When I first brought couplings I didn’t read too much into the different types or what is best etc. Needless to say I ended up with some couplings that really didn’t work well. I managed to track down some new couplings and I think my CNC will be much better off for having them.
The couplings I was using for connecting the stepper motor to the leadscrew were jaw type Lovejoy brand couplings. I had seen people use these before and without thinking much into it I decided they would do the job.
Upon getting them I was amazed by the terrible backlash! The jaw couplings fit well into the middle piece (called the spider) but I was easily able to feel a huge amount of play between them.
The seller had included a rubbery material similar to that of a party balloon. This stretchy rubber was to be fit in-between the coupling pieces. It did remove mostly all of the backlash. However after running the CNC over time, centrifugal force moved the rubber material and the backlash returned.
As you can imagine having a little backlash leads to a lot of inaccuracies when cutting. It wasn’t that bad but I did often notice parts being out on the measurements.
Now that I’m getting ready to build a 3D printer I knew I needed the accuracy so I went in hunt of flexible one piece couplings. I found some on eBay very quickly just by searching for flexible couplings. They also only came to $23 USD, I wouldn’t have minded paying more but these particular couplings were the only ones that matched what I needed (12mm one side, 1/4″ the other)
These new couplings have no backlash at all as they are one part but due to a cool spiral like cut in the centre they still allow for a little radial error. Which is nice because I’m sure my stepper motors aren’t perfectly aligned with the leadscrews.
The couplings are made from aluminium so at first touch they seem so much weaker than my old steel Lovejoy couplings. But I think that’s just how they are, I’ll have to watch them carefully and make sure to watch for any cracks or weaknesses developing in the aluminium.
To finish here’s a video of the new couplings in action:
