Slop in the smooth rods bushings

How much slop should be in the smooth rod bushings?

I purchased a used Mini and when I set my layer height to 1.0mm I noticed after a while that my the head was bouncing up & down like a car down a dirt road. I stopped the print because it looked so bad, then I noticed there seems to be a lot of slop in the bushings.

How do I know what is proper amount of slop?

How do you remove/replace them and what is the recommended replacement parts?

I tried to do a search for this info, but the search engine ignored nearly every word I tried, sorry if this is a common issue.

Thank you.

I can’t give a quantitative answer to that question, but based on a couple other statements I’m wondering if there might be a different explanation for the print problems you saw.

Did you really mean 1.0mm here? The stock mini nozzle is 0.5mm, and it’s generally a good idea to keep layer height below 80% of that, or 0.4mm at most. Trying to create 1.0mm layers probably won’t work very well. Or did you mean to say 0.1mm?

Do you mean the head was riding on the previous layer, bouncing up and down from contact with the print? That is frequently a sign of over-extrusion. Have you calibrated E-steps? Entered measured filament diameter into slicer? What extrusion multiplier? This could also be a mechanical problem, like Z-axis not moving correctly, but over-extrusion would be my first guess.

Not sure what behavior you are actually seeing, so I may be completely off base – and it may indeed be a bearing slop issue. Could you post a photo of a print, or even better, a video?

I’d have to agree with ScottW. The nozzle dragging along the previous layer can cause bumps/rumbling sound. Overextrusion can be a cause or the nozzle could be too close to the bed initially. The nozzle can extrude wider than the nozzle opening, but layer height should be kept smaller than the nozzle diameter.

To make sure the Mini is auto-leveling properly, clean the nozzle and probe points… also check the wiper (flip to use the other side).


Manually move the tool head and bed with the motors off to check that there is no binding. If there is binding, it could be something simple as a slightly skewed bearing holder creating more friction than necessary.

ScottW, you’re right, I meant 0.1mm layer height. The over-extrusion makes a lot of sense. I need to research more on calibrating, I don’t know how to calibrate my Mini yet. I’m such a newbie at this, I’m sorry.

I have a design that I’m working on, and noticed when I used the default Cura high detail profile, that I had bubbly/pimple area on the print. So I was playing around with the settings to reduce the layer height and make a better quality print. But, part way thru the print is when I noticed the bouncing, and cancelled the print. The over-extrusion makes complete since.

Attached is a pic of the first print, using the default high detail profile, that has pimples on the exterior surface. I don’t have pic’s or video of the 0.1mm part.

Is there a good video or step by step instruction on how to calibrate my Mini w/Cura?

Yes – That area of your print looks like over-extruded. But it also appears that the first layer seems more squished towards the left than on the right (and you’ll notice the over-extrusion looks worse towards the left, too). That really shouldn’t happen with the mini if the bed leveling is working properly. Does it seem to be probing the washers correctly, and not pushing them down at all? Being too close to the bed, either because the leveling isn’t working right or because the z-offset is wrong, can also cause similar extrusion issues particularly in the first few layers.

Lulzbot has a step-by-step procedure for E-Step calibration here:
https://ohai.lulzbot.com/project/extruder_calibration/calibration/

That procedure is for a Taz, but the principle is the same. Ignore the stuff about the feed tube and LCD, since the mini has neither. Also, I recommend using an extrusion speed of 50mm/min rather than the 100mm/min stated in the procedure, as 50mm/min is closer to typical printing extrusion rate. Once you have the new number, use the M92 and M500 commands as described in step 7 to store them.

From reading threads here, most people seem to end up with an Estep value around ~800 for the mini. The default from the factory (in firmware) is 833. Aside from the Estep calibration, it is really important to measure your filament diameter and enter that into Cura. I think the Cura profiles have 2.85mm for the mini, so if your filament is larger (say 2.95mm) you’ll get over-extrusion unless you enter the 2.95 into Cura.

