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Author Topic: Router cuts angles wrong  (Read 2953 times)

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Offline bradD

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Router cuts angles wrong
« on: June 16, 2013, 10:38:17 PM »
Machine is a CRP4896 with CRP NEMA 34 drives & electronics, latest Mach3, Dell optiplex running Windows XT Pro.

I was trying to rout some angled dadoes and ran into this  problem:  The dadoes are off about a degree. Picture a ">" pointing in the X+ direction, with an included angle of 38 degrees. Each side of the ">" is off by about -1  degree (the included angle comes out as 36 degrees). I trigged out the gcode and it is correct. X & Y axis are both 1272 steps/inch. It comes out the same when cut left to right or right to left, 10 IPM or 50 or 125 IPM. The machine is square and backlash in both axes is less than .005". 

The problem is consistently repeatable. It is not due to cut deflection, as it does it with a V cutter set at .025" DOC as well as a .25 endmill taking a quarter inch deep cut.

The XML file and sample Gcode are in the attached zip.

Someone please check that the gcode really produces 19 deg per side, not 18. It wouldn't be the first time I thought I did something math-y and actually did something else.   ???

Offline stirling

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Re: Router cuts angles wrong
« Reply #1 on: June 17, 2013, 07:39:54 AM »
Plotted your gcode in Rhino and the angle between your lines is 36.4 degrees. Both are equally above and below the horizontal by 18.2 degrees.

Cheers

Ian

Offline bradD

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Re: Router cuts angles wrong
« Reply #2 on: June 17, 2013, 10:37:59 AM »
Many thanks, Ian.  Here's part of the problem:

X departure = 14.75 - 3.503 = 11.247
Y departure = 3.998 - .25 = 3.748
sin(x) = 3.748 / 11.247 = .3332
arcsin(.3332) = 19.46 deg.
arcTAN(.3332) = 18.4 deg.!!!!!
 >:(

Oops. I've been calculating the wrong trig function. That's embarrassing. I needed to refresh my brain on what function I was calculating before I did it. At least I can duplicate that mistake.

So the problem lies within the design chain of DesignCAD 3D Max -> .DXF file -> CamBam. -> gcode. DCad swears the angle is 38 deg.

Now all I have to do is figure out where that degree got lost. Anyone? Beuller?

Again, many thanks, Ian.

Brad
« Last Edit: June 17, 2013, 10:45:26 AM by bradD »

Offline RICH

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Re: Router cuts angles wrong
« Reply #3 on: June 17, 2013, 11:36:32 AM »
3.503 is 3.3503?
Dimensioned backplot for your use attached.

RICH

Offline bradD

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Re: Router cuts angles wrong
« Reply #4 on: June 17, 2013, 12:24:28 PM »
3.503 is 3.3503?

Close enough for the girls I go out with. Typo.

Thanks, RICH

Brad

Offline bradD

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Re: Router cuts angles wrong
« Reply #5 on: June 17, 2013, 01:37:33 PM »
Well, this might forever remain a mystery. I started over, drew the part in DCad, exported to DXF, imported to CamBam, generated toolpaths, and viola (some folks think that word is "walla")!!!  Perfection!

Obviously operator error. Somewhere.

Thanks, Everyone.
Brad

Offline stirling

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Re: Router cuts angles wrong
« Reply #6 on: June 18, 2013, 04:48:28 AM »
Well, this might forever remain a mystery. I started over, drew the part in DCad, exported to DXF, imported to CamBam, generated toolpaths, and viola (some folks think that word is "walla")!!!  Perfection!

Obviously operator error. Somewhere.

Thanks, Everyone.
Brad

LOL - and some other folks think that word is "voilĂ " and that viola is a stringed instrument - sorry - couldn't resist  ;D

Ian

Offline bradD

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Re: Router cuts angles wrong
« Reply #7 on: June 18, 2013, 10:04:24 AM »
I knew that. ::)  I just don't know how to make that little hickey above the "a."

Don't much care, either. You can keep your little secret and it won't bother me. How often do I need that? Next thing, you'll be telling me what the hickey is called. Actually, I tried to pencil it in, in my first post. It just didn't come through, I guess.

lol
Brad