adding a 4th axis?

[airbrush]

Has anyone attempted this?
From what i've researched so far, this machine looks fairly easy to build, but I would like the option to have a rotary 4 axis for more complex parts.
Is this possible with this design? Does anyone know of such 4 axis plans?

[NC Cams]

In order of the way your questions were asked:

1. Add a 4th axis, yes.

By the time one crafted up all the electronics and pneumatics for the type of 4th axis used on my machine, it is easier and cheaper to find a used one and plug and play.

2. Which design are you referring to?

3. Haven't found any.

You probably could do a crude adaptation of a manual rotary table with a servo motor fitted to it. You could use a servo based encoder to simplify feedback and then use gear ratio based math to coordinate table motion.

For true and precise accuracy, you'd rather have the encoder fitted directy to the table via direct drive or zero backlash gears.

[Chris64]

Tormach has a CNC 4th axis that I heard was around $800. As far as price this is by far the cheapest I've seen even compared to used ebay stuff.

I'd like to hear more about why you couldn't just put a motor on a manual rotary table. I had a really heavy 12" rotary table that I was considering converting but even that required that you put the brake on after you put it in position. Probably just to keep the backlash from rattling around - but it didn't seem to have any noticable backlash.

[airbrush]

Originally Posted by NC Cams In order of the way your questions were asked: 1. Add a 4th axis, yes. By the time one crafted up all the electronics and pneumatics for the type of 4th axis used on my machine, it is easier and cheaper to find a used one and plug and play. 2. Which design are you referring to? 3. Haven't found any. You probably could do a crude adaptation of a manual rotary table with a servo motor fitted to it. You could use a servo based encoder to simplify feedback and then use gear ratio based math to coordinate table motion. For true and precise accuracy, you'd rather have the encoder fitted directy to the table via direct drive or zero backlash gears.

I was referring to the rockcliff design, the standard design, fixed gantry.
Could you not just use a fourth stepper motor for the rotary axis? ..xylotex sells packages with 4 motors and Mach 3 software will support up to 6 axis.

Do you know who has tried to add a fourth axis that i could get in contact with?

thanks

[airbrush]

Originally Posted by Chris64 Tormach has a CNC 4th axis that I heard was around $800. As far as price this is by far the cheapest I've seen even compared to used ebay stuff. I'd like to hear more about why you couldn't just put a motor on a manual rotary table. I had a really heavy 12" rotary table that I was considering converting but even that required that you put the brake on after you put it in position. Probably just to keep the backlash from rattling around - but it didn't seem to have any noticable backlash.

Checked out the Tormach site, I am just a beginner and researching right now before i decide what to purchase to get started. I assume you would also need one of their standard tables to attach the rotary to...pushing cost over the $2000 mark. Not sure about that sort of investment for my first machine. Although from what i've been reading so far, a fourth axis is the only way to achieve more detail for 3d models. Unless someone has figured out a way to do this on a 3 axis? (cut one side, turn the part etc??)

[mad.sculpture]

Hi Dude,
I want to do exactly same thing,been looking on this site for info,
if you look at the 5 axis commercial mill reference in forums they'll point you to a scottish example of most peoples dream mill.....(i was drooling like homer simpson)
hell i didn't even know where a 6 th axis went till this...
i thought a cheap ass (still not that cheap)rotary table with stepper would be way to go to so i was thinking several hundred gbp (england)

anyhue many people seem to think that HARMONIC drives will cure our needs.
from what i can make out:

AND PLEASE FEEL FREE MEMBERS 2 CORRECT ME AS NEWBIE

A Harmonic drive is essentialy a gearbox whos ratio's are commonly high 50,100 & 160 :1 mostly.

Because of it's unique design it has essentialy no backlash(i think they mean the play between gears of leadscrew)
I don't mean it's barely detectable or minimal as in very high quality convential products I mean it just aint there !

They work by MAGIC......Ok so they don't but i can't wrap my head around it,I found an old reference on this site where a guy had 1 in pieces (only 3 bits realy)that he showed in action by hand but the link to the video file is no longer valid)
one manafacturer listed principle of operation but lost me..

So i think we track down 1 of these puppies mounted to a servo motor with an encoder on it....

