CNC Dividing Head

[Dinkum]

Hi All,

I am considering cutting some gears and therefore I need a rotary table or dividing head. I am considering building a CNC dividing head.

The basic idea is to build a dividing head like Harold Hall's basic one and then power it with a stepper motor to get the divisions.

So here are my questions: first, what exactly do you need for precise motion control? Will a stepper motor, motor controller, and breakout board be enough for this sort of precision? I will have it geared down (to the motor). Software shouldn't be an issue, I should be able to sort that side out.

It would seem that I could build something like this very cheaply - that is the chief attraction of this idea. (+ I should be able to cut gears with any number of teeth)

 

[stevehuckss396]

Look around the board for Chuck's build. He is in the middle of a CNC dividing head right now. Lots of good info there.

 

[Tin Falcon]

So here are my questions: first, what exactly do you need for precise motion control?
so simply need to

Will a stepper motor, motor controller, and breakout board be enough for this sort of precision?

with some gears timing gears or shaft connection and some software you have it. if you are only running one controller you may be able to get away without a breakout board. but BBS often include circuit protection like optical isolation.

I will have it geared down (to the motor). Software shouldn't be an issue, I should be able to sort that side out.
any cnc software will control on axis.

I wrought this with a full cnc build in mind but should be helpful.
Tin
http://www.homemodelenginemachinist.com/index.php?topic=9787.msg107506#msg107506

 

[Blogwitch]

It seems to depend on whether you want a stand alone unit, or one where you have to drag a computer into the shop to run it.

I made a stand alone kit and they are not cheap by any means, but they can be used VERY accurately and used to mill with if you fit a large enough stepper, as well as step up to 9,999 divisions, more than enough for anyone.

This is the complete build.

http://madmodder.net/index.php?topic=4040.0


John

 

[Dinkum]

Steve, thanks for the pointer. I found the thread.

Tin, thanks. I looked there already but I wasn't sure what was meant by "motion control hardware" (point 7) ?

Also, would I need an anti-backlash coupling?

And, Bogs, yes, I would drag a computer into the workshop. How would the following do for electronics:

http://www.ebay.com.au/itm/Nema-17-...Electrical_Test_Equipment&hash=item257056e34d
http://www.ebay.com.au/itm/Stepper-...Electrical_Test_Equipment&hash=item256ece073f
http://www.ebay.com.au/itm/5-Axis-B...Electrical_Test_Equipment&hash=item415ea33457


Lastly, how would a straight cut gear-drive perform as opposed to a worm drive?

 

[stevehuckss396]

I brought it up in chucks thread also but the motor torque should be high. Not so much to drive the head but for holding power while machining. 70 OZ is very low. I cant say for sure what you need because that will be based on how you build it. Most people I know go direct drive with a belt at 3:1 or so ratio so holding power is important. If you go gear drive at 30 or higher to one, holding power will be less important.

 

[Dinkum]

Is the holding torque important at all if you have lock down clamps?

 

[Blogwitch]

High torque is definitely required if you want to use it for machining rather than just point positioning.

John Stevenson has done some very nice things with a Divisionmaster. Driving a spindexer through a right angle gearbox, driving an absolutely huge dividing head with one, plus if you go onto the DM site, you will see how people have fitted steppers to all sorts of rotary drives, including straight geared setups.

I am not trying to get you to buy one, but sooner or later, I think you will want more than just point positioning, which can be done manually using cheaper division plates.

[ame]http://www.youtube.com/watch?v=P1ifPuImERA[/ame]


John

 

[stevehuckss396]

Is the holding torque important at all if you have lock down clamps?

Clamps are great until you get to the 54th tooth and forget to loosen them and try to move. Then you are starting over.

 

[Noitoen]

If you don't use the motor's torque for machining, you can use a miniaturized version of this http://www.alibaba.com/product-gs/208187205/FGRA_003_Band_Brake_B05_160.html with a small solenoid actuator to hold the motor shaft. The microcontroller would release it before each move.

 

[Dinkum]

Clamps are great until you get to the 54th tooth and forget to loosen them and try to move. Then you are starting over.

LOL! I do see your point though.

Can anyone please verify whether the electronics I listed previously would be suited for each other? I am really unsure about the compability of the breakout board with the stepper motor controller and also the compabilty of the latter with the motor itself. If I get a 4 phase motor should it work with any 4 phase controller? Also, is every controller compatable with any breakout board? How do the voltages work? Where is the power supply connected to?

Thanks for all the help so far. As you can see I have absolutely no experience with these things.

 

[RonGinger]

A breakout board is used between a parallel port and motor drivers. If you are building a control using something like an Arduino you wont need a breakout board.

Generally most stepper drivers will work on a 5v signal, commonly refereed to a a TTL signal. Note, "generally", be sure to look at the specific board you want to use.

Steppers are not really 4 phase. They have two coils, but can have the coils separated so you have the choice of connecting each coil as a series or parallel set. The only motor that causes a problem is a 5 wire motor, because it has its coil center tap connected together. This is not very common now.

On stepper drivers the critical factor is the current rating. If the driver is rated for the current your motor needs it should work. Most of them have some method of setting the output current, either by a dip switch on the board, or by placing an external resistor which is calculated to set the current as needed.

Stepper driers are an unusual device in that they are a constant current device. We are more familiar with constant voltage devices, Typically the drive is supplied with a high voltage, 24-48v in common for the size steppers we use for home shop CNC. The drive chops the voltage on and off, and senses the current the motor is taking. When that reaches the set point the drive switches off the voltage. The result is the motor see a nearly constant current.