My Z-axis drive is giving me problems when printing large objects. Halfway it tends to skip a few steps because the friction is simply to much.
Yesterday when I took a quick peek I saw again my object of 5.5 hours was smashed of the printbed at the very end. I knew it was my Z-axis because I could see brown scourch marks…again.
This “issue” is starting to cost €€€. Normally when a print survives the 1st hour it will come out just fine. But now -_-"
ATM I have the stepper driver at 0.61V. As that motor doesn’t have to turn longer than 0.3 seconds I don’t fear it overheats during a print.
I tried everything between 0.55V and 0.65V and I have the feeling that the friction is getting more.
Is it recommendable to use machine oil or WD40 on the spindle?
Do/can I buy another compatible stepper driver?
Should I build in another spindle on the other side to reduce friction by lifting the extruder bar from 2 sides?
If you have the stock K8200 Z axis drive, then some adjustment will normally be required. If you do it well, then you should be able to get very good prints.
A lot of the trouble is the bent aluminium piece that holds the motor. If the bend is not quite accurate, then the screw thread will jam up. When I first assembled my own, I discovered that the motor was held at a slight angle to the frame, also the motor spindle was not the same distance from the frame as the top bearing.
I suggest that you put a block under the extruder arm to hold it up, then loosen off the plastic block that is attached to the extruder arm that holds the drive nut. Next, undo the nuts that hold the top bearing, and slide this up out of the holder. The threaded rod should now be only held by the motor at the bottom. The plastic drive block should be free from the arm. Now, does the top of the threaded rod come through the centre of the top bearing holder. If it is resting against the side, then the motor bracket is not accurate, and this will put a lot of tension on the motor. Just check by rotating the motor that the spindle is not bent. It needs to be as straight as possible. Then the motor bracket has to be bent until the threaded rod comes through the centre of the top bearing bracket. When this is done, measure the gap between the spindle and the frame. It should be the same measurement at the top as at the bottom. If the spindle is not parallel, then either the top bearing bracket or the motor bracket needs to be shimmed out until when the spindle is parallel and still in the centre at the top bearing holder. With the bearing back in place, the motor should turn easily. The next thing is to look at the plastic block holding the arm drive nut. Generally this needs to be shimmed out. It should be just rubbing against the face of the arm attachment plate. If there is a gap, then add shims until you can tighten this up against the plate without bending the threaded rod. The motor should still turn easily. If it has got tight, then something is still out of alignment.
You have to be very patient doing this, but when it is right it should work well.
The other alternative is to use ichbinsnur’s ideas. This will get round any misalignment by hanging the rod from the top, and not having a bottom bearing. Even with the normal threaded rod, this idea will improve printing.
Sorry if this is a bit long winded, but it is a bit difficult for me to describe easily.
Have fun
It sounds not very realistic that the Z-motor is loosing steps. The movement in the z-direction requires very little torque.
I think that your problem is related to the phenomenon I have describe a few days ago.
First thing to do before printing anything with the stock printer is replacing the rigid Z-axis coupler by a flexible one.
And some shimming, as mentioned in other posts.
The axis will move much smoother then.
I used some feeler gauges (about 0.3 mm) under the plastic nut-support, see picture (I use a trapezoidal axis)
First the most important: The locknut on top of the spindel was not touching the top bearing, so all the weight was pressing directly at the motor axle. When I screwed the locknut on the bearing, the axis was somewhat smoother but still not well enough.
Second, I noticed over time that the problem became worse. I replaced the aluminium bracket of the motor by a printed one with flexible attachment holes thingiverse.com/thing:361064. Now I see the motor wobbling during Z-axis operation. That is a good thing because now the spindel is not wobbling. I am convinced that the wobbling is now caused by the Z-axis coupler and I understand now why I should replace it.
Third. I also replaced the part on the extruder arm with the nut, by 2 printed parts which allow for a little backlash thingiverse.com/thing:304424. I didnt have an extra nut and spring which I should use according to the thingiverse page. But I think that is totally redundant. If the spindle is through the 2 nuts it is a bit useless to put a spring in between IMO. I do not think that this part was wrong in any way, but I must say that that object did wear out and the motor was black of the black stuff but this could have been because of the wobbling.
Fourth: the top plastic part which holds the top bearing is perfectly fine and does not need to be replaced with anything. Unfortunaly I already printed something for it and now I will never use it
My conclusion is that the problem was caused by 2 things, namely not having the top locknut reducing the load of the motor and the crappy motor-axis coupler and I think the first problem lead to the second problem. The only things which were truly needed were to replace the coupler and turn the locknut on the top bearing. Instead of replacing of the faulty coupler, the new flexible motor mount solved the problem. I am still in doubt if I should have replaced the nut holder on the extruder arm, like I did. Butt I guess I will never know now
Now I have a perfectly fine working Z-axis I am wondering why people create such complicated things such as a 2nd spindel, a cable system or the upside down hanging Z-motor. Though it would propably work slightly better when your extruder arm lifts itself on the filament. but as I dont have that problem it is unneeded IMO.
