Re: Fine tune your MK3 Z axis
Nice find. Thanks for taking time to do this!
Do you guys think Prusa will implement these changes to fix the incorrect size?
If not ill have to print these when i get my printer in march/april.
Re: Fine tune your MK3 Z axis
Prusa changes things up pretty quick when they identify something. Unfortunately there is a little lag in making back into the repository, but it wouldn't surprise me that they are aware if this is an issue, and working on it, but the community pushes them to their best. I am printing a set now to see what I think. Was this same issue present in the MK2/S variants of the printers? I noticed when dropping the Z on for the first time that it was a bit loaded, perhaps this was what was going on. We'll see. Thanks for the work.
Re: Fine tune your MK3 Z axis
All parts are drawn in Inventor as IPT files.
Unfortunately, I can only convert them to STL files, not SCAD.
Actually, if you are comfortable sharing the IPT files, or save as STEP, that would work as well. I use Fusion 360 which can read either.
I don't have short term plans to modify either, but it would be nice to have the capability.
Actually, for those of us who use Fusion360, it would be AWESOME if you could release the entire printer assembly from Inventor.
jzkmath posted the printer assembly on grabcad at https://grabcad.com/library/prusa-i3-mk3-solidworks-1 see his post https://shop.prusa3d.com/forum/original-prusa-i3-mk3-f30/cad-models-for-mk3-parts-t6875-s40.html
Re: Fine tune your MK3 Z axis
Actually, if you are comfortable sharing the IPT files, or save as STEP, that would work as well. I use Fusion 360 which can read either.
I don't have short term plans to modify either, but it would be nice to have the capability.
Actually, for those of us who use Fusion360, it would be AWESOME if you could release the entire printer assembly from Inventor.
jzkmath posted the printer assembly on grabcad at https://grabcad.com/library/prusa-i3-mk3-solidworks-1 see his post https://shop.prusa3d.com/forum/original-prusa-i3-mk3-f30/cad-models-for-mk3-parts-t6875-s40.html
I am aware of those. Please, see my earlier post referencing this thread and the issues I had with those models.
Re: Fine tune your MK3 Z axis
I am aware of those. Please, see my earlier post referencing this thread and the issues I had with those models.
Yes, what I saw before I posted and what I can now find of your posts speaks to .stl files. I was referring to the posted STEP file(s).
Re: Fine tune your MK3 Z axis
Guys, if I may.
The goal is perfect linear motion.
So the first order of the day is to decide who the true reference is, because you have multiple moving things, but you really just want linear motion in one direction.
Let's say the smooth rods are the reference. They're the bosses.
Now what you want is for everything else to follow those two rods. You want the threaded rod to be spaced perfectly from the smooth rods at all points. If that spacing varies, then you get layer artifacts.
Problem: you have at least two parts fighting each other per smooth rod.
You have the motor mount which determines the threaded rod distance to the smooth rod.
And you have the Z-gantry where the threaded nut is mounted ... which also determines the distance to the smooth rod.
Ultimately, you don't really care what that distance is because it doesn't matter, you just want the two parts to agree on that distance.
And for fun, ALL OF THESE PARTS ARE PRINTED. So you WILL have imperfections and disagreements.
Either the threaded nut is the boss, or the motor mount is the boss. Pick one.
Let's assume the threaded nut mount is the boss. He is fixed and does not move at all.
Somebody must compensate for the difference, so the last man out is the motor mount.
So what you do is you leave enough slack around the motor, *plus you oversize the motor screw holes* in the mount. Essentially, the motor will float around in the mount until you lock it down.
When you assemble, don't tighten the Z axis motors all the way, put the gantry on, and then drop it to it's lowest position, as this is where the greatest misalignment deflection will probably occur. Once in this position, the threaded nut hopefully is constraining the motor to the correct position, and then you can tighten the motor screws to lock it in position.
Voila, you just made 2 printed parts agree nearly exactly with each other.
Bonus: put a slot or something in the mount so you can remove the motor mount by itself without disassembling anything else.
Re: Fine tune your MK3 Z axis
...Once in this position, the threaded nut hopefully is constraining the motor to the correct position, and then you can tighten the motor screws to lock it in position.
