3D printer bed leveling

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stevedee
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3D printer bed leveling

Post by stevedee » Saturday 11th December 2021 4:02pm

PartierSP wrote:
Friday 10th December 2021 10:22pm
Yes. But since the first pass on a printer is always at a non zero height, the program is expecting to have that gap as your first pass, nothing more. And this makes sense compared to traditional CNC programming/machining practices in general (Z zero is usually top or bottom of the part, generally not somewhere in between).

So essentially your first pass wont have enough plastic resulting the expected pressure against the bed and/or each pass on the first layer will be spaced out too much not getting enough pressure against each other. Now the shim you're using is a very thin one so I don't expect you'll notice too much. Its just you're not at the 'theoretically perfect'. And if you use glue on your bed you may be easily making up for this extra gap and some. But one thing I've learned with automated equipment, if it works for you, then it works for you. ;)

I have heard of people getting so called 'elephant's foot' error on their prints. This is where the first layer (or first few layers) bulge out at the bed. I'm not sure if this is a sign of the nozzle being set too low on the first pass, or a temperature issue, or what. But its something to look out for if you try new techniques.
Thanks for your input Mike. What you say makes a lot of sense.

I thought we'd better wander into the Lounge to continue our chat, since this is more about 3D Printing than Gambas programming.

I moved away from using copying paper to set/check the gap because it is compressible. Hence I'm using a 1960s set of steel feeler gauges, which were made before we introduced the metric system, over here in the UK. The 2, 3 & 4 thou gauges are very approx equal to 50, 75 & 100 micro-metres. From my comparative checks, it looks like a sheet of 70gsm paper is around 80um (0.08mm) thick.

Earlier this year, I did a few tests with my printer where I compared results with the the nozzle-to-bed gap set to 2, 3 & 4 thou. I was printing with a 0.4mm nozzle and a layer height of 0.2mm. My printer seemed to print OK with a 3 thou gap, but when set to 2thou, the first layer was smeared on the bed. My conclusion was that the nozzle was too close to the bed, although it was not touching it.

I rationalized this by thinking that the bead of molten PLA was being 'pulled' slightly at 90 degrees to the nozzle, maybe at a rate slightly faster or slower than the x/y movement of the bed. (sounds a bit crazy now I've written it down!). But of course, if the extruded PLA does curl very slightly (due to this small extra gap) and stick to the bed, subsequent layers will do exactly the same, and all layer heights will be roughly equal. In my earlier example, the final layer will still be printed approx 0.075mm below the nozzle.

However, the next time I have a spare evening, I'll run these checks again and also try the 'no-gap' configuration. Have you noticed any smearing? How do you compensate for the paper thickness when you dial in a Z value?



Re: using glue, hairspray, blue tape... to help stick prints to the bed... I've always thought that a crazy idea. I have a glass bed and just keep my fingers off of it. I clean the bed with isopropyl alcohol (IPA) from time to time, and that's all I seem to have to do for good adhesion.

Elephants foot generally seems to be caused by either lack of cooling or too high a bed temperature (the first few layers should be printed with the cooling fan off, then the rest with it on.

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Re: 3D printer bed leveling

Post by PartierSP » Sunday 12th December 2021 9:22pm

When I just before starting to write this program I switched to a metal feeler gauge - 0.008" (~0.203mm). So I just program it at 0.20mm. Canada has gone metric back in the 70s as well yet at a machinist I'd say +90% the jobs I get at work as still in inches. So we actually keep everything inch based (measuring tools and machines).

So far I've liked the feeler gauge much better then using paper. I haven't had any issues except if I mess around with the printer (possibly bumping the bed levelling knobs) and didn't re-level. I'm also waiting to see what will happen after running it for a year or two. I'm sure I'll start to develop some backlash in the Z, especially right near the bed where it moves (and hence wears) the most. If I do develop backlash, I may find I simply need to run my program telling it my shim's thickness is it's thickness + backlash distance to compensate.

I want to have a closer look at how my printer homes. I know it bounces on/off the limit switch at least twice. **edit see below** But if it does the final movement in the down direction, the backlash will show up in the first layer as its the first movement in the other direction. It would be much better if Z home is determined by moving Z up off of the limit switch. Then the backlash would be eliminated for printing as the head only moves upwards throughout the entire print.

But there are other ways to deal with backlash. I could use my program as normal, but if I could force a 'Z-Hop' prior to printing each layer in Cura, then my system should be spot on as the Z-Hop would replicate the movement my Levelling system does when finding Z-zero.

