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How to get an exact representation of the build plate dimensions?

Posted by drmaestro 
How to get an exact representation of the build plate dimensions?
May 14, 2017 04:28PM
Hi,

My printer's build plate measures 220x220 mm. However I cannot use all of the surface for various reasons (like clips to hold adhesion plates, end-stop location or mechanical constraints) and end up with a smaller usable area (on the X axis the printable area is between 9 mm - 200 mm and on the Y axis it is between 0 to 161 mm: I have calculated these values after homing at X and Y axis and moving the hotend using manual controls. I use Duet3D, where you can define your build size using the M208 commands (the exact commands are as follows:

M208 X9 Y0 Z0 S1 ; Set axis minima
M208 X200 Y161 Z200 S0 ; Set axis maxima

I also use Simplify3D where you define the built plate size. There, I've set the values at 220x220 mm.

My problem is, I can't get an exact representation of my real built plate size on Simplify 3D. The prints tend to be placed closer to the left side and the back side even tough they look like centered in Simplify3D. What is confusing me is that I am defining the build plate size on the firmware, but also on Simplify3D. How can I ensure that the representation I get on Simplify3D is an exact representation of my printable area?

Thanks
Re: How to get an exact representation of the build plate dimensions?
May 14, 2017 06:15PM
For the Y axis I think you can just tell S3D that the Y size of the build plate is 161mm.

For the X axis, I don't think there is a way of telling S3D that the printable area starts at X9. So you may need to change the M208 commands to define the printable region as 0 to 191mm instead, and tell S3D that the build plate size is 191 X 161mm.



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: How to get an exact representation of the build plate dimensions?
May 14, 2017 07:00PM
I would say the miss alignment issue comes from the two different bed settings. Can you slide your X end-stop over 9mm so that X0 is the start of the printable area? (I would say you could try a software offset but I haven't used a Duet board yet, have one in the mail but )

Also what printer do you have? You have lost over 20% of your y build area just due to constraints? I would think about adjusting the printer to make use of the full bed or get a smaller bed. You are wasting time by heating up bed area that you cant print on
Re: How to get an exact representation of the build plate dimensions?
May 14, 2017 10:01PM
Slic3r allows you to load an STL file that describes the bed layout. You can make a model of it including the clips, etc. and load it. Then you also need to tell it to home position of the extruder nozzle. Since the home position is on the addressable Y axis space, the Y coordinate is 0. The nozzle starts at X=9.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: How to get an exact representation of the build plate dimensions?
May 18, 2017 09:23AM
Sorry, a bit confused. Why are you setting your build plate size to 220x220 in S3D? You have offset your axis (endstops) in your firmware. S3D will generate g-code based on the xyz origin that you have set (either by endstops or, in your case, the offsets). Set your build plate size in S3D to what it actually is, based on your M208 offsets, and you should be good to go.
Re: How to get an exact representation of the build plate dimensions?
May 18, 2017 10:32AM
I've done some research into mapping the bed in the slicer recently. The confusion arises because the printer's coordinates and the slicer's coordinates aren't always the same.

Assuming that when you face the printer, X runs left-right, Y runs front-back, and Z is down-up, the printer origin (0,0,0) should be at the left-front corner or the right-rear corner to conform to the CAD standard right-hand rule for coordinate space. The printer firmware and slicer also go by the right hand rule. In the slicer, you tell it the physical dimensions of the bed, then you enter offsets. The slicer assumes that the left front corner (or right rear corner) of the bed is (0,0,0). The offsets to the printer's origin are typically (but not always) 0 or negative values- whatever the physical distance is between the two points.

For example, if the printer's XY envelope is 350 x 300 mm, and the bed is 280 x 250 mm, and the X offset is -20 (the printer's X=0 is 20 mm to the left of the left-front corner of the bed) and the Y offset is -15 (the printer's Y=0 is 15 mm forward of the left-front corner of the bed), the slicer will place parts at the center of the bed which it locates by dividing the bed dimensions by 2 and subtracting the offsets. In this case the coordinates of the center will be 280/2-(-20) = 160 and (250/2-(-15)=140. So the center of the bed will be at printer coordinates (160,140).

