1 Topic by redbarret (edited by redbarret 2015-02-10 19:11:16)

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Topic: Bushings or bearings? Doesn't matter.

I've read through bunch of articles on the internet about users of 3d printers replacing their 3d printed/plastic or bronze/brass bushings with linear/ball bearings and vice versa.
I've come to conclusion that unless you have step skipping from friction (and I'm not 100% sure on this either) bushings give no difference from bearings in terms of print quality.

Owners of 3d printers using linear bearings mod their 3d printers by switching to bushings and vice versa.
There's few reasons people switch but I honestly think none is worth the time.
Linear bearing printer owners mod their printers to use bushings instead to reduce the noise, but I don't get how that bothers them when there's more noise from fans and motors.
And then some swap their stock bushings with bearings to get rid of slack, but in reality its too small to make any noticeable difference on a modern FDM printer (3rd link below). Not to mention cheap bearings aren't perfect when it comes to tolerance either.

Here are few of the many links of people switching from bushings to bearings and vice versa, comparisons and good points:
http://www.reddit.com/r/Reprap/comments … s_vs_igus/
https://groups.google.com/forum/#!topic … 60SiLLrnf4
http://forums.reprap.org/read.php?1,221763

https://www.youtube.com/watch?v=tCUEYB1U6UY
http://www.thingiverse.com/thing:526660

REAL LM8UU bearings (like $6 each from Misumi, not the $0.80/ea Chinese crap) are also super quiet.

Can be a source of backlash [the play in a bushing], yeah. Although gravity tends to keep them pretty well centered. The carriage's weight is trying to accelerate it downwards at 9800 mm/s2, and your bot acceleration is probably under 3000mm/s2, so gravity is definitely winning the fight on where the bushing sits on the rod.

If your bot is still, the bushings will contact the rod at 0 degrees (top of rod). Let's say you crank up your bot to 9800mm/s. The bushings will sit at 45 degrees now. If you have 0.1mm of play between the bushing and the rod, the net horizontal deflection due to shifting from a 0 degree contact to a 90 degree contact would be 0.05mm. Then at 45 degrees, it's sqrt(2)/2*0.05 for about 0.035mm error. Double that to find the backlash, 0.07mm. That's pretty small -- rod flex at that insane acceleration is way larger.

http://i.imgur.com/IAqcENt.png

And my fav from all the links:

Honestly, it's kind of a "grass is greener" thing. A lot of FlashForge people upgrade their carriages from linear bearings to bushings, and a lot of Makerbot people upgrade their bushings to linear bearings.

I hope these links helped clear some things up.
If you're a Solidoodle owner and your carriage is damaged, then go for bearings, because the designs of the stock carriages are not open source and printable and the ones on sale are too expensive and the only alternative carriage we have on thingiverse uses LM8UU bearings.
If, however, you have no problem, I wouldn't advice replacing bushings with bearings just for the sake of improving your machine's print quality, because it likely won't.

It was already pretty evident from the direct drive mod results by several people that any backlash issue is caused by the short looped MXL motor belt (read this: http://www.soliforum.com/post/81693/#p81693), not bushings, bearings, shafts, motors or VREFs. But here's some more evidence.

Solidoodle 4

2 Reply by wardjr

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Re: Bushings or bearings? Doesn't matter.

We are all entitled to our own opinions.
Having two SD3's side by side one with bearings and one without I can assure there is a tremendous difference in quality, not to mention speed.  The one with bearings will easily print at twice the speed while maintaining the same level of quality as the one without.
I wonder who's opinion the Soliforum users will trust more?

Printit Industries Model 8.10 fully enclosed CoreXY, Chamber heat
3-SD3's & a Workbench all fully enclosed, RH-Slic3r Win7pro, E3D V6, Volcano & Cyclops Hot End
SSR/500W AC Heated Glass Bed, Linear bearings on SS rods. Direct Drive Y-axis, BulldogXL
Thanks to all for your contributions

wardjr's Website

3 Reply by redbarret (edited by redbarret 2015-02-10 21:13:37)

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Re: Bushings or bearings? Doesn't matter.

I don't think this is just a matter of opinion. There's also facts by people who have tried both and those who know the physics that there is no difference really, unless you compare low quality version of one with an expensiver one from the other.

As to your two Solidoodle 3s, yeah I remember you said you had two, but is the only difference between the two really just one having bearings and the other having bushings? I remember you had a different hotend on one of them at least.

Solidoodle 4

4 Reply by jagowilson

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Re: Bushings or bearings? Doesn't matter.

The stock hotend is actually very well equipped for high speeds because of its long melt zone wink so am e3d is actually not to your exteme advantage for speed.

5 Reply by wardjr

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Re: Bushings or bearings? Doesn't matter.

redbarret wrote:

I don't think this is just a matter of opinion. There's also facts by people who have tried both and those who know the physics that there is no difference really, unless you compare low quality version of one with an expensiver one from the other.

