[mgutierrez237]

hello I'm new to the forum and am working on designing a 5 axis machine based on a fixed trunnion and moving column and head (kinda like the hurco design) and am having trouble figuring out the most ridgid and precise way to drive the rotating axis's.I will be machining aluminum and steel and am looking at a 2x2 foot working area any help/advice is greatly appreciated thanks.

[IMT]

Sounds like a fun project.
I would use a worm+worm gear set to drive the rotary axes. Use as large a diameter as you can fit and a large gear ratio. i.e 100:1. Backlash will be an issue but you can lap the gears if necessary to reduce it. Check out bostongear.com. I have used their gear sets on rotary stages for semiconductor processing equipment.
Good luck.

Dan

[mgutierrez237]

thanks Dan for the help I'm finishing up the design and hopefully i can get started soon. how low can i get the backlash and will it compound the more i change direction?

[hanermo]

Very ambitious project.
For machining steel, AND 2x2 foot size ! You are probably way out there in terms of mass.

A Haas UMC cannot do 2x2 feet, and thats thousands of kg.
Alu is not much easier, still looking at 2000 kg minimum.

Thats a 20k+€ project in terms of components cost.
(Standard) Worm gears wont work.

You must have zero error, or the backlash will destroy the cutters due to vibrations.
Harmonic drives, very good planetaries, or 2 independent worms gears would work.
Or a dual-envelope preloaded worm gear.

For 2ft envelope, you are looking at huge heavy rotaries.1000 kg plus.

If you actually want to proceed, I can give more detailed advise.
What spindle were you planning ?
What do you want to make ?

FYI .. the ones I have seen like this (old spanish designs) were about 10.000 kg each. Not too rigid (had tall z axis column).

[Tkamsker]

I do a small trunnion as well And i already got me some harmonic Drives ,..

[IMT]

thanks Dan for the help I'm finishing up the design and hopefully i can get started soon. how low can i get the backlash and will it compound the more i change direction?

We were able to get the backlash down to <30 arc-sec with lapping the gearset in place. The worm is hardened steel and the worm gear is bronze. Lapping will wear in the variations in the worm gear to match the worm. In this approach you are limited by the runout of the worm shaft and the runout of the main rotary bearings. For a cutting application you also will need a brake of some sort to provide friction greater than the cutting forces. Error due to back lash does not compound with multiple direction changes.