The servo works as normal but it's output is up to 160 times slower and as the encoder is mounted on the motor end we'll have a huge number of steps per degree.

one i've seen had 360 steps/rev so i think you'd have 360 * 160 steps/per rotation of output shaft (with your model in achuck mounted to it)

= 57600 steps/turn of your model

so 360 degree /576000 = 0.00625 of a degree resolution (i don't know my arc/radians)


ok, so what i don't know is what rating servo you go for with what gearing for the material we'll be machining.

catches : always !!!!

we'll need to mate a servo (i think we could use steppers but these things are relatively new technology = high end industrial = servo's normally) to the harmonic drive and a faceplate/chuck to the output of the drive so we'll need shaft reducers brackets etc.

you can get lovelly units that look totaly star trek with motor,sensor and gearbox integrated but they're expensive (as in thousands sometimes)
when they are powerfull.(the biger one also sometimes have large hollow shafts all way through so you can pass cables through centre of rotation of each joint on robot arms which is a common application)

I've just bought one on ebay but i'm taking a chance as out of my depth realy
so don't know if it'll work as not massive and only 50:1 reduction
plus although i've used loads or Radio Control servo's and understand principles of industrial ones i don't know if i can steer the thing yet as not been able to get much info yet(what servo driver it needs and if i can interface it for a practial cost) i paid 85 pounds for it (but it's a classy 1 Kollmorgen), if it only uses some exotic driver i'm probably screwed

There is one on Ebay for $100 now and it's beefy but it's standalone gearbox only
if you can machine already you could adapt it relatively easily i think so regular servo and encoder + $100 and a second hand chuck could be great alternative to indexing table

I'm only a newbie so take all this under advisement, just thought i'd tell u where i am with it as took a while to find the above info out and i missed a major bargain on ebay as result

p.s read today someone saying in all practicality they can't detect any backlash in their Nema true precision head (planetary gearbox i think)but haven't followed this up yet.

p.p.s. Harmonic drives are filled with oil,how we check this is right level/amount + service interval - no idea at moment



* Also someone wrote harmonic drives not that robust, but from what i've seen this not true as they make some very tough ones with flanges for direct mounting,so your motor + sensor +gearbox + actual robot (industrial remember) arm pivot is all one unit AND all your cable go through a hole in the middle....HOW COOL IS THAT???

'Spensive

But...Maybe they are magic after all...

Alien technology from the same source as microwaves,velcro,wankel engines
and mechanical torsen diffs (not fluid filled) a la MIB

Anyhue I digress..

I started out to cobble together a rockliffe type creation but as a sculptor seeing the 6 axis machines has sent my mind star treking with design ideas that my wallet can't afford so it'd be good to hear from other people on this thread

Cheers Ross

[airbrush]

thanks for the info, a little over my head at the moment as i'm just a newbie also. I am willing to go with a 4 axis machine as I think I can work around the limitations by chopping the model up into parts and reassemble them after.
any and all info on diy 4 axis machines are appreciated.

[mad.sculpture]

if you google rainnea graphics you'll see their cnc machine,the links page has the guy making the rotating axis heads.
he quoted about $750 each axis I think ready to ship now
they're new (i think) patented no backlash units with good size motors

ross

[airbrush]

hey mad.sculpture,
what sort of rotary table do you have? did you make it or buy it or have you not gotten that far yet?

[turmite]

http://www.doughtydrive.com/


Here is a guy that makes a real nice unit that can be use alone or combined for a 4/5 axis.

Mike

[airbrush]

Originally Posted by turmite http://www.doughtydrive.com/ Here is a guy that makes a real nice unit that can be use alone or combined for a 4/5 axis. Mike

Thanks for the link Turmite...you're a wealth of knowledge it seems.
Do you have a 4 axis as well?
Do you have any experience with the above mentioned unit? The site doesnt have very much info on it...not even contact info other than email, which makes me a bit leery to buy from anyone that doesnt provide an address at least.

[mad.sculpture]

Originally Posted by airbrush hey mad.sculpture, what sort of rotary table do you have? did you make it or buy it or have you not gotten that far yet?

Hi airbrush
My whole setup is theoretical so far, well some of it's in the post to me..

