Rotary (4th) axis for my cnc mill

[stefang]

Hi folks,

to machine the scales on the handwheels of my bonelle I had to build a rotary axis for my cnc mill...at first I only wanted to add a stepping motor to my vertex 150mm rotary table...but then, the project got out of control...

I ordered a small Harmonic Drive gear from ebay Thailand and took some time with the cad system...

And now, for the pictures:

The Harmonic Drive, it has a gear ratio of 1:50 and is almost free of backlash:



A lenghwise cut through the 3d model of the rotary axis:


The big blue piece is the buisness end with the t-slotsm where the workpiece will go, the small red thing behind is the Harmonic Drive, paralell to it is the stepping motor, that is coupled with a toothbelt.

As the model was finishded, I started making chips:

Machining the main spindle, from a piece of 80mm leaded steel:


Almost finished spindle:


Finishing the front end, pretty heavy cut with my 9x20 lathe and Hss tooling:


Machining the back housing for the Harmonic Drive and the belt wheel:



So far finished parts:

Front/back housing, end cap, working spindle (t-slots missing) and the bearings:



Machining the t-slots:



Note the very special clamping setup


The bearing package shrinked on the spindle, using a hot air gun:


Machining the holding bracket for the stepping motor:


Cutting the slot for the belt into the back housing:


Thats a little special, you might notice the little black groove in the middle of the part, there is a o-ring about to go in. It was machined using the tool in front, its a small saw blade, 15x0,8mm on a long shank.


Machining the securing nut for the spindle, the thread is M35x1


Cutting the slots for clamping:


Finished nut (need to shorten the grub screws), with the screws, the nut can be secured, as the upper parts of the nut are pressed against the thread, pretty clever design (of course not my design   )


Assembled as far as possible, on the right side is the front housing with the spindle and the flex spinde of the Harmonic Drive, already filled with oil, the securing nut can also be seen. On the left is the back housing with the toothed ring of the Harmonic Drive:


Timing belt wheel, shaft that goes into the Harmonic Drive and one of its bearings:


Backside of the back housing, with the timing belt fiddled in:


The part finished rotary axis:


Machining the motor holding disk from a piece of aluminum plate:


Took a little time, its a pretty tough grade of alumium:


Backside:


Machining of the excentrical hole for the stepping motor:


Finished rotary axis:




And finaly a short video of testing it:

Some work has to be done, but not very much..

greetings
Stefan  

[Brass_Machine]

 


Very very nice work.

Eric

[dsquire]

stefang

Like Eric said. Wow! You sure put a lot of thought into that before you started making chips and it shows.  

Cheers  

Don

Edit:
Stefang. I edited your post to fix the double post of the one picture and addition of the missed picture. Don

[DaveH]

Stefan,

Just fantastic 
 
DaveH

[PekkaNF]

stefang,

Absolutely admire that. Weird thing is that I bought rougly same sitze fanuc robot spare harmonic drive few weeks ago and had pretty much same general layout in mind.

Would you elaborate a little of the bearing arragement? Did you just happen luckily to have some spindle bearings (or such) at hand or maybe there is cunning plan? I get the two bearings at the front, but that rear bearing looks just a little overkill. Please excuse me if I'm all of on this one after all I am an electrical engineer

Pekka

[saw]

Absoluty nice work 

[modeldozer]

Stefan,
 

Great design and work.  If I may ask, were did you get the harmonic drive from?  Need to do similar for my CNC router.

 

Abraham

[dickda1]

Wow

A work of art 

-Dick

[stefang]

Thank you for the kind words

Stefang. I edited your post to fix the double post of the one picture and addition of the missed picture.

Ah, thank you, think i missed that one.

Absolutely admire that. Weird thing is that I bought rougly same sitze fanuc robot spare harmonic drive few weeks ago and had pretty much same general layout in mind.

Then you should go for it

Would you elaborate a little of the bearing arragement?

One axial bearing in front to take axial loads, two radial bearings (two, because they are slim-ring-types, they dont take that much load as a normal one) and the tapered bearing in the back to preload the axial bearing and take radial loads.
And yes, the tapered bearing may be a bit overkill...but who cares

If I may ask, were did you get the harmonic drive from?

Found it on ebay Thailand...took a few days of shiping to germany..

now heading for my bed...
Stefan

[Bernd]

As the others have said truly a marvelous piece of work. You make it look so easy. 

Two things I noticed. One is your carriage stop. I realy like that. Very neat looking. The other is your tool post. I've never seen one like that. Seems like you have the angle setting number on top making it easier to set the angle of the tool. If possible a couple of close up picks of each would be nice. Thanks.

Bernd

[PekkaNF]

The other is your tool post. I've never seen one like that. Seems like you have the angle setting number on top making it easier to set the angle of the tool. If possible a couple of close up picks of each would be nice. Thanks. Bernd

Just a quick note. This looks Multifix toolpost type
http://www.anglo-swiss-tools.co.uk/tool-posts.html

Pekka

[thewho]

  amazing work!

[loply]

Forgive my ignorance but why is the harmonic drive neccessary? Is it just a simple case of the steps are too large without it?

[CallMeAl]

Very impressive work!   I would be even more impressed if I know what it was.

[Pete.]

Woah, what a neat project. I had never heard of a harmonic drive until this post but after looking it up on wikepedia I'm impressed by such a simple device that does such a good job.

100:1 gearing and no backlash means you can get fantastic control and holding torque from a tiny stepper/servo.

Very impressed!

[stefang]

Ahoi,

tomorrow I will meet a friend, where we are going to cast the clamping bracket and a tailstock for the rotary axis out of alumium.

The other is your tool post. I've never seen one like that

Pekka is of course right, its a Multifix Style toolpost, they are over here in Europe very common, almost every lathe in a professional shop here in Germany has one mounted...and also on very much lathes in hobby shops
Not very cheap, but pretty precise..there are chinese clones (mine is also a chinese one), that are not to bad.

Forgive my ignorance but why is the harmonic drive neccessary? Is it just a simple case of the steps are too large without it?

The Harmonic Drive multiplies the torque of the stepping motor by 50, and also increased the precision by facor 50.

I would be even more impressed if I know what it was.

Think of a rotary table on a conventional milling machine, only computer controlled.

Stefan

[loply]

Do you mind me asking how much the harmonic drive was, and which seller it was from?

[stefang]

Hello,

The seller was "xyza.part", and it was about 80$ if I remember correctly..

Yesterday was a good day, as I had the chance to cast the clamp to mount the rotary axis and the tailstock from alumium.

The mould with the sand-core:


The finished cast of the clamp and the tailstock:


The rough casting of the clamp is not very nice, but seldom...it will be machined on all sides, so i can live with that crappy casting. On the other hand, the tailstock came out pretty nice.

greetings,
Stefan

[Pete.]

That dividing head is jaw-droppingly nice

[John Stevenson]

Forgive my ignorance but why is the harmonic drive necessary? Is it just a simple case of the steps are too large without it?

You need some form of gearing in a 4th axis to prevent the cutting forces winding the stepper back.
Work gearing like in a rotary table at 60:1 as an example is ideal as it can't be back driven.

There has recently been an article in MEW that describes building a 4th axis that is nothing more than a stepper driven spindle with a timing belt reduction.
I built on of these some years ago and had to scrap it as when doing splines for instance it was impossible to keep a straight cut, you could see and feel it notching over under cutting forces.

John S.

[stefang]

Done!

Machined the casting for the spindle clamp, first on the shaper:


Then over to the mill, boring the hole:


Pretty close, there is only about 0,5mm between the spindle head of the mill and the part left:


Then I made a mounting plate...


..and screwed everything together:


Pretty happy how it came out, runs smooth and without backlash

I got also a short video:

Dull endmill, to low feed and acetal, so I get a lot of burr...but you get the idea

Time to go to bed...
Stefan

[doubleboost]

Nice
Castings came out fine
 
Spindle is a piece of art
John

[madjackghengis]

That is some mighty fine work there, Stefan, I had a bunch of questions, but they all got asked before I got to the end.  I was also going to comment on the very fine carriage stop, and the fine tool post, then noticed everything you show in your shop is a fine piece of equipment, and am left with "very nice indeed".  That tail stock casting came out a beauty as well, and the other casting ought to be fine when it's cleaned up, all in all very impressive looking, and fine finishes.   cheers, mad jack

[Rob.Wilson]

  Excellent  job Stefang   

Rob