If you are experiencing the bed bouncing during feed moves, you are over extruding.
Not per se. Like @jkirgis says: It is always when doing waffle fills on empty spaces. I suspect the plastic tends to sag a bit at the crossings and starts to form a point upward, which after a while causes the bouncing.
Anyway, if that really is the Z bouncing up and down then I'm afraid I cannot help you.
I do agree on the bed being attached at 2 ends... And auto calibration etc 
Not per se. Like @jkirgis says: It is always when doing waffle fills on empty spaces. I suspect the plastic tends to sag a bit at the crossings and starts to form a point upward, which after a while causes the bouncing.
you've got it exactly.......now my question is how to fix it? The most I've come up with is ocassionally pausing it and trimmimng down the peaks, its a total pain but I just want to get to the end of this print. In the future, is there something I can do to avoid this issue?Design? print settings? Keep in mind that I'm a novice and have only been printing for two weeks...
I've never noticed this - I'm kind of surprised. How much bouncing are we talking about? What infill percentage are you using? I'm using 20-24% usually - at 25% the algorithm changes drastically.
Obviously one fix is to use 0% infill. I have found that works much better than one would think.
Instead of clipping you can raise the nozzle to 240C and lower the speed to 10mm/sec and it will melt those "peaks" down just fine. You could do that from the tune menu ever 10 layers or so or create a plugin that does this automatically.
But I've never seen these peaks as an issue.
A MUCH bigger issue is when you have overhangs you get raised edges - sometimes as much as a whole millimeter. The head can hit these raised edges and knock the part off the bed.
I've never noticed this - I'm kind of surprised. How much bouncing are we talking about?
Do you know what a drumroll looks like? Well... that
It doesn't happen very often with me but indeed, if it does I usually up the temp and slow down until it recuperates. Haven't been able to consistently reproduce it.
A MUCH bigger issue is when you have overhangs you get raised edges - sometimes as much as a whole millimeter. The head can hit these raised edges and knock the part off the bed.
I so hate that and it's like every heavy overhang. But there it's slow speed, lower temp and up the fans if you can. That helps a bit, but not always.
But it seems we've hijacked @lars86's thread a bit 
It sounds like the bouncing over sparse infill is a result of the force generated between the molten filament leaving the nozzle and the printed part. If the printing speed and infill spacing set up a frequency that resonates in the bed assembly, it could definitely be amplified. In that case, stiffening the bed will change the resonant frequencies and could help the issue. It is not going to help the collision with a curled up, cooled portion of the print, so that is probably solved best in its own thread.
@lars86, I've not noticed this bouncing before - it sure is clear in your video. I will keep an eye out for it in the future. But there are settings:
ZACC - Z acceleration and ZJERK settings that you can play with - I think maybe they can be messed with DURING a print in the TUNE menu. If not hopefully they are in the motion menu. If not you can mess with them with gcodes. If you don't do a M500 they go back to default on the next power cycle which is probably desirable when experimenting.
Anyway I would set the ZJERK to zero and lower the ZACC by a factor of 2 or 4 and see if that fixes your bouncing.
On the UMO which had a wood bed this was more of a problem. Some people added a weight - typically a one pound hunk of metal underneath the front edge. This also changed the resonant frequency.
I remember increasing my Zspeed and Zacceleration to have less z scarring and faster performance, I'll have to look into that as soon as I install my HBK!
@lars86, I've not noticed this bouncing before - it sure is clear in your video. I will keep an eye out for it in the future. But there are settings:ZACC - Z acceleration and ZJERK settings that you can play with - I think maybe they can be messed with DURING a print in the TUNE menu. If not hopefully they are in the motion menu. If not you can mess with them with gcodes. If you don't do a M500 they go back to default on the next power cycle which is probably desirable when experimenting.
Anyway I would set the ZJERK to zero and lower the ZACC by a factor of 2 or 4 and see if that fixes your bouncing.
On the UMO which had a wood bed this was more of a problem. Some people added a weight - typically a one pound hunk of metal underneath the front edge. This also changed the resonant frequency.
