Electronic Dividing Head

[cfellows]

I've long had an interested building something CNC but have always been intimidated by CNC milling machines, lathes, etc.

I ran across this video and thought it looked like an intriguing project. One stepper motor, probably pretty simple circuitry, and a very useful tool in the end.

Anybody thought of something like this? Any additional information from anyone?

Chuck

[ame=http://www.youtube.com/watch?v=V2NOHWKqqi8]http://www.youtube.com/watch?v=V2NOHWKqqi8[/ame]

 

[Brass_Machine]

Nope. No help here. But that is pretty cool!

Eric

 

[GailInNM]

Here are a couple of photos of my version. I first built it up about 10 years ago. It is an Ellis dividing head with the dividing plate and handle removed and a NEMA 23 step motor drive added. Takes about 3 minutes to change back to manual operation. It is set up with 400 steps per revolution on the motor, 2.25:1 belt reduction and the head hase a 40:1 worm gear in it. This makes for 36,000 steps per revolution of the output. 1/36000 gives 0.01 degree per step. The output end has a set true type 5C collet closer mounted.

I first built this with an old 34 series motor on it, and only recently replaced it with a much newer and smaller 23 series motor. The more modern motor has more torque and is faster. Control has been by a Simple Step stepper control board where the control program is downloaded with a RS232 line and the control program steps through with either a push button or an index out/index back command on my CNC mill. It works well enough, but is cumbersome to use as I have to down load the steps from an external computer. I have cut about 70 sets of 48DP bevel gears in various ratios and about 250 48DP spur gears in about 6 different sizes.

I have a new control design using a PIC 16F6xx processor. It has an LCD display and a keypad for input. Input can be either in divisions/360 degrees or in decimal degrees in 0.01 steps. The program distributes odd steps when in the division mode for cases where 36000/N is not an integer. The program has been run on a breadboard and with the exception of a few tweaks for the operator interface is ready to go to a printed circuit board. I have not laid out the PCB yet. That is a winter prioject. I will be driving a commercial step/direction amplifier and the whole thing goes into a box that can be mounted/removed from my milling machine. The box is self contained so it could be moved else where.

Gail in NM,USA

 

[wareagle]

Chuck, I like it. Sure makes gear cutting look easy! Gail, that it a great setup as well!
_________________________________________________

CNC is still very much VooDoo to me. I am intriged by the possibilites CNC opens up, and the speed at which it works. I have nothing to offer anyone onthe CNC front, and I really enjoy doing the work in the shop "old school". Heck, there isn't even a DRO in my shop! Two sets of digital calipers is the extent on the digital maching technology in my place (and one VFD if you count that).

But... One day... I have been considering buying a mini mill and lathe that are set up for CNC. It will be a while, and I really think I would invest in a DRO for the mill and lathe before throwing money into CNC equipment, but temtation is there; no doubt. I think a Friday night watching a CNC machine whip up parts would be great entertainment! It sure as heck would beat the stuff that's on TV these days!!

Dreams... They give us direction!

 

[John S]

I have had a lot to do with stepper driven tables and heads, that much so that you will probably hate me

I don't have time now but will post later tonight, as a teaser go here
http://www.divisionmaster.com/

Go to the examples of use page and most of these examples except the Sherline and the Myford based ones are mine.

 

[BobWarfield]

CNC becomes its own sort of "universal toolkit" once you get going with it. The neat thing about something like the dividing head coupled with a controller like the one John S. mentions is it cuts out a lot of learning curve. It's a simple project, and you completely sidestep a lot of the Mach 3/gcode learning requirement with a dedicated controller.

Even for those that don't ever want to mess with full CNC, I would think an indexer/dividing head/rotab project like this would be very useful.

Best,

BW

 

[cfellows]

Gail,

Sounds like you are working on exactly what I had in mind. I do prefer a dedicated controller box like you're putting together.

May I ask why you went with the PIC controller? I know very little about microcontrollers and have found the following 4 out on the WEB:

BasicX (Basic Stamp Clone)
PIC
Basic Stamp
PICAXE
ATMEL

I suppose the best strategy would be to use the microcontroller with the greates popularity among hobbyists.

Chuck

 

[John S]

Could be long - go get a coffee.

Right ready ?

First off Gail's method and the ones on the Division master forum are the way to go. The one in the video in the first pic isn't a good idea and it's direct drive and the average stepper motor doesn't have enough detent torque to hold it accurately in position when parted. If you select microsteps to smooth it out that also reduces torque.

