I have been working on a comercial quality 5-axis mill design with very little engineering skills. I have the two rotational axises on the y-axis idea and am wondering how the table is rotated. I dont think gears are a good idea so I am down to a chain and sprocket plan or a timing belt plan. I would like to know which would be more accurate.
Thank for your help
Cadfish

I belive they use 'harmonic drives' which are gearboxes with high efficiency and no backlash.

http://www.harmonicdrive.net/

Commercial machines use worm gears or direct drive rotary.
You won't get enough reduction with belts or chains.
Bob

I had an engineer tell me to use a dual lead worm gear, then I called up an old friend and he said that it would cause wear. I like the worm gear idea but to reduce wear I am thinking of an item that I might be able to do both, I also might have to get a patent on it, so I probably shouldn't tell you what it is, sorry.:wee: :D

No question, the harmonic drive [don't let the name scare you] is the best route to go. ZERO backlash ZERO.. which is a big concern w/ worm gear stuff [which can hit zero if adjusted regularly to keep them there]

Harmonic drives also have high reduction ratios [100:1 is no big deal] which is also something you'll want for two reasons. 1. You'll want to be able to absorb large force numbers and yet have a reasonable drive size. 2 Positional accuracy. If you have a standard 200 step stepper w/ a 100:1 drive you can position the table to w/in 0.018degrees. If you had a 10 step micro step drive it'd be 0.0018 deg. [Now we all know micor stepping isn't that accurate.. but in theory]

If you had a 500 line encoder on a servo it'd be 0.0018deg.

Anyway, you get the idea..

Got any CAD shot's of the machine?? How big is it going to be when completed? Intended use?

Jerry

Is there any 3d cad drawings of a harmonic drive any where? I have some mach up drawings in SW '06. The table if I remember right is about 6 in. dia.. I am just doing this for fun so far, maybe when I get older I can afford to make the real thing, as of now it is a project for a college student with some free time between studying.

If you search of harmonic drives on the net you'll find a couple companies which make them. You'll be able to find cad drawings of them but I doubt you'll find models which you could download. I haven't found any, anyway.

J

Hi Cadfish,

any chance you could post some screen shots of you drawings for the people who cant view solid works files.

Thanks
Splint

Good idea Splint, here are the screen shots.

Hi Cadfish, here are the pictures.

I think this thing is patented and only one company makes them. Not only they're expensive, but the service life is limited to something like 4000hrs.

Very simple device, works on a principle of controlled deflection.

1. input bearing called wave generator (pictured left)- oval in shape, that's where the motor goes

2. Output side aka flexible spline (pictured right)- this part turns inside the housing

3. Housing with teeth on the inside aka rigid circular spline (not shown). Housing can be filled with transmission fluid, bearing required on the output side.

http://i233.photobucket.com/albums/ee298/mineral-casting/th_IMG_3038.jpg (http://i233.photobucket.com/albums/ee298/mineral-casting/IMG_3038.jpg)

http://i233.photobucket.com/albums/ee298/mineral-casting/th_IMG_3043.jpg (http://i233.photobucket.com/albums/ee298/mineral-casting/IMG_3043.jpg)

http://i233.photobucket.com/albums/ee298/mineral-casting/th_IMG_3045.jpg (http://i233.photobucket.com/albums/ee298/mineral-casting/IMG_3045.jpg)

The trick is to buy complete gearhead with sealed housing and output bearing- the most expensive state. Medium size 4-5" gearheads go for $1000 or more (company direct). Ebay has them too, unit without the housing goes for $50-100. Complete gearheads attract bidding wars and go for hundreds.

Here's the big one, 7" dia 1:160 ratio. It's got massive crossed roller bearing on the output side and can easily cost over $2k.

http://i233.photobucket.com/albums/ee298/mineral-casting/th_IMG_3051.jpg (http://i233.photobucket.com/albums/ee298/mineral-casting/IMG_3051.jpg)

http://i233.photobucket.com/albums/ee298/mineral-casting/th_IMG_3048.jpg (http://i233.photobucket.com/albums/ee298/mineral-casting/IMG_3048.jpg)

More info here http://www.waltmusser.org/HD.htm

hi, newbie post,

won't help you but is funny..

I wan't to make a 4 axis mill and was bidding on ebay yesterday for a lintech linear slide which was same price as others but just happened to come with a complete industrial robot arm on top,I didn't offer full buy it now price because would be so heavy to ship to the UK,but you know when you just have that feeling......it had a big harmonic drive and I wasn't sure what it was and was late for dinner at my parents......

Oh nuts...

Thank you Walter, the pictures are very interesiting, I had a therory that they worked like they do. I read the whole link and I was thinking to my self, "why didn't I think of this, its ingenious." I think I will draw the harmonic drives into my plan, I am still a college student with very little money so I might buy a mill later on. I just want to find out just how much I know about machine design, and test my knowlege (sp?) on how much I do or dont know.