Keyway or not to keyway... That is the question

[jessbussert]

Hi Folks,

I just bought some sweet NEMA-23's from Probotix. The only problem is that they don't have keyways. My couplers use set screws. Should I cut a flat in the motor shaft for the set screws to rest against, or is there a better solution?

Thanks,
Jessica

[HR CNC]

Evening Jessica
Sometimes it's 50/50 on flat for the set screw. So this just my opinion. I don't use flats. It's a safety thing. You find some that go as far as using lovejoy connectors., which are two piece four lugs that mesh with a rubber shock absorber between them, They help take the shock. I want my motors to be able to slip in case of a lock up condition if I'm not watching. I take a piece of .500 delrin round stock and drill a .250 hole all the way thru. I then mill a small flat on the outside of the connector and drill two holes thru that flat to the center of the rod. then tap both holes and insert a set screw. The flat on the outside is to make it easier to start the set screws. I then slide on to the lead screw then install the stepper motor and snug them down. A good solid connection, very minimal backlash and safe. If you need some made up email me. check out my little shop at hickoryridge-cnc.com Have a great evening. This is just my way, you'll find others. RIck

[jessbussert]

Hi Rick,

Thanks for the tip. Nosing around elsewhere, I've been told to use the vacuum hose / hose clamp method. From your website, it seems that you don't favor that method. Why not?

Thanks,
Jessica

[HR CNC]

Hi again Jessica
I forgot all about having the page on my site about how not to build a machine. The reason behind me not liking the hose clamp system of connecting the shaft to the motor is slippage i.e. negative Backlash. I had tried that way and it seemed ok when used with 17's but the larger the motor I used I slipped more. As long as you get a hose that just about has to be man-handled onto the leadscrew and is really tight on the motor shaft then it works better. When machining you will sometimes see and here smaller chips jam the cutter a little. This can actually "stutter" ( my term) the x or y axis if it lets the motor shaft slip in the hose. giving you one more backlash hassle to watch out for. Now if you are going to do soft routing or milling, wood, foam, plastic, alum and want to keep costs on your machine down then the hose and clamp might just work for you. You'll be able to judge for yourself when machining. What I would do, if I was going to use this system to purchase a good ty wrap gun. Instead of the clamps. Different clamps manufacturers use different quality of spring steel when making their clamps. But if you use the ty wrap gun, and get used to it. It will cinch down the wrap tightly on the shafts. Plus it's great all around the house and shop, stereos, wiring, etc. You can find them at RadioShack or ebay. You can always start with the hose and if it becomes problematic, then Beyonce ( Upgrade ) to the next level till you find the best for you. If you have any slippage, in multipass cuts then it will show up as two tone machine marks on the surface. One way to fix that is to calculate your two or thee passes to leave say .0625 off your passes and then make a final dressing pass to clean up the cut. Depends on time factor, and looks you want and also if it shows. Like I said before, you'll get lots of opinions and folks telling you how to do it. You become a Master by learning that everyone has something to contribute, look at lots of methods and then find the combo that makes you and your system work. After 40 years of machining, I can still learn stuff from the young pups. Enjoy!, hope this helps a little. Rick

[Baketech]

Originally Posted by jessbussert Hi Folks, I just bought some sweet NEMA-23's from Probotix. The only problem is that they don't have keyways. My couplers use set screws. Should I cut a flat in the motor shaft for the set screws to rest against, or is there a better solution? Thanks, Jessica

Yes, there is a better solution...use a clamping style coupler such as a "Heli-Cal" and eliminate the setscrews altogether...

Edit:
The added benefit is that they allow minor amounts of parallel, angular, and axial misalignment while maintaining zero backlash and tremendous torque capacity.... :twocents:

[ger21]

Or these.
http://www.dumpstercnc.com/couplers.html