@pesce Interesting fix, do you see platform banding when moving up and down z?

Thanks!

I'm not quite sure what it's called specifically...  The print walls would have a deep and predictable sinusoidal pattern perpendicular to the bed.

The picture in my first post shows it pretty well

thing verse com/thing:34397

To my setup with the springs going from the front bed leveling screws to the front bottom case screws. I used a short compression spring in conjunction with this object.

All is well again with my printing!

Makes me wonder if my springs are doing anything.  I'll let you know.

That throws all physics out the window.  I can't think of a reason that when they are attached to the top it is perfect,  but when they are on the bottom it goes to hell. 

Any thoughts?

Congrats on exploratory work!

My only concern is that using springs makes the loading force dependent on the bed position, increasing the strain on the bed as it gets lower.  Using something that provided a constant force seems like it would be safer.  Perhaps the spring could be attached to an arm that was threaded onto the rod at one end and pulled the bed from below.  Alternatively, someone in the past has suggest just weighing down the bed.  It seems like hanging some lead weights off the near end would have much the same effect but would provide a constant force downward.

Thank you!

I totally agree,  I've been trying to dream up some rigging device.   I used 2 pound springs,  but if they are fully extended they have a lot more force than what is needed. 

I don't think hanging weights will have the same effect because it doesn't provide lateral support like the angled springs. 

I'll give it a try though!

It seems to me that this is very similar to some of the spring loaded anti-backlash devices, except by loading the bed you not only reduce play in the main rod but do the same for lateral movement in the bushings at the same time.  I personally hadn't noticed a lot of banding that I would expect from horizontal movement (shifted, like a wobbly stack of coins instead concentric rings of differing size) but anything that removes looseness from the system sounds like a good idea.

My only concern is that using springs makes the loading force dependent on the bed position, increasing the strain on the bed as it gets lower.  Using something that provided a constant force seems like it would be safer.  Perhaps the spring could be attached to an arm that was threaded onto the rod at one end and pulled the bed from below.  Alternatively, someone in the past has suggest just weighing down the bed.  It seems like hanging some lead weights off the near end would have much the same effect but would provide a constant force downward.

Awesome tips 3dcad!  I haven't printed anything large enough to notice yet,  I think I'll try to run the springs to some new holes on the frame base and see if I get the the same results without the risk of running into the springs.

Thank you!

All you engineer types... Am i going to break something?

I have seen my extruder hit the bolts on the Y axis several times. As far as I can see your extruder can also bump into one of the springs.

Also you might want to put a extra nut on the y axis end stop bolt to prevent the spring from slipping off.

I'm no scientist..  But correct me if I'm wrong, the basic issue with a bent rod or even the minutiae of backlash is the print bed moves left, right,  forward and back during the z axis change.  This is due to all sorts of physics that have been explored in depth by other people. 

Solidoodle tried to combat this issue with two smooth z axis rods,  which in a perfect world would have eliminated the wobble.  (I'm using the term wobble generically)

But due to the play in the bed bushings relating to these rods,  the wobble remains. 

The wobble is there because of the play in the bed, you never know where the bed will settle after a z axis change.

I played with the print bed while I printed,  and noticed the wobble was reduced significantly when I pressed the front of the bed to the extreme up,  left, right or down position. 

This is due to when I pressed on the front of the bed,  it maxed out the play in the bushings.

I figured I could get the same effect using springs. 

I decided to mount the springs like I did,  simply because of the availability of the bed leveling screws and the front belt screws. 

I'm sure you would get the same effect if you were to drill holes in the bed support and the bottom of the frame. 

The springs simply remove the play in the bed bushings.  Therefore removing the wobble. 

I'm thinking of removing the springs and using two adjustable braces that press on the smooth rods and force the bed to one of the z extremes. 

I think this will work because the rods and the bushings are circular and if you push hard enough,  the bed will settle in a predictable location

I noticed when I moved the z axis up and down, my rod was bent.  The motor rocked on the base and the top of the screw/bolt wobbled as much as 1/4".

I read a ton of information on the forums and wikis..

I tried the thingiverse thing:36177 part plus a 2" tall  5/16-18 nut.  (nothing changed)

I updated the firmware solidoodle.com mlaws-solidoodle2-marlin-6dc60f1-October-12-2012.zip (slight fix for the wobble)

I noticed some slight play in the print bed bushings and the smooth z rods.  I could move the bed front up, left and right.

Ultimately I decided to attach springs to the bed leveling screws and connect them to the front axis belt screws.  This removed the play between the 4 bed bushings and the z axis smooth rods.

The result is an almost perfect print.  (Top before, bottom after)

I am going to experiment with this further...  but it was an instantaneous drastic improvement.

All you engineer types... Am i going to break something?

I am thinking of replacing the springs with a brace/support that will push against the smooth rod and force the bed front up...   something adjustable with a scew

What do you think?