I can't tell if you are for the modification or against it, can you clarify? Just so everyone is clear, OP's opening post shows that the mount is slightly too small for the motor to fit into, much less be allowed to float and screwed into a correct aligned position like you are suggesting. The new brackets allow for what you are talking about.
My MK3 Parts: [Bowden] [New Shoes] [TPU Micro Springs]
Re: Fine tune your MK3 Z axis
gz1, what you say makes sense.
Questions this raises:
It sounds like, from the original post, that the motor mount is too narrow and in the wrong position. Both would be non-ideal following your logic.
The next question is does the new mount fix the issue?
The amount of horizontal play required (space and bolt hole slop) may be quite small if the parts are correctly aligned and the threaded rods are very close to vertical by design anyway.
Re: Fine tune your MK3 Z axis
Printed the new parts to see what they'd look like. I was thinking about mounting them, so I popped off my top mounts.
The threaded rod in the top mount is totally loose. 2mm or more of play in all directions, not really connected at all. The smooth rod has a deep positive socket with zero play.
This makes sense, it means the smooth rod is king, and the threaded rod is controlled horizontally at two points: motor mount and threaded nut on the gantry. So far so good.
So I pulled out the trusty micrometer. Remounted the original orange parts, powered up, and raised the gantry as high as it would go. I then checked the distance between the threaded rod and the smooth rod just below the gantry and just above the motor mount. Tricky because of the threads, but I used a piece of card stock to bridge the threads.
On both sides, the threaded/smooth rods were parallel within my ability to measure repeatedly (call it 0.05mm). I measured the gap between them, and I measured outside of rod to outside of rod. I was only measuring in the X direction, not distance from the frame for each.
I then dropped the gantry all the way down, thinking that this would maximize the side deflection of the top of the threaded rod if there was any misalignment. Measured at the bottom and the top: no difference, parallel. This was a bit tougher, as I had to stop when I first hit the threaded rod, or it would easily deflect to the side, as it was not anchored at the top.
Looking at it and thinking about the geometry, I don't think there is any issue here, even if things were slightly out of true.
When the nozzle is on the bed, the motor mount is ~100mm from the nut. When the nozzle is at max height, the distance is about 300mm.
Lets say the motor mount is horizontally 0.5mm unaligned from the threaded nut. That would give us a ratio (opposite over adjacent sides of a right triangle) of 0.5/300mm at the top, 0.5/100mm at the bottom.
position ratio angle from vertical cos angle z rise deviation
-------- ----- ------------------- --------- ----------------
bottom 0.5/100 .005 rad 0.9999986 1.25e-5
top 0.5/300 .0016667 rad 0.9999875 1.39e-6
If the Einsy asks for a 1mm rise, because of the angle of the threaded rod the gantry will rise slightly less, (1mm * the ratio of true vertical line to the longer angled line). That ratio (adjacent over hypotenuse) is the cosine of the pointy end angle. That angle is the atan of the ratio of the narrow end (0.5) vs the height (100 or 300).
Bottom line: as long as there is no binding, what you'll get is a very slow variation in absolute Z calibration over the full height of the bed. It'll be off by a thousandth of a percent at the bottom (where the angle is highest), and by a ten-thousandth of a percent at the top.
And that is with 0.5mm unalignment, which I don't think I'm seeing.
If that is the worst of my misalignments, I'll be quite happy. I'm sticking with the Prusa printed parts for now.
It's been a long time since high school trig, so I'm happy to have anybody convince me my math is wrong.
BTW, RHDreambox, I still appreciate your noticing the discrepancy and pointing it out. I suspect your parts are an improvement over the original, so keep it up!
Re: Fine tune your MK3 Z axis
Thank you for all the positive and even critical comments.
My goal is that anyone who wants to fine-tune their MK3 should be able to do that.
The large mounting holes in the original console allow you to adjust the console in the correct position.
But there is probably a greater risk that the console will be placed incorrectly, which may cause malfunction.
For IPT files, I will upload them in STEP format.
The IPT files are version dependent (as Tomaz pointed out) but it does not apply to the STEP files.
