Wanhao Duplicator i3 Plus bed temp issue?

[Fusilier]

I can’t get my Wanhao Duplicator i3 Plus bed temp to stabilize and it seems to be causing issues with my prints.

The machine has been updated with a Micro Swiss all metal hot end, an all metal direct filament drive, a rear mounted 3D printed cooling fan mount with 3D printed duct, and a Wham Bam PEX flexible metal magnetic bed.

For months and months it printed absolutely perfectly with the PEX bed. Lately I either get very good print adhesion except pulled up corners. Corners, like on a box, are now consistently pulling up and away from the bed. The layers above the base few, seem to be shrinking inwards and pulling the corners up. It isn’t an issue along the sides away from the corners,

If I set the bed temp to 70 I get generally good bed adhesion but I still get shrinkage in the layers above the first layer (something about layer 10 I guess) resulting in the side walls being pulled in and the corners of the print pulling up and away from the bed. It looks like crap and depending on the model it results in a print that doesn’t function as designed.

The print adhesion for the majority of the flat surface is perfect, just the corners seem to pull up. I do not use tape or glue or any other surface prep because that was the entire reason I purchased the Wham Bam PEX surface - non of that is needed. And up until this problem raised its ugly head a few months ago, the curling up corners wasn’t an issue.

This seems to be a relatively new problem for this printer which used to print divinely. The problem showed up in late November/early December.

When printing, the bed temp can fluctuate from +/- 5 degrees on a good day and sometimes as much as +/- 10 degrees or even more some times. I honestly do not know if this is a new problem or one that’s been happening for months and I just didn’t notice.

I suspect the problem, or a least part of the problem, is the inconsistent bed heat temp and/cooling fan speeds.

I’ve done a bed temp and hot end PID autotune several times and that doesn’t seem to help.

My first layers look perfect. The squish is great, the fill is perfect, the print always gets off to a perfect start. The problem seems to occur once a couple of layers are printed and the cooling fan kicks in

Might I be on track or could it be something else?

What might be causing the bed temp fluctuations? A bad thermistor? A bad bed heater? Something else? How should I diagnose this issue?

[LEGOManiac]

Before tinkering with the thermistor, check to make sure it is properly attached to the bed. On my machine it’s held on by a little bit of (capton?) tape but if the tape comes loose and the thermistor is no longer in firm contact with the bed, there will be a serious time lag between when the bed changes temperature and when the thermistor recognises it. In my case, I have a piece of fibre insulation stuffed under the bed. It helps keep the bed from cooling and I’ll never have to worry about the tape coming loose.

Having said all that, as you correctly stated, warping is caused by part shrinkage which in turn is caused by temperature changes. The big difference between now and the last few months is that it is significantly colder outside.

Make sure there are no drafts and that the room temperature that the printer is in is as constant as you can make it. Keep it way from windows, doors and air ducts.

Consider a full or partial enclosure.

Also, if you are using Cura, there is a feature in the settings called Draft Shield. You enable it in Preferences->Configure Cura->Settings then search for “draft” and enable everything. I use a shield distance of 5mm and a height of 20mm.

Alternatively, or in conjunction with it, print a brim.

[Fusilier]

Thanks for suggestions / ideas.

My machine is in a fully enclosed enclosure. It’s a fabric on tube frame but it certainly keeps any drafts away.

I’ve not taken my machine apart before - other than taking the bottom plate off to deal with tightening the belt, and dealing with the hot end of course.

The thermistor looks OK, at least as best as I can tell without removing the bed. I think I’ll take the bed off and give it a good look though. I might as well as I’m not having any success at all of late.

The actual bed temp seems to be 5 to 8 degrees hotter than what’s reported, based on using a laser hand held thermometer. Also the hand held thermometer suggests the bed temp isn’t as flaky as what the front panel is displaying.

So like many things I do, I’ve got more data and fewer solutions. Isn’t that always the way.

Thanks again.

[LEGOManiac]

I suppose there’s an outside chance you could have a connector with an oxidised terminal. Try unplugging and re-plugging the thermistor wire, both on the motherboard and the other end (not sure what to call it - the end of the wire the thermistor (with its own attached wires) plugs into. Repeated plugging cycles should scrape off any oxide that may have formed. I had a furnace motor that failed for this reason. The HVAC company wanted to charge me $800 for a new motor which I refused because the guy didn’t even do the most basic of tests. It turned out to be oxide on the plug.

[Jason]

I would tend to agree with LEGO, Looks like a bad connection somewhere. If you have PID tuned which I know you said you did. The only other options I could think of is a bad thermistor or you are starting to get a weak power supply.

I would tap a voltmeter into it and when the temp starts to fluctuate see if the voltage does as well.

Just another thought.
Jason

[LEGOManiac]

@Jason : Good point on the possibility of it being the power supply. I should have thought of that.

[Fusilier]

Well I finally did what I should have done in the first place: I removed the print bed completely and took a good look at the thermistor installation. I should have done this at the first sign of bed temp issues. Instead I was lazy at the time and just peeked underneath with a flashlight which showed the thermistor securely stuck on with Kapton tape but I couldn’t actually see where the bulb rested.

What did I find underneath but a thermistor that was just taped to the underside of the bed. The thermistor bulb was not installed in the little recess designed for it but instead it was taped on about an inch or so away from the recess. I’ve been printing with this install for just shy of 2 years now without noticing.

So I gently pealed back the Kapton tape, tucked the thermistor bulb in its recess where it should have been all along, and gently reapplied the tape. I have some more tape on order from Amazon.CA so I’ll replace the old tape with new stuff when that arrives.

Then I did a new bed temp PID tuning. It’s amazing how easy this is once you’ve done 10 or 12 of them.

Anyway, I’m trying another print as I type. The bed temp is set to 70 degrees and except for an occasional slide down to 69 or up to 71, it’s holding its own at 70 quite nicely. At least orders of magnitude better than it was before I reinstalled the thermistor properly.

So, thank you all for the suggestions and ideas. They’re all good to have in my references in case this doesn’t actually solve the print quality issue. I’ll probably know for sure if this solved the end product problem (print quality) and I’ll let you all known in an hour or so.

Thanks again. Your help and patience is truly appreciated.

[Fusilier]

I should have noticed the incorrectly installed thermistor when I tipped the bed up yesterday - See Photo 1. I didn’t really know what I was looking at until I removed the bed completely today.

Photo 2 shows the incredibly bad initial layers before sorting out the thermistor install and Photo 3 shows what I’m getting now. Looks like I still might need a little bit of tweaking but at least now I can print something that’s useable.

[Jason]

that’s awesome, looks like you have it narrowed down.

[Fusilier]

Thanks. I’m now able to print workable but not perfect prints. I’m still getting shrinkage around the first couple of layers that is still pulling up on the corners but the overall results are significantly better than I was getting two days ago.

Now I’m hoping to play with my Cura settings to get clean first layers without any pull up and straight sides down to the first layer.

At least I’ve solved the bed temp issue and hopefully I can focus on slicer settings until I get this beat.

Cheers. Stay safe and stay kind.