Harmonic Drive 4th axis - PEU

Hi guys, after virtually years of wanting to have a fourth axis on my cnc router I finally got the part I needed the most, a small harmonic drive. It wasn't my first one, but the first one was way too big for my table, an ebay purchase error :)

http://i.imgur.com/ltE6gXj.jpg

Anyway, after thinking about the design I started drawing in cad what I think it should have to work properly, here are the renders so I can show my current stage, my main doubt is if I'm overengineering the thing, keeping in mind that it will be used for wood mostly and every now and then to do super light machining on aluminum or brass:

http://i.imgur.com/v1Ta5Dt.png
http://i.imgur.com/SLxOo2K.png

What you see from right to left is: Nema 23 motor>Mounting of motor>4th axis enclosure half>size 14 harmonic drive>shaft>two preload nuts>two angular bearings>enclosure other half.


First question, for the intended use, are the angular bearings really needed? They are expensive...

Thanks for looking, hopefully at the end of this thread I can show a fully finished and working unit.


Pablo

PEU

No the AC Bearings are not needed, What you have in the drawing will work very well, you will need to put a cap with a labyrinth seal, or something to keep chips/dust out, on the front, & you will have a nice 4th axes

Thanks!

Yes, of course, the left side needs parts, but I wanted some feedback on the general design before moving forward.


Pablo

I want one too!

Neil, I had a search running for years at ebay looking for an harmonic drive at the right price (under $150) big one cost was 70ish small one was 150 but is mint new, both work perfectly. Having these search terms allows you to avoid the pain of constantly looking, ebays sends you en email every day a new item that meets your criteria is listed.

What do you think of the design? its still wide open to modifications, and I have no problem giving the final result solidworks (2011) files away.


Pablo

Are you making 4th axis? Why not make the part that holds it all larger, so it can clamp direct to the table.
Separate the AC bearings with a spacer so that bending moment is better on shaft, unless the shaft is just driving something and not a chuck, directly.
If not direct, then it all gets a bit springy again.
On my 4th axis (worm drive) I have an air operated axial clamp, that locks the axis one positioned.
The air clamp is run from one of my spare outputs ( the coolant plug)