Bonded Heat bed for 12"

[Chadd]

I did this test with my printer last week. The Z banding was much better but I still had a periodic Z band spaced at ~.8 mm so to me that indicates that there is still some issue with hardware as .8 mm is the pitch of the threaded rods.

The banding with the heat bed on is horrible so I know that the heat bed is causing the majority of the issues.

I am just going to go down my list of things and try to get it taken care of, too many people are having banding issues with the 12" printers so there has to be some inherent issue with the design/components used in them. I think we will find it is a combination of things that are stacking up and causing the problems.

Understood..., and thx for the specific pointer to an SSR.

When I have an excuse to unseal my next spool of PLA..., gonna give it the blue tape vs heated bed test. And for sure..., a trip to Amazon for a new metric dial indicator is in the works.

And heck..., the SSR is probably worth it, even in bang-bang mode, just for the quiet.

[lakester]

Hey Chadd: would you be able to post A/B photos that illustrate the difference w/ heated vs not heated? It would be cool if for no other reason that it's kinda rare to see "smoking gun" diagnostic photos related to 3d printing!

I did this test with my printer last week. The Z banding was much better but I still had a periodic Z band spaced at ~.8 mm so to me that indicates that there is still some issue with hardware as .8 mm is the pitch of the threaded rods.

The banding with the heat bed on is horrible so I know that the heat bed is causing the majority of the issues.

I am just going to go down my list of things and try to get it taken care of, too many people are having banding issues with the 12" printers so there has to be some inherent issue with the design/components used in them. I think we will find it is a combination of things that are stacking up and causing the problems.

[Chadd]

Hey Chadd: would you be able to post A/B photos that illustrate the difference w/ heated vs not heated? It would be cool if for no other reason that it's kinda rare to see "smoking gun" diagnostic photos related to 3d printing!

Here is a picture, I am sure you can guess what one is with the heated bed on.

IMG_20150829_000447.jpg

These two were printed with the exact same settings on both, except the one on the left is with the heated bed on the one on the right is with the heated bed off. As I mentioned earlier even with the bed off I still have some periodic banding at .8mm intervals.

[lakester]

Now THAT illustrates the point..., thx!

Is that just the standard 24mm cube?

Here is a picture, I am sure you can guess what one is with the heated bed on.

IMG_20150829_000447.jpg

These two were printed with the exact same settings on both, except the one on the left is with the heated bed on the one on the right is with the heated bed off. As I mentioned earlier even with the bed off I still have some periodic banding at .8mm intervals.

[lakester]

Chadd: Another couple of questions:

Is the banding effect equal on the 4 vertical faces? Or is it equal on opposing faces? Just wondering if it's dominant on one axis or the other.

The other question: is your heat bed "pre" or "post" stiffener upgrade? (The ribs underneath the bed that Colin added after the warping problem became really apparent).

I ask because when I look at the 24mm cubes I first printed, they don't show anything like the effects you're showing. BUT..., not too long ago, I went around and did a general tightening of things, in particular the belts and x-carriage, and ended up with some artifacts I didn't have before. I haven't tried reprinting a cube since "the tightening"..., but I wonder if it would show something similar to what you're seeing now...

[Chadd]

Yes the banding is the same on all four sides.

I have replaced the wood heat bed mount with an aluminum one, my stock wood plate would warp so bad that the rollers would come in contact with the cross brace at the back of the printer.

Chadd: Another couple of questions:

Is the banding effect equal on the 4 vertical faces? Or is it equal on opposing faces? Just wondering if it's dominant on one axis or the other.

The other question: is your heat bed "pre" or "post" stiffener upgrade? (The ribs underneath the bed that Colin added after the warping problem became really apparent).

I ask because when I look at the 24mm cubes I first printed, they don't show anything like the effects you're showing. BUT..., not too long ago, I went around and did a general tightening of things, in particular the belts and x-carriage, and ended up with some artifacts I didn't have before. I haven't tried reprinting a cube since "the tightening"..., but I wonder if it would show something similar to what you're seeing now...

[lakester]

So your "y table sandwich" is the following, from bottom to top?

• aluminum
• cork(?)
• heat pad
• glass

I wonder if that "system" is just simply more responsive/compliant than with the wood. It fixes the big warping problem, but is more prone to the cycling error.

FWIW, I looked at the hysteresis management code in Marlin. I'd swear that my system operates exactly like the code would have it, if it were enabled..., which it supposedly isn't. Just the same..., it's a very dumb implementation, and not particularly tuneable..., doesn't seem worth fiddling with.

Enabling PID on the other hand seems like the way to go, maybe especially with an aluminum table.

Yes the banding is the same on all four sides.

I have replaced the wood heat bed mount with an aluminum one, my stock wood plate would warp so bad that the rollers would come in contact with the cross brace at the back of the printer.

[Chadd]

So your "y table sandwich" is the following, from bottom to top?

• aluminum
• cork(?)
• heat pad
• glass

I wonder if that "system" is just simply more responsive/compliant than with the wood. It fixes the big warping problem, but is more prone to the cycling error.

FWIW, I looked at the hysteresis management code in Marlin. I'd swear that my system operates exactly like the code would have it, if it were enabled..., which it supposedly isn't. Just the same..., it's a very dumb implementation, and not particularly tuneable..., doesn't seem worth fiddling with.

Enabling PID on the other hand seems like the way to go, maybe especially with an aluminum table.

Yes that is how mine is setup. I had the same banding issues with the original wood plate also, but if I had a long print the wood would warp enough to cause the Y axis to crash into the rear support.

[printbus]

A few closing comments before I try and stay out of this (really, I promise).

An SSR is an electronic device, not mechanical. I've already mentioned there is a functional difference between an SSR for switching an AC load vs DC load. Note that the outputs on an SSR for DC control have a polarity to them. This needs to be considered when you're wiring them up. I don't know from first hand experience if wiring them backwards will damage them, but they certainly won't work that way. Unlike (most) mechanical relays, the control input to a SSR are also polarized.

Being an electronic device, "on" resistance is going to be more of a concern that it was with the mechanical relay. I've read comments of some SSRs people bought for 3D printer heat bed use where they complain the on resistance was unacceptably high, even though their heater drew less than the SSR rated current. The more on resistance the SSR has, the more power you'll lose as heat in the SSR. Some SSRs state they need to be installed on a heatsink to operate at the rated load current, and that internal power dissipation explains why. If the SSRs you are looking at don't specify the on resistance, consider purchasing one for a higher current than you need. A 40 amp SSR will likely have less on resistance than one rated for 25 amps. Yeah, the heftier ones or ones that specify a lower on resistance will cost more.

In retrospect, beefing the hell out of heat bed wiring in order to reduce warm up time may have aggravated the problem. It could be that Marlin was inadvertently sort of optimized around a slower responding heat bed. All it would have taken is for the person developing the control loop to have an inefficiently wired heater.

For those comparing quality between printing PLA on a heated bed and printing on a cold bed, consider that there may be another factor involved in any difference that you see. I know that on some small prints of mine, heating the bed has seemed to add just enough residual heat that the PLA part never properly cooled until the print completed. This meant that the entire print involved layers extruding onto material that was softer than if I printed on a cold bed. Extruding onto soft material is another easy way to end up z artifacts. For example, I know I've seen this happen on 20mm calibration cubes if the infill is high enough. This may not be as much of an issue for ABS, but I've been surprised at what it can take for PLA to cool. Adding more heat from the print surface just makes this worse.