Leadscrew anti backlash , Z axis

Hi guys,

I am almost finishing my mendelmax 1.5 (rework) build.
I am using leadscrews for my z axis, and i got rid of the heavy backlash using 2 nut's and a spring in between.
Take a peek at the pictures

What do you guys think,

Cheers

Edited 4 time(s). Last edit at 03/06/2016 11:28PM by Govahnator.

Looks great, heavy duty even.
I like how the pre-load spring works on the leadscrew, may even do that to one of mine.

Have fun printing!
MarkB

It is really needed with leadscrews and these brass nuts with 4 starts?

Do you have after/before prints?

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My printers:
-Makerbot TOM (#5215, circa 2011), MK6 extruder, ABS 3 mm
-HICTOP Prusa i3 (modded for auto-level, thread screws), ABS/PLA 1.75 mm

About me:
[www.thingiverse.com]

Hi,

I am still building the printer so i don't have pictures of print's, but i can do a test as soon as the printer is finished.

Even without testing this (cheap) upgrade, i think it is a must, especially when using auto level.

There is a lot of backlash on these nut's (before this upgrade i could move the leadscrew atleast 2mm within the nut and thereby move the whole x/z axis by hand):

When homing it affects the repeatabilty of homing the z axis.

When probing for auto level, the calculation's are affected .

When printing with auto level, the leadscrew goes up and down wich the backlash affects.

The repeatabilty of the print's layers is affected

The whole x/z axis isn't stable because of the backlash on the nut's. On my prusa i3 the vibration's when printing fast make the leadscrew's move within the nut wich makes the whole x/z assembly move and even makes the whole frame vibrate even more, and therefore also the hot end. ( this might not be an issue with the mendelmax but still )


All of the above issues should be fixed with the extra nut, all of the backlash on the leadscrew is gone, it feel much more stable.

The X axis may be movable by hand in the +Z direction, but gravity (specifically the weight of the X axis) should keep the nuts loaded so antibacklash nuts aren't required unless the mechanism binds. If the mechanism binds I think it would be better to fix the binding problem, because it implies that things are misaligned, than to solve it with antibacklash nuts.

Edited 1 time(s). Last edit at 03/07/2016 07:08PM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

That looks really nice - both the nuts and the whole build. But backlash really shouldn't be an issue on the Z axis as long as the bearings run smoothly. The weight of the X axis will always keep the same side of the nuts bearing on the leadscrew. Backlash becomes an issue when the only force operating on the moving object is from the leadscrews, and then you have to switch bearing surfaces when the direction of travel reverses.

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the_digital_dentist
The X axis may be movable by hand in the +Z direction, but gravity (specifically the weight of the X axis) should keeps the nuts loaded so antibacklash nuts aren't required unless the mechanism binds. If the mechanism binds I think it would be better to fix the binding problem, because it implies that things are misaligned, than to solve it with antibacklash nuts.

What you are saying is true when the backlash is only in the Z axis( and you are not using auto level) .

But there is backlash in x and especially in y within the nut, wich makes it a whole different story.
This upgrade made my whole x/z assembly MUCH more stable, and i advice it to anyone using leadscrew's, the less stable the frame the more it's worth it.

I tried this because i had an extra pair of nut's and springs around, and i as well didn't have much of an expectaton of this, but i can assure you it's worth it, and this time i will order extra nut's just for this upgrade on my prusa i3.
I can make a video of the backlash i am talkin about if you like, i am sure it will convince you .

Edited 2 time(s). Last edit at 03/07/2016 02:13PM by Govahnator.

Double post, ignore.

Edited 2 time(s). Last edit at 03/07/2016 02:09PM by Govahnator.

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But there is backlash in x and especially in y within the nut, wich makes it a whole different story.

Um, exactly the opposite actually. The play in X & Y is intentional and reduces the tendency of the lead screws to force the x-axis in those directions. The lateral position of the gantry should be determined solely by the linear shafts - that's what they are there for. If you take out the play in X & Y from the leadscrews you will likely make Z wobble worse.

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JamesK

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But there is backlash in x and especially in y within the nut, wich makes it a whole different story.

Um, exactly the opposite actually. The play in X & Y is intentional and reduces the tendency of the lead screws to force the x-axis in those directions. The lateral position of the gantry should be determined solely by the linear shafts - that's what they are there for. If you take out the play in X & Y from the leadscrews you will likely make Z wobble worse.

Then why do professional cnc machine's use the technique i am using?
I am not saying you are wrong, but i am confident this is a large improvement, plus you can buy anti backlash nut's wich aren't adjustable in tension while this is.
I guess the only way to tell is to do a test print with and without ( i can do that with my prusa i3 now already), even though i am confident that the upgrade does just as much to the precision of your parts as to the looks of it.

Edited 1 time(s). Last edit at 03/07/2016 02:22PM by Govahnator.

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I guess the only way to tell is to do a test print with and without ( i can do that with my prusa i3 now already), even though i am confident that the upgrade does just as much to the precision of your parts as to the looks of it.

Certainly. In my opinion the nut will even add resistance to the rotation. Which is your theory behind auto-leveling being affected by backlash?

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My printers:
-Makerbot TOM (#5215, circa 2011), MK6 extruder, ABS 3 mm
-HICTOP Prusa i3 (modded for auto-level, thread screws), ABS/PLA 1.75 mm

About me:
[www.thingiverse.com]

CNC machines use antibacklash nuts because there is mechanical force applied to the cutting tool by the material being cut in all three axes. In other words, the material resists the motion of the tool. In a 3D printer, we aren't cutting or drilling into a hard material- all we are doing is positioning the extruder nozzle, which in theory, should touch neither the print nor the bed plate. In the Z axis, gravity will keep the X axis pressed against the Z axis screw threads at the nuts.

If the mechanism binds, there is resistance to motion and antibacklash screws will help ensure that the X axis boom/nozzle gets where you intend it to go, however, it is better for the mechanism not to bind, and therefore not to need antibacklash nuts.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Ok guys thanks for your expertise, i will test this soon and provide some test results
Just one more thing that comes to mind, the original mendelmax 1.5 uses a spring between 2 regular nuts on the threaded rod as well.

Cheers

Edited 1 time(s). Last edit at 03/07/2016 07:33PM by Govahnator.

Sorry, didn't mean to sound so negative. All that matters in the end is how it works - if you get the results you want it's all good!

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JamesK
Sorry, didn't mean to sound so negative. All that matters in the end is how it works - if you get the results you want it's all good!

Hi James,

You didn't sound negative, i made this topic to discuss the possible pro's and con's, wich we did, and i am glad you shared you're thought about this subject