MGN12H and kossel metal carriages
Posted by DjDemonD
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Re: MGN12H and kossel metal carriages July 26, 2016 07:59AM |
So got these magnetic ended carbon rods and carriages/effector from Aliexpress. (not all exactly the same length but I can fix that).
But I was under the impression that the distance between the rods at the carriage end and again at the effector end had to be exactly the same. In this case they converge from the carriages to the effector substantially. Whilst I have not built the machine yet just moving them around in my hands the movement at the more extreme end of the range results in the effector twisting.
Any thoughts?
Simon Khoury
Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions
But I was under the impression that the distance between the rods at the carriage end and again at the effector end had to be exactly the same. In this case they converge from the carriages to the effector substantially. Whilst I have not built the machine yet just moving them around in my hands the movement at the more extreme end of the range results in the effector twisting.
Any thoughts?
Simon Khoury
Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions
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Re: MGN12H and kossel metal carriages July 26, 2016 08:17AM |
the converge because you have the arms to the effector on the wrong magnet countersunk part
Also i would change the small screws that hold the belt restraints to slotted stainless steel ones as they easily get rounded the ones provided are not stainless but chrome i think
Edited 1 time(s). Last edit at 07/26/2016 08:48AM by chris33.
Check my rubbish blog for my prusa i3
up and running
[3dimetech.blogspot.co.uk]
Also i would change the small screws that hold the belt restraints to slotted stainless steel ones as they easily get rounded the ones provided are not stainless but chrome i think
Edited 1 time(s). Last edit at 07/26/2016 08:48AM by chris33.
Check my rubbish blog for my prusa i3
up and running
[3dimetech.blogspot.co.uk]
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Re: MGN12H and kossel metal carriages September 11, 2016 04:45PM |
Okay so I took a close look at the carriages and the magnets are all fixed the same.
The effector was another story - 3 were pressed into it with their surfaces flush with the effector. The remaining 3 were protruding, 1 was angled, relative to the effector.
So having heeded your warning about magnets breaking decided to press them into place.
I've placed one large washer on each side of the effector, the magnets hold the washers nicely in place, then pressed them on the bench vice.
Now they are all equally fixed in the effector.
Very grateful to BramV for identifying what would be a frustrating source of inaccuracy and fixing it early on.
Simon Khoury
Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions
The effector was another story - 3 were pressed into it with their surfaces flush with the effector. The remaining 3 were protruding, 1 was angled, relative to the effector.
So having heeded your warning about magnets breaking decided to press them into place.
I've placed one large washer on each side of the effector, the magnets hold the washers nicely in place, then pressed them on the bench vice.
Now they are all equally fixed in the effector.
Very grateful to BramV for identifying what would be a frustrating source of inaccuracy and fixing it early on.
Simon Khoury
Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions
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Re: MGN12H and kossel metal carriages September 13, 2016 04:51PM |
DjDemonD, that seems like a good way to level the magnets in the end effector, I'll try something similar when I receive the new magnets tomorrow!
Here are some pics of the one I'm building. The red parts are all custom designed, as simple as I could make them. If someone was looking for one of those parts I can share them, just let me know. Right now I have micro-switch endstop mounts, bottom-stops for the rails, belt-tensioners (mounted on the belt itself) and covers for the extrusions designed (all for 2020 extrusions). I'm also going to design a special double-fan duct for the filament cooling, and some plate to hold the arduino due + RADDS in place, and some other small components I need to fix all the electronics. The idea for the double fan mount is that two fans are placed at 120 degrees from each other, so you can attach them to the effector in such a way that they won't hit the towers when you go near the edge of the build plates. However, the fan ducts will be bent in such a way that the air flow will come neatly from 2 sides at the filament at 180 degrees, such as you see often with Ultimaker etc.
Obviously, the stops at the bottom of the the rails are not necessary when you have carriages that keep the balls in place when they fall off the rails, but I got genuine Hiwin carriages, and if they fall of the rails, all the balls will fall out
And those original carriages run smooth enough to fall out even with no load on them. For the belts, I chose not to go for the 'normal' way of tensioning the belts as kossel does. It seems stupid to me to sort of skew the whole frame to tension the belts I'd rather built the frame completely symetrical and use other means to tension the belts.
DjDemonD, about the rails running not so well: one thing I was doing when I was testing the rails if to move the individual carriages at various speeds. You can hold your fingers on them during a move to 'feel' if they run smooth. Specially at low speeds you can feel problems with bad rails/carriages. I send the 'chinese' rails back because I had the same problem as you: they were not equally smooth. One was pretty good, one was OK, and the third one was giving vibrations at low speeds. I am not sure how much it would impact the printing quality though, maybe not at all. But because I was aiming for a custom 'high end' kossel, I traded them for the genuine ones, which costed about 2.5 times as much as the chinese ones.
Oh and I'v seen people using springs between rod-pairs to lower vibrations. MAYBE it also helps with them being too flexible? not sure...
And one other thing. Do your carriages (with the magnets) also have holes for the bolts that are too wide? Mine were 3.5mm, while the carriage on the rails had 3.0mm holes. I noticed that because the holes were too large, I could fix the magnetic carriage onto the hiwin carriage in slightly different rotations... which seemed like a very bad thing to me, they should be exactly level. So I ended up printing a very small hollow cylinder of 3.5mm, then glued those into the holes in the magnetic carriage, and then put the bolts into them. That really seemed to work as the holes were small enough now to center the bolts.
Edited 2 time(s). Last edit at 09/13/2016 05:00PM by BramV.
