[GregGleason]

I milled the centering ring (see earlier post), but the dimensions came out wrong.

The bit I used was a 3/16" flat tip, which I set in the DP library as 0.1875". I verified the shaft diameter with my digital calipers.

I double-checked and the roughing and finishing pass were using that same bit.

The outside diameter should have been 2.915" but was 2.957" (+ 0.042").

The inside diameter should have been 1.640" but was 1.591" (- 0.049").

What am I doing wrong? Is the shaft diameter for the bit a different size than the hole?

What else can I check?

Greg

[Lennings]

Hi Greg,
The dimensions of your part are influenced by the Precision settings that you made in the Operation parameters.
DeskProto will project a pattern of toolpaths over your geometry, and for each XY position of that path calculate the Z-value. That means that the distance between the toolpaths (one of the Precision settings) will influence the accuracy of the result. A simple example: when machining a 10.5 mm cube with a toolpath distance (stepover) of 1 mm, the result can never be 10.5: DeskProto will make it 11.
Even for waterlines the Precision settings play a role, as these decide the grid size: all calculation are done on a rectangular grid, called the Z-grid - further see the Help on that subject.
So for a ring that needs an exact diameter it is better to use 2D toolpaths, as in DeskProto these are more accurate. For 3D toolpaths you can improve the precision by choosing better Precision values.
Lex.

[GregGleason]

Hello Lex,

Thank you for the explanation.

Is there a tutorial on the 2D toolpaths? Do they use the .stl file, also?

Greg

[tjb1]

Hi Greg,
The dimensions of your part are influenced by the Precision settings that you made in the Operation parameters.
DeskProto will project a pattern of toolpaths over your geometry, and for each XY position of that path calculate the Z-value. That means that the distance between the toolpaths (one of the Precision settings) will influence the accuracy of the result. A simple example: when machining a 10.5 mm cube with a toolpath distance (stepover) of 1 mm, the result can never be 10.5: DeskProto will make it 11.
Even for waterlines the Precision settings play a role, as these decide the grid size: all calculation are done on a rectangular grid, called the Z-grid - further see the Help on that subject.
So for a ring that needs an exact diameter it is better to use 2D toolpaths, as in DeskProto these are more accurate. For 3D toolpaths you can improve the precision by choosing better Precision values.
Lex.

That seems like the entirely wrong way to work a program. It should calculate the stepovers from finished geometry...I find it hard to believe that any CAM program would do stepovers like that.

[ger21]

Most if not all CAM programs that work with .stl files work this way when using a parallel finishing pass. You specify the stepover, and the toolpath rasters back and forth, stepping over by the stepover amount between passes.

[Lennings]

A tutorial on 2D toolpaths is available in Lesson 5 of the DeskProto Tutorial book, which can be downloaded at DeskProto >> download >> downloadable manuals
Lex.