Wednesday, May 20, 2015

Project Edge Lit Sign - Trying Edge lit Sign Again, PART 1

Revisiting my Edge Lit Sign project.  I'm dividing this up into 3 segments due to the separate challenges that I encountered working through each part of this project.  This segment addresses just the engraving of the sign, other segments will address the electronics and mounting/housing.

Many, many people have made acrylic signs illuminated with LED's on the edge.  Adding illumination to the edge of the acrylic causes it to light up only in the areas that it has been cut or engraved. I've previously tried this using window glass engraved using diamond glass cutting bits – it didn't end up being very bright (turns out acrylic transmits light better than glass).

With my 3D Printer build last summer, I shelved this project until I had the time to come come back to it and that's what I'm finally doing.  Instead of etching glass, this time I'm trying it with acrylic that is custom made for edge lit signs (it is clear but has metal flakes embedded in the acrylic that reflect light when the acrylic is cut), you can find it over at Inventables.

I was inspired to do this sign project as a gift for my wife, she owns and runs a nut free bake shop (Callie's Cuties) and I wanted to make her a fun sign for inside her shop with her logo on it.  After getting a vector file of her logo, I opened it up in Inkscape (an open source vector editor).  I only changed a few parts of it to make it a little more friendly for engraving on my CNC (primarily different fonts).  When I finished my changes I selected the whole graphic and made certain to change it all to a Path (selected Object to Path in the Path drop down menu), then I flipped it to make it a mirror image and then rotated it on its side (to fit the dimensions of my CNC).

After working out the size and layout of the sign I made a cardboard mockup to better visualize what my goal was.
measuring and cutting out the cardboard

Reversed image to be engraved (should have used normal image)

Checking image against acrylic stock

Assembling the base

Finished base

Mockup Done!
After reviewing this with my wife, I needed to make a few changes - adding "Open" and "Bake Shop".  So, the orientation changed and the sign became 8" wide by 10" high instead of 9" wide and 8" wide.
 
On to my first hurdle, figuring out the feed rate and depth of cut took a bit of trial and error, I'm using a 1/16" single flute end mill by Kyocera (purchased from CarbidePlus).  Initially I thought I would need to cut fairly deep into the acrylic cut so my first try was cutting to 0.1" depth (almost 1/2 the thickness of the sheet) with a step down of 0.05" (so 2 passes to reach target depth).  First test at 30 in/min was much to fast, I lowered to 20 in/min - still to fast, and then to 10 in/min.  Now that I had a good speed I needed to adjust the cut depth for each pass, 0.1" was definitely to deep, it resulted in to much friction and the end mill getting clogged with melted acrylic.  In addition to that, I felt I was aiming much to deep for my target depth.  I decided on another trial at 8in/min, 0.01" target depth with step down of 0.005".  The first pass achieved the results I as looking for.

I changed the cutting parameters in MakerCAM, selecting the entire graphic and using the "follow path" on the CAM menu: tool size 0.0625", depth of cut 0.004", safe height 0.25", step down 0.004".  After saving the new G-Code file I placed a new piece of acrylic on the bed and ran the code through Universal G-Code Sender.  You can see my result below.

Milling the Reversed Image

The finished image (before cutting extra stock off)

I should note that in my impatience I wasted a sheet of custom acrylic but trying to cut first before determining optimum speeds and depth for my CNC.