A worm and wheel drive of greater than 20:1 is required if the drive has to stop being reverse driven.
Dividing heads, rotary tables and even propitiatory off the shelf gearboxes make good 4th axis to give them one correct name.

Here's one setup for use on a Taig.

Just a hollow shafted gearbox driven by a stepper thru an Oldham coupling, this one has a 14mm output shaft to give an idea on size.
They come in all sizes and this one off my electronic hobber has a 25mm shaft size.

Build up of these heads / tables etc is very simple, a stepper mounting and a metod of driving the work usually thru a coupling to remove any mis-alignment.

Here is one part done, the handwheel has been replaced with a drive dog that has thrust bearings inside it.
Simple enough job to do, anyone who can make a small engine has enough skills to do this purely mechanical conversion.

Here is one of those little 3" tilting rotabs that's been converted.

That takes care of the mechanics, next is the power supply and then the controller.
Power supply is just a transformer, large capacitor and a bridge rectifier, literally but we'll cover this in another post if there is enough demand.

Controller.
Can be varied.
PC based using a full CNC program like Mach 3 or TurboCNC
PIC based using something like the Division master down to small simple pulse generators.

There are even a couple of programs that run on the PC just to run a rotary table or dividing head for gearcutting or indexing

So depending on skill levels and equipment you can get a working 4th axis going for not much outlay.

.

 

[CrewCab]

Well,
I'm sitting comfortably, got mi' coffee ................ and I'm all ears  8)

over to Mr Stevenson 

CC

 

[wareagle]

John, let's make an assumption that one has the diving head, spin fixture (which modded is darn cool!) or rotarty table, what would it cost roughly to buy the stepper motor(s), the power supply (or components of), and a basic stand alone controller? I realize this could run a million different directions with the options available, mounting methods, transmission of the stepper to the device; but just a ballpark guess....

 

[cfellows]

Great Post, John, and what you're suggesting is what I had in mind. I have a dividing head that I built and it has a 40/1 worm. I had thought it would be a better idea to use a stepper through the worm, rather than direct.

You mentioned an electronic hobber? Got any pictures of that? I was thinking today that an electronic stepper driven hobber would be a lot easier and more flexible than a gear driven hobber. I was also thinking that worm gear cutting and helical gear cutting could be facilited with an electronic stepper / indexer.

Chuck

 

[GailInNM]

Chuck,
There is no real good reason for choosing a PIC over other processors for simple indexing. I am comfortable with them and they are easy to source. I like the PIC family as I can get most any configuration that I want. Where space is not a consideration I have been using 16f877 for most everything. It is not much more expensive than a less capable processor and allows room for expansion. My original post said 16f6xx, but should have said 16f8xx. I will change it.

If you build your own controller, make it very operator friendly. That was the only real problem with my original setup. It was just enough of a pin to use, that for simple jobs I would switch it over to manual rather than set up the program for it. I will have most of the functionality of the Divide Master, although I have not put in any backlash compensation. For everything I have done, a single direction of operation has been all that has been necessary. I probably should put in compensation when I do the finished program. I do want to add one function that the divide master does not have and that is a knob for feedrate override, mostly for use in free running mode. This is only for use while truing up oversize arbors with the milling cutter so the arbor runs very true. My 5C arrangement is good, but it still has a couple of tenths runout that is slightly bothersome when cutting small gears, 64dp or smaller, that are spaced for minimum backlash. I could do it with the previous setup, but it was a pain to do.

Most of my PIC programing is done in MikroPascal, but you can program most of the microprocessors using about any language you are comfortable with. I just happen to like Pascal. There are free compilers for it and many other languages.

Summary:
The functions in the controller are fairly easy to implement. The key is the operator interface. If it is hard to use then, if you are like me, you won't use it. The hardware is the easy part, but at least think about making it easy to change back and forth for manual operation should you desire to do so. I think that with a good operator interface you won't want to, at least that is my goal. If the Divide Master is a reasonable price (I have not checked) you could get going quite quickly if you have a suitable head.

John,
Thanks for all your insight on the topic. You have a lot of experience and that is respected. Also thanks for the Divide Master link. I was not familar with them. I think thay have the right approach. If I was not as far along with my controller I would certainly look in to it in a serious manner. I might even do that anyway.

