Friday, May 8, 2020

CNC Panel work

I mentioned a while ago that I had upgraded my CNC a bit and one of the tasks I have been working on in the past week or so has been the design and cut of my instrument panel inserts.  I used carbon fiber on the 9A but since the frame is all carbon fiber I decided to try something new.  The inserts are .064 aluminum and rather than color them with paint or something I decided to try to go with the brushed aluminum look.  The idea is that I "brush" the aluminum to a consistent smooth sheen and then clear coat it for protection.  So far I like the results.

I also decided to try my hand at engraving with the CNC.  Theoretically it should work great but in practice it didn't start out so good as you will see in the pictures below.  Just for future reference the settings I used for the CNC are 6 IPM at .01 depth for the engraving.  The depth number was a bit arbitrary since its really hard to set it exactly.  What I ended up doing was to run the depth at .01 and then run the job a second time after lowering the Z0 setting by an appropriate amount to get the letter width I wanted.

This was my first real attempt at engraving.  As you can see the letters look horrible!  This was done at a speed of about 22 inches per minute.  Most of the literature I have read talks about engraving at much higher speeds so I thought I was being conservative.  After watching my little home built CNC jump and jiggle during this process I decided to slow it down to about 4 inches per minute.

This is what 4"/ minute looked like.  MUUUUCH better.  But notice that the top engraving is not as deep and in fact the lines disappear on the right side.  Well, my CNC was not perfectly flat nor was the aluminum panel held down consistently.  Next I went through a "leveling" process for my CNC bed, and then I paid a bit more attention to how the aluminum was held down to try to keep it consistent.  The next two pictures are the final result.  

Almost perfect (or at least as perfect as I can get it).  There are a couple of defects in this engraving but they were directly related to me missing a step when I changed out the router bit from an engraving bit to the cutting bit.  The process for cutting this type of panel is to first do the engraving, then change the bit and cut the interior cuts (holes and interior openings).  Finally I cut the exterior as the last step.  In this case I forgot to reset the Z axis depth when I changed out the bit and if you look closely at the Mixture hole you will see the result.  The CNC dutifully plunged into the aluminum and went all the way through.  The system is not rigid enough to take this type of torque and as such the X and Y axis' were skewed slightly.  The hole became slightly elongated and then the remaining cuts were just slightly off center from the engraving.  I ended up redoing this one as you can see in the picture below.

Much better. 

This is the one that I was most happy with.  The engraving looks professional and even the color fill process I went through to fill the engraving went well.  I followed up the color fill with a bit of brushing to see what the final look would be.  I'm pretty happy so far but the final verdict will occur after I do some clear coating of the brushed aluminum.

Just because the engraving was going so well I decided to put the pilot side panel back on the CNC and see if I could get the engraving done on it.  I'm very happy with how this came out!  I did add a little enamel color to the cuts but I will likely add a bit more as it doesn't show up as dark as I wanted it.