RE: [CAD_CAM_EDM_DRO] Re: Digital screwcutting "gearbox"

To be fair. The software/firmware to do this is pretty simple.

Measure the time between pulses from the spindle encoder using an interrupt,
I'm impressed how well TCNC does with a 1pulse per rev encoder.

Divide by the pitch constant.

Set the time period of a square wave generator (user a timer interrupt or
PWM output to make this run in the background).

The fiddly bit is the user interface. You might get by without a display,
just two multiposition switches, one for length one for pitch..... nope,
you're gonna need a display, a couple of buttons and maybe a rotary encoder
knob. Particularly if you want to prompt the operator to wind the slide
back so you can move the saddle back to the start position.


PK


-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of afogassa
Sent: Wednesday, 19 October 2005 1:50 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: Digital screwcutting "gearbox"

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "majorityuk2000" <john@h...>
wrote:

>
> Hi all,
>
> I am sure that thius question has been asked and answered many

times,

> so apologies in advance if it is tedious. However...
>
> I am interested in adding facilities to my Super 7 lathe to allow

it to

> cut threads using a stepper to drive the L/S, synchronised to the
> headstock through a phase-locked loop. A side benefit should be
> variable slow feeds and a "virtual saddle stop". I have worked out

a

> scheme to do this which I think will work but would like to see if

I

> can learn from others' experience first!
>
> Can anyone please point me to material on the web, or elsewhere,
> suggesting how this can be done, and/or other peoples' experiences

of

> doing it?
>
> Cheers,
>
> John Haine.
>

Hi John,
I'm also on this,I was thinking about the use of a microprocessor
like atmel 90s2313, and a 2x16 lcd.
FROG does make one for this purpose,but it does not have a lcd
display, instead it uses a series of "bips" and bops.
I was thinking of something a little more sofisticated.
Using the atmel chip and A3977 step driver from Allegro and a
little programming in bascom, I was able to have the motors moving
nice.
Still need to find a way to include a ramping in the software,
after that I'll think in how to sincronize the headstock and
steppers, I think this is not as dificult as implementing
acceleration for step motors.
if you want it off the shelf,do a search on the net for FROG CNC.

Fogassa.





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