**Edit**
My printer just finished its print and am able to check the Z homing. Z will move down at a medium speed until it turns on the Z home limit switch. Then it moves up 1 or 2mm so Z home limit switch is off again. Finally it moves down slowly until the switch just barely turns on. Done. This means all your backlash will be taken up by your first layer as its the first move in the other direction. :? I guess what can they do when they only use a single switch for each axis.

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Re: 3D printer bed leveling

Post by PartierSP » Sunday 12th December 2021 10:16pm

stevedee wrote:
Saturday 11th December 2021 4:02pm
Earlier this year, I did a few tests with my printer where I compared results with the the nozzle-to-bed gap set to 2, 3 & 4 thou. I was printing with a 0.4mm nozzle and a layer height of 0.2mm. My printer seemed to print OK with a 3 thou gap, but when set to 2thou, the first layer was smeared on the bed. My conclusion was that the nozzle was too close to the bed, although it was not touching it.

I rationalized this by thinking that the bead of molten PLA was being 'pulled' slightly at 90 degrees to the nozzle, maybe at a rate slightly faster or slower than the x/y movement of the bed. (sounds a bit crazy now I've written it down!). But of course, if the extruded PLA does curl very slightly (due to this small extra gap) and stick to the bed, subsequent layers will do exactly the same, and all layer heights will be roughly equal. In my earlier example, the final layer will still be printed approx 0.075mm below the nozzle.
Actually that doesn't sound as crazy as it may seem. 3D printers are a constant volume devices. Meaning the volume of plastic passing by the extruder is equal to the volume of plastic being ejected out of the nozzle. Their velocities however are different. But by changing the nozzle diameter, you can change the velocity of the plastic ejecting out of the tip. But this speed doesn't have to be perfectly set to the velocity of the X-Y travel as plastic is um, plastic. That's plastic as in deformable. But this velocity difference between the extrusion and X-Y will build up some stresses and the bead will pull like an elastic (I've had that occasionally just at the start of a print).

If we know our extruder velocity, our PLA filament diameter, and our nozzle tip diameter, then we can calculate out our extrusion speed: Vn=(Ve*Df^2)/(Dn^2)
Where:
  • Vn = Velocity at the nozzle (mm/s)
  • Ve = Velocity at the extruder (mm/s)
  • Df = Diameter of filament (mm)
  • Dn = Diameter of nozzle (mm)
So, if you're lagging behind on the extrusion, we'd probably want to reduce the size of the nozzle hole a bit. The question then is how's your nozzle? Is the hole wearing at all? My printer came with a spare so I expect they are highly wearing parts.
However, the next time I have a spare evening, I'll run these checks again and also try the 'no-gap' configuration. Have you noticed any smearing? How do you compensate for the paper thickness when you dial in a Z value?
I did have some smearing at the start. Heck day one I put a gouge in the plastic build surface that came with my Ender 3. :oops: Yep, kinda too close there. I've just bought my first 2 spools of Overture PLA and they both came with free build surfaces that appear similar to my Ender's original, just smaller (200mm x 200mm).

Re: using glue, hairspray, blue tape... to help stick prints to the bed... I've always thought that a crazy idea. I have a glass bed and just keep my fingers off of it. I clean the bed with isopropyl alcohol (IPA) from time to time, and that's all I seem to have to do for good adhesion.
With you there 100%! :D
Elephants foot generally seems to be caused by either lack of cooling or too high a bed temperature (the first few layers should be printed with the cooling fan off, then the rest with it on.
Ah so the print is basically running at the bottom. Yes then I could see that as being temperature issues then.

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stevedee
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Re: 3D printer bed leveling

Post by stevedee » Monday 13th December 2021 8:13am

Wow! At last an intelligent discussion on 3D printers...thanks for sticking with me! (...a lot of the chat on the Creality forum is very low level, maybe there is a better forum I should be following)
PartierSP wrote:
Sunday 12th December 2021 9:22pm
...I'm sure I'll start to develop some backlash in the Z, especially right near the bed where it moves (and hence wears) the most. If I do develop backlash, I may find I simply need to run my program telling it my shim's thickness is it's thickness + backlash distance to compensate.
Its very important to carryout routine maintenance on 3D printers. This includes checking for free-play and making adjustments to minimise it; especially maintaining belt tension and replacing worn rollers.

Also remember that during printing, Z doesn't only keep going up, it sometimes goes down. (I may have to trawl through some g-code if you need some examples).
I want to have a closer look at how my printer homes...


Yes, it tries to creep up on the limit switch in an attempt to find the same position every time. Not only is this a compromise (e.g. the slower the better for accuracy, without testing the patience of the user) but the limit switch on my printer is just a simple micro switch which contains a spring...so spring temperature is also a factor in where the extruder comes to rest. I wonder what repeatability looks like; i.e. within umetres, tens of umetres?
Last edited by stevedee on Monday 13th December 2021 8:40am, edited 1 time in total.

