Replacing 8mm rods with 10mm in MendelMax. What properties should I look for?

Hey Folks,

My standard size MendelMax currently uses 8mm steel rods. Since the rods were included in a kit, I'm not sure if they are hardened, but they are not chromed. I've noticed that there is a significant amount of flexing when pressing lightly on the y-axis table, and the x-axis extruder assembly twists fairly easily. To remedy this, I'd like to get reasonable quality 10mm rods to hopefully increase the quality of my prints at high speeds, but don't want to break the bank either. I'm currently using LM8UU bearings, but would consider moving to a different bearing/bushing for the 10mm rods as LM8UU are a pain to align.

I gather than I want precision hardened steel rods. Here's some that were suggested by another member of the forum: [www.mcmaster.com]. Can anyone attest to these? Should I get chrome plated rods instead? Should they be stainless steel as opposed to steel?

Thanks for any guidance!

Hey guys, I'm revisiting this again. The main motivation is my layers don't sit perfectly on top of each other; they tend of be offset more than I'd like (for example, when printing a simple box). I've seen some really nice prints and so I know it is possible. The thought is that increasing the rigidity of all of the smooth rods by upgrading from 8mm to 10mm rods with LM10UU bearings would increase the quality of the prints. Or, am I attacking the problem the wrong way?

Most likely the problem is in your Z axis, not your Y or X axes. Give this (https://www.evernote.com/shard/s211/sh/701c36c4-ddd5-4669-a482-953d8924c71d/1ef992988295487c98c268dcdd2d687e) a read and see if what you are seeing looks like what's shown in the article.

But for what it's worth, the hardness and surface coating (ie chromed) of smooth rods will not have much impact on their stiffness. The best way to increase stiffness is to increase the diameter. If you really want to get rid of any flex I'd go for no less than 12mm diameter. The problem is then cost of the rods increases pretty quickly, as does their weight. Linear bearings/bushings also become more expensive.

For use with linear bearings, you need a surface hardness of Rockwell C60 or better, or the bearings will wear grooves in the rods.

you would be better off with brass bushings if you want a precise fit. the loading of the linear bushings allows for slop under load.

even at 8mm the bushings would reduce play substantially.


now if you want to remove the greatest slop, look at the spacing between the bearings/bushings and the parts that it mounts to. make sure it is a tight fit, even use tape, and heated glue gun if you need too. you want the bearing/bushings to be firmly attached. usually this is done with zip ties

Edited 4 time(s). Last edit at 12/17/2013 10:57PM by jamesdanielv.