Re: Couplings

Hi, I just joined the list...today. Motor shaft couplings have weighed heavy on my mind for a while. I am on a 'nothing' budget (as most are these days). I was reading your post about couplings, and I thought that I'd share what I came up with. I actually have not seen this one yet...but I'm sure I'm not the first to think of it...it's just too simple.

Description taken from my web album...

my solution to cheap and easy to obtain & build motor shaft couplings. This particular coupling is being used on a 5/16" (all thread) lead screw. I used a nylon 'spacer' bought from the local hardware store, and a 1/2" shaft collar. The spacer is 1" long, 1/2" diameter, and a 1/4" bore (1/4" bore matches my motor shaft). I 'force' tapped the bore half way through with a 5/16-18 tap...it was not hard to do at all...just take your time and keep it square. Then I cut a slot on the opposite end, for the collar to squeeze onto the motor shaft. I marked the split w/ a marker (on the screw end) so that I know how to orient the collar when locking it to the shaft, make the set screw 90 degrees from the split. I screw the nylon spacer onto the lead screw until it bottoms out (end of the threads), and tighten a jamb nut against it (actually using a regular nut for a jamb nut). Then slip the collar on, place the motor, and tighten the collar (pretty tight!). It seems to be working quite well so far.

Link to photos: http://picasaweb.google.com/rhaag71/MotorCouplings?feat=directlink

Let me know what you guys think, so far they seem to be working pretty good, it took a bit of experimenting to get the 'installation method' down. Now that I have them staying tight, they work well even up to 80ipm with pretty fast acceleration.

This is my first machine, and so far all it has done is draw with a marker on paper...so I'll see how they hold up.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "johann_ohnesorg" <bigdukeone@...> wrote:
>
> ...price can't be beaten at 9,90 euros for 3 units! what do you
> > think?
>
>
> Hola Alfredo,
> this would be waste 10 euros. There is no flex in the coupling because there is no plastic or rubber anywhere between the two drilled holes, it�s a stiff piece of metal with two holes and a few grub screws.
>
> The job of a coupling is to mitigate small angular and parallel misalignment that would lead to stiffness in your drivetrain and to add a little bit of dampening by taking out the stiffness from the drive. In case you don�t use these couplers, you may experience resonances from the motor and also you may have a stiff position (even if it�s only slightly) in the spindles rotation thay may lead to step loss at higher speeds. It also contributes to noise and will eat up power that would otherwise enable you to use higher feeds and cost you drive torque.
>
> The right way to go is via couplings or to use a toothbelt plus two wheels and offset the motor from the axis. This is not necessary on your smalll machine. You need something that will eliminate or soften misalignment but keep your drivetrain as stiff as possible. If the couplings are to expensive go via a the tube routine. If you want to simulate bigger couplings and you don�t want to rework the standoffs of your motor carrier plates in case you switch to couplings (which are huge compared to the tube solution) then cut two pieces of aluminum to size and attach a rubber hose with say 20mm ID on the larger chunks of aluminum. It�s not a shame to do it this way. Being tight on the money with the couplings will lead to problems further down the road.
> In case you need someone to convey information to a german seller after you bought the couplings, feel free to email me in English, I�ll translate it.
>
> Cheers,
> Johann
>