On Saturday 19 May 2007, Ed wrote:
>Gene Heskett wrote:
>> Greetings;
>>
>> Yesterday I pretty well wrecked the 2nd copy of the bottom of the floor
>> plate I was tracing a couple of weeks ago, with the g2 command. I thought
>> I was tracing just under a 180 degree half circle, but it turns out that a
>> very minor .001" change in the r number made it go from just reaching the
>> endpoint, to a gouge a nice .010 deep notch in the part over 180, and also
>> moved the midpoint diameter of the cut such that a nearly .050" change in
>> the x at start-stop was required. I was using g2, cutting from the back
>> to front around the right end of a boss, or again, g2, cutting from the
>> front around the left end to the rear stopping point. I was under the
>> impression that a larger r would result in a less than 180 degree arc, but
>> it appears in the results that a larger r effectively starts at 180
>> degrees and goes up.
>>
>> My intention was to cut maybe 175 degrees as the part is less critical
>> about that, and esthetically pretty ugly if it went over 180 degrees and
>> gouged the side. My understanding is that a larger r will result in fewer
>> degrees being traversed, but such didn't appear to be the case. Humm, now
>> that I think about that, it was a no-no overcut too as the bit was turning
>> clockwise, so I should have reversed that and used a g3 move so the bit
>> was always cutting 'up' against the works motion. Is/was that my problem?
>
>Radius's in corners must be tangent to get a smooth corner. Are you
>using cutter comp, G41 and G42? Cutter comp and the tool table are your
>friends. Once you get it in your head on how cutter comp works in
>corners life gets MUCH easier. The site that helped me most is
>http://www.nfrpartners.com/nfrg2g3.htm , pay attention on the use of
>negative R numbers in certain situations. Ever since I figured out
>cutter comp life is easier,I use it all the time. Part a little
>oversize? Change the tool diameter and run it again
Thanks Ed.
I set tool 2 in the stepper.tbl to be .250" in diameter, which it almost is,
as the current tool, until I can get some fresh ones from Hemly, is a 1/4"
upcut spiral 2 flute solid carbide router bit from Lowes, Bosche brand, and
mikes at about .247". Cuts alu very well though. Along with a visible gouge
in a clamp where I should have raised the bit another .005" going over it.
But, since I did that, any 'g41 d2' is good, but the book says 'g41 D2- .'
or 'g42 d2- .' and that's a bad character when the dash dot is added.
A 'g41d2' seems legal, but also doesn't do _anything_. So what exactly do
you type to make it work?
>From what I read, that bit comp is supposed to be blended into the next move
after its been turned on, so if I turn it on when its at x1y1, and then
g1x0y0, it moves to exactly where it would go without the g41 turned on.
Sorry to be so dense, but it is a bit hard to figure out how to use this when
it apparently has zero effect for the only syntax it seems to accept from the
MDI interface.
Thanks again.
--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Against stupidity the very gods Themselves contend in vain.
-- Friedrich von Schiller, "The Maid of Orleans", III, 6
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