Here are some pics of the one I'm building. The red parts are all custom designed, as simple as I could make them. If someone was looking for one of those parts I can share them, just let me know. Right now I have micro-switch endstop mounts, bottom-stops for the rails, belt-tensioners (mounted on the belt itself) and covers for the extrusions designed (all for 2020 extrusions). I'm also going to design a special double-fan duct for the filament cooling, and some plate to hold the arduino due + RADDS in place, and some other small components I need to fix all the electronics. The idea for the double fan mount is that two fans are placed at 120 degrees from each other, so you can attach them to the effector in such a way that they won't hit the towers when you go near the edge of the build plates. However, the fan ducts will be bent in such a way that the air flow will come neatly from 2 sides at the filament at 180 degrees, such as you see often with Ultimaker etc.
Obviously, the stops at the bottom of the the rails are not necessary when you have carriages that keep the balls in place when they fall off the rails, but I got genuine Hiwin carriages, and if they fall of the rails, all the balls will fall out
And those original carriages run smooth enough to fall out even with no load on them. For the belts, I chose not to go for the 'normal' way of tensioning the belts as kossel does. It seems stupid to me to sort of skew the whole frame to tension the belts I'd rather built the frame completely symetrical and use other means to tension the belts.DjDemonD, about the rails running not so well: one thing I was doing when I was testing the rails if to move the individual carriages at various speeds. You can hold your fingers on them during a move to 'feel' if they run smooth. Specially at low speeds you can feel problems with bad rails/carriages. I send the 'chinese' rails back because I had the same problem as you: they were not equally smooth. One was pretty good, one was OK, and the third one was giving vibrations at low speeds. I am not sure how much it would impact the printing quality though, maybe not at all. But because I was aiming for a custom 'high end' kossel, I traded them for the genuine ones, which costed about 2.5 times as much as the chinese ones.
Oh and I'v seen people using springs between rod-pairs to lower vibrations. MAYBE it also helps with them being too flexible? not sure...
And one other thing. Do your carriages (with the magnets) also have holes for the bolts that are too wide? Mine were 3.5mm, while the carriage on the rails had 3.0mm holes. I noticed that because the holes were too large, I could fix the magnetic carriage onto the hiwin carriage in slightly different rotations... which seemed like a very bad thing to me, they should be exactly level. So I ended up printing a very small hollow cylinder of 3.5mm, then glued those into the holes in the magnetic carriage, and then put the bolts into them. That really seemed to work as the holes were small enough now to center the bolts.
Edited 2 time(s). Last edit at 09/13/2016 05:00PM by BramV.
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Re: MGN12H and kossel metal carriages September 17, 2016 10:08AM |
I replaced all the magnets. The new magnets look all exactly the same and are stronger than the original ones. If I place a new and old magnet on a rod, and start pulling the magnets, the old magnet always comes loose first. Based on my manual test I'd say about 20%-40% stronger.
I started pushing the magnets from the bottom of the effector and used a big glue-clamp (not sure how to call it) to press them in and level them. Replacing the magnets in the carriages was harder because the old ones didn't come lose easily but I got them.
I'v tried first installing the magnets in the new effector only but the effoctor still wasn't completly flat on the build surface when I lowered it. After I replaced the magnets in the carriages, it comes close to a good fit on the build plate, see pictures.
However, I'm not sure how well it's supposed to be aligned with the build plate, in other words, if the deviation I see is a problem. My guess is it's not, any idea? Did you check the alignment of your effector with the buildplate?
I started pushing the magnets from the bottom of the effector and used a big glue-clamp (not sure how to call it) to press them in and level them. Replacing the magnets in the carriages was harder because the old ones didn't come lose easily but I got them.
I'v tried first installing the magnets in the new effector only but the effoctor still wasn't completly flat on the build surface when I lowered it. After I replaced the magnets in the carriages, it comes close to a good fit on the build plate, see pictures.
However, I'm not sure how well it's supposed to be aligned with the build plate, in other words, if the deviation I see is a problem. My guess is it's not, any idea? Did you check the alignment of your effector with the buildplate?
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Re: MGN12H and kossel metal carriages September 17, 2016 07:03PM |
Correct me if I'm wrong, but I don't think you can compensate for the tilt of the effector. The firmware can only move the carriages around, but that tilt will be there no matter where the carriages are.. a rotated effector stays a rotated effector 
Edited 2 time(s). Last edit at 09/17/2016 07:04PM by BramV.
Edited 2 time(s). Last edit at 09/17/2016 07:04PM by BramV.
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Re: MGN12H and kossel metal carriages September 19, 2016 01:48PM |
The effector tilt is the same on all parts of the bed. I cannot tell if the bed is not 100% level or that the effector is tilted. The frame can of course also be to blame. Perhaps all imperfection together contribute to the effector having a very very small gap on one side when lowered on the bed. It's really 0.3 mm or so, so I don't expect that I can do any better. I could compensate by slightly rearranging the the magnets in the effector, but I'm not sure if I'm then just tilting the effector to match the tilted bed. I think I'm very happy with the current situation so I'll just move on Working on designing the fan ducts, sort of getting done. They won't be extremely pretty but hopefully functional
If you have a video of your kossel in action I'd love to see it!
Edited 1 time(s). Last edit at 09/19/2016 03:54PM by BramV.
Working on designing the fan ducts, sort of getting done. They won't be extremely pretty but hopefully functional If you have a video of your kossel in action I'd love to see it!
Edited 1 time(s). Last edit at 09/19/2016 03:54PM by BramV.
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