RE: [CAD_CAM_EDM_DRO] Re: Metric measurements.

Change your code to have the proper G70/G71 or G20/G21 in it, which will
tell the controller to interpret the units in the code as either inches or
millimeters.

Andy Wander

-----Original Message-----
From: Keith Bucklitch
To: CAD_CAM_EDM_DRO@yahoogroups.com
Sent: 7/21/2005 3:16 PM
Subject: Re: [CAD_CAM_EDM_DRO] Re: Metric measurements.

Hi Dave
Thanks for the suggestions.
I have worked around the problem by changing the measurement units from
metric to imperial before coding the .dxf file, but would prefer to be
able
to feed the original metric units directly to the controller, hence my
request.

I will have a look at the idea of amending the CNC to run as you
suggest. Not immediately sure how to go about that, so I shall have to
do
some reading. My mill is a Taig /Peatol Micromill which has the
leadscrews
on a 20tpi pitch (50 thou"). The interface is in half-step mode, with
the
steppers having therefore 400 pulses revolution. I calculate that as
8000
pulses per inch of travel. Correct?

So, to get 1mm of travel, should I set the interface to give me
8000/25.4 =
314.96 steps/mm. In fact, we probably need to be more accurate in the
conversion than that, what is the correct inch to mm ratio?

Surely, the control software ought to be able to do that automatically.
It
asks what units I am working in, imperial or metric, so why does it not
do
the conversion?

Keith

At 23:07 20/07/2005, you wrote:

>One possibility would be to change the unit in your CAD before making
>the DXF. My CAD allows me to jump back and forth at will.
>
>But, another problem may be that you have your CNC set to run in
>inches. a 5 TPI leadscrew with 1,000 steps per inch will move 1,000
>steps per "ONE UNT"
>
>If you set the driver so a 'unit' is a mm, then moving one 'unit'
>would be 25.4 steps and not 1,000 steps.
>
>Dave
>
>
>
>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "kbucklitch"
><keith.bucklitch@w...> wrote:
> > Hi folks
> >
> > This is my first posting to the group, in the hope that someone will
> > be able to assist me.
> >
> > I create my CAD drawings with TurboCAD. For several years, I have
> > produced my drawings using metric (mm) measurements. Before I
> > started experimenting with CNC, if I printed the drawing full size,
> > then it was printed almost exactly the size of the item (within the
> > accuracy of the printer).
> >
> > To use the drawing to create a toolpath for the CNC cutter, I export
> > the drawing initially as a .dxf file. I have then converted the
> > file to G-code using two programs - KCam or Simsoft Mach 2. Both
> > of these will produce a G-Code script. I then use the software to
> > drive the CNC controller. At present, because I am driving my CNC
> > control with KCam on an old laptop under Windows 98 (Mach 2 requires
> > WinXP.) However, I have found a problem. The CNC driver seems to
> > work in imperial units (inches). Hence, a component that should be
> > say 20mm long, becomes 20 inches long. This is a little difficult
> > on a milling machine which only has around 12" of travel.
> >
> > In the KCAm Setup/Table Setup menu, it asks if you want (are using?)
> > imperial or metric measurements. However, choosing metric in this
> > dialogue box does not appear to make any difference to the finished
> > size of the article.
> >
> > Does anyone with experience of these programs - Mach 2 or KCam know
> > how I can set them up so as to convert metric .dxf files to metric
> > machine codes?
> >
> > Thanks
> >
> > Keith
>
>
>
>
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