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stevedee
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Re: 3D printer bed leveling

Post by stevedee » Monday 13th December 2021 8:32am

PartierSP wrote:
Sunday 12th December 2021 10:16pm
...3D printers are a constant volume devices. Meaning the volume of plastic passing by the extruder is equal to the volume of plastic being ejected out of the nozzle. Their velocities however are different. But by changing the nozzle diameter, you can change the velocity of the plastic ejecting out of the tip. But this speed doesn't have to be perfectly set to the velocity of the X-Y travel as plastic is um, plastic...
Yep, I certainly struggle to visualise Plastic Dynamics...I may have just invented that terminology!

I can't really visualise how you get an apparently uniform 0.2mm diameter bead/string of plastic out of a 0.4mm diameter orifice (nozzle).
...The question then is how's your nozzle? Is the hole wearing at all? My printer came with a spare so I expect they are highly wearing parts...
I guess you haven't had the joy of replacing a nozzle yet. If you were worried about burning your fingers during bed-leveling, just wait til you have to step the nozzle temperature up to 260'C to replace it. Yes, brass nozzles wear out surprising quickly. See my post: http://captainbodgit.blogspot.com/2021/ ... ozzle.html
My [current] recommendation is to buy a dozen cheap nozzles.

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Re: 3D printer bed leveling

Post by PartierSP » Monday 13th December 2021 9:56am

stevedee wrote:
Monday 13th December 2021 8:13am
Wow! At last an intelligent discussion on 3D printers...thanks for sticking with me! (...a lot of the chat on the Creality forum is very low level, maybe there is a better forum I should be following)
Several years ago I started to build myself a 3D printer. It was roughly based off of a Mendle Max, but I was going to give it a more industrial build (aka, stainless steel tubing, CNC cut plates, etc). I got the design, frame, and electronics completed and started to work on the slides. But my work vs play lives got all out of wack and wasn't able to spend time at it any more. So needless to say, I studied a fair amount on their designs and theory of operation. Everything I learned about the electronics were found on the RepRap forums. I haven't been back there in a few years so not sure what they've been up to. If you want, I'll get photos of how far I got with that printer. ;)

My biggest problem is besides the past month or so with this printer, I have only done a few prints at the library. Otherwise I've had no direct experience with a 3D printer. And this is where I really need to learn off of people like you who have been running them for a while. 8-)
Its very important to carryout routine maintenance on 3D printers. This includes checking for free-play and making adjustments to minimise it; especially maintaining belt tension and replacing worn rollers.
Yep maintenance is SO important! I can never stress it enough to my brother at work. Its nice to just turn on a machine and run, but it needs to always have that once over first.
Also remember that during printing, Z doesn't only keep going up, it sometimes goes down. (I may have to trawl through some g-code if you need some examples).
I'll have a closer look too. I haven't noticed much up/down other then the up commands between levels. I have noticed Cura tends to do supports first, then walls, and finally infill. Maybe it does a Hop between on of them. I know there are Z-Hop options that they normally keep hidden from settings bar on the side, but if you search the hidden sections for 'Hop' you'll see it under the Travel section. I played with this a bit when I was doing a few tall and skinny prints. The nozzle kept knocking the print off of the bed when it would rapid across the part (I've since found using a Brim and adding the occasional support helped that out a lot).
Yes, it tries to creep up on the limit switch in an attempt to find the same position every time. Not only is this a compromise (e.g. the slower the better for accuracy, without testing the patience of the user) but the limit switch on my printer is just a simple micro switch which contains a spring...so spring temperature is also a factor in where the extruder comes to rest. I wonder what repeatability looks like; i.e. within umetres, tens of umetres?
Maybe that's something I'll do over Christmas/New Years. We've got a large old school dial indicator that's in 0.0001" (~0.0025mm) graduations. For I'm sure my Ender has the same micro switches that yours has. Hmmm, I think I may have another upgrade for this printer. Maybe I'll fit one of the Opto-Endstops I made for my other printer to this one (This was the page I used to build my electronics from: Gen7 Board - its basically an Arduino Mega without the Arduino boatloader flashed onto it). It would be a good comparison. And even if it doesn't improve the performance, it would add an indicator LED so I could see when its tripped.
Last edited by PartierSP on Monday 13th December 2021 10:48am, edited 1 time in total.

