I know that there are some posts, infact i remember hoss and i having a conversation about 4th axis, but after quite a bit of searching, i cant find it, so i thought i'd just start anew.

so i have my x3, but i have a few parts drawn up that i'm gonna have to have a 4th axis for, so i'm trying to come up with the cheapskate solution.

my first thought was to get something like a rotarty table.. but some of thoes have lots of slop in them, or are pretty expensive..

so then i thought about something like a mini lathe headstock. i could modify it to take a stepper motor, with a good belt setup, and a nice beefy stepper motor, and that should work.. i havent measured it yet, but i was thinking that perhaps i could even use the headstock and tailstock together if i needed to hold a part that way..

if i remember right hoss used his y axis as a 4th axis motor one time.. as as i remember it worked by just running the part normal, and just setting mach so that an inch of "Y" axis movement was an inch of movement around the circumfrence of the part

thoughts, ideas, suggestions, pictures, please.

I searched, i couldn't find it either.
I think we were talking about using a single servo motor instead of separate
motors like I used.
It was a lathe attachment (http://www.hossmachine.info/projects_5.html) first that I just added horizontal 4th axis (http://www.hossmachine.info/projects_5.html#4th%20axis) ability to.
It was super cheap for me but I already had most of everything already.
I made lots of timing pulleys with it.
If you're really just wanting it for 4th axis work you'd be better off with a good little rotary table.
It would only need a tiny little stepper, a 185 oz/in would be good enough.
The huge gear ratio in the rotary table would give you tons of holding torque.
Even with 4:1 pulleys on the lathe head you'd need a good 495 or 640 if you want to cut something big.
The lathe head and chuck would run you around $200 at LMS.
A decent rotary goes for that or a tad more.
Hoss

if i go with the rotary table, wont i then need to add the price of a chuck?

if i go with the rotary table, wont i then need to add the price of a chuck?
Price of the chuck is similar if you are bolting it to a lathe headstock or a rotary table. In fact depending on the part you're making you may be able to clamp to the rotary table directly skipping the need for a chuck.
Do you need this 4th axis to undergo simultaneous (at least with respect to 2 other axis) motion, or can it just be indexed?

Also remember that you get the through hole that the lathe spindle gives you. In my case the through hole is a must for the parts I intend to make with it.
I have it in my future projects to build a 4th axis either using the mini lathe spindle that gives approximately a 3/4" clearance hole or make my own that could also be used horizontally as well. Right now I just watch for threads like these to give me ideas.

Rick

the 4th axis will be full time motion, and not just indexing, and i'm liking the sound of the pass through hole like on a lathe... i would like to be able to run some of my stock in longer lengths, one to save on waste, and 2 cause it'll make making multiple parts easier. but in reality, the deciding factor is gonna be the money it takes me to get it done. cause to do it right, i'm gonna need another driver(which i can build myself, but is only 1/2 stepping and is limited to 4A per phase) and a motor, and any other hardware...

one of the things that i want to make with the 4th axis is a couple of pump impellor designs that i've been working on.. and to do that, i definately need full time 4th axis...

let me ask this.. what kind of torque do i need to hold my part in place? lets figure that the part blank will be 2 inches in diameter, and probably the largest endmill i'll ever use for this would be a 1/4 inch. More likely i'm gonna be running 1/8 or 1/16, but i can see bigger on occasion.

i remember that some of the things that Hoss and i talked about was the torque required, but we cant find it, so i'd like everyone's input..

if i were to use, just for example, a 500oz-in motor, half stepped, direct drive, then i'd get 2*3.14=6.28 inches around. 6.28/400steps=.0157 inches per step. thats not fine enough.. so, belt drive it 4:1. then i get .003925 inches per step. still on the big side. 8:1 = .0019625, 10:1 = .00157.... ofcourse, each gearing increase also increases the torque that the motor can apply to the part.. so at 10:1 i would in theory have 5000oz-in of holding force...

this is getting to be a gearing nightmare.. maybe the worm drive rotary table would be easier.. and would require lots less input torque cause you wouldnt be able to back drive the worm. Im just worried about the slack and whatnot of using a cheaper rotary...

looking around for parts, i found this video, this is the kinda stuff i wanna be able to make, this process.. different parts... hehehe
http://www.cnc-router-routers.com/html/rotary_table_indexer__4th_axis.html

go to the page, and watch the video.. awesome..

the 4th axis will be full time motion, and not just indexing, and i'm liking the sound of the pass through hole like on a lathe... i would like to be able to run some of my stock in longer lengths, one to save on waste, and 2 cause it'll make making multiple parts easier. but in reality, the deciding factor is gonna be the money it takes me to get it done. cause to do it right, i'm gonna need another driver(which i can build myself, but is only 1/2 stepping and is limited to 4A per phase) and a motor, and any other hardware...

one of the things that i want to make with the 4th axis is a couple of pump impellor designs that i've been working on.. and to do that, i definately need full time 4th axis...

let me ask this.. what kind of torque do i need to hold my part in place? lets figure that the part blank will be 2 inches in diameter, and probably the largest endmill i'll ever use for this would be a 1/4 inch. More likely i'm gonna be running 1/8 or 1/16, but i can see bigger on occasion.

i remember that some of the things that Hoss and i talked about was the torque required, but we cant find it, so i'd like everyone's input..

if i were to use, just for example, a 500oz-in motor, half stepped, direct drive, then i'd get 2*3.14=6.28 inches around. 6.28/400steps=.0157 inches per step. thats not fine enough.. so, belt drive it 4:1. then i get .003925 inches per step. still on the big side. 8:1 = .0019625, 10:1 = .00157.... ofcourse, each gearing increase also increases the torque that the motor can apply to the part.. so at 10:1 i would in theory have 5000oz-in of holding force...

this is getting to be a gearing nightmare.. maybe the worm drive rotary table would be easier.. and would require lots less input torque cause you wouldnt be able to back drive the worm. Im just worried about the slack and whatnot of using a cheaper rotary...
Big gearing in a small place, no backlash, can't be backdriven. Sounds like a job for a harmonic drive. They aren't cheap, but some careful surplus/ebay scrounging might bring something up.
I'll put up a couple of pics later of the one I have in my build thread, I'm looking for another one as well. The one I have is 96:1, 5HP input rating, maybe 4.5" in diameter or so, and about .75" thick.

i'm not at all familiar with the concept of harmonic drive, can you expound?

i was looking at something like this, but i'm aftaid that there will be too much backlash in it, and i really dont know if these are adjustable...

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=97208

I'm betting someone out there has tried this, and they either figured out how to make it work, or they know of the shortcommings of going this route...

dont be shy, speak up!

i was looking at something like this, but i'm aftaid that there will be too much backlash in it, and i really dont know if these are adjustable...

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=97208

I'm betting someone out there has tried this, and they either figured out how to make it work, or they know of the shortcommings of going this route...

dont be shy, speak up!

Spend a few dollars more, and get a Phase II rotary table. The backlash is adjustable, and can be adjusted to essentially zero.

Regards,
Ray L.

ok, thats a little more.. hehehe but i guess you get what you pay for.

i'm not at all familiar with the concept of harmonic drive, can you expound?
http://www.harmonicdrive.net/reference/operatingprinciples/

ahhh ok, got it.. very interesting.. small package, good ratio, and good torque.. and "zero backlash"

i sent them an email for some information and a quote.. we'll see what they say..

they say $700.

they say $700.

Like I said, not cheap, but now that you know what to look for you might find one on ebay or in a surplus store. It's hard to do better for rotary motion.

yea, definately, the specs were impressive...