Stepper controller to manually input a specific degree

[Web Goblin]

I am thinking about building a 4 axis for my manual mill using an old lathe headstock shaft and a stepper. What I am looking for is a controller for the stepper that I can set manually ie something that I can input say a specific degree of rotation via a keypad or suchlike.
Think of gear cutting but setting the degree of rotation manually for each tooth.
Anyone seen such a beast?

Ian

[HankMcSpank]

I am thinking about building a 4 axis for my manual mill using an old lathe headstock shaft and a stepper. What I am looking for is a controller for the stepper that I can set manually ie something that I can input say a specific degree of rotation via a keypad or suchlike.
Think of gear cutting but setting the degree of rotation manually for each tooth.
Anyone seen such a beast?

Ian

If you don't get a custom solution, this should be do-able from within your standard CNC app using something like a g-code command e.g. G0 Axxx command (where 'A' is the label given to your 4th axis & xxx is your required rotation in degrees 0->360).

Assuming a 1.8 degree per step stepper

You need to arrange it so that your CNC application thinks that one full revolution of your 4th axis stepper is 360mm

So, assuming you work in millimetres as the unit of measure within your CNC app....

A standard 1.8 degree per step stepper would mean 200 steps = 360mm

therefore 1mm (or 1 degree of rotation) = 360/200 = 0.55555 steps per millimetre ....which obviously isn't ideal, so for the 4th axis stepper, crank your driver micropstepping up as far as it will go, let's say you can get 64 microstepping, then it would be

200 x 64 steps = 360mm

12800 steps = 360mm

1mm = 12800/360 = 36.5 steps per unit

So set your steps per unit for your 4th axis to 36.5.

Now in your CNC app

G0 A1 = 1 degree
G0 A10 = 10 Degrees

etc...

I think I have the maths right, but no doubt someone will correct me where I'm wrong!

[Jonathan]

How are you coupling the stepper motor to the spindle? If it's just with a belt then forget it. The torsional stiffness of even an unreasonably large stepper motor, combined with the stiffness of the belt means you'd probably be able to cut foam with it but not much else.

You need something like a worm drive or harmonic drive. Worm drives are good here since although they have a bit of backlash, this can be minimal and they generally don't backdrive. You can make one easily by attaching a stepper motor to a rotary table. This post shows one I made recently. It's just two simple parts you can easily make if you've got a lathe. Or you could buy one from Arc Euro.

[m_c]

DivisionMaster - Model Engineers Digital Workshop

I'm sure I've seen mention of other cheaper options, however I've not really paid that much attention to them. A search of homeshopmachinist might turn something up (bbs.homeshopmachinist.net/forum.php)

[johnsattuk]

Have a look at this, I built one works well

World of Ward :: Overview

[Web Goblin]

Thanks for the replies guys.
Johnsattuk thats exactly what I was looking for. Looks like I will be busy at my bench when I get back to work later next week.
Many thanks.

Ian

[Jonathan]

There's been threads about it before. The option m_c has posted looks good, but it is rather expensive for what it is.

Other options:
http://www.mycncuk.com/forums/electr...ndexing-3.html

EDIT: Sorry, didn't spot that that had already been linked to.

If you need someone to program the PIC pm me and I'll do it for you. Could probably write the code for my own with a display in about an hour... it's very simple.

Personally I just plug it into the controller for CNC router/mill and use the method hank describes. I don't really see much point in using the above methods when you can just use a computer you found in the skip, connect the parallel port a cheap stepper driver and run it on mach3 / linuxcnc. You don't even need a breakout board if you use an opto isolated driver (e.g. m542) and the parallel port is old enough to output 5V.