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Low Cost Rails

A project log for Pick and Place Machine

A custom-built pick-and-place machine running OpenPnP.

LanceLance 02/23/2021 at 01:590 Comments

Introduction

After extensive reading about low-cost rails, there seemed to be a mix of experiences.  Some of them worked without issue, some had minor issues that they were able to resolve, and some had major issues with them that rendered them useless.

I purchased two sets of low-cost rails.  For purposes of discussion, I will refer to them by the colors of their end caps (green and black).

Green Set

https://www.aliexpress.com/item/4000706013922.html?spm=a2g0s.9042311.0.0.27424c4dYpvk0n

Green Rails
The set of rails referred to as the "green rails."

Black Set

https://www.aliexpress.com/item/32899285305.html?spm=a2g0s.9042311.0.0.27424c4dpy21Gc

Black Rails
The set of rails referred to as the "black rails."

Discussion

An initial examination of both sets of rails left me to conclude they were pretty well made.  Both sets of rails were well oiled. There were not any visible defects.  There was a little bit of roughness around the counter-bore holes in the rails, but it was pretty minor and should not interfere with the operation since the carriage is not in direct contact with the top of the rail.

After working the rails for a while, both sets seem to exhibit intermittent sticking.  It was repeatable but not completely consistent in location.  I searched for the source for some time.  Eventually, I concluded the issue was in the plastic end caps where the ball bearings did a 180-degree turn.  It seems that because they are made of plastic, they have both a larger manufacturing tolerance and a higher coefficient of friction.  One, or both, of these was causing occasion sticking.

End Cap
The ball bearings reverse direction in the plastic end caps.
Path of Ball Bearings
Approximate path (red loop) of the ball bearings in the carriage.

Solution

I applied a generous amount of Unilube and worked it into the carriages.  After lubrication and working the carriage back and forth, the sticking seemed to be largely resolved.  I think these rails need a little "breaking in" and to be kept well lubricated.

Discussions