Bonded Heat bed for 12"

[pichuete]

well i have done Steps 1 and 2 with no significant improvement . im pretty sure that in my case the heated bed is causing my banding . my layer offsets are not in a particular pattern . .as we usually see when Z banding is caused by threaded rods wobble .

Im curious about the SS relay but i dont know how this work . for what i understand the rambo board (what i have on my printer) is capable of doing PWM on the HB . but im not sure if it can handle the current .

Also im planing to convert my I3v 12" to all metal similar to the new model that colin have on makerfarm (Pegasus) maybe if more users are interested in this solution we can work together to come with a good design.

[lakester]

idle speculation...

(FWIW..., the one mod I was contemplating was the addition of the bearing/guide for the top end of the z-rods..., haven't tried it yet)

..., back to speculation...

I wonder if a firmware mod might be worth a shot, specifcally, one that tweaks the "hysteresis" assumptions regarding bed heating.

My intuition doubts that the periodicity of heating cycles substantially change the overall expansion/contraction of the glass or overall structure in a fashion that would correlate with the z-banding issue. The heating system is more or less responding to the behaviour of the portion of the system with the least thermal mass, i.e., the heating pad itself. Is it really plausible that the overall structure responds significantly with the same periodicity?

I'm guessing that heat cycling correlates poorly with what is essentially a geometric effect in the form of z-banding.

Just the same..., maybe it would be worth reducing the hysteresis built into the heating algorithms and see if it changes anything wrt z-banding.

Again..., my feeling is that there is a geometric problem at work here, independent of heating..., but maybe if the heat cycling were tweaked..., it would help settle the issue once and for all.

0.02USD

(additional thought: heck..., for the sake of experiment, what if we disabled heating altogether, and did a z-banding test print with PLA on blue tape?)

[Chadd]

I tried the bearing/guide on the top of the Z rods and it made the problem much worse.

These two videos show the difference between ON/OFF heat bed vs PID.

ON/OFF

https://www.youtube.com/watch?v=0T5BE5XC2-8

PID

https://www.youtube.com/watch?v=RRSI2TJ3Trs

Those aren't my videos but some I came across. You have to figure with a 12" bed it would be even worse.

idle speculation...

(FWIW..., the one mod I was contemplating was the addition of the bearing/guide for the top end of the z-rods..., haven't tried it yet)

..., back to speculation...

I wonder if a firmware mod might be worth a shot, specifcally, one that tweaks the "hysteresis" assumptions regarding bed heating.

My intuition doubts that the periodicity of heating cycles substantially change the overall expansion/contraction of the glass or overall structure in a fashion that would correlate with the z-banding issue. The heating system is more or less responding to the behaviour of the portion of the system with the least thermal mass, i.e., the heating pad itself. Is it really plausible that the overall structure responds significantly with the same periodicity?

I'm guessing that heat cycling correlates poorly with what is essentially a geometric effect in the form of z-banding.

Just the same..., maybe it would be worth reducing the hysteresis built into the heating algorithms and see if it changes anything wrt z-banding.

Again..., my feeling is that there is a geometric problem at work here, independent of heating..., but maybe if the heat cycling were tweaked..., it would help settle the issue once and for all.

0.02USD

(additional thought: heck..., for the sake of experiment, what if we disabled heating altogether, and did a z-banding test print with PLA on blue tape?)

[lakester]

Cool demo of the problem (thx!).

2 questions:

1. What does "PID" refer to? (Sorry..., been puzzling on that...)
2. What is the table structure of the Mendel90 in the vids? What are its similarities to the MakerFarm wood+glass table?

I tried the bearing/guide on the top of the Z rods and it made the problem much worse.

These two videos show the difference between ON/OFF heat bed vs PID.

ON/OFF

https://www.youtube.com/watch?v=0T5BE5XC2-8

PID

https://www.youtube.com/watch?v=RRSI2TJ3Trs

Those aren't my videos but some I came across. You have to figure with a 12" bed it would be even worse.

[Chadd]

Cool demo of the problem (thx!).

2 questions:

1. What does "PID" refer to? (Sorry..., been puzzling on that...)
2. What is the table structure of the Mendel90 in the vids? What are its similarities to the MakerFarm wood+glass table?

1. To put it simple PID uses PWM to control your bed temp so it turns the bed on and off very quickly to maintain the temp vs turning the bed on 100% for 5 seconds at time to maintain the temp. The reason you have to have a Solid state relay is because a mechanical relay can't handle the quick on and off switching. In that video link what you are seeing is the bed distorting when it turns on @100% power and then returning to its normal position after the power is off to the bed. The second video shows the same thing with PID, the bed switches on and off quickly to maintain the temp so it doesn't stay on/off long enough to show the change in distortion.

http://techteach.no/kybsim/pwm_control/index.php

2. The bed designs are pretty well identical.