Yes, those settings are available to tune during a print, but really they would be just a bandaid for the real issue: a lack of platform rigidity.
Z jerk, accel, and velocity should be tuned in order to give clean crisp motion without missing steps or causing the print head to dwell long enough to scar the print.
The platform should be stiff enough to accommodate the tuned Z motion without excessive flex or resonance.
I used to have a big chunk of weight glued under my original bed to lower the resonance. I actually think that the original platform was stiffer despite being wood. It had a FAR taller aspect ratio.
Before I added the HBK my wooden bed would droop easily .1mm every day and I would have to relevel constantly. Partly because I had a heavy home built heater. Now it stays "level" consistent for a month no problem.
Before I added the HBK my wooden bed would droop easily .1mm every day and I would have to relevel constantly. Partly because I had a heavy home built heater. Now it stays "level" consistent for a month no problem.
I believe it. Though, that "creep" you had in the bed was a result of the wood changing with its environment. The new aluminum bed is far more environmentally stable, but a less rigid structure. Even though it sags more, the sag is repeatable and can be tuned out with bed leveling. The bouncing cannot.
I finally tore my build platform back apart for modifications. I used two 12" sticks of .75"x.75" aluminum angle stock from McMaster Carr to stiffen the assembly. I found them to be pretty flat out of the box, but I went ahead and gave them a sanding on my granite block to ensure I wasn't forcing the bed to conform to a curved surface.
Installation was a piece of cake. I used three M3 bolts on each brace, through-bolted into M3 nuts, to avoid relying on tapped aluminum threads. There were already two thru-holes in the bed platform that I made use of for the frontmost and rearmost bolts. Once those two bolts were secured, I drilled a 3rd hole through the bed and brace, in the middle of the span.
While I was at it, I drilled two more holes in the platform, at the Z nut mounting position, to allow use of an anti-backlash nut I got from Robotdigg (for Tr8*8 Leadscrew). It ends up with a slight amount more friction (which I think will come down after break in ), but in return you ensure the Z position is more repeatable. This is especially helpful during Z reversal moves (like Z hop on retract), when this style linear bearing has a tendency to bind slightly.
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I had an issue at that time which ruined the print quality (horizontal banding caused by the bang-bang mode of the heated bed).
Was this an issue with your UM2 as delivered? Did you have to modify the firmware settings to fix this?
@lars86: Yes, the bed is set to PID mode since then.
Did you uncomment just "#define PIDTEMPBED"
or "#define BED_LIMIT_SWITCHING" as well?
@lars86: Yes, the bed is set to PID mode since then.
Did you uncomment just "#define PIDTEMPBED"
or "#define BED_LIMIT_SWITCHING" as well?
Just the first.
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Would there be any benefit from switching the Z microstepping from 8 to 16 after the bed upgrade? It's quite a bit faster pitch.
Would there be any benefit from switching the Z microstepping from 8 to 16 after the bed upgrade? It's quite a bit faster pitch.
Noise is reduced.
Thanks man. Since Z moves are fairly sparse, noise isn't a big concern for me. I'm thinking more about higher velocity/accel, or better precision for thin layer change moves / microstepped spiral vases.
Some questions:
- Has anyone used an anti-backlash nut in general or specifically on this new Z screw? http://www.robotdigg.com/product/18/Anti-backlash-Nut-for-Tr8*8-Leadscrew
Yes, I used the exact anti-backlash nut on my UM2 which has the same heated bed. But I had to dismount the black part of the nut and mount the UM2 nut instead. And a printed adapter piece was needed.
Is this design published anywhere???
Most probably not. But I can put it on Youmagine. Please remind me if I don't do it within one week.
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lars86 42
If you are experiencing the bed bouncing during feed moves, you are over extruding.
This bouncing motion in my video is purely a result of Z layer change motion.
I do think it is possible to have a bed supported at both ends and achieve a high level of quality. It's a bit more complicated than its worth though, I think.
Simply stiffening the platform is pretty easy.
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