On 4/11/24 11:38, Chris Albertson wrote:
On Apr 10, 2024, at 1:14 PM, gene heskett <ghesk...@shentel.net> wrote:
On 4/10/24 13:30, Chris Albertson wrote:
Do you even need a rotory table to cut a spiral?
Now that you ask, I think the answer is probably no. Take a look at the nurbs
command G5.2 where a group of points describes the curve. Then rotate the
points about one end in polar/rectangular space. I haven't played with that
myself, perhaps Andy has a better way?
If you know how to find the 3 or 5 or 10 points that define the curve, then you
can use the same method to find 10,000 point on that curve and just do a
straight line between them.
Finally to TEST your idea, you need a way to calculate the error. You find the
exact solution for any arbitary point and then to compare that to what you are
doing. If you know how to calulate the exact solution, then why bother with
approxomations like nurbs? The nuirbs thing is for filling in points you have
no way of knowing.
What nurbs is good for is when you want to mill a copy of some object that you
don’t have an exact solution for. The perfect example is that you were given
an STL and all they have is triangle vertici. You can’t know where the STL
got its shape, is the curve a circle, elipse or an artest’s pen stroke. But
the nurbs-like or spline-like fitting funtion will generate a smooth curve
through the list of points.
All of the above is my weak point. I only got to a couple months of my
freshman year in high school, and the math teacher fancied himself as a
standup commedian, far more interested in what was in the girls panties
that in teaching math. And eventually got ran out of town by an irate
father with a 12ga in hand cuz a 13 year old he got pregnant was his
daughter.
My electronics education is 100% self taught. My mother gave me an IQ
good enough to pass the CET test w/o cracking a text to study it. I
understand the physics of it including Relativity. Electronics and
Relativity go hand in hand, cannot be separated.
On Apr 10, 2024, at 12:09 AM, gene heskett <ghesk...@shentel.net> wrote:
On 4/10/24 01:57, John Dammeyer wrote:
A friend and I have been discussing exactly how to write the G-Code to
create a spiral scroll.
His rotary table 90:1 reduction with a 1600 micro-step motor could be set up
to move N steps for each step of the X axis to create the spiral. But that
approach seems clumsy.
Say I wanted to cut a scroll with a 6mm pitch using a 3mm cutter.
Without using G2 or G3 it's really just a triangle isn't it? Move rotary
table distance A and move X axis distance A'. Do it in small enough
increments and you get a spiral. But I feel like I'm missing something
really simple.
Do you need a rotary table to cut a spiral? It is just a series of locations
in (x,y). OK, if you wanted to use only (say) the X and A axis then you should
use polar coordinates, not cartesian. The equation of a spiral on polar
coordinates is very simple. Then you evaluate itat many thousands of points
and at each point write gcode to “cut to” that point. You would not need the
rotary table.
Also why think in micro-steps and worm gear rates, you are using LCNC to do the
kinematics, Use millimeters.
I think this problem shows that in some cases you really can not write the
gcode by hand. FOr continous curves in (x,y) there might be 100,000 or more
lines of code in the file, especially if you don’t do the cut in one pass. You
would nee towrite software to generate the g-code. Or use existing software,
a lot of CAD systems will do this for you
First, a 90/1 is quite high. I have two rotary's, both consisting of a 3NM
3phase stepper/servo I made by combining the 3NM motor with a 5/1 worm. Using a
screw in the worms output hub as a single prox sensor index pulse generator. To
calibrate a complete rev, I measure the steps by starting the count on the 3rd
turn ans stopping the count on the 103rd turn, which gives me a scale*100.
Shift the decimal point 2 places left this becomes the scale for the axis in
the .ini file. All this math in linuxcnc is floating point so I can ask it for
33.333 degrees and it will run to what it thinks is 33.333 degrees. This
stepscale:
STEPSCALE = 22.22222222222 = 1 degree
So one count is about 1/22.22222222222 degrees, probably less than the backlash
in the rvs39 worm, a pretty cheap worm.
Currently to make one of my maple vise screws, starting at 0 degrees its around
60,000 degrees it turns for around 400 mm of screw that y travels. Then I lift
the tool, turn it another 180 degrees, re lower the tool and bring y back to
zero and b=180. Makes a perfect two start buttress thread. The B is turning, in
perfect sync with the Y motion, at something in the 300 to 400 rpm range. That
3NM motor is heating but not dangerously so.
There is no reason you couldn't lay it down to make a C drive, and simultaneously
drive X Z & C to carve an impeller in a quite serviceable scroll.
The versatility of the closed loop stepper/servo, which does EXACTLY what the
TP tells it to do, without a PID in the path, is amazing. I have them rigged to
e-stop linuxcnc in about a millisecond if they make an error, like losing a
step. Tested till the cows come home, has yet to happen working a job. I
haven't hobbed any gears, but it certainly seems accurate enough to do it.
Suggestions?
Thanks
John
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Cheers, Gene Heskett, CET.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
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Cheers, Gene Heskett, CET.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
_______________________________________________
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Emc-users@lists.sourceforge.net <mailto:Emc-users@lists.sourceforge.net>
https://lists.sourceforge.net/lists/listinfo/emc-users
_______________________________________________
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users
Cheers, Gene Heskett, CET.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
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Emc-users@lists.sourceforge.net
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