5th Gen build plate too low despite Z offset

[Eric Schimelpfenig]

I've got a 5th generation MakerBot replicator that I've been having problems with getting the build plate high enough...

I run through the build plate leveling procedure with the Z offset set to default. My nozzle ends up way to far away from the build plate.

I incrementally set the Z offset lower and lower -.1mm all the way to -.4mm, the max. At -.4 it's closer, but not close enough. I even added BuildTak to the build plate which is thicker than the blue tape and it's still too far away. Outside of manually dialing back the leveling knobs does anyone have any suggestion?

I know that Z offsets are something that needs to be adjusted from time to time, but I feel like there's something wacky going on with my machine that I need to have the adjustment so far out and I still need more... Has anyone else run into this?

I'm in contact with Makerbot support. So far we've tried a new extruder and that had no effect. I'm fine with fixing it myself, so far support hasn't been able to figure it out so I figured I'd ask here.

[TobyCWood]

Rotate the adjustment knobs.

[Ryan Carlyle]

I think what Toby is saying is to use the assisted leveling system with the knobs cranked down, then when the print starts, loosen them back up to raise the bed as needed to get the first layer or raft to stick. You wouldn't be the first person to do that.

Adding thickness to the build surface won't help in this case, because the printer uses nozzle contact on the bed for Z height control. 

If you've replaced the smart extruder, that probably eliminates issues around the hall sensor that detects nozzle height. Could be a wonky firmware issue with some kind of hidden offset. Have you updated firmware?

Is your bed mechanically functioning properly? Pretty well flat against the gantry plane? Not excessive drag when moved up and down?

On Sunday, August 28, 2016 at 2:01:05 PM UTC-5, TobyCWood wrote:

Rotate the adjustment knobs.

[Jetguy]

Something you should know, leveling is wonky compared to systems you might be familiar with.
On the 5th gen, the bed has a "universal joint" connection in the center of the bed, then springs front and back and left and right, but only 2 adjuster screws front and right.
Because the system uses the nozzle actually hitting the bed to "home" that sets the distance.
What I'm saying is, on older bed systems and other brands, leveling screws can both adjust overall bed height, as well as leveling
On a 5th gen, they can ONLY affect leveling of the surface.

Being honest, it's the cheapest piece of junk. That central joint is a pin that nothing more than friction holds it in place, It's quite possible that pin slide out and if the center joint isn't right, then you will have a wonky floppy bed that just isn't going to level or be stable.
I need to post the extensive rebuild mod and heated bed I added to the one from Jeff. It's been a project collecting dust, but all the hardware mods made it 10 times better than stock.
Here are some not great pictures of that rebuild https://www.flickr.com/photos/90025904@N04/25219154124/in/album-72157665975635936/
The heated bed is a 200x300mm aluminum heater PCB style I bought so long ago I forgot where it came from. I mounted 20x20 extrusions directly on the steel subframe of the Z stage front and back, and then used 1/8th inch aluminum stock to make 2 mounting bars so i could use M3 long leveling screws and thumb nuts. It's cheap and extremely effective. I also needed this extra lift or space up from the Z stage to hit the now non-smart extruder mounted directly to the gantry using an aluminum right angle NEMA17 bracket.
Consider it like this, I ripped out EVERYTHING, all electronics, the smart extruder, the stock bed, had to drill and brace the back Z frame. I coated all metal with Dynamat (asphalt car sound deadening sheets).
I plan on running with DUET +PanelDue in place of the 5th gen electronics.

Entire album is here https://www.flickr.com/photos/90025904@N04/albums/72157665975635936/with/25219154124/

[Jetguy]

I do want to give some tips on this. Look, yes, I'm jaded against 5th gen only because it simply is a step backwards from previous designs.

When you own this machine, you bought into it, you might be stuck with it and lost a lot of money and time and are frustrated.

So back to the problem at hand, the 5th gen homes using the nozzle. Basically, the entire lower hotend "floats" inside the smart extruder housing. If filament is loaded, or there is melted plastic or any number of mechanical issues, they can determine how well that nozzle can rise and fall inside the smart extruder and that is critical for the homing sequence. Adding to loss of precision is there is a separate plastic molded part that sits on top of the heatshink fins that holds the magnet that is used to detect the movement via a hall effect sensor. Because the entire hotend is not one single piece with this magnet attached, and instead, there is nothing more than a mechanical not even press fit connection, it's simply help by spring pressure, there are hundreds of ways this can go wrong.

So really, observe or make a video of the homing sequence from a side view of the nozzle Try to determine is the nozzle is freely going up and then returning back to the same position. If there is melted plastic in the cone shaped seating area, this could be one cause of it hanging up.

Try a different smart extruder if you have a spare.

Double check that universal joint pin I described in the center of the bed under the glass.

Make sure all the springs are under the bed and didn't fly out.

Try to wiggle the bed in various directions and see if there is any extra slop.

[Eric]

Thanks for all of the advice... So what I've been doing to solve it for now is to run the leveling process and then to just back each knob off an equal amount. This works for me personally because I understand what's going on, but this printer is setup in a school library where less experienced people are going to be using it so I want them to be able to follow the standard instructions and get it level.

Good note about that universal joint. I'll check that. I did wiggle the bed and check for excessively lose bolts and everything seems to be tight... 

How do you start pulling the bed off completely? Are there nuts under the bed that you remove?

JetGuy, that's an awesome rebuild. I'd honestly do that if I didn't already have a few other more reliable printers around (that includes my original Rep Dual!)

--

-Eric

[TobyCWood]

I was able to adjust the bed height for removal of the tape and using just glass and Aquanet using the SW based offset (which it seems the OP has already done) then an additional adjust of the knob, but NOT during the height adjust procedures in the onboard FW. Instead I eyeballed it by turning the knob to the left to get the bed closer. IOWs I had to bypass what MBI thinks I should do so that it would actually work. If I did it per the programmed procedures it never got close enough.

It's amazing to me how the Rep Gen 5 seems to do so well at pushing the buttons for perceived quality, even to an Engineer (who is not well versed in 3D Printing), yet is such a poor design. Everything on the surface looks so good yet it really sucks. If I was still teaching I'd do a lecture on comparing a well done i3 to a Rep Gen 5 as a exemplary case in design focus.

[Jeff Davis]

Before I sent my Gen-5 to Jetguy I had a few nozzles that were doing the same thing, trying to print too high.  What I did was to move the nozzle its self down by getting the extruder hot then pull the extruder assembly off the mount and loosen the brass nozzle about a 1/2 turn then use a rag (it's hot) and turn the aluminum cooling fins down against the brass nozzle and re-tighten the brass nozzle against the feed tube.  Sometimes these "smart" extruders don't get built with the correct distance set.