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Re: 3D printer bed leveling

Post by PartierSP » Monday 13th December 2021 10:22am

stevedee wrote:
Monday 13th December 2021 8:32am
PartierSP wrote:
Sunday 12th December 2021 10:16pm
...3D printers are a constant volume devices. Meaning the volume of plastic passing by the extruder is equal to the volume of plastic being ejected out of the nozzle. Their velocities however are different. But by changing the nozzle diameter, you can change the velocity of the plastic ejecting out of the tip. But this speed doesn't have to be perfectly set to the velocity of the X-Y travel as plastic is um, plastic...
Yep, I certainly struggle to visualise Plastic Dynamics...I may have just invented that terminology!
Lol! And don't forget to throw some Thermo Dynamics into the mix too! Thermo Plastic Dynamics :lol:
Oi I think I just made my head hurt! :)
I can't really visualise how you get an apparently uniform 0.2mm diameter bead/string of plastic out of a 0.4mm diameter orifice (nozzle).
Just think of it as a pub just opening up in the evening. Everyone runs in each taking a seat at the bar. Um ok, I don't think that ever happened nicely in a pub before. So yeah. Good question. :P

Actually its probably just due to the consistent pressure that builds up within the nozzle tip and the constant velocity. I've always been amazed by how nicely a robot can lay a bead of weld, or a lathe on power feed can cut a shaft. Try to do this by hand and you'll always spot the human's work vs machine's.
I guess you haven't had the joy of replacing a nozzle yet. If you were worried about burning your fingers during bed-leveling, just wait til you have to step the nozzle temperature up to 260'C to replace it. Yes, brass nozzles wear out surprising quickly. See my post: http://captainbodgit.blogspot.com/2021/ ... ozzle.html
My [current] recommendation is to buy a dozen cheap nozzles.
HOLLY MOLLY! That's some wear! :shock:
I know it was bothering me everytime the nozzle would rapid across the printed part. Sounded like a file banging against the print. Here its the file banging against the nozzle. Maybe I should look into Z-Hop some more.

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Re: 3D printer bed leveling

Post by stevedee » Monday 13th December 2021 3:42pm

PartierSP wrote:
Monday 13th December 2021 9:56am

Several years ago I started to build myself a 3D printer... If you want, I'll get photos of how far I got with that printer.
Yes, please post a couple of photos.
...And this is where I really need to learn off of people like you who have been running them for a while.
I'm no expert. I was hoping to learn quality stuff from people who knew what they were talking about, but so much stuff on the net is just Chinese Echos (i.e. stuff that gets repeated that has either become corrupted, or was never right in the first place). Just because you find 10 websites that say exactly the same thing, it doesn't make it right!
... I know there are Z-Hop options...
Yes, I have Z-Hop on, and that's a good example as to why you can't accept free-play in the Z axis.

Maybe that's something I'll do over Christmas/New Years. We've got a large old school dial indicator that's in 0.0001" (~0.0025mm) graduations. For I'm sure my Ender has the same micro switches that yours has....
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Re: 3D printer bed leveling

Post by stevedee » Monday 13th December 2021 4:17pm

PartierSP wrote:
Monday 13th December 2021 10:22am
...Just think of it as a pub just opening up in the evening....

Hmmm! Beer!

...so I'm back from the pub and I think I've got it.
For a 0.2mm layer from a 0.4mm nozzle, the layer is simply a flat strip of plastic, 0.2mm high by 0.4mm wide. Its drawn out into that shape by the relative flow rate and linear X/Y speed of the extruder.

Still not sure why the starting point (where the plastic initially attaches itself to the bed) is not just an ugly blob shape!

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Re: 3D printer bed leveling

Post by PartierSP » Sunday 19th December 2021 12:56am

Been a busy week. I haven't had much time to put towards my 3D printing projects. Thankfully its the weekend again, so I'm back.

You asked about my printer I was making, I've attached a few pictures of it here. I need to look in my work shop to find the opto endstops I made. They weren't with the rest of the printer. But I'm sure they'll show up.

This is the overall shot of the printer and components. The printer was loosely based on the Mendel Max. Thus an A frame design with moving Y axis bed, duel stepper motor drive Z axis, and X axis gantry. In the bags at the lower right are the drive belts and pulleys. To the left is a programmer I made to flash Marlin (or which ever OS in there I want) onto the controller board. Left of that is the hot bed with the controller board that I made sitting on top. Extruder is to the left of that, and finally the bed support
Over all shot of the printer and components.
Over all shot of the printer and components.
normal_IMG_9991.JPG (556.8 KiB) Viewed 1669 times
The main frame is shown here (along with the inspector).
Main Frame
Main Frame
normal_IMG_9994.JPG (580.76 KiB) Viewed 1669 times
Top side of the controller.
Top side of the controller.
normal_IMG_9995.JPG (361.39 KiB) Viewed 1669 times

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