Y carriage replacement

So my stupid curious cats got on my desk....and knocked my brand new filament spool off it's guide and smashed my build plate. I have an aluminum plate on my heated bed plus glass, but it snapped two corners off my plastic carriage mount.

I'm on ebay and see some nice looking aluminum replacments

[www.ebay.com]


My question is this... when i got my printer back in feb...i remember thinking i was missing a y bearing mount. I emailed folgertech and they said it was a updated design. I never liked the 3 bearing design as it makes one side a bit wobbly. Why did they change it ? I would imagine 4 bearings would be much more stable.

There is one on ebay [www.ebay.com] , but it's the only on and no aluminum bearing holders.

So why are there no 4 bearing carriages? I even see printable carriages on thingiverse, but they're also 3 bearing.

Edited 1 time(s). Last edit at 05/23/2015 08:01AM by Badkitty.

Extra bearings would drive part count, cost, and weight (and in this case, the weight would be added as a moving component of the Y axis, which is a fast-moving and fast-accelerating axis highly sensitive to extra weight).

With a carriage, PCB, insulator, and glass (and often a heat spreader as well), the Y axis assembly already has a fair amount of torsional rigidity and if your machine is properly set up it should not see any meaningful amount of torsional loading during use.

If you have one of the designs that has the Y endstop obstructing the smooth rod on the single-bearing side, going to a two-bearing design on that side without additional design changes would also limit your Y axis travel.

One of the nice things about open-source designs is that you could make an 8-bearing Y-axis if you for some reason decided you wanted one...But for the cost, weight, and complexity tradeoffs involved, most think 3 a good number.

Two bearings on one rail limits carriage motion to the axis of the rail. Adding a third bearing on a second rail prevents the carriage from rotating around the first rail and thus completely constrains carriage motion. Adding a fourth bearing on the second rail does nothing to constrain the motion of the carriage, but can cause problems if the rails are not perfectly parallel. A carriage on four bearings on two rails is an "overconstrained" mechanism. All this assumes minimal or no flexibility in the rails or the carriage.

If the carriage is a flexible, a fourth bearing may help keep it from flexing a little.

Torsional is not my concern.. its vertical movement (flex)

. The two bearing side seems very rigid..I can push down on the corners and its still level. But the single being side doesnt always come back level. And it's easier to move up and down...since there is only one bearing (center pivot) as opposed to two bearing where there is no pivot.

The point about the y end stop being in the way doesn't apply to me. Mine is on threaded rod outside the frame.

Plus..in my thinking...having four would make getting the smooth rods parallel much easier. Having the one allows to much flex on the side.


Ehh.idk. guess I'll just stick to whatever is available.

Does the bed plate have 4 level adjusters, one at each corner, that anchor in the undercarriage plate?

4 levelers for a flat plate is also an overconstrained mechanism. Three points define a plane. Adding a fourth point of adjustment makes leveling the bed more difficult- misadjustment results in bending the bed plate- you can't make it level if it is bent! With 4 adjusters each time you turn one of them you tilt the bed around both X and Y axes, and flex the bed.

Some of the printer makers seem to have figured this out, others have yet to do so. With three levelers, two are in a line along one axis, and the third adjusts the roll around that axis. You level the one of the first two set their edge of the bed parallel to their axis (pitch), then adjust the third to roll the bed on the first axis until the plate is parallel to the XY plane as defined by the guide rails. When you adjust the third leveler (roll), it doe not have any effect on the bed's pitch.

Using fully supported guide rails and a three point leveling system makes for a very stable bed that's very easy to relevel if it ever goes out of level.

Edited 1 time(s). Last edit at 05/23/2015 04:33PM by the_digital_dentist.