The 1 expansion what would be somewhat sensefull would be a holder for a 2nd bearing with locklut right on top of the motor. So that the entire weight is distrubited over this bearing and the top bearing. Than the axis coupler would propably not bend at all and the motor axle wouldnt be under any stress.
The only thing that leaves me to do is to print a holder for the filament coil as that coil tends to resonate and produce noise during the Z-axis operaion
Nice work! Having just installed the Z-axis upgrade kit, I also have come to believe the flex motor coupler is the key ingredient to smoothing the z-axis.
The zero-backlash part does want to have a spring installed, because this forces each nut to act against the threaded rod in a different direction to eliminate any gap between the threads.
But I think zero backlash is overkill on this printer design, and may actually be counter-productive. First, any vertical backlash will be countered consistently downward by gravity, so the spring and nut are not adding that much more downward force. But also, backlash is usually only a problem if you are doing a lot of back-and-forth motion on an axis, or if you have back-pressure against a CNC tool and the part being worked which is not the case in 3D printing. If you don’t use any vertical head retraction (and it seems to not be necessary in my experience) then the z-axis only moves in one direction during a print. Finally, the zero-backlash mechanism will add friction to the vertical drive, so you’re increasing the odds of skipping steps, etc.
TL;DR: flex coupler good; zero-backlash not needed and may make your problems worse.
[quote=“ichbinsnur”][quote=“djkirkendall”][quote=“ichbinsnur”]It would be helpful to know what setup you have for your z axis drive.
Is it still the stock configuration?
If so maybe have a look at these 2 mods i made to my k8200 to get better performance of the z axis.
The results are really amazing.
Can you post a source for the MXL belt you used?[/quote]
Here is the link to the spupplier where i sourced the belt : zahnriemen24.de/[/quote]
I’ve printed all of the parts, I’m just waiting on the 2nd K8204 kit and the timing belt. Your original callout for the belt cited MXL @ 460 teeth, but the printed pulley looks like XL pitch @ 5.08mm. I worked it out to 230 teeth +/- 12, and sourced an XL belt from amazon: amazon.com/gp/product/B00CMI … ge_o00_s00
It comes out to 46" (116.84cm), which sounds a bit long to me. The gap between supports measures out to 46cm, putting 2 way travel at 92cm.
Thanks for the quick reply![/quote]
Have a look at the description in Thingiverse, i put the span of lengts that should fit in the descriptions.[/quote]
That’s what had me scratching my head:
“1 MXL (XL) closed-loop belt, pitch 2.54mm (1/10 inch) , teeth 460, width 6mm (I deliberately made the belt tensioner to fit a wide range of belt lengths for easier sourcing. Tooth counts of min 430 to max 480 should work)”
MXL is set at 2.5mm pitch, so I bought up a MXL belt at 461 teeth. After I printed/measured the pulleys, I measured the pitch to 5.08. This led me to cancel the order and try to match the tooth count to XL. This gave me 230 +/-12T, but I’m not terribly experienced with timing belts. The 460XL025 belt should arrive Wednesday along with the 2nd K8204 kit. I’ll find out for sure then.
In the meantime, I’ve installed the K8203 extruder/hotend, and I’m fiddling around with that. I’m hoping to have it running by tonight!
Thanks again for the help, that design you shared looks SOLID!! I can’t wait to see the impact it has on my prints!
[quote=“hbzandbergen”]First thing to do before printing anything with the stock printer is replacing the rigid Z-axis coupler by a flexible one.
And some shimming, as mentioned in other posts.
The axis will move much smoother then.
I used some feeler gauges (about 0.3 mm) under the plastic nut-support, see picture (I use a trapezoidal axis)
Out of curiosity… I understand that a trapezoidal axis runs smoother, is faster, makes less noise so is better in every possible way. But still, during printing it barely moves at all so why buy a rather expensive trapezoidal axis if you don’t have to. I mean it is not that it gives you a better print and it also might be faster… but those few seconds on a 5 hour print… IMO it is not even remotely worth the money
[quote=“ichbinsnur”]Nice to hear.
Please share your results.[/quote]
Update 1/15/16 (pictures uploaded to thingiverse: thingiverse.com/make:185860)
The mechanicals are done, an easy install. The only liberties I took with the design:
1.) Countersink most M5 holes an additional 5mm so that square nuts for frame mounts would reach
2.) Replaced cantilever-side top retaining ring with extra flex coupler from 2nd K8204 kit; that M4 setscrew just wasn’t up to the job
3.) Replaced all receiving M3/M4 ends with locknuts
The belt worked out great, and I used 10" bits of wood to synchronize both ends with no measurement required.
Tomorrow: electrical and a test print. I’m a little concerned with the motor cable dangling in the wind, so I might design an arm to retain the cable under tension away from the moving parts.
