Tips/Techniques Shaft couplers

[slow-poke]

I'm getting close to wrapping up the mechanical aspect of the CNC conversion of my knee mill. I have two different style shaft couplers and both will require a little tweak to my motor mount to make fit.

The long one is about 1/8" too long to fit my existing bracket, so I would need to either:

Use the long coupler and
a) machine about 1/8" off the leading edge of the face of the ballscrew (the edge that mates against the bearing) or
b) shorten the bearing spacer that fits in the bearing block by 1/8", the spacer appears to be hardened.

c) Use the short coupler (diaphragm style) and shorten my mounting block by about ~5/8"

The question is....... of these two style couplers is one better than the other (Stronger, more compliant etc.)?

 

[whydontu]

The Lovejoy spider couplings have much more flexibility and survive greater misalignment.

What size are the shafts? Quick n dirty, the shaft depth of engagement only needs to be the same as the shaft diameter. Can you shorten the Lovejoy coupling halves?

 

[DavidR8]

I'm getting close to wrapping up the mechanical aspect of the CNC conversion of my knee mill. I have two different style shaft couplers and both will require a little tweak to my motor mount to make fit.

The long one is about 1/8" too long to fit my existing bracket, so I would need to either:

Use the long coupler and
a) machine about 1/8" off the leading edge of the face of the ballscrew (the edge that mates against the bearing) or
b) shorten the bearing spacer that fits in the bearing block by 1/8", the spacer appears to be hardened.

c) Use the short coupler (diaphragm style) and shorten my mounting block by about ~5/8"

The question is....... of these two style couplers is one better than the other (Stronger, more compliant etc.)?

View attachment 41724

I used the one with the red elastomer damper on my CNC router. Works great but I do think they are used primarily in situations where the axial alignment is spot on.

 

[Aliva]

I've read on other forums that the element style may have too much axial flex for a ball screw, leading to a more than acceptable backlash. A disk type or solid coupling is preferred, the downside, is alignment is very critical.

 

[Former Member]

I've had spider type couplings and found that under cnc use on a mill take a beating. I have since replaced them with solid couplings did a proper alignment and found that elastic couplings cause inaccuracies and other issues.

Solid couplings are the only choice at least for me.

Precision....thats what we do.

 

[slow-poke]

The Lovejoy spider couplings have much more flexibility and survive greater misalignment.

What size are the shafts? Quick n dirty, the shaft depth of engagement only needs to be the same as the shaft diameter. Can you shorten the Lovejoy coupling halves?

Servo has 19mm shaft, ballscrews are 20mm and 16mm

I think my alignment is actually quite good, I used the DRO always off the center point and aimed for < 0.001".

I'm going to try the diaphragm style on the Y axis and the elastomer on the X axis and see how they compare, Details will be tweaked as required.

 

[Former Member]

Secret that I use for fast alignment is over size holes slightly run and tighten as it stabilizes.