But first I will post part 2 and 3 in the Fine Tune series
Bear MK3 with Bondtech extruder
Re: Fine tune your MK3 Z axis
There's an email that prusa have to send improvement suggestions in, I'd suggest the op send in the problems the solution the files and this thread maybe. Then no one down the line has to print these if they evaluate it to be a change worth making 🙂
Re: Fine tune your MK3 Z axis
Thank you for all the positive and even critical comments.
My goal is that anyone who wants to fine-tune their MK3 should be able to do that.
The large mounting holes in the original console allow you to adjust the console in the correct position.
But there is probably a greater risk that the console will be placed incorrectly, which may cause malfunction.
For IPT files, I will upload them in STEP format.
The IPT files are version dependent (as Tomaz pointed out) but it does not apply to the STEP files.
But first I will post part 2 and 3 in the Fine Tune series
Props to you for trying to improve the design, regardless of the outcome I enjoyed reading the thread. With regard to the ipt files... I believe, though I may be mistaken, that the files are forward compatible, i.e. a new version of Inventor can open an old file but not the other way around so as long as someone is working with the same or newer version than you they should be able to open the ipt file. Though I get your wanting to maintain control of your part... The problem with stl files is that you really can't do a lot with them if you want to "tweak" something. I can't even pull a decent dimension or snap a line on an STL part I import into Creo, my software of choice. Fortunately jzkmath put the parts out in Step format that I can easily import and pull dimensions from.
Re: Fine tune your MK3 Z axis
Thank you for all the positive and even critical comments.
My goal is that anyone who wants to fine-tune their MK3 should be able to do that.
The large mounting holes in the original console allow you to adjust the console in the correct position.
But there is probably a greater risk that the console will be placed incorrectly, which may cause malfunction.
For IPT files, I will upload them in STEP format.
The IPT files are version dependent (as Tomaz pointed out) but it does not apply to the STEP files.
But first I will post part 2 and 3 in the Fine Tune series
Props to you for trying to improve the design, regardless of the outcome I enjoyed reading the thread. With regard to the ipt files... I believe, though I may be mistaken, that the files are forward compatible, i.e. a new version of Inventor can open an old file but not the other way around so as long as someone is working with the same or newer version than you they should be able to open the ipt file. Though I get your wanting to maintain control of your part... The problem with stl files is that you really can't do a lot with them if you want to "tweak" something. I can't even pull a decent dimension or snap a line on an STL part I import into Creo, my software of choice. Fortunately jzkmath put the parts out in Step format that I can easily import and pull dimensions from.
If you haven't tried Sketchup before, it is a fairly robust application that allows you to modify/create STL files (including adding dimensions). The free version of the software is called "Sketchup Make" (it's owned by Google). It does take a bit to get used to (at least for me it did).
Re: Fine tune your MK3 Z axis
......
If you haven't tried Sketchup before, it is a fairly robust application that allows you to modify/create STL files (including adding dimensions). The free version of the software is called "Sketchup Make" (it's owned by Google). It does take a bit to get used to (at least for me it did).
I'll have to give it a try, hopefully it will be relatively easy as the printer part designs aren't very complex... Unfortunately I'm kind of firmly in bed with Creo, started with Pro/Engineer decades ago, but can do basic 2D in Autocad for simple layouts. I've played with Solidworks, Solid Edge, and Catia over the years but am pretty much stuck in the old dog frame of mind with Creo...
Re: Fine tune your MK3 Z axis
...Once in this position, the threaded nut hopefully is constraining the motor to the correct position, and then you can tighten the motor screws to lock it in position.
I can't tell if you are for the modification or against it, can you clarify? Just so everyone is clear, OP's opening post shows that the mount is slightly too small for the motor to fit into, much less be allowed to float and screwed into a correct aligned position like you are suggesting. The new brackets allow for what you are talking about.
If I'm reading OP's post correctly, he increased the clearance but reduced the mount screw hole sizes. That being the case, the new mount wouldn't allow for adjustment. It would just help the motor fit better inside the mount.
Re: Fine tune your MK3 Z axis
Bottom line: as long as there is no binding, what you'll get is a very slow variation in absolute Z calibration over the full height of the bed. It'll be off by a thousandth of a percent at the bottom (where the angle is highest), and by a ten-thousandth of a percent at the top.
Good post. I haven't checked all your math but the setup looks correct. It sounds like your printer happens to be within spec, which is good news.
