Busted Couplings...

The appearances of square parts are a poor judge of machine accuracy...

I’ve been cutting those door pulls but in testing of a profile cutting tool I stumbled across a problem. My machine developed a “thud” when changing directions on the Y axis and suddenly struggles with location repeatability after tool changes. Some further investigation revealed why…

Drive Coupling

The above is a picture of a new replacement drive coupling for my machine. These are called Lovejoy style couplings, I assume named after the person who invented them. The red part is plastic, and is meant to be sacrificial. If you over-torque the drive for whatever reason, the plastic will break and you won’t be grinding metal against metal and possibly doing more expensive damage.

And here’s a picture of my X axis coupling…

Drive Coupling

No wonder I’m off a few thousandths. I’ve only been cutting square parts without critical dimensions so the problem here wasn’t immediately noticeable. As long as your movement involves an even number of axis direction reversals, your parts will ‘look’ fine for lack of a better word, but micrometers have a way of revealing the truth about them. On my ~5 inch long part I was losing 4 thousandths on the X, and a whopping 50 thousandths across 2 inches on the Y. I suspect the Y axis, with its thud, will have two of the sacrificial teeth broken rather than just the one as you can see here on the X coupling.

Since I need two there’s no reason in only ordering that many, I went ahead and ordered replacements for all three shafts/motors.

And the best part… the Y axis coupling is under the Z column. Guess I gotta find a friend with a hoist again.