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  • Author Author: ralphjy
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CNC - First Try at Engraving

ralphjy

I'm starting to get some experience with my CNC router and quickly learning that there are so many variables due to material, cutting tools, and individual machine capability that there will be quite a lot of trial and error.   As with most tools,  the only real way to get more proficient with them is to use the tool for an actual project.

 

I'm still looking for a tool flow that will work well for me.  I recently got an RPi4 and I 'm going to try to use that as my workshop computer.  I currently use a mishmash of different computers to support my 3D printer, the CNC router, and my development boards and digital oscilloscope.  I use a Mac Mini with my 3D printer, a Win10 box with the CNC and another Win10 box for application development and the oscilloscope.  An RPi4 with dual monitors seems like just the ticket to consolidating all this stuff.

 

As for a fabrication workflow, almost everything that I currently use or am considering has a Linux version.  The one notable exception is Fusion 360.  I haven't invested time learning Fusion 360 yet, so I'm going to postpone that until later.  I'll see how well I can do with FreeCad.  I'm sure I'll get back to Fusion 360 when my designs get more complex.  But even FreeCad has quite a learning curve and for a beginner it would be nice to separate hardware issues from software issues.  So, I've decided to start with some simpler programs to get a feel for different cutting tools and material with different machining operations.

 

I thought I'd start with some simple engraving to get a feel for spindle speed and feed rate for different tools and materials.  I found a program called F-Engrave by Scorchworks https://www.scorchworks.com/Fengrave/fengrave.html .   It's a pretty basic tool.  It does text engraving and v-carving with text and images.  I bought 1/4" birch veneer plywood slats from a local crafts store to practice.  For simple text I find that I like the look of solid line stick fonts rather than the two line silhouette fonts.  I downloaded a set of CAMBam stick fonts to use (the program uses true type fonts).  For engraving you need to manage the character spacing and depth based on the tool (cutting bit) that you are using, the program doesn't do any auto-adjusting but it does preview the effect of the settings.

 

This was a simple exercise but it surfaced a few issues.  The most significant one is the surface flatness of what I was engraving.  Part of it is the dimensional variation of the plywood, some of it is the flatness of my extruded bed, and a lot of it is due to the warp from clamping soft wood.  Secondly, I really don't have any feel for these cutting bits (also that I don't have a great selection to choose from).  You can see from the program setup that I'm using a very slow feed rate of 127 mm/min.  I'm using a 20 degree v-bit that came with the kit.  The 775 spindle motor that I have is rated at 3000-9000 RPM (12V-36V).   I'm running it at around 7000 rpm.

 

Here is my setup in F-Engrave (the spindle speed is set manually in the G-Code header).

image

 

Rather than watching the CNC router cutting, I found it more interesting to watch the controller executing the toolpath.  For engraving the solid stick font the cutter makes precisely two passes for each segment.  The sequencing of the toolpath is pretty neat.  The F-Engrave program is written in Python.  It would be interesting to look at how it is implemented.

 

Here is the G-Code running in Candle (GRBL controller):

 

 

And the finished output.  The cut is rough around the edges.  Next try will be to use an endmill instead of the v-bit.

image

 

I can see that it is going to take me a few months and a lot of scrap to get somewhat proficient at this.

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  • That is really impressive work Ralph, well done. I'd be keen to make a similar setup.

    I've used wood routers before (the 1/4" and 1/2" chuck versions) but never any CNC of wood.

     

    The cut is rough around the edges.

      7000rpm is a little on the low side IMO for cleanly cutting timber fibres, although I note you can only get to 9000rpm with your motor. Wood routers cut at up to 24,000rpm

     

    Next try will be to use an endmill instead of the v-bit.

    I think the V is the better choice and the endmill would likely splinter the edges even more. Perhaps taking several successively deeper cuts with a V tool would give cleaner edges?

     

    It is strange how the vertical cut for the 'E' is so torn whilst very close by the 'l' is not. I do know that some wood types have great variation in grain direction and consistency. Perhaps Birch is one of those awkward types? Manufacturers probably don't put the best wood into ply either. Lastly you mention the bed flatness but perhaps the grain was raised on the torn area: you could try sanding the surface nice and smooth prior to engraving?

  • in reply to 14rhb

    Hi   - you could also try adding some sticky tape (eg decorators paper tape) to the top surface and engraving directly through it, or varnishing the plywood prior to engraving (might hold the fibres together better ?)

  • in reply to 14rhb

    Didn’t think about trying varnish.  I have some spray on clear coat that I could try.  I’ve been been hesitant about using tape because I’m not sure how well it will cut and whether I’ll get residue on the cutter.  Probably just need to find the right tape to use.  Have not heard of decