3D Finishing - What am I doing wrong?

[smobley]

Hi All,

So I am creating a part that requires a relief for a tube to be placed underneath it when it is mounted and for some reason I am getting some weird behavior that would almost have to be user error somewhere so I am looking for help.

I have simplified it down to a 3"x4" block with a relief on the surface. This is created with the following steps and I have attached the Aspire file:

Create new job setup with 3"x4" by .735 thickness material surface, xy center, very high resolution
Draw a long narrow rectangle, in this case .4 wide (x) and 1.5" tall (y) in the center
Copy rectangle to a new layer called component and turn off layer 1
Go into node edit and cut at all 4 corners of the rectangle, deleting the two short pieces
Create a circle with a diameter of .4 to the side
Node edit the circle cutting it at the 90/270 deg nodes to form two half circles and delete the upper segment
Go to the Modeling tab and select two rail sweep
Select the left and right segments of the two long line segments, reversing rails as needed to get them both in the same direction, and hit use selection
Click on the half circle, making sure sweep between spans is on and scale cross sections is off, and apply
Close two rail sweep

This creates the half-circle relief component.

Go to tool pathing
Click on material setup and make sure the model has 0 gap on top, and Ok (this is my first issue, it will not allow 0.0, instead resetting to .0152)
Click the component if not already selected and then 3d finishing
Select the end mill to use, I used a .125 tapered ball nose (tried a normal ball nose as well)
Select model boundary (tried putting a bounding box around the component, but same results)
Select Raster and 90.0 degrees, and Ok

This creates the cut and if you look at it, it is not a half circle, but more like a sine wave as shown in the picture below.

So my questions are:
1) Why can I not set the gap above the model to 0.0?
2) Why is my half circle being distorted?

Thanks for any help you might be able to provide on what I might be doing wrong.

[eph210]

It helps the software define the upper edges if a zero plane is used on a concave model. It also helps to locate the model in the block. Once I added a zero plane to your file the .0152 went away. Use selected vectors (your rectangle) to limit the calculation.
When you make your rectangle and circle, instead of cutting and then deleting (possibly introducing an error) in node edit mode, hover over a span and press D on the keyboard. This will delete the span back to the nodes.
When the ball nose cutter is cutting the very bottom of the recess, it is cutting on the dead centre of the nose. As it comes up the sides the contact point moves to the side of the ball nose. Aspire calculates this and the resulting toolpaths are what you see. If you run the toolpath preview it will show the cylindrical recess that you are after.

Euan

[smobley]

Thanks Euan,
I was under the impression that Aspire 9 added the zero plane automagically, but apparently I was incorrect. I did look for that, but forgot it was moved to a new menu location and I only have done a few play 3D parts in Aspire following the older tutorials.

As well, the apparent ledges appeared to me to be way to large just to be the ball offset, but I think it was a combination of that correction and the zero plane issue.

Thank you again for helping.

[smobley]

So I am still having issues here.

I am doing a two sided part.
Machine bed as the Z0
Z-plane set

I am still getting a notch in the channel.

(I had to delete the top component to get the size for attaching in the project where the z-plane is)

[highpockets]

Try using a -.0625 (half dia of bit) boundary offset

[smobley]

Thanks Highpockets,

I added the offset and it appears the edges are good now.

Do you think opening would still be .4, or would I need to compensate by increasing the radius of the circle?
I can't measure the preview directly, but moving the mouse it looks like the diameter is reduced by .012.

[highpockets]

Smobley,

After playing around with your drawing a bit more there's something a miss. I can't set the zero plain to zero it always reverts a small decimal offset.

I'd start from scratch, and make sure to add a Zero Plan Component.

[highpockets]

It's hard to measure the exact dimensions. If you need an exact down to the thousandth then you might want to run a test cut. Some dimensional errors may also be introduced by your machine. So a test cut would be a good idea anyway. And it this is being cut in wood, good luck getting thousandth accuracy, wood moves.

[smobley]

The issue with the file is most likely because I had to remove the component the zero plane was on (top) to get the file size down to attach.

All I did was create a two sided job
added a circle to the top and created a dome with a base of .4
added a zero plane
copied the circle to the bottom and created an offset circle to the inside for the lip
pocketed out the inside
profiled the outside with a .25 em

then drew the channel parts

I have a Camaster Panther and its highly accurate, down to a thousandth or so.

Appreciate you looking

[smobley]

Just in follow up in case someone else runs into something similar.

The zero plane took care of the gap above the model.
The minus .5 diameter offset got rid of the tool digging into the edge of the model.

I understand the first, but the latter should in my mind have been handled by the tool definition since there is specifically a Ballnose, and specifically a Tapered Ballnose.