The hotend on my new printer is basically loose when the third lower mount screw is removed, while the two upper screws are still firmly in place. See my video…
This means that the hotend fixation entirely relies on a single 2.5x30 mm screw.
And this is by design…
The top of the heatsink has a milled slot to fit the mount bar of the extruder gearing case. Two screws are mounted to hold the heatsink in place. But the way the parts are made, the screws don’t have a fair chans to hold the heat-sink firmly in place. No matter how hard you tighten them.
The threads for the screws are made in the heatsink itself. So to get any fixation from the screws, they have to compress the slot in the heatsink. But the heatsink isn’t designed to flex like that. At least not as much as needed to overcome the clearance of the slot on my printer.
This design could have worked, if both heatsink and the mount bar on the gearing case would have been machined to tight tolerances. But Sovol makes no attempt to. For some reason they choose to machine only one surface of the mount bar on the gearing case. The opposite surface is the “raw” aluminium casting.
I assume the machined surface was intended to serve as the reference plane, to which the heatsink/hotend should be fixated. But as the parts now are made - that doesn’t happen…
A simple fix for Sovol to get that, would be to clear out the threads from the heatsink, and in stead thread the holes in the mount bar on the gearing case.
I noticed I uploaded the wrong image of the heatsink, and it seems like I don’t have permissions to edit my post anymore. so I’ll put it here, and hope it might help to clarify the issue.
I have been thinking about the problem and possible ways to fix it.
First of all, it’s not a deal-breaker. The hotend is held reasonable secure by the third, lower screw. On some units, like mine, the top mount screws are merely decorative. But that doesn’t matter much, as the top of the hotend is still held in position by the round tap and recess for the filament tube, and can’t move much (both with the same dimension in the cad drawings).
Sovol could implement a very simple and backwards compatible fix for this. It only affects the machining process of the aluminium gearing case, just by tapping the two mount holes with M3 treads, and replace the two hex cap-head screws M3x16 with a shorter pair of M3x10 (that don’t reach into the threads of the heatsink). That’s all…
That would insure a firm fixation of the top of the hotend heatsink, against the machined surface on the left side of the gearing case. Possibly as originally intended..? - No more wiggling around…
If there is anyone, like me, who would like to address the issue with the parts we already have. I have some suggestions, but it’s till a work in progress…
Also… It would be interesting if anyone of you who have a spare toolhead kit would be willing to investigate the unit:
Unscrew only the lower mount screws for the hotend, and
Keep the two upper tightened.
Check if the hotend feels tight, or loose and can wiggle like mine.
Possibly. The fact the screws appear to be acting as locating pins, rather than securely affixing the top to anything, in my mind suggests there’s reason for such design.
It’s not something which appears to cause any issue, so my opinion is it’s best left alone.
Allowing for thermal expansion is certainly a valid argument for a loose top mount.
But then one have to ask: What is the purpose of two screws at the top? It can’t be purely delusive? To give the “impression” that the hotend is fastened. While it actually is intended to be loose and be able to move upp/down…
Why bother to drill and tap those two holes in the heatsink, and and then mount two screws, when they don’t add to any stability? Why are they there..?
I doubt guiding pins. Not with two screws… And the round tap on the underside of the gearing case mount bar, and the corresponding recess in the heatsink serves that purpose perfectly well.
If the heatsink originally was intended to bee loose, the machined surface on the left side of the mount bar would be unnecessary. It could have been left untouched, just as the right side. Now they machine a surface that serves no purpose.
Was it vibrations from 4G accelerations that made an initially solely top-mounted hotend come loose - Calling for an extra third screw in the bottom - Leading to thermal expansion issues - Ending up with the current design..?
They seems to still make features that serves no obvious purpose. Which makes me wonder if they’re just “lazy” (limited resources), or if the actually think the design works in a way it doesn’t? Or is it dual usage? Same part in multipla applications.
Now I must admit the subject title I wrote is exaggerated. Something like “has a weird design”, would be better. But I can’t edit…
I haven’t studied the Zero’s hot end and heat sink design. Fortunately I haven’t needed to despite using the Zero for my daily driver 3D printer (it’s printing ABS-CF now and has been all day), but reading the above description, I was already thinking in terms of what cardoc said. It sounds as if the lower screw rigidly mounts the lower end of the hot end and the upper screws loosely constrain it so it can’t pivot on the lower screw while allowing for thermal expansion. Novice mechanical engineering students tend to overly constrain a design and not adequately consider issues such as thermal expansion. Even in a nozzle crash, there isn’t much force on a hot end because the stepper motors aren’t that powerful so it doesn’t need three screws firmly mounting it. I’m not arguing that Sovol engineering is infallible but they’ve been designing and building 3D printers for many years so they probably have good reasons for the way they designed the Zero hot end mounting.
I did recognize thermal expansion as a valid reason to let the top end to be loose, while fixed at the low end. At least I tried to…
A rough estimate gave a differential expansion of 0.15 mm at a temp diff of 50°C, between the plastic (ABS?) “base plate” and the aluminium parts. That would make the parts go banana…
50°C diff is a bit extreme, but reasonable for high temp materials.
I’ve connected two small extra thermistors to my toolhead PCB. One is intended for permanent monitoring of the hotend heatsink, and the other is for auxiliary use (I just realized it could be a perfect chamber temp sensor).
Just for reference, my heatsink stabilize at around 72-73°C when printing ABS at 270°C for 30 minutes, and a chamber temp at 45-55°C (preheated).
For the two screws… It’s hard to understand why Sovol chose to use the sturdier screws, and two of them, just to loosely hold the top end in place, while using a single weaker screw for the rigid fixation in the bottom? When they’re not even needed, as I described in my last post.
I believe this, and the machined surface on the gearing case, that is left with nothing attached to it, is a result of:
- It seems to work acceptably - Now: All hands on the M1D.
It’s not lack of competence, it’s lack of time, as in all commercial organisations.
We didn’t know it at the time, but the Zero was a Limited Edition printer.
It is no also unclear if the Zero Head will truly fix on the MAX.
Whatever you find, it will be up to the users to decide to fix or not.
Yes, I was fully aware that the Zero was discontinued already when I ordered mine. So I have no expectations that Sovol should fix any issues.
Possibly, if this printhead also is used for the MAX.
Meanwhile. I intend to proof myself wrong.
By completely removing the two top screws on the heatsink. Thereby only relying on the single bottom screw to firmly hold the hotend in position. And I will promise to report here whenever I would discover any issues from that. (it might come quick, we’ll see)
I did a comparison print of a pair of Benchys, with and without screws. Perhaps not the best choice, but I had to print something…
Surprisingly, the one without screws actually came out slightly better. It has a little less ringing (VFA) on the hull sides. I should probably print some test-cubes or a proper VFA-tower…
I tried to take some photos, but it’s so difficult to get just pictures. And my phone camera sucks…
This wiggling line resolution/backlash-test came out near identical both at 4.5k and 20k acceleration.
No difference in resolution: 0.1 mm bearably visible on X-axis and 0.15 on Y-axis.
But this time there was a hint of VFA on the print without screws. so maybe it’s a mater of repeatability?
The numbers represent the wiggling amplitude peak-to-peak (mm):
Sorry about the confusion…
I would have shared images. But I couldn’t produce any decent and fair images of the prints. Hence slicer previews to visualize what I was printing. And the prints were so similar that there were not much to see anyway.