I thought if i was making a rotary axis the difficult part was the positioning of it rather than the mounting and plate which i thought if i was lazy could just be sherline/taig type headstock/faceplate.

so after reading the responses about harmonic drives by other forum members i've been looking into that.

to correct my earlier post, yup they are quite fragile according to the data sheets.They make them like i said earlier as a complete robot arm joint so i thoght i'd easily just put a faceplate on that but even though i found one large one that wasn't too insanely priced the warnings in the data sheets i found on the web have pretty much put me off (suscebtible to impact don't hit it with hammer during installation warnings + vibration ratings which are beyond me)
of course we'd not hit it but if you imagine a robot arm clobbering something - all that leverage (or you crashing the cutting head into it)- don't know how they're robust enough for their intended app. and harmonic drive co. haven't replied to my email queery.

basically at the bottom of my A4 piece of paper regarding parts sources & orders it currently says

FOR ROTARY TABLE JUST BY SHERLINE PROBABLY! Honestly i mean that

of course you could mount the harmonic drive with a coupler like you use at the end of leadscrew/ballscrew (those that cope with slight missalignment)so
that you isolate the drive from certain loads) but vibration will still pass through it some.
I've got a harmonic sevo drive coming but it's almost definately going to be to weak as it's only rated at 21 oz/in continuous 215oz peak 46W - My FXXK up
however a guy on the net's got a sherline rotary table with a 75oz servo that's working(he took normal sherline servo apart to see what made it tick end weakened it lots so now just uses it on table) so if i gear the drive 3:1 via a wide toothed belt i'm still wondering if i may be able to do something with it ie.machine jewelers wax/foam wood at a strech but unlikely.
The belt is obviously going to be inferior to direct drive and introducing the very sort of inacuracys that i went harmonic in first place
but it's also the only thing i can think of (as a mech. engineering dunderhead)
that would provide the protection the drive seems to need.

short story long :

by the time you get a servo/harmonic all in 1 with output flange assy big enough to be definately usefull to us the servo requires an exotic amplifier
that you'll be lucky to find on ebay and if you do i'd guess it'll be $150 - upwards (think 600+ new) and then there's the shock/vibration issue

if you can address these issues though the accuracy is truly all you could want.

ebay just had a very beefy looking unused industrial H.drive on it for $100 so you could prob. google that and still make him offer as i don't think it sold (auction ended last night) it's a stand alone unit so you could put any servo on it (1 shaft in & 1 out 160:1) and just make sure you used a good encoder, then just drive a faceplate in a good set of bearings via a 1:1 belt purely to make sure your creation lasts.
as far as i can see at the moment with what i've learned so far the hard way this is your best bet if you realy want to make one,i reckon $50 motor +100 drive + $50 second hand cheap lathe headstock & then 2 pulley +belt so $200 ish versus sherline $390 i think (none yesterday ebay)
- if you read info when sherline rot.table released it wasn't just the std. one modified so be aware of that as quite a few manual ones on ebay.
'course by the time you've done the work coupled with the fact that you could get it wrong and sherline's guaranteed i'm not sure it's worth it.
I don't know how much a belt in this situation will screw accuracy up,it's going to be all that's holding that faceplate as you machine it but they have a reputation for being much tougher than they look.my dads HP printer shakes the whole shelf as carriage travel changes direction + several big motorbikes have belt drive)

anyhue, sorry it's a bit long winded and defeatest but don't want you/other newbies making my mistakes

final thoughts :

there was a 5" table for $175 i think it was on ebay yesterday,as in manufactured,so they keep postin new ones but are warning the material stock running out 35 left,listings are about 29 dollar at moment but 6 days to go so i think from meory last one went for above figure.
it looks thorough but could only find good reviews of seller not the product(didn't have much time though)it uses planetary set up and huge reduction ratio but don't know what the backlash is - possibly not great as i didn't see it mentioned.

You could just look into nema planetary gearboxes as someone else mentioned in other forum but at least if you're using a worm gear it's got that inherant backdrive resistance

There's always the things we'd like (insane resolution)and what 99% of us can get by with.

That doughty drive link is the unit that Rainnea graphics are using by the way that i mentioned in the previous post & is impressive.
Plus Rainnea Graphics(check spelling in previous post) have lot's of very educational tech stuff for anyone wanting to do 3+ axis particularly software methods of generating G code from any art/model cad files
You also get to see the quality of the work the machines are capable off by the shop/gallery sections
when i say that i mean machine + exellent craftsman of course!

Cheers dude, hope this helps someone

p.s. honestly i'm not the new sherline agent in your area !