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JW1977
22-04-2021, 02:24 PM
Hi!

Iím unsure of what couplings to use. As it seems I will go with alu couplings with a slit in them. Any thoughts about that?
Iíve noticed that the ball screws are round at the end. Is there any reason that they donít have a flat surface as the motors has?
Iím thinking that maybe if something goes wrong they will come loose and prevent further damage.

Thanks, JW

29827

JAZZCNC
22-04-2021, 05:16 PM
No, they are the worst coupling to use. you are better using an Oldham-type coupling like this.

http://www.fbtmotion.com/html/16.html

Or better still a disc type coupling like this

http://www.fbtmotion.com/html/17.html

Regards the ball screw then just file a small flat onto the shaft, the machined portion is soft enough to file.

JW1977
25-04-2021, 11:22 AM
Thanks!

I guess the coupling is flexible above a certain amount of torque right?

dazp1976
25-04-2021, 01:07 PM
Thanks!

I guess the coupling is flexible above a certain amount of torque right?

I've snapped 3 of those metal 'flexible' couplings so far.
I now use the spider type with no problem at all.
https://ae01.alicdn.com/kf/HTB1MDweX5LxK1Rjy0Ffq6zYdVXag/D20L25-jaw-flexible-motor-coupling-aluminium-CNC-spider-flexible-jaw-coupler-5x8mm-3mm-4mm-5mm-6mm.jpg_Q90.jpg_.webp

JAZZCNC
25-04-2021, 03:26 PM
Thanks!

I guess the coupling is flexible above a certain amount of torque right?

It's all to do with parallel and Angular misalignments and to a lesser degree axial growth or misalignment.

Read this it will explain the different types and Torque ratings etc.
https://www.thomasnet.com/articles/hardware/coupling-types/

JW1977
07-06-2021, 08:43 AM
*JAZZCNC*

Do you have any idea or an example of how much runout that can be accepted in a ballscrew?
Offcourse its hard to answer and its related to length but i was thinking that maybe you have a general idea?
Im asking because i had some of mine modified in the ends for different reasons. The guy who did it is an experienced machinist used to high precison machines so i guess that in his world my screws are pretty bent. I dont remember exactly but i think that my 900 mm screw where off by 0,4 mm. Im gonna check for myself when i get it back but i think the measure he referred to was when the screw was laying flat and you measure from the flat surface up to nearest point of the screw...

Cheers