Z-Axis rods and bearings

[Scott Goldthwaite]

I noticed that the build plate arms on my Rep2 will move a tiny bit when I wiggle them.  Upon closer inspections it seems the source is the bearings on the Z-axis are just a little lose.  It's just a tiny amount, but it would be nice if the bearings had a snug fit and no play at all.  Is there a way to upgrade the bearings so they are tighter?

I was reading about the aluminum arm upgrade from Bottleworks which seems pretty nice.  There's a couple opinions on if the ball bearings are a good idea or not on the coated aluminum z-axis rods.  If I were to get this aluminum arm upgrade I'd probably replace the z-axis rods with hardened steel rods - McMaster 6112K102.  Would the ball bearings in the aluminum arm upgrade have little or no play?   Are the z-axis rods 300mm?

[Clinton Hoines]

Your Z axis rods are already very high quality hardened steel no need to replace them. If you have wobble in your bearings replace them when you do the upgrade, but no need to swap out the rods as they will most certainly still be in perfect shape.

[Jetguy]

No, on the 2 series, the z rods are coated aluminum according to the threads on using Bottleworks z arms. There was a decent discussion on this.

[Clinton Hoines]

Oh sorry my mistake, thought the Rep2 still had the steel and the Rep2X went to the aluminum. Learn something new. ;)

[Jetguy]

I could be mistaken as well, I just remember that it came up in the Aluminum Z arms / upgrade beds discussions.

Further, It might be best to ask Bottleworks directly http://www.bctechnologicalsolutions.com/arm-upgrade/index.html

 

In my own experience, yes, every single linear ball bearing I have touched (LM8UUs, LML8UUs, LM12UUs, SW06s) they all have sufficient preload to have zero backlash from what I have seen on proper hardened rods from the same vendor intended for the application. I mostly use VXB rods and bearings but have done a fair amount of mixing and matching with expensive Thomson linear stuff and it's all the same in my informal tests.

 

Also, don't be mistaken that there is still backlash in the Z screw, we have gravity, the ultimate backlash preventer. Unless your bot is printing while accelerating vertically (and that's a fun pic to see), in real world usage there is no resulting error.

All adding an antibacklash nut does is add more friction. Given the z motor is already high inductance, you are more likely to skip steps and introduce new problems, requiring even more upgrades (new bigger motor, driver adjustments to match the motor, etc).

All anitbacklash nuts are is 2 nuts being pushed apart by a spring which greatly increases the friction to the shaft. In the z axis, we already fight gavity and therefore do need another nut and spring bushing back down.

http://www.cncroutersource.com/precision-acme-leadscrew-nut.html

[ccsg tech]

Is there something really wrong with the original oil lite bushings? I am currently machining some z arms and i am tempted to put in the brass ones. With the arms, the middle plate and back plate all in hollowed out aluminium, solidworks tells me its only 350 grams more heavy. Plus the O.D. is the same diameter as the linear bearing so if i want to fit some bearings in later its no big deal. 4 linear bearings on mcmaster carr brings the bill up to 80$ plus shiping. ouch. I just wich bottleworks had updated his website monday before i bought the metal. At 150$ he is probably making next to no profit.

[Clinton Hoines]

I use Bronze bushings through out my Rep1 dual XL and have no issues at all. I did upgrade my Z rods to 10mm and machined my own bushings but they work exactly the same as the Rep2 bushings I installed. Which BTW were $1 each direct from Makerbot. :)

[Bottleworks]

Because of the duty cycle of the Z stage, you shouldn't damage the rods with bearings.  But with that said, it sounds like your issue isn't with the OEM bushings.  Gravity should be removing the play you're seeing with the OEM Z-stage.  What is the issue, overall, that your having?  Vibration issues?  When you say a wiggle, have you checked that the bolts are snug on the Z-stage?

And the few who are interested in my arms, but are convinced that they don't want the bearings can just reuse the bushings.  You just have to print out different bearing/bushing retainers.  I designed it to use bearing because that's what people on here wanted.  (From a design standpoint, it would have been easier to stick with the bushings).

[Scott Goldthwaite]

I'm not really having an issue; my Rep2 is printing fine.  I just think it would be better if my build plate was more rigid.  I don't think anything is loose and I don't think it's backlash with the lead screw.  If I grab the plastic piece that that holds the z bearing, it seems like it's a tiny bit loose on the shaft.