My custom Cartesian
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Here are two small updates. In the second to last image above one can see that the plug was still exposed and I also wrote that it does no longer look like that already at the time of posting the image. So here is how it looks now:
Also I did some experimentation with my Z axis. I changed it from direct-driven via flexible coupler to a belt-driven approach where I also introduced a 2:1 reduction ratio to get my 8mm lead down to a 4mm lead. The motor is shifted to the front and attached with a separate motor holder bracket. The lead screw sits inside a printed base with a thrust bearing in the bottom and a 608ZZ bearing to take the radial forces from belt tension.
But as I mentioned earlier I will revert this approach. The main reason for this decision is that it is virtually impossible to get the motors well aligned because the screws that fix the holding brackets to the frame are covered by the motor once it is installed. So this is an extremely tedious mount-check-unmount-adjust-loop that so far has not yielded the results I am very happy with. The belt tension is influenced a lot more than I would ever have expected by moving the motor only 10th of a millimeter. So this is no fun to do.
I already have all the parts on my desk because I will not simply go back to how it was before but will also replace the lead screw by a 2mm lead and the coupling will be replaced by a zero-backlash jaw coupling that will eventually be suspended on a thrust bearing that sits on the motor housing so the motor shaft gets relieved of the axial downward forces. Images will follow once this is done.
Manuel
Duet 3 6HC (v0.6) with RPi 4B on a custom Cartesian
with probably always latest firmware/DWC (incl. betas or self-compiled)
My Tool Collection -
Manuel,
Is that motor mount bracket slotted where it fixes to the extrusion so that you could raise it a bit higher? If so, you could turn the motor 180 degrees so that the shaft is pointing down, and mount the motor on top of the bracket. Then you would be able to get at the fixing bolts to set the belt tension. Or would that mean that you lose too much travel in Z due to the bed hitting the motor? Just a thought.........
Edit. If you fitted the pulley the other way round on the motor shaft, you probably might need need to move the bracket vertically (but that won't help the bed hitting the motor).
2nd Edit. Just scrolled up to see your original pics and it looks like the gantry moves in Z not the bed, so it might work if there is enough clearance to fit the motor that way.
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Hi Ian,
Thanks for this idea. It might work. The brackets are slotted and also mounted at the outside of the frame. And the bed runs strictly inside the frame (with some clearance) so there is no way the bed could ever collide with the motors - if it does I guess I have a whole different set if issues.
And yes, it's an i3 style Cartesian where the X gantry moves in Z. Whether or not the extruder carriage collide with the Z motor I cannot say right now but I don't think this would be an issue - could also be solved by just using longer belts to get the motors a little bit more to the front.Anyway this approach might still not work due to some reinforcement struts (no idea how to describe this better) that are part of the bracket and makes sure it cannot fold on itself. In the image below you can see a little bit better what I mean (sorry for the bad quality, just have nothing better at hand right now)
They might be in the way of the belt path and I do not know whether the slots will allow me to move the motor high enough up so that an upside-down mounting approach would be able to align with the pulley on the lead screw horizontally. I might compensate a little bit by making the lead screw base a little less tall (my English is not at its best today
) but there is not much to gain there. I guess 1mm max to not risk the structural stability of the base since it is not supported at the bottom (because usually this is where the motor is mounted).Also having the motors where they are now also makes it very hard to get to my leveling screws since the motors are perfectly aligned to in the way.
Turning them upside-down is probably the only way to make this situation even worse. And last I am looking forward to a 2mm lead. Not that I ever had any issues with 8mm lead.
EDIT: Looking a little bit closer on the image above I don't think these struts are in the way of the belt path. But from what I can tell the slots for mounting won't allow me to raise it enough to get a good alignment of the belt horizontally.
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Do you need to move it up?
I think that if you move the bearing on the screw above the pulley (attach it to the vertical extrusion), both pulleys will be roughly aligned. -
@obeliks said in My custom Cartesian:
I think that if you move the bearing on the screw above the pulley (attach it to the vertical extrusion), both pulleys will be roughly aligned.
