Going For Broke

Well, dumb me again. Sometimes I just have to learn by experience and just blame myself. I actually like problem shooting and it is something I usually do quite well. I should have been a CSI or some kind of forensic engineer.

My problem is I broke another coupling on the HB2. Same place and I am certain the same reason. There is nothing wrong with the selection or type of coupling. They are perfect for the work they were selected to do. Actually, the helical beam is one of the most rugged, with the highest torque and deflection ratings of the couplings I have researched.

My problem is shaft alignment. I am using the original slotted aluminum tubes around the couplers as debris covers. They have no affect on spacing or alignment. However, they did prevent me from clearly seeing, thus correcting my real problem on the Y axis steppers.

The first two axis I set up were X and Z. They were the easiest for me to measure and eyeball. They both have run super smooth. The double Y axis drive is what I did last and has been more of a problem. Since X and Z aligned so well, I ASSUMED assembling Y would be a no brainer. I put them together with the covers on and the open slot down. That made it extremely difficult for me to see the shaft misalignment. I used a mirror so I didn’t have to stand on my head to look up. However I couldn’t see the vertical alignment problem, only the horizontal which was fine. (The assume part.)

All the other work, end play, screw/guide alignment, was on the right track but not the major issue.

I am an energy and HVAC engineer. Motor coupling alignment is a major component of every large mechanical room I have ever built. I hire professionals who do nothing but pump/motor shaft alignments with very specialized test equipment. It is that critical! DOH!

This time I left the covers off and was alarmed at the amount of vertical misalignment I had permitted. The couplers are good for up to 0.010″ axial misalignment (a lot!) but this looked more like 0.100″ Of course 0.000″ is the goal. The problem is I made the mounting parts and their holes so tight in tolerance; there was no room for adjustment. A little reaming solved the problem.

What is amazing is the couplers could actually withstand the extreme abuse for awhile. One clue I have noted for future reference and I share, is the Y stepper with the alignment problem felt slightly hotter than the other stepper running exactly the same steps. I told myself, “This stepper is doing more work…”. Yes it was.

That extra work was being absorbed by the coupler until the point of failure. Lesson learned. The axis “appeared” to be running quite well. It is this ability I have to observe, question and remember every detail (the overly warm motor) even when nothing seems wrong. This is called “valuable experience”. Not everyone cultivates this power of observation to their advantage. To some folks it is called “shit happens”. 🙂

What I did this time is assemble the mounting with the coupling clamp screws loose. When I can turn and move the coupling freely on both shafts with no binding, I know they are aligned. I clamp down the motor mounting while constantly checking the coupling freedom, and then tighten the coupling clamps last.

If it wasn’t for the everyday problems, we couldn’t appreciate the good life.