bed.

The fix is to replace the wheels or linear bearings if the printer uses them. If it uses sleeve bushings and the gantry spars themselves are worn in this pattern, you might be able to rotate the spars to put an unworn (or less worn) band of metal on the top of the spar, depending on how the spars are mounted into the endcaps of the frame and y-axis carriages.

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  • $\begingroup$ You can use a high quality straight edge to determine if it's the bed or if something like described in this answer is likely the cause. $\endgroup$
    – R.. GitHub STOP HELPING ICE
    Commented Jan 11, 2020 at 17:55
  • $\begingroup$ Monoprice ultimaker does use bushings on rod. $\endgroup$
    – Trish
    Commented Jan 19, 2020 at 9:31
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From experience, my PEI sheet did not stay flat after multiple use, this may be causing the problems you are facing. It could be the adhesive is failing on different locations.

As you mention, a new sheet of PEI may work for you; indeed the glass will not be necessary then, glueing it directly onto the aluminium bed would be enough provided that the metal bed is straight. Note that glass is straight as a result of the production process to make glass, so this can always be used. To remove the PEI sheet, a sticky glue residue is left behind on the build plate, please read "How to clean up my build plate for a new build surface?" for more information. It is probably easier to remove glue residue from the glass than from the heated bed as that is usually bolted and wired to the printer, but a wet cloth works fine. Personally, I print on glass or directly on the heated bed using an adhesion spray. You do not require the use of a PEI sheet.

Note that printing PETG filament is not recommended without glue stick or any other bonding agent like hairspray. This is not to get it to stick, but to get the print loose from the build plate, PETG fuses to PEI...

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I just placed a PEI 1 mm sheet directly on the aluminum build plate with the supplied 3M double sided tape and all is well so far. I paid a lot of attention to detail on preventing, or minimizing bubbles during the process which could impact even heating. I love the surface and ease of removal with the prints. I did not place anything between the aluminum plate and PEI material to minimize great transfer.

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