I think this might result in a very odd and unfavorable angle to fix the bearing. If you look at the picture of the full printer in the second post you can see that it is quite a distance from the vertical extrusion to the lead screw.
Still, reverting-with-improvements will give me the best solution, I think. I will get an even finer Z resolution and free access to my leveling screws again. And from what I read in another thread these jaw couplings should also reduce noise a little bit (which is nice but honestly not really important on the Z axis).
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Oh, I didn't notice the distance.
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@obeliks Yeah, the recent images are misleading in this aspect.
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Just converted to a 2mm lead screw, now I can print at any layer height to 2 significant digits without worrying about height accuracy.
i.e. 0.10, 0.11, 0.12..... etc
Previously, with a 'normal' lead screw, the only accurate heights where , 0.1, 0.15,0.2....etc.
first print is on as I type
oops, meant to mention, you are unlikely to need a reduction ratio because the torque needed is much reduced from an 8mm pitch.
Torque needed should be about 25% of what is needed for an 8mm pitch, the number of steps has changed from 400 to 1600.
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@stewwy said in My custom Cartesian:
Just converted to a 2mm lead screw, now I can print at any layer height to 2 significant digits without worrying about height accuracy.
i.e. 0.10, 0.11, 0.12..... etc
Just did the same today.
Images will follow.Previously, with a 'normal' lead screw, the only accurate heights where , 0.1, 0.15,0.2....etc.
That seems odd to me. What lead did your lead screw have previously? On 8mm lead it would be 0.04mm increments. To get to 0.05mm increments it would have needed a lead of 10mm. I rarely came across this type of lead.
oops, meant to mention, you are unlikely to need a reduction ratio because the torque needed is much reduced from an 8mm pitch.
Torque needed should be about 25% of what is needed for an 8mm pitch, the number of steps has changed from 400 to 1600.
I never used the reduction ratio because of lack of torque. I only used it to convert a physical 8mm lead into a logical 4mm lead.
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@wilriker said in My custom Cartesian:
That seems odd to me. What lead did your lead screw have previously? On 8mm lead it would be 0.04mm increments. To get to 0.05mm increments it would have needed a lead of 10mm. I rarely came across this type of lead.
You are right, we had a party last night so still a little hazy!
Note to self: don't press submit without thinking it through lol
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As well as better resolution, you get other benefits too from using a finer lead. Effectively you get better gearing so can use a smaller motor or a single motor to drive say 3 screws via a single belt. The shallower helix angle also means that if you have a heavy bed, it will be less likely to drop under it's own own weight. I did a bit of a write up on my blog almost two years ago which explains things https://somei3deas.wordpress.com/2017/01/31/z-axis-lead-screws/
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@deckingman said in My custom Cartesian:
As well as better resolution, you get other benefits too from using a finer lead. Effectively you get better gearing so can use a smaller motor or a single motor to drive say 3 screws via a single belt. The shallower helix angle also means that if you have a heavy bed, it will be less likely to drop under it's own own weight. I did a bit of a write up on my blog almost two years ago which explains things https://somei3deas.wordpress.com/2017/01/31/z-axis-lead-screws/
That write up is one of the things that prompted me to order one, so thanks
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@stewwy said in My custom Cartesian:
That write up is one of the things that prompted me to order one, so thanks
Blimey - that's 3 people who have read it
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@deckingman said in My custom Cartesian:
Blimey - that's 3 people who have read it
Does that include me already? Because I read it, too.
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@deckingman I read the whole rag front to back when I was planning out my printer. There must be a few of us with more time than sense.
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Definitely, that is a very helpful blog.
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Strewth - there are 6 of you who have read it!
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@deckingman I even have a subscription to your blog added in my feed reader, so I get notified of new entries even if you do not announce them here.
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@deckingman said in My custom Cartesian:
Strewth - there are 6 of you who have read it!
Ian,
Add me to the list. Now it's 7 people -
Hi
Is it possible that you can Upload your config for the anet am8 ?
Because i have the am8 with duet wifi and i dont know how to beginnThanks a lot