In SLA machines that print from the bottom, pulling the print up from the tank, Z is reversed, so the origin has to be a the right-front corner or the left-rear corner to conform to the standard right-hand rule coordinate space.

Edited 6 time(s). Last edit at 05/19/2017 11:50AM by the_digital_dentist.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: How to get an exact representation of the build plate dimensions?
May 18, 2017 05:22PM
Thenk you very much for the info and examples. I tried to fix the problem by designing a new endstop holder for teh Y axis. The old one was directly on top of the printer's frame. The new one goes 3 cm deeper, so the bed is covered almost completely in the Y axis. I have also changed the X endstop's position, so that the hotend is at the border of the build plate when it hits it. So, the X axis can start at 0.

2 more questions come to my mind:
1) Is there a better way, compared to the binder clips, to hold build surfaces on top of the bed? I know magnets can be used with suitanle surfaces but I would appreciate if there was another nonmagnetic solution with a smaller surface area.
2) What happens when you have an independent dual extruder printer? It needs to go outside of the printing area, so there could be problems with the coordinate system.
Re: How to get an exact representation of the build plate dimensions?
May 18, 2017 07:05PM
Endstops can be placed anywhere that is convenient, but you must assign min/max and coordinate values that ensure that the printer's origin is at the front-left (or right rear) corner of the machine. If the front-left is the origin and you put an endstop at the right end of the X axis, you have to declare that that endstop is a "home to max" type, and then give it the distance from the origin, maybe 340 mm, or whatever it happens to be. It can be useful to have the extruder home to a location that is away from the bed- that allows you to clean the nozzle with a wire brush as it heats up in preparation for a print. I added some custom gcode to the printer's slic3r profile to move the nozzle to the front-center of the machine and drop the bed 50 mm before a print starts to make nozzle cleaning extra easy.

Attach PEI to the top of the bed using 3M 468 tape and you won't need binder clips. As a bonus, there won't be anything there for the extruder to bang into, and prints will stick reliably without any glue or other slop that might gum up your bearings. People using my printer at the makerspace used to tear through the 5 mil kapton tape I was using weekly even though it lasted me 3-4 months between replacements, so I put a piece of 60 mil PEI on the bed and in 8 months no one has managed to damage it yet. I put a piece of 30 mil PEI on my CoreXY build. ABS, PLA, and TPU all stick reliably when it's hot and let go with minimal effort when it cools off. If you ever want to test the reliability of your design/build, leave it at a makerspace for others to use - you'll find out the weaknesses in a hurry!

I have no idea what the independent dual extruder people do. Figuring that out is part of the fun of developing new stuff.

Edited 3 time(s). Last edit at 05/18/2017 07:15PM by the_digital_dentist.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: How to get an exact representation of the build plate dimensions?
May 19, 2017 02:58AM
Swiss clips are another option, used for attaching simple picture frames together:



Personally I just use countersunk screws straight through the build surface. I lose out on 7-8mm but If I need to utilise that print area it is usually just a skirt anyway. I don't use a glass print bed though.
Re: How to get an exact representation of the build plate dimensions?
May 19, 2017 03:37AM
Quote
drmaestro
1) Is there a better way, compared to the binder clips, to hold build surfaces on top of the bed?

If you want a removable bed plate, then Swiss clips (picture frame clips) take up a lot less room than binder clips.

Quote
drmaestro
2) What happens when you have an independent dual extruder printer? It needs to go outside of the printing area, so there could be problems with the coordinate system.
[/quote]

No problem at all with the Duet/RRF that you are using. Define the common area that both heads can reach to start at X=0 and go up to whatever, and give S3D those figures. For the first carriage, use M208 to specify the actual reachable X lower and upper limits (the lower limit will be negative). The second carriage is the U axis in RRF, so do the same for that. It's described at [duet3d.com].



Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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