On 5/18/2010 6:00 AM, Mark Wendt wrote:
> Morning Gents,
>
> Now that I finally have the machine completed, and up and running, it's
> time to actually learn how to use the damn thing.
>
> To set the scene:
>
> It's a two axis machine, X and Z axes. Fairly simple operation. The
> machine will be cutting tapered bamboo strips, ranging in length from
> about 32" to 54", in one pass, using two saws set in a "V" on the Z axis
> with the "point" of the "V" towards the bottom.. The taper is not a
> linear taper, and in some places it tapers more than others and in other
> places less. The tapering is based on one inch centers - ie
> X0 Y.125
> X1 Y.123
> X2 Y.120
> and so on, and may not vary even that much between the X points.
>
>
> Bamboo fly fishing rods typically are made in two sections, the tip and
> the butt. The sections are made of of six strips each, and normally two
> tips are made for each rod. So, for the tip, you'll have 12 identically
> tapered strips, and for the butt, you'll have 6 identically tapered
> strips. The tip strips will all be milled to an identical thickness
> before being put on the machine, as will the butt strips (though the
> butt and tip strips will not necessarily be the same thickness). The
> strips, whether butt or tip, will be mounted on the vacuum hold-down
> with the end where the cut begins in exactly the same place every time
> (X axis touch off point). The Z axis touch off will be the only thing
> that differs, and that will only differ if it does between the butt and
> tip strips.
>
> There will be a separate G code file for the butt strips and the tip
> strips, mostly hand coded.
>
> Now we start getting to the crux of my questions and confusion. In the
> User Manual, Chapter 10, "G Code Best Practices", there's a paragraph
> titled "Put important modal settings at the top of the file", and
> included is this string - G17 G20 G40 G49 G54 G80 G90 G94. Some of
> those are pretty straight forward, and some have me not sure why they
> would be included, or which of the codes i should actually select.
>
> G17 - Plane select - since this is a two axis machine, and uses the X
> and Z axes, should I include this code, and i do include it, would it be
> G18 - the XZ plane?
>
> G20 - inch units, that's what I'll be working with
>
> G40 - Cancel Cutter Comp - used even if cutter comp is not used, won't
> hurt anything to call it
>
> G49 - Cancel tool length offset - same principle as G40
>
> G54 - this one I'm not sure about why it would be included. When you
> home the machine, you're on the machine coords X0 Y0, right? Does this
> inclusion just automagically zeroize the G54 coords and match them to
> the machine coords?
>
> G80 - Cancel motion modes - similar to G40 and G49
>
> G90 - Distance mode - Absolute distance - this one, though seemingly
> straight forward gives me questions on some of the other codes - the G54
> - G59 codes - though they are consider coordinate system codes, aren't
> they also technically an incremental distance code based on where you
> call the axis zero?
>
> G94 - units per minute feet code - in my case, since I selected G20,
> that would be inches per minute.
>
> Now, in some other G Code files, I've also seen feeds and speeds in that
> initial line. Is that good practice too, or should I just call it out
> when needed?
>
> Thanks,
> Mark
>
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Everyone has their own style. I try and let a cam program do most of
the heavy lifting for Gcode generation as it makes fewer mistakes than I
do. ;-)
Anyway, you are best to not assume much at the beginning on your
programs. Set everything the way you want to operate when you start
up. Do the same on all of your programs and you won't have as much
to second guess. A lot of things in Gcode are modal. Some are
remembered from program to program. If you set your G54 offsets in one
program and load up another program, those offsets from the previous
program are still in place.
The less you assume, the fewer tools you will break. :-)
I tend to put a default feed and speed after each tool change. That way
you are also starting in a consistent "place", ie 500 rpm at 2 ipm etc.
If you copy and paste then you also have a reminder that you need
to change from 2 ipm for the next code segment.
G53 is machine coordinates. You can set your G54 offsets so they mimic
the G53 coordinates but you don't need to. G53 coords are usually set
by homing. G53 is not modal - so you can't change to machine coords and
then have that stay in effect for the following lines of G code. But
you can do a move in machine coordinates via something like G53 X10 F10.
Axis has a pull down tab so you can look at the DROs in machine
coordinates.
Dave
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