To answer your original question:
There should not be any noticeable play between the bearings and rods. It’s normal for the Y (bed) and X (tollhead carriage) bearings to wear with use. Fortunately, replacement bearings are inexpensive and easy to replace.
LulzBot sells them https://www.lulzbot.com/store/parts/solid-polymer-bearing-rjm-01
We have them too https://itworks3d.com/product/solid-polymer-bearing-igus/?v=68f7689e853d

As a side note, make sure the play in the bed is actually “bearing to rod”, as we’ve see the screws that hold the bearing retainers loosen, which also causes similar play. Those are easy to tighten.

I’ve gone through the calibration steps as the Lulzbot web page says, but there is issues with it. The web page says to use Pronterface, but it’s not available on their web site, and I’ve only started using Cura. I don’t see a way that Cura allows me to set a extrude amount of 100mm or adjust the speed rate. I can only tap the extrude 10mm button ten times to get 100mm of extrusion, but I don’t know what speed that is.

Thank you for the suggestion, I’ll measure the diameter of the filament to verify what mine is. I’m very new at this, but my gut is telling me that it’s over-extruding. I was able measure/mark the filament, and in Cura, I was able to tap the extrude 10mm ten times to get 100mm, and it was right on the money. But I wasn’t able to control the extrude speed. If it was wrong, I don’t know how to have Cura adjust the firmware.

My hope right now is that my diameter of filament doesn’t match the Cura setting.

I’ll try to video the play that I’m seeing in the bushing, then post it here to get your feedback. I’ll also check the screws and other bushing too.

Thank you all for your help in trying to work this minor issue out with my machine. Aside from this issue, I love the technology that is at our finger tips!

You can use Gcode to perform the extrusion at desired speed.

Preheat to extrusion temp, then enter the following three commands in the Cura control window. You will enter them in the field at the bottom right of the control window, hitting enter after each one:

G90
M83
G1 E100 F50

That third line commands extrusion of 100mm at 50mm/min rate. You can change those two numbers as desired.

Here’s a good source for more information on Gcodes:
http://reprap.org/wiki/G-code

That’s what the M92/M500 commands do (see step 7 of the procedure referenced earlier). M92 will let you set a new “active” value for E-steps, and M500 saves that value to memory so it isn’t lost when the printer resets/restarts.

Thank you for your help, so far the calibration info has helped, but I would like to get back to the subject of the thread. I have very noticably play in the bushings. To me, there is so much play that I almost wonder if they have the 10mm bushings installed instead of the 8mm :laughing:

I was hoping to upload a short video to the thread, but here is a link to it instead. https://youtu.be/ISSCPMFMPTk

Let me know what you think.

Thanks :smiley:

I watched your video. Those bearings do look a bit worn, but probably not enough to cause any significant print problems. Even brand new, putting pressure in one direction can be expected to produce a tiny “gap” on the opposite side. But I’d say your bearings show maybe 2-3x what I would expect from “new” bearings.

Here’s a shot of my lower X carriage bearing. This printer probably has about 200hr usage on it. You’ll see there is a little play, but a lot less than your video shows. I haven’t experienced any print issues from this.
http://youtu.be/BiNb1iO4lag

Thank you ScottW! That amazes me that these machines have so much play in them.

But should I replacement???

My opinion (and it’s just an opinion)… Just because they deflect and show slop when pushing on the carriage by hand, doesn’t necessarily mean the carriage won’t track just fine under normal operation/extrusion.

So what I would recommend: Get the extrusion rate (e-steps, diameter) dialed in, then use a standard Cura profile to run some calibration prints (the typical cubes and such). If they look good, then no worries. On the other hand, if you see some artifacts, post pictures and ask for a diagnosis from the folks here on the forum. If someone pops up and says “that’s caused by worn bearings” then it might be time to replace them. :slight_smile:

My Mini came with considerable play in the X and Y bearings when it was new.

What I did (as mentioned in another thread), is to loosen the bearing holders and tilt them. This puts pressure on the bearings and removes the play.
You have to be careful not to put too much force on them.

The four leveling washers need to come off along with the bed. Then you can get to the X bearing holder screws.
The print head has to come off to be able to loosen the Y axis bearing holders.

With both, loosen one bearing holder and put side pressure on it. Then tighten the screws. It takes a few tries for me to get it right without binding.

I have done this twice now. No slop at all after it’s done, even with loose bearings!