As to your two Solidoodle 3s, yeah I remember you said you had two, but is the only difference between the two really just one having bearings and the other having bushings? I remember you had a different hotend on one of them at least.

They both have E3d V-5's on them so yeah that is the only difference.

My printer with the bushings would never pull this off.

Printit Industries Model 8.10 fully enclosed CoreXY, Chamber heat
3-SD3's & a Workbench all fully enclosed, RH-Slic3r Win7pro, E3D V6, Volcano & Cyclops Hot End
SSR/500W AC Heated Glass Bed, Linear bearings on SS rods. Direct Drive Y-axis, BulldogXL
Thanks to all for your contributions

wardjr's Website

6 Reply by redbarret (edited by redbarret 2015-02-10 22:00:34)

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Re: Bushings or bearings? Doesn't matter.

Hm, so same shafts, same tensioners, both using fishing lines or same types of belts, same (or both lacking) pillow blocks, same buildog extruder, same heatbed and same filament?

If no, each can have an effect itself.
If yes, then this is getting interesting...
I'll even go to the extreme and use 3d printed ABS bushings like some guys in those links for my comparisons.

And then I'll try to source some bronze bushings, like the ones on a Replicator 2.
http://ts3.mm.bing.net/th?id=HN.607994071941516574&pid=15.1&H=125&W=160
...right after I get a working heatbed, that damn thing...

Solidoodle 4

7 Reply by wardjr

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Re: Bushings or bearings? Doesn't matter.

A bed heater is an important thing to have wink
They both have different upgraded bed heaters.  Since they both are silicone pads of the same configuration and both hold temp fine it doesn't matter for what I am demonstrating in the video.
Both machines are the same except for bushings/bearings.  I wouldn't even attempt to run the bushing machine at those speeds (240 mm/s).  It would simply fail and skip as the mechanism's are just not precise enough. 
The only drawback to higher speeds on the machine with bearings is really the hot end and how i have it configured.  Simply it can"t heat the plastic fast enough.

Printit Industries Model 8.10 fully enclosed CoreXY, Chamber heat
3-SD3's & a Workbench all fully enclosed, RH-Slic3r Win7pro, E3D V6, Volcano & Cyclops Hot End
SSR/500W AC Heated Glass Bed, Linear bearings on SS rods. Direct Drive Y-axis, BulldogXL
Thanks to all for your contributions

wardjr's Website

8 Reply by redbarret (edited by redbarret 2015-02-10 22:52:35)

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Re: Bushings or bearings? Doesn't matter.

I remember you used one of your SD3s to show how you had managed to not have backlash on a "stock" machine. Looks like you've upgraded both quite a bit since then if both have a  pillow block now, fishing lines and a new extruder. I havent had time to do much since 2014...

Anyway, the step skipping you say you'll get with stock bushings... friction maybe?

Solidoodle 4

9 Reply by jagowilson (edited by jagowilson 2015-02-10 23:14:55)

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Re: Bushings or bearings? Doesn't matter.

Yup friction is a force, opposite the force of the motors. When friction is high enough (higher speed), the motors can no longer provide the required force and friction wins, resulting in step skipping. I am of course referring to kinetic friction but static friction is also a factor--it's simply harder to start moving bushings, as well.

Bushings get the job done but they don't do it precisely and do it slowly. Anyone who "upgrades" to bushings from bearings should give me $5 because I could do better things with their money. It just doesn't make sense.

Easier to move = higher accuracy assuming mechanical rigidity. There are no exceptions to this rule in this case. Newtonian physics are pretty simple.

10 Reply by wardjr

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Re: Bushings or bearings? Doesn't matter.

My printers are in a constant state of modification.
Thus far I have yet to do a mod that didn't make my printer better.

Printit Industries Model 8.10 fully enclosed CoreXY, Chamber heat
3-SD3's & a Workbench all fully enclosed, RH-Slic3r Win7pro, E3D V6, Volcano & Cyclops Hot End
SSR/500W AC Heated Glass Bed, Linear bearings on SS rods. Direct Drive Y-axis, BulldogXL
Thanks to all for your contributions

wardjr's Website

11 Reply by redbarret (edited by redbarret 2015-02-10 23:34:52)

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Re: Bushings or bearings? Doesn't matter.

Well, if the issue is friction, I did say

redbarret wrote:

I've come to conclusion that unless you have step skipping from friction (and I'm not 100% sure on this either) bushings give no difference from bearings in terms of print quality.

The whole point is there's a... point where the differences in parts are going to be miniscule and aren't going to make any difference for an FDM printer.

That's all I have to say really. I posted some links to discussions. No need to repeat the stuff here. Likely the quality of the bushings on Solidoodle 3 and maybe the rest are shit if you want to run your printer faster than its advertised. I'll do my own comparison tests like I said when I fix my machine, as I'll encourage everyone else to do as well.

Solidoodle 4