Profiling a taper

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Profiling a taper

Postby 1350519287 » Mon Oct 14, 2019 11:41 am

This is a pretty simple drawing. A flat plate with two holes.

The drawing is scaled up by 3% to make it a pattern for casting aluminum and a 3 degree taper on each edge. I took the easy way out for the outside edges using the table saw set at 3 degrees and cut up a 5/8" piece of MDF to the dimensions.

The holes were cut using a CNC router with 1/2" spiral bit, 1/8" depth of cut. I suppose, ideally, I should be using a tapered cutter but I didn't have one. No matter what I tried I wasn't able to set up a profile to follow the contour of each hole so that the taper was part of the hole.

The holes are now cut and I'll use an oscillating spindle sander to add some taper so I can get the draft for easy pulling from the green sand.

But how does one configure AlibreCAM so that as it profiles that it also tracks the taper?

The holes are larger at the top than they are at the bottom so I'd think it would be possible but nothing I tried worked. Some of the generated paths were really strange too.

The attached ZIP has the drawing and a pdf showing how it will ultimately be used.
Attachments
SpindleMotorPlate.zip
(314.96 KiB) Downloaded 364 times
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Re: Profiling a taper

Postby 1350519287 » Mon Oct 14, 2019 10:37 pm

Here's a quick example of what I expect if I profile a tapered surface. In this example it's a hole and the taper is 10 degrees, but really any set of surfaces should result in a series of moves that progress down the hypotenuse of the taper angle. Or in math terms the reduction in radius = Z distance * tan(taper angle)
And if it's a large enough hole I don't want to wait hours for it to mill out the center. The attached screen shot shows how it's milled.
%
N1 G17 G20 G40 G90
(TestHole)
(N2 T1 M06)
N3 S2000 M3
N4 G0 Z0.25
N5 X0 Y0
N6 G01 Y-0.875 Z-0.01 F18
N7 G03 X0 Y-0.875 I0 J0.875
N8 G01 Y-0.853 Z-0.125
N9 G03 X0 Y-0.853 I0 J0.853
N10 G01 Y-0.831 Z-0.250
N11 G03 X0 Y-0.831 I0 J0.831
N12 G01 X0 Y-0.809 Z-0.375
N13 G03 X0 Y-0.809 I0 J0.809
N14 G01 Y-0.787 Z-0.5
N15 G03 X0 Y-0.787 I0 J0.787
N16 G01 Y-0.765 Z-0.625
N17 G03 X0 Y-0.765 I0 J0.765
N18 G00 Z1.0
N19 X0 Y0
N99 M30
%
Attachments
TestHole.png
TestHole.png (107.37 KiB) Viewed 5782 times
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Re: Profiling a taper

Postby MecSoft Support » Tue Oct 15, 2019 8:53 am

You can program the taper using 3 axis horizontal finishing.
Attachments
SpindleMotorPlate-REV1.zip
(60.45 KiB) Downloaded 357 times
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Re: Profiling a taper

Postby 1350519287 » Tue Oct 15, 2019 9:19 am

Thanks. That's the only one of all the options I did not try.
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Re: Profiling a taper

Postby 1350519287 » Mon Mar 09, 2020 9:51 am

I ran into the same problem on a smaller pattern except it's more complicated now.
1. The horizontal finishing works on a smaller 1/2" MDF pattern as far as tracking the taper on the hole on the inside.
2. When tried on the edge on the outside it tries to mill out the the entire inside hole leaving the outside alone.
3. When the inner holes are suppressed and horizontal surfacing is tried it throws up an unknown internal error.
a) this results in either a complete failure and crash of Alibre
b) or complains it can't create the tool path after the unknown error dialog OK has been clicked.

I've attached the part as reference and a screen shot of the error along with a zoomed in screen shot of the 'profile' operation that doesn't follow the taper.

So how do I convince AlibreCAM to profile the taper on the outside?

Why the unknown error when the hole are suppressed?

There really needs to be a 3 axis profiling operation. It appears I'm the only one using CNC to create draft on casting patterns?
Attachments
AlibreCAM_Error.zip
AlibreCAM does not allow milling draft on outer perimeter of part. AlibreCAM crashes with unknown error when holes are suppressed and 3D horizontal finishing is tried.
(447.19 KiB) Downloaded 143 times
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Re: Profiling a taper

Postby MecSoft Support » Mon Mar 09, 2020 5:11 pm

The face edges or sketch you select acts as a containment region. So when programming around the outside, you would need to create/select a sketch that is offset this away from the outer edge of the part and select this as your containment region for horizontal finishing so there is enough room for the cutter to be able to generate toolpath around the exterior edges of the part.
If you would like to exclude the hole from being machine when programming around the exterior edge, select the face edge around the hole in addition to the sketch. This would contain the toolpath between the 2 areas.
When the inside hole feature is suppressed, it is not necessary to select containment region to program around the exterior of the part.
Attachments
MotorMountPlatePattern-REV1.zip
(80.88 KiB) Downloaded 148 times
Exterior Taper.jpg
Exterior Taper.jpg (76.26 KiB) Viewed 3251 times
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Re: Profiling a taper

Postby 1350519287 » Mon Mar 09, 2020 5:55 pm

Thank you. One of the members of the Alibre forum supplied the same information. Still the error message is wrong.
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Re: Profiling a taper

Postby 1350519287 » Wed Mar 11, 2020 1:07 pm

Primed pattern with 3 degree draft.
Attachments
SpindleMotorMountPattern-Primed.jpg
SpindleMotorMountPattern-Primed.jpg (287.37 KiB) Viewed 3193 times
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