CNC Machine Questions

[mndless]

I have a newbie question... I've searched the forum and think I have a good idea of the type of machine I need... but the devil is always in the details.

I am making panel parts for an aircraft simulator.

The parts will be milled from clear polycarbonate (plexyglass).

The process is be:
1 - mill the part to shape, drill holes.. etc.
2 - Cover the top with a white translucent coating.
3 - Paint the top with the finish color.
4 - Router through the finish coat, while not penetrating the white, the lines and text needed on the panel.

A link to a sample picture of what these look like is shown below.

Sample Panels

So, the material is relatively soft. I need to do rather course shapping but also very fine depth control and precision routing for the text...

Your comments and suggestions to help me get started in the right dircction are greatly appreciated.

[ger21]

So you just want to route through a layer of paint?

[mndless]

No, that will be the last step... first, I have to shape the poly to the shape of the panel itself. Some are rather complex and need to be shapped via cnc.

[ger21]

How thick is the panel?

[WhiteTiger]

May be preaching to the choir, but here goes with the suggestion anyway...

For your lettering, how about fixturing the parts? couple of rails on your table, machined to reference height, then a separate slab to sit on top of them with your workpiece clamped face up against the bottom of the top slab. Locating pins on the table rails with matching bushed holes in the slab, and openings in the slab only where you need to cut the workpiece.

That way you just reference your cutter to your rail tops and your cut depth becomes reliably referenced to your finish coat surface.



Tiger

[mndless]

The maximum panel thickness should not exceed 1/2".. a typical panel might be 3 inches wide x 8" long and only 1/2" high. other than creating holes most relief cuts will only be 1/4" thick.

[Geof]

A minor point that could be important when you are doing your painting step; polycarbonate is not plexyglas, plexyglas refers to polymethylmethacrylate (acrylic plastic). The trade names for polycarbonate are Lexan and Tuffak.
The two plastics are very different in their machining properties and also a paint suitable for one may not be suitable for the other.

You engraving step will require very precise height control so if you want to be able to do all your machining and engraving on a single machine I think you will need a CNC metal working machine (VMC) not a CNC router.

Have you seen panels made by the procedure you describe? I have worked a lot with both polycarbonate and acrylic and finding a coating that bonds well to these plastics but which does not cause crazing adjacent to machined edges in my experience has not been easy.

[mndless]

In reality, the substrate is not critical, as long as it will allow light to pass through from bottom to top.

I haven't started the process of determining exact materials and coatings as of yet... unless that is critical to the process/machine I need to do this, I was going to research that next....

[Geof]

Originally Posted by mndless In reality, the substrate is not critical, as long as it will allow light to pass through from bottom to top. I haven't started the process of determining exact materials and coatings as of yet... unless that is critical to the process/machine I need to do this, I was going to research that next....

I suggest you start your research at a place that makes the substrates for signage. I have used various types of multilayer plastic sheet with a colored layer that is engraved through and a translucent layer behind. Some give an effect similar to what you describe while others are designed to be engraved fairly deep from the back side with the engraving then filled with a white pigment so the front side is a smooth untouched surface.

A problem you may encounter with doing your own coating is that many paints do not adhere well to polycarbonate plastic. When you engrave a painted surface you might find the paint chips along the engraved edge so you will have poor edge definition.

[mndless]

Thanks for the input.

Will do...