Mechanical CNC NOT Laser CNC - Questions - Panels

[Masterploxis]

Hello,

what i do to get the correct position for engraving: I do not cut out all the holes. I just mark the position of one or two holes with the mill (just move the top of the end mill a little bit into the material) . The position of the center of the hole is clearly defined in Autocad, or Rhino.
I select usually holes for encoder or switches, as the diameter is 6 mm and i can drill them later - so not need to cut them with CNC.

When the spray paint has dried, i just put the panel onto the work table of the CNC machine. Then i position the end mill exactly over the marked spot. As i know the relative position of these marking from autocad (or rhino), i just make the input of the related X and Y values into Mach 3. This way Mach 3 now knows whery my mill is positionen and i can start the engraving.

For painting: Please make sure that you use some scotch brite or metal wool to apply a roughness onto the acryl surface. Then use some primer before painting. AND IMPORTANT: Give the painted panels minimum 3 - 4 days drying time. The color spay hardens in that time. If you try to engrave earlier, you will pull away the color layer when engraving small letters.

This method (positioning of the panels after painting) works very good for me. I am able to position engraving mill with a accuracy of 0.3 mm and this is very sufficient for engraving....

Cheers
Andy !

[shearder]

Hey Andy

Thanks a ton for that helpful info. Do you simply use some standard plastic primer? I will be using Rustoleum spray - but the primer I would recon most plastic primers would be ok?

[shearder]

OH i nearly forgot does anyone know the font type for King Air 200 etc panels?

Thanks.

[jonesthesoftware]

I approach this differently. I spray the large sheet of acrylic first then allow to dry for at least a week to allow the acrylic paint to harden. Then I cut the holes and engrave at the same session, because then you don't have to lose your XY zero point. When engraving I re-zero the Z axis for every word and sometimes for individual letters. The reason for this is the acrylic sheet thickness can vary by as much as +- 1mm! The paint also is only perhaps 0.050 mm thick so just your finger pressure can change the engraving from "not deep enough" to OK. I then mask off the top surface completely, cut out the holes and then spray the cut edges, sometimes I hand paint the edges if it is going to be hidden areas.
Remember of course if you cut out with CNC accuracy and then paint the edges, the holes will be smaller by 2x the thickness of paint. Not a lot but if you design accurately, your CNC cuts accurately and then your components don't fit. When all dry spray with acrylic clear matt laquer. I've found that if you rough up the surface using 400 grit wet and dry paper then spray 6-7 very thin coats of acrylic paint (to get opacity)you don't even need primer. This is only for acrylic though not other plastics, Usethe 400 grit with slightly soapy water as this prevents static electricity which tends to hold the dust on the acrylic. I dry each sprayed coat with an infra red heater as this gives very fast drying and also hardens the layers.

regards
geoff

[shearder]

AH GREAT ideas there Geoff. Appreciated. I will try different techniques on a couple of panels and see which works best for me.

[Westozy]

OK I am planning to go and buy some white acrylic today for some panels for a King Air B200. I have an idea of what i will do BUT i thought let me pass it via the forum first:

I have the designs for the panels and they are almost ready for cutting. Plan is to cut all the holes and pockets etc THEN spray as necessary and THEN engrave the lettering.

Now: my question is: how are yuo doing the engraving after cut and paint? DO you put it back into the "cutout" and use shims the size of the end mill i.e. 3mm or 1/8" and the machine would have kept the 0 settings for XYZ OR do you reset the center pont and engrave?

OR how do you do it? I am hoping Gwyn can answer

Hi Shearder,
I'll pass on my simple method of realigning the panels after painting, it's quite easy. Let say you have cut out the electrical panel for a 737 overhead. It is white 3mm acrylic and has all the necessary square cut outs, switch holes and small holes for the mounting screws etc. It's finished and you have removed the panel from the machine for painting. After light sanding with 400 wet and dry I paint the acrylic in etch primer before the top coat of RAL7033, (I think that's the right code!). When it is ready for engraving, I generally fit a waste piece of MDF or plastic to the machine bed and plane it flat, it is most important to have an accurate flat surface to work on for engraving as you probably already know. From your original drawing, create a tool path file that spot drills the mounting holes of the panel, you probably only need two holes across diagonal corners to hold the panel down as engraving creates next to no load at all on the work piece. When you have spot drilled them about 2mm in diameter, you will have your locating holes ready to remount the panel with a couple of small screws. Use countersunk head screws as they tend to pull the panel into correct alignment and they are less likey to damage they paint. Don't do them up too tightly, just slight pressure is enough to hold the panel in place. X & Y axis are now set at zero and you will only have to zero the Z axis with your engraving bit. I usually engrave to a depth of 0.1mm, if it doesn't cut all the way through the paint just go a bit more but try not to cut into the acrylic too much as this can cause quality issues. This method is especially good when I'm making multiple copies of the same panels.

Cheers, Gwyn

[shearder]

AH GREAT!! Thanks for that Gwyn. I will try that this weekend. Well I may only get to cutting and sanding and spraying and sometimes in next week do the engraving. All this feedback is a GREAT help!

Thanks all!

[shearder]

I will post the samples here - also doing an annunciator panel for the King Air B200

[shearder]

Hey Guys

Ok so I gave the paint over a week - cos i was busy - and then started to engrave. OK i think i need to change the text type to true type. I am Using Aspire and it looks great in the preview but actual engraving is BAD! I have some scrap MDF which I machines a pocket out of so that the panel fits into it and then I screwed it down. I was using a 45* 3mm with a 0.2 (i think) tip and i lost a lot of definition. SO perhaps i need a different font and a 10* or something engraving bit?

Will need to redo the panel. What tip are you guys using??

Thanks in advance.

[shearder]

OK this weekend i am going to try engrave with a 3mm (1/8") 10degree 0.2mm tip and see how it works out. Also I changed the text to a TTF rather than a 3 line text type and use a fill engraving rather than on-the-line engraving.

I am using Aspire.