Bed Stability Issues. (Page 1 of 2)

I actually manually perfectly leveled the bed (+- 0.05mm). The Z stepper motor doesn't move during layers now. The shake is coming from the bed being 'loose' and sharp print head movements applying a bunch of force to the whole rig. I think I need to devise a way to make the bed more secure.

I did see a bit of dragging on the previous layer during the first few layers. But the rest of the print seemed fine. I think the bed shake is coming from the whole printer shaking, not so much the print head pushing the print. If that was the case, I'd expect to see movement on the bed at other times, not just during sudden print head velocity changes.

Yea I can easily push it up against the direction it is normally tilted.

the bed is connected to a plastic block and the block has a brass looking threaded connector on its top that the Z axis threaded rod uses to raise and lower the bed. There is nothing on the bottom of the block to guide the rod and enough of a gap around the threaded rod the bed tips

I was wrong on part of it. It is a metal box that the bed mounts to but it has a plastic insert that the threaded rod goes thru on the bottom

First thing I did when I received my Press was to wipe off the thick lithium grease they applied to all moving surfaces.  Then applied light machine oil (3 in 1).  Machine is much smoother than it was at first, as it would hardly move.  Don't forget to oil the z rod also.  I don't know if this will void their "warranty", but at this point, I don't care.

I had similar Z axis issues - up was fine, but down set the bed vibrating, prints were bad.
  The front end of the bed would jump up and down 3-4 mm, pretty nasty.
  Removing the glass changed the frequency and amplitude, so it looked like just a nasty resonance.
  Tried a simple bed stabilizer and antivibration feet under the printer, but that didn't really solve it.
  Tried lifting the front by hand just a bit, vibrating stops. A clue!
  Also bed took way too long to heat to 90C, couldn't get to 100C.

There are no linear bearings in the bed support, and that 10" long bed puts quite a tilting force on the rods as they slide through the 2" long plastic holes. Combined with the grease as shipped, bed was binding, not moving freely.

Diagnosis:
1. Raised the bed to the top, reached underneath and undid 2 screws right at the front, removed the black plastic part at the front of the bed. It has no structural function I could see, and it adds more weight at the front, making things worse. So it stays off.
2. Removed the z axis cover (2 screws near top of rods, then some twisting).
3. Lowered the bed to the bottom, removed the 4 small screws holding the brass z axis nut, spun it up to the top of the rod.
4. Now the bed can be raised/lowered by hand.
5. Easy to see the issue - left alone the bed sticks, it doesn't slide down.
6. But lift the front just a bit to relieve the tilting moment that binds, bed drops like a stone.
7. It seems the stock grease is not good enough at overcoming static friction.

Fix 1, more heat:
1. Noticed the heater mat wasn't completely stuck to the bottom of the bed, rubbed that back on.
2. Cut a piece of 1/2" fibreglass acoustic ceiling tile to fit under the bed, peeled off decorative plastic layer that might melt
3. Wrapped it in a layer of aluminum foil to stop loose fibers getting out, stuffed it under the bed.
4. Now bed heats faster, gets to 100C - that plus a layer of Monokote and hairspray on the glass  means stuff sticks now!

Fix 2 for vibration didn't quite work:
I wiped off the stock grease and spayed on a Dupont dry lubricant with teflon. That was slightly better, and now occasionally the bed would slide down a bit under its own weight. But if I push down where the acme nut was attached, bed still vibrated going down.

Fix 3 for vibration worked:
1. After some thought, pulled out my automotive moly bearing grease and used that because it is designed to slide under high pressure.
2. Applied it all around the z rods, made sure some worked into the bearing holes, lots of sliding the bed up and down.
3. Bingo - now the bed now slides slowly down when released. Push down and it just goes faster.
4. Reattached the acme nut and the z axis cover - and motor driven up/down motion was smooth, no vibration!
5. I'm aware auto grease may eventually eat the bed plastic, by then I'd like to have a redesigned part with linear bearings.

Tried a Bender head print from Thingverse, and FINALLY got a decent print.
The ABS stuck, and the bed didn't!

I think the Press is especially vulnerable to a sticky Z because it relies on active compensation for bed tilt. It's easy to see that even while printing one layer, the bed is always moving slightly up and down.

When the z axis is sticky, that just causes vibration which:
  Looks like the extruder needs calibrating 'cause lines get wobbly
  Looks like the acme nut needs anti-backlash, but really the nut should be loaded by the platform weight- but it ain't if it sticks
  Looks like bed pulldown springs are needed - but they shouldn't be
  Looks like manual bed leveling helps - but it only does because now there is less z axis motion.

So...
1. Wipe off the shipped z axis grease, it's NFG
2. Apply a grease designed for high pressure (auto moly worked for me)
3. Get rid of the excess plastic weight bit at the front
4. Stick the bed heater down, insulate it
5. Use a Monokote covering plus hairspray.
6. Use a 100C bed and a 235C extruder.
7. Long term replace the plastic part of the bed with a new piece with linear bearings.

So my cold vibrating bed is now lubed and hot and sticky. 3D printing or porn?

Might be missing lube near the top of the travel range.
During startup the motor pulls the bed up, leaving the screw biased to pull nut up.
When printing starts, threaded rod turns slightly, expecting platform to drop a fraction of a mm.
But...if the bed is sticking - and the nut does have dead space - it may take a mm of "down" threaded rod turning before threads engage the other part of the nut and actually start pushing down.
And in that time the extruder is adding layers - but the bed hasn't started moving down yet.

If the bed slid down on its own weight, or springs pulled it down, no problem.

Make sure you get the old grease off and the new grease on right to the top of the travel range. Temporarily unbolt the brass nut and spin it up out of the way. See if the platform slides down under its own weight - if not, try a different grease.

Do you realy know why they have litium in first place ? its because we dont have any metal bearings or bushing.  its all plastic exapt for z brass thing..

i if apply  light oil then need know that its not harming the plastic parts  lithium is good for plastic

some oils can harm plastic    we have metal rods and plastic carriges only.
i use lithium grease only

"there is no plastic or metal bearings/bushing on x y" !!!!

So. Would something like this be worthwhile for us with the Press?

Also. What material would be the best if I wanted to make some flanged bushings that would slide into the holes in the z axis carriage here? I was going to drill the holes out a bit to get the bore in them smooth, then turn a few flanged bushings in the lathe so they are a press fit.

Bearings would be much harder to pull off given the design of the carriage, since they need c clips to hold them in and all. Also, as you said, the whole thing with needing to possibly replace the rods with bearings, I'd prefer to not deal with.