Your bottom line is the part I don't exactly agree with.
A couple of counterpoints.
You caveat your conclusion with "as long as there is no binding", but... what exactly do you think causes binding in the first place?
Perhaps a different way to ask -- how much deflection is necessary to cause binding? How much deflection would it take to change the pressure on the bearing against the smooth rod?
If phrased like that, even a seemingly small amount of deflection becomes noticeable, particularly in a machine which uses software leveling. If the Z-axis only went in one direction during the print (upwards), it might be OK. But on this machine, it constantly moves back and forth within a print, and within a layer. So it's less forgiving about stuff like this.
On top of that, this is only one part we're looking at. Start adding the cumulative effects together from all other sources of error, and ... it may be worth it to be opportunistic and fix the things you can fix, even if minor. Some things you can fix, other things you can't. If the cost of the fix is "look, just oversize the holes and use a proper procedure", maybe go ahead and do it.
To take this out of theory-land, there is a third way to ameliorate, if not solve, this issue. It's just not available on the MK2/3.
I've fixed two other printers where I could adjust neither the threaded nut nor the motor mount. In those cases, I still allowed the smooth rod to be the boss because the flexible coupler allows the deflection error to be pushed into the threaded rod and not.. everything else. So while printing, the threaded rod wobbles like crazy at the top, but the layer registration still comes out nearly perfect. Technically better than my MK2, and perfect enough to make other 3d printer owners do a double-take when they see my prints.
The general theory is this: this is a constraint system. Overconstraining the system with parts that don't agree leads to bad things, like poor print quality, or worse *cough* PRINTER DAMAGE. This is, at its heart, a design issue.
Re: Fine tune your MK3 Z axis
Bottom line: as long as there is no binding, what you'll get is a very slow variation in absolute Z calibration over the full height of the bed. It'll be off by a thousandth of a percent at the bottom (where the angle is highest), and by a ten-thousandth of a percent at the top.
Good post. I haven't checked all your math but the setup looks correct. It sounds like your printer happens to be within spec, which is good news.
Your bottom line is the part I don't exactly agree with.
A couple of counterpoints.
You caveat your conclusion with "as long as there is no binding", but... what exactly do you think causes binding in the first place?
...
I think binding would be caused by too high an angle between the threaded rod and the nut insert in the gantry. If that threaded rod got close to the motor mount (say if it was mounted lower on the gantry), there could be an issue. However, at least with my threaded rod/nut, the tolerances are nowhere near tight enough to bind with the 0.3 degree deflection which would be generated by a (quite extreme) 0.5mm offset of the motormount.
One quick way to tell this: turn one of your z-axis lead screws by a turn, so that the gantry is slightly angled. Then turn both lead-screws to raise/lower the bed. I feel no difference in resistance. Between the tolerances of the screw/nut, and the flex of the PETG mount, I'm not noticing any increased resistance, and this is with a huge angle compared to the 0.3 degree (at the most extreme) case I'd expect from a z-motor horizontal offset.
Your other point (every little thing adds up) is true. I've got no problem with you adjust this to line up. I'm just not clear it needs a new printed part to do it (as my correctly aligned kit with original Prusa parts indicates). I'd be concerned that people with perfectly vertical threaded rods tear down their printers to install new parts they've printed and end up making things worse due to print quality or tolerance issues in their new components.
Suggestion for folks:
It's not that making this perfect will hurt anything, it won't. I just suspect that effort might be better spent on fine-tuning other aspects of the printer (belt-tightening, extruder calibration, extruder-gear adjustment, slicing, etc.)
Re: Fine tune your MK3 Z axis
Here is a picture showing the difference between the original and the modified motor bracket.
In order for the original features to fit together optimally, the Z-screw must also be mounted incorrectly, otherwise bearings and screws will fall when the Z unit runs upside down.
If the Z-screw is mounted correctly, the friction in the bearing and screw will be bigger near the motor bracket.
For machine manufacturing, small screw holes give precision, large screw holes are used where the location is not so careful.
Bear MK3 with Bondtech extruder
Re: Fine tune your MK3 Z axis
Deleted.
Re: Fine tune your MK3 Z axis
Hello. Tell me, infill percentage?