MK3 printer on a MK2 frame  

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Lex
 Lex
(@lex)
Active Member

I have a Prusa MK3 and also a MK2.5

Over time I have collected a fair amount of spare parts.  I have a spare mk3 board and also a spare 24v heatbed.  I have an extra 24v power supply as well.  What I am wondering is this.  If I purchase a mk3 Y carriage plate, is there any reason that i couldn't have a MK3 printer on a MK2 frame?  It seems like it would work fine and i will just loose a bit of print volume.  That would be ok with me as this would be a very cheap upgrade and I would prefer to have another MK3.  Am I missing anything?  Is there any reason this would not work?

Posted : 20/02/2021 6:35 pm
chad.k
(@chad-k)
Eminent Member

I did the opposite with MK2.5-ish hardware in a MK3 frame, and I'd guess that most of the problems you'll likely experience would be on the Y axis and firmware.  On the Y axis, the rods and bearings should fit perfectly fine, but on the Y motor mount and/or belt clip, the end stop holder might interfere with proper homing (it was a problem going the other way around since I needed end stops on bits that didn't have them, but it's also possible that they won't cause you any difficulty).  Not much as changed with the X and Z axis parts and the frame it hits for homing, so those shouldn't be a problem.

You'll also have to find 24V fans (with the fan speed reporting pin), a PINDA 2, a filament sensor (either the new IR one with associated magnets and ball bearing or the older optical one) and obviously motors.  The filament sensor can easily be turned off in the menus, but the others will need a custom recompiled firmware if you need to disable them, and since Prusa Research isn't building new MK2 firmware, you never know if or when the ability to disable these features might be removed or inadvertently broken.

You'll probably need to rebuild the firmware either way to fix the motor current settings unless your motors exactly match what Prusa supplies, and you'll want to fix the Z max in there to ensure homing/calibration works correctly anyway.

This post was modified 2 months ago by chad.k
Posted : 22/02/2021 11:00 pm
JoanTabb
(@joantabb)
Moderator

@chad-k

I thought the Mk3 Fans were 5volt

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 23/02/2021 3:10 am
chad.k
(@chad-k)
Eminent Member

@joantabb

You're right.  My mistake.

Posted : 23/02/2021 4:41 am
Lex
 Lex
(@lex)
Active Member

@chad-k

Thank you very much for this info.  That just raises one more question with me.

Are the motor voltages different from the MK 2 to the MK3?  I thought they were the same.  I have the prusa LDO motors for the MK 2.  I thought they were exactly the same. 

I don't think I want to get into modding firmware.  If I can't use the MK2 motors then that is probably the deal breaker.  I would just keep it MK2.5 because that is still a solid printer.

Posted : 23/02/2021 1:57 pm
Clemens M.
(@clemens-m)
Honorable Member

@lex

Have a look - they are similar for MK2 and MK3:

Best regards, Clemens

Posted : 23/02/2021 2:13 pm
Lex liked
chad.k
(@chad-k)
Eminent Member

@lex

Last time the motors needed to be swapped was the MK0/1 to MK2 upgrade.  The MK2 to MK3 upgrade didn't include new motors, so they should be the same (or at least compatible).  So, if you've got original motors, a full set of replacement 24V and 5V hardware for heatbed, hotend, PSU and fans, you should have a pretty easy time of it.

I doublechecked the firmware config and it looks like the MK2.5 and MK3 both use a Z max of 210mm, so there should be little chance of the hotend crashing into the bed before even starting calibration.  If you find the calibration process looking for the calibration points in the wrong place, or crashing into the frame while running calibration, you will have to look at building custom firmware.  Building a customized firmware variant is actually fairly easy, although if you want to keep up to date, it can certainly be a hassle.

There's also probably a good chance the belt self checks will fail because the physical opening in the MK2 frame is 10mm shorter for X than the MK3.  You can always just use the manual methods of testing belt tension, so I doubt this'll cause significant problems.

Posted : 23/02/2021 5:35 pm
JoanTabb
(@joantabb)
Moderator

@clemens-m

the main difference is that the  Y motor is on the opposite side of the belt,  on the Mk2 / Mk3... 

3 options, 
1, Mirror the Motor mount STL and reprint... 
2, swap the motor windings to reverse the motor, 
3, Adjust the motor direction in Firmware... 

Options 1 and 2, are once only changes, 
Option3 is a repeating situation as you will need to make changes to every new firmware.. 

I used Option 1

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 23/02/2021 6:24 pm
Clemens M.
(@clemens-m)
Honorable Member

@joantabb

The funny thing is, that for both printers there is only one spare parts set available. If the problem of the wrong rotation direction occures, I would take your opportunity 2 which is in my opinion the easiest way to solve it.

Best regards, Clemens

Posted : 23/02/2021 10:11 pm
JoanTabb
(@joantabb)
Moderator

@clemens-m

The Y motor direction is normally managed in firmware, 
the Mk2 uses the standard motor and has motor direction set one way in firmware, and the Mk3xx series have the same motor but firmware is set to rotate in in the reverse direction in Firmware. 
the issue occurs if we want to use Mk3 Formware on the Mk2 Hardware, simply be because the motor mounts on the two printers put the Y motor of opposite sides of the Y axis Belt.

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 24/02/2021 2:05 pm
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