CNC Rotary table/lathe head indexing

[Ross77]

Brilliant idea I will definetly bulid this, after the other 10 or so projects. Hope you dont mind but a have a question not related to this Thread.

Im looking to build a stepper driver using an L297 and 2x 6203 and I want to use a PIC to control the holding torque. (by varying Vref) I noticed in the last post that your controller was designed to do this. Would you be able to shed any light on the code to do this and how it was integrated in to the circuit?

Many thanks and sorry again to hijack your thread.

[Kwackers]

Hi Ross,
It's pretty trivial. VRef is normally provided via a voltage divider, basically you simply provide your VRef fed via two voltage dividers, one fed from +5v like normal the other fed via the enable line. Unless you isolate the two dividers there's a degree of 'interdependence' on their adjustment so you need to tweak both to get the current correct. (I think I also fed the enable via a diode to prevent it pulling VRef low when the enable line dropped.)
In software terms it's simply a line that's pulled high whenever the motor is running.

Another way that I experimented with and worked well, was to feed one of the PWM's via an RC chain (series resistor feeding a parallel cap, feeding another resistor feeding another cap). Set the frequency high(ish) and change the PWM to alter the voltage (and thus the current). The VRef input seemed quite high impedance so there was no need to buffer this. A 50% pulse width ratio would result in half voltage available. Again in software when idling all that I did was quarter the PWM ratio to drop holding current to 25% of max when the motor wasn't running.
The only reason this didn't make it into the final device was that it worked out cheaper and less messing to buy ready made drivers, which meant that the setup options for setting the stepper current made no sense.

Hope this helps,
Steve.

Brilliant idea I will definetly bulid this, after the other 10 or so projects. Hope you dont mind but a have a question not related to this Thread.

Im looking to build a stepper driver using an L297 and 2x 6203 and I want to use a PIC to control the holding torque. (by varying Vref) I noticed in the last post that your controller was designed to do this. Would you be able to shed any light on the code to do this and how it was integrated in to the circuit?

Many thanks and sorry again to hijack your thread.

[Ross77]

Thanks Steve, thats great. Unfortunatly I've never used Pic's before and therefore I'm a complete novice. Irving and Tribbles have offered to help with the code but just wondered that as you have allready done it we wouldnt have to reinvent the wheel

Im looking at a slightly different set up where the pic is soley used for varing the vref based on the incoming step signal from Mach. If you can help any further maybe you could take a look at me my thread "Help with DIY L297 + 6203" (or some thing like that:heehee:) to save clogging up this one.

Thanks again

[dchobby]

Hello.

Would never have been able to do this without kwackers (Steve), this thing works great, thank, thanks, thanks.



I still need to find a box for the driver, small issue. I am just so happy it is working.

Roy
Elkhart, IN USA

[Nipper]

Hi,
I am new to MYCNCUK so you will have to patient with me I am not an Electronics person but I have worked on very large commercial CNC machines I have a small lathe and a small Knee Mill and I am going to attempt to convert them both to CNC First question is could I use this control to index a six position tool post for the lathe. Second question do you sell this control already made Regards nipper

[irving2008]

Nipper,

Welcome. I'm sure Steve will be along sometime to answer this but my 2p (or should that be 2c) worth for Q1 is that, yes it could, but its overkill since you don't need the complexity of a fully variable positioning, you need a 'rotate to position x'. The hardware would be similar but it would need different software. If I was doing it i would put some positive position indication, or even tool type indication as feed back (replacing the keypad effectively) so that you can have 'position to parting tool', 'position to facing tool' type commands irrespective of where the tool was in the toolpost.

As to Q2, I know Steve has said he doesn't do these pre-built in the past, but I'm sure there are people in your part of the world who could help you there...

[Kwackers]

Hi Nipper,

It's pretty much as irving2008 says. You could use the divider but it's overkill for a toolpost, also it raises the question of how do you make the whole thing 'stiff' enough to work properly? If it's for a fully automated system then you need a method for locking it down and if not then I think you'd be better with a manual indexing toolpost.

Regards
Steve.

[irving2008]

I think auto-toolchangers have a locking plunger with a solenoid or stepper driven retractor to lock the post and a switch to indicate the plunger is clear so that the software wont turn the post until it unlocked. A switch to show the locked position would also be useful.

[cncguy]

hi guys

i tried running the hex code on proteus and the processor is been reset every 23secs by watchdog timer. itried compilling the v1.1 still the same problem. can someone tell me what i am missing

[rasta]

Hi,
I am new to MYCNCUK so you will have to patient with me I am not an Electronics person but I have worked on very large commercial CNC machines I have a small lathe and a small Knee Mill and I am going to attempt to convert them both to CNC First question is could I use this control to index a six position tool post for the lathe. Second question do you sell this control already made Regards nipper

Hi Nipper;
there is someone in OZ that has done a tool changer for a herbert lathe, I think that is
in SA , he is a nice fellow , have a look at this

http://www.cncathome.com/latheturret.html
also there is a very nice fellow in Melbourne ,his name is Frank Tkalcevic, he is
very active in the emc forums .
regards from Sydney
mariano
mariano