How I fixed Z banding on my 12" i3v. AL Y bed and solid state heat bed relay/PID

[Chadd]

I have fought Z banding with my 12" i3v since I bought it and assembled it. I tried all sorts of things to fix the issue but never could get the Z banding under control.

The two things that I did to finally get it under control were.

1. Replace the wooden Y axis bed with Aluminum.

My Y bed would warp so badly on long prints that the rollers under it would crash into the cross support at the back of the printer.

2. Replaced the mechanical relay with a solid state relay and enabled soft PID within Marlin.

With the stock mechanical relay I would see the heat bed and glass print surface warp ~.3 mm every time the heat bed turned on and off to maintain the bed temp. This would happen every 5 seconds or so depending on the heat setting so ever 5 seconds the print surface would warp more than a full layer height when printing at .2 mm producing very prominent Z banding, poor first layers and in some cases layer separation when printing ABS. After installing the solid state relay and setting up PID the bed only moves ~.03 mm once up to operating temp.

The Y bed was replaced with a sheet of .125" 6061 that I ordered from Amazon

http://www.amazon.com/gp/product/B00...rch_detailpage

I used the stock wooden bed and some transfer punches to mark the aluminum plate to drill the holes for all the components. I also remixed a Y bed belt holder that I found on thingiverse to work with round mounting holes instead of the stock square holes.

http://www.thingiverse.com/thing:880755

This took care of the Y bed warpage issue that I was seeing. A side note, Makerfarm is now selling its own aluminum Y bed plate as an add on to the 12" kit.

The stock mechanical relay was just setup to control the heat bed in bang bang mode. Meaning that the heat bed would either be 100% on or off and it would swing high and low of the actual temp setting of the bed so when the heat would turn on the bed would warp one direction and when the heat turned off the bed would return to its normal position. This was instantaneous and the print surface would distort as the relay turned on and off.

I purchased this DC-DC solid state relay from Amazon

http://www.amazon.com/Lightobject-ES...id+state+relay

This relay seems to be fairly well made but I can't vouch for its longevity. I measured a .41V voltage drop across the relay while it was on with the heat bed hooked up to it and I don't notice any difference in the time required for the heat bed to reach operating temp.

along with this heat sink also from Amazon

http://www.amazon.com/Aluminum-Solid...PWQKFZSZFP7VZR

You will also want to get yourself some heat sink grease to put in-between the relay and the heat sink. Don't think about using the relay without the heat sink and grease or it will burn up on you and a solid state relay can fail in the on state that would keep your heat bed on without control so be careful.

As far as hooking up the solid state relay there are plenty of diagrams out there, just google it. One thing to note is that solid state relays are polarity sensitive so make sure you get the + and - correct.

Here is what I did to get the PID settings to enter into my Configuration.h file.

In Simplify 3d machine control I entered

M303 E-1 S100 C8

This will enable PID auto tuning and will heat up your bed to 100° and then cycle the bed around the set point 8 times. It will then return the P, I and D settings that you will need to enter into your Config.h file. You may need to preheat your heat bed if it takes a long time to reach operating temp as the autotune can timeout if it takes too long.

Now once you have your P, I and D settings you need to edit your Configuration.h file

You will need to find and uncomment

#define PIDTEMPBED

That will enable PID heat bed control.

You will then enter your P, I and D settings in the following location

#ifdef PIDTEMPBED
//120v 250W silicone heater into 4mm borosilicate (MendelMax 1.5+)
//from FOPDT model - kp=.39 Tp=405 Tdead=66, Tc set to 79.2, aggressive factor of .15 (vs .1, 1, 10)
#define DEFAULT_bedKp 460.33
#define DEFAULT_bedKi 87.81
#define DEFAULT_bedKd 603.32

Those are the P, I and D values that my Autotune resulted in.

Once you get this done you need to upload the changes to your printer.

That's all there was to it.

Here is a picture of before and after print results. These were all printed with the exact same settings of .2mm layer, 250° Extruder and 110° bed temps with no changes to the printer other than installing and setting up the Solid State relay.

Right was with the heat bed off, middle was the stock relay setup with no PID and left is with the Solid Sate Relay with PID tuning.

IMG_20150902_140057.jpg

Hope this helps others facing the same Z banding frustration that I did.

Thanks,
Chadd