Gail in NM,USA

 

[John S]

Wareagle,
I'll try to base this in US pricing and links as giving my sources in the UK isn't a great help but for the Brits most things can be had from Arc Euro, RS and / or Maplins

First off the stepper doesn't need to be massive as it has the gearing needed to obtain torque something like 170 to 250 oz in will work on 4" up to 8" heads, add to this a driver for it if you are not into making one.

Go here [ no connection ] http://www.kelinginc.net/NEMA23Motor.html and in section 3 there is one at the bottom. the KL23H276-28-4B that fits the bill nicely.
Same place has a driver for it. http://www.kelinginc.net/KLDriver.html second one down the 4030.

This now sets what we want for power as the driver is maxed out at 40 volts DC.
So going back to our first post we need either an off the shelf power supply or build one from bits.

For a simple stepper driven table where accuracy and position is foremost against power as not many people use these for cutting you can get away with something like a 24volt laptop power supply rated at 2 amps or thereabouts.

If you are going to build one you need a 24 volt transformer $20 ? a bridge rectifier $5? and a capacitor about 10,000uf and 60 volts working $25 - $30 ? all at new prices.

Stick all this in a box and all that is missing is the logic supply from the controller / PC that makes it go forward or backwards.

This bit is really the stumbling block as you have many choices and need to work out 'do I need a PC in the shop?, can a laptop run it?, can I build a simple pulse generator?,

I'll make this a subject of another post if there is any interest.

As a note the Divison master from Tony Jeffree has been discontinued and it's now handled by a guy in the UK called Lester Caine who also does these as a kit to get the price down, there is a link on the prices page that takes you there.

[Edit]
I'll post tonight and may be able to show something new as regards a controller, I need permission first.

 

[cfellows]

So it seems to me, at a macro level, these are the electronic components that would be needed for an electronic dividing head:

I suppose there is some opportunity to combine power supplies for all the different modules?

Chuck

 

[spuddevans]

I'll make this a subject of another post if there is any interest.

[Edit]
I'll post tonight and may be able to show something new as regards a controller, I need permission first.

I for one would love to read more about this, Please start another post on this.

Tim

 

[BobWarfield]

Another thought on drivers. I built a real simple CNC rig around a kit from Xylotex for my CNC Minirouter:

The kit can be had with all the goodies but the PC: http://www.xylotex.com/3AxSysKit.htm

Mind you, it is 3x what you need for a rotab project, as this is a full 3-axis kit. But you get the power supply, drivers, and computer interface. It might be fun if you think you'll want to experiment with a variety of CNC gizmos. For just a rotab, I like John's Divisionmaster better. Similar price, but no need for PC and its set up with the rotab in mind.

It fits nicely in a toolbox so I can drag the rig out to show kids, friends, clubs, or whomever will tolerate it!

The little CNC router has been good fun:

Cheers,

BW

 

[John S]

Got back in real late tonight so can't post a lot as it's just gone one am here and I need my beauty sleep [ probably need everyone elses as well :big: ]

Just a quick link.

http://www.diycnc.co.uk/html/onestep.html

I'll post about this tomorrow, well later today, it's similar to a Division Master in that it's all self contained except a wart wart as a power source and will run a stepper at up to 2 - 1/2 amps but very simple.
It's drawback is if anything it's too simple, it's really a pulse generator with a display but it should be cheap.

More later on this and also a program for the PC that just runs one axis and was designed for gearcutting.
Need to find the damn link for it though.
.

 

[wareagle]

John, thanks for the info! I am eagly watching this thread. It is seeming like a CNC indexer isn't that far out of reach cost wise.

Must resist temptation, must resist tempatation.... : ;D

 

[spuddevans]

John, thanks for the info! I am eagly watching this thread. It is seeming like a CNC indexer isn't that far out of reach cost wise.

Must resist temptation, must resist tempatation.... : ;D

I too thank you very much, Hmm, yet another tool I have to think of an excuse, I mean reason for!! :bow: :bow:

Tim

 

[macona]

Picked this unit up off CL a couple months ago. I think this is Haas's original product before they got into CNC.

Its just a stepper that drives it so I am going to use another compumotor stepping drive that I have laying around to drive this connected to the CNC mill.

Heres another 4th axis I built for the mill last year. It is a 200 step stepper into a 10:1 bayside gearbox into a 5:1 worm box. Really low backlash. What I didnt realize until using it was there is slop in the bearings so the output shaft is not as rigid as one would like

Some of the titanium rings I made: