Any cons to using all bushings instead of bearings?

I want to build an ultimaker style gantry system. I want to use bronze bushings (eg. A 7Z41MPSB10M from SDP-SI.com) for the gantry system AND the printhead. Does anyone know if I lose any print quality if I use bushings instead of bearings? I like that the bushings are quieter than bearings.

And will bearings wear out the steel rods after some time?

I used bronze bushings in my printer very early on. I quickly replaced them with linear bearings because the bushings chattered a lot. Friction is higher with bushings. Bronze is softer than steel and will wear more and faster than the steel they ride on. Bearings will cut grooves into steel rails unless the rails are hardened.

I think linear bearings are preferable to bronze bushings, and I think fully supported rails with bearings or linear guides are better still.

They chattered? I thought they were supposed to be quiet, but maybe I'm wrong or maybe I have to get a certain kind of bushing.

The higher wear from friction is something I'm worried about. I'd hate to have to replace the bushings after 6 months of heavy use (assuming the wear decreased the print quality in that time).

But doesn't the ultimaker use bushings? If anyone has an ultimaker, can you comment on if you've needed to replace the bushings after a while?

Jessica, I have experience with bushings on my CoreXY machine. They work nicely on the X and Y stage which is interconnected similarly to that of the Ultimaker which you are correct in saying that it uses bushings. As for the Z axis, I believe the Ultimaker uses linear bearings(may not be correct so don't quote me). I tried bushings on my Z stage and they caused a lot of chatter like Digital Dentist said. This is because the Z platform is cantilevered out from the vertical rails. This causes a large moment to be placed on the bushings due to the weight of the platform. Consequently, they slide on two points on opposite sides of the rod instead of the whole bushing and they do not slide very easily while supporting this weight. Linear bearings and the other hand can handle this torque. It is probably because there is minimal contact with the rods where as the bushings theoretically contact the rod all around. Depending on what type of machine you have and how well balanced it is in the Z you may be able to use them but I would suggest skipping these and going for bearings.

Now it is a different case for the X and Y. Usually you will not expect the bushing to support this type of load on these axes. But you need to be sure your belts are not applying any torque off the axis of motion to any of the bushings in order to get smooth motion. So you may choose to use bushings on the X and Y and be happy with their performance. They are very quiet!

Hope this helps!
JTT

Edited 1 time(s). Last edit at 06/18/2015 12:56AM by jtoombs.

I use bronze bushings on all axis. Cartesian style printer. No chatter, but the axis are light weight. I can't give you an answer on wear yet, it's only on it's 4th spool.

Oh I forgot about the z axis. I was planning on using the bushings everywhere except the z-axis since the z-axis is doesn't move that much anyways and wouldn't generate too much noise.

I will have to use bushings for the X and Y rotating rods on the outside, but for the rods that move in the X and Y direction with the printhead, I can choose linear bearings or the bushings. And since they probably won't chatter there, I might just go ahead and try the bushings.

Igus makes delrin bushings... Longer wear profile and quieter. Pricey maybe

I switched from linear bearings to sinter bronce bushings and never looked back. Lighter, more silent and at the masses involved practically as longlived and reliable as bearings. I use the for all three axis and even tried them as bearings for the extruder.

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Usually brass or Oilite type bushings may need to be press fit into a cylinder with the correct ID in order to be compressed to the proper size or if undersized, they can be reamed to fit. Igus bushings definitely need compressed to fit the shaft. Properly sized bushings can be much more accurate than linear bearings, but this will depend on the class of bearings as well.

I replaced the 8mm rods + cheap bearings on my Y axis with rods and brass bushings from printers. They run quiet and run much smoother
On my Z axis I run two 10mm rods with .375 inch bushings I bored out to 10mm. They do not run as smooth as the factory matched ones on the Y axis but they have no play in them. It requires more torque to move the Z but with 5mm threaded rod there is a lot of torque and speed is not neeeded.
Brass bushings need to be lined up a lot more accurately or they will bind. Cheap bearings have a lot of play in them.
In my opinion bearings are better than cheap bearings but good (expensive) linear bearings are better than bushings