FIX: motor shaft and drive screw alignment, coupling

[fivefishcnc]

This community has helped me with tips when I was having problems milling Aluminum. Now, I'm glad I can contribute something back. I'm sharing this tip, and I'm assuming this type of problem (non-perfect alignment of motor shaft and drive screw) is a common problem with DIY CNC. This solution really worked well for me. Hope you can find a use for it.

The coupling between the stepper motor and drive screw of my eBay DIY CNC was a primitive rubber hose forced-fit into the shafts of the motor and drive screw.

As time goes on, it wore out (the rubber became too flexible) and eventually, my Y axis doesn't work anymore. The motor would spin, but the drive screw wasn't spinning with it.

I bought some metal shaft couplers on eBay to attempt to replace the "rubber hose" coupling. It required some additional boring on the drill press because the holes were like 1mm too small. Installed it, tightened the set screw and tested it. It wasn't good.

Because it was a rigid, metal shaft coupling... alignment of the drive screw and motor shaft must be 100% perfect. Well, it's not considering it's a DIY machine. The result is lots of vibration and chattering as the motor turns.... pitching up and down, which causes the the spindle assembly to vibrate, (and therefore the cut being wavy and rough too).

I'm thinking of going back to the rubber hose coupling route...

but while browsing at McMaster, I found this "Ultra-Flex Double-Loop Shaft Coupling". I decided to try it.



I bought it, shipping was fast and it arrived in no time.

While it says "ultra-flex", don't think it's some soft rubbery thing. It's not... It's very hard to even compress it, or move it side-to-side using just manpower. It's very stiff and very durable... not at all soft.

Installed it, (and the size/length is even perfect!) and ran the machine through it's paces. WOW! It works very nicely. Vibration has been eliminated. My CNC moves perfectly smoothly now (at least on the Y axis).

It worked so good that now I'm thinking of getting another one and using it for the X axis motor and shaft coupling. No more rubber hose couplings for me!

[CarveOne]

Looks interesting. I wonder how much lag there is in the direction reversals. I guess you will know about that when you do some test cuts looking for possible problems with it.

CarveOne

[fivefishcnc]

Originally Posted by CarveOne Looks interesting. I wonder how much lag there is in the direction reversals. I guess you will know about that when you do some test cuts looking for possible problems with it. CarveOne

I did test cuts... photo here. 15/16" circles on anodized aluminum 3.0mm? thick....



No lag at all during direction reversals... As I said, don't let the "flexible" look of the part make you think it's soft. It's very solid and sturdy.

Accuracy was also improved ALOT. Before, it was so-so.



Perfect fit, so much so the Neutrik XLR jack stays in the milled hole just by a little friction. I'm just happy with this new development.




I'm not a machinist and I just have simple needs for this DIY CNC machine. But it helps me in production of my custom-built audio products and make it look professional.

[CarveOne]

Looks like Huco/Dynatork makes them.

http://www.huco.com/products.asp?cat=62

McMaster-Carr link:

http://www.mcmaster.com/#double-loop-couplings/=ioy2g

Your audio components sure look good. Sure can't see any problems with the panel routing either.

CarveOne

[jemmyell]

The usual method for most motion control systems is a Helical Beam Rotary Coupler. Many people make them now, but these guys invented them...

http://www.rocomcorp.com/

-James