View Full Version : Sturdy Rotary Axis for CNC table

Boyan Silyavski
30-08-2014, 12:47 PM

I know the question is old. I reread many material on the net these days. Now the case is the following:
I started building my next machine (http://www.mycncuk.com/threads/6619-Quite-an-Unusual-one/page6), this one will be for myself.

Definitely i would like a rotary axis. This axis will serve mainly for the following purpose:
-3d pieces made from wood with dimensions no more than 750 x 50 x 50 mm.
-cutting teeth on aluminum and plastic custom pulleys max 150mm diameter. It would be great if i achieve this.

Now i know of the types and goods and bads. I don't want any bads. So the only possible design i see as possible is similar to the http://www.theinturn.com/, which de facto seems to me the best diy solution.

So i would like to achieve something similar on smaller scale, as it will not be mounted on a mill. However my machine Z would be very ridgid, so i believe if mounted at the proper place i can even do some small lathe jobs, tools mounted on Z. Again-aluminum, plastic and wood. i dont expect to mill steel.

I don't have mill or the skill, though our forum friend Jeff lives very near and has surprising workshop, machines and knowledge. Good for me.

My conclusions till now:
-head will be best to be 5C collet system in my case
-singular or multiple HTD belt driven
-brake is a must
-hi encoder count 750w or 400w servo is a must. leaning towards the second.

Now before i say more, i have small hobbymat lathe that i am very inclined to fit directly on the top of the table or split it and use the main parts fitting it somewhere or combination of these two. Cause it seems it will be the cheapest, as i have it already and what i need to do is fit servomotor and change the pulleys and belts with HTD 5

Or if i start it from scratch, i will need to machine some parts and most importantly find suitable big cheap roller bearings for the head stock / 5C /,

But my biggest question is how to brake the thing on the cheap. I assume a disc from something and ...

And what is this stuff called dynamic balancer the Inturn 4rt axis implements. I would not need it i assume.

30-08-2014, 08:52 PM
For the moment I'm ignoring 'on the cheap'.
I can't see how you could use it as a 4th axis and also as a 'lathe' with the same drive motor.
What about if you used it as a 4th axis with a stepper motor via Mach3, you would not need any braking in this instance and implimentation would be easy.
Then when you want to use it as a lathe you could use a cheap standard induction motor driven by a vfd, the vfd would provide variable speed and dynamic braking with ramp down.
You would just need a simple way to swap from one drive motor to the other.

Boyan Silyavski
30-08-2014, 09:45 PM
For the moment I'm ignoring 'on the cheap'


I meant not too much money. And use what i have at hand.

And about the Hobbymat lathe, i meant fit a servo drive and use it mainly on the CNC as 4rth axis. may be only the head part. All via Mach3. If i need lathe, i have small stepper generating circuit.

How is that i will need no braking, of course i will. Or you think a stepper or servo can hold enough. It cant. Especially if i make pulleys there.

30-08-2014, 10:04 PM
You're talking about 3 requirements.

1. cnc 4th axis
2. Indexer
3. Lathe

From the InTurn web site;

Custom made articulated pneumatic caliper provided over 100 ft-lbs of holding torque on 90psi shop air.
Cylinder rated for 200PSI leaving a great deal of added capacity, although so far no operations have needed more than 90psi.
DOT approved hardened and ground steel vehicle disk brake rotor is mounted on a thick steel collar and balanced.
Note, the Tail Stock II has a combined spindle damper/lock provided by an internal band brake.
CNC controlled solenoid operated pneumatic valve controls the spindle lock. The valve and a CNC compatible relay are included."

So I'm thinking about a brake disc and caliper from a car scrap yard with an air over oil actuator.

Boyan Silyavski
30-08-2014, 11:02 PM
Ok, so 100ft-lbs for a big mill. 135Nm. Then it seems a bicycle hydraulic brake will be sufficient. http://www.bikeradar.com/mtb/gear/article/how-we-test-hydraulic-disc-brakes-24345/
That is good.

I like the look of this one + coupled with bike brake some how.http://www.ebay.com/itm/cnc-rotary-table-sherline-maxnc-taig-cnc-router-cnc-milling-machine-pool-cue-/151078782316?pt=LH_DefaultDomain_0&hash=item232cff456c Still have not figured the dimensions of the shaft and bearings necessary.

30-08-2014, 11:30 PM
electromagnetic brake or clutch

31-08-2014, 09:33 AM
And what is this stuff called dynamic balancer the Inturn 4rt axis implements. I would not need it i assume.

Like you balance car wheels the Spindle and brake rotor system need balancing so that's what that will mean.

Steve used to use 2 motors on the early prototype, stepper and DC treadmill but I think he's since switched to one servo with high ratio gearing for high speed. Then opposite Low ratio gearing for Resolution. Been along time since I looked so could be wrong.!

If your using Servo's then just use a braked servo and it will be enough for most wood work. Only if your milling steel where cutting forces are high will you need more braking power. But yes bicycle brakes will work and good ones like the Hope brakes on my Mountain bike have amazing stopping power in tiny package with rotors that weigh next to nothing.

The Hobby Matt lathe should work well I think upto Lathe speeds but if your wanting higher speeds more often than low then head stock bearings will die quickly.
I think if you Fit decent sized braked Servo on it with gearing you'll be ok for wood in both lathe and indexer/4th axis use.

Boyan Silyavski
31-08-2014, 11:53 AM
Thanks Dean. That clears some doubts.

Here is the lathe, it seems obvious enough what to do. Have to disassemble all and take measures of the shafts and pulleys that will need.

13237 13238 13239

I assume the correct motor will be 400w, will have to make some calcs and if 1 or 2 pulley. The original motor is 250w.
I assume the final ratio should be something like 1:6 to 1:9 . I am a bit lost here as this is my first lathe and still haven't had the time to go deeper in lathe jobs. and what speeds i need for what.

I assume the holding torque of the servo works just like the power, so if geared enough the force will multiply.

Have seen very cheap taper roller bearings on eBay + the housing is aluminum, so heat will not be e problem even if rarely i need to spin it faster.