Weekly Hardware

Week 4:

Precision Linear Axis + Actuator

This is the Actuator I mounted to my Precision Linear Axis.

The Process:

Picking up from last week's design of the actuator location, I headed to the HobbyShop to ​scrounge something comparable to a lead screw. I was extremely lucky to find a high helix lead screw like the one shown below. After looking up this type of leadscrew on the internet, I learnt that the nut is made from POM-C plastic which requires no lubrication. Some online stores claim that the high helix profile is better at reducing backlash. I measured the lead of the shaft to be 25.4mm/rev (1inch/rev) which is much larger than the 2mm/rev that I estimated for my rising table.

Ideally, I would have liked to have coupled the leadscrew to my stepper motor shaft with an Oldham style coupling, and have the shaft supported by a thrust bearing at the end closer to the motor and a self aligning bearing at the other. However, I wanted to hold off on investing in these components, at this early stage of my desk design. I was unsuccessful in acquiring regular roller ball bearings as well, and hence was not able to support the shaft of my actuator with bearings.

 

I bored out a hole in a block of soft wood, to press the nut into. I then glued this bock in place of the existing block on the slider.

At this point, I was looking forward to testing the slider. Far from ideal, I coupled one end of the shaft to a hand drill. While trying my best to keep the shaft as parallel to the ground as possible, I actuated the hand drill. The slider moved up and down fairly smoothly. (as seen in the video above)

 

However, quick to my disappointment, the block with the nut split in half! 

I learnt a valuable lesson in the importance of alignment and appropriate supports for the lead screw system. Without a flexible coupling between the hand drill and the leadscrew shaft, there was a significant moment loading imparted to the nut and hence the soft wooden block. With the hand drill set to "Drill Mode", the drill was able to easily overcome any resistance from the binding of the slider. Thus the large reaction moment at the block caused it to fail. 

As this happened on Saturday evening, I was unable to replace the block with a newer one and fabricate any supports for the lead screw shaft. I am determined to make amends by the end of the following week!

©2019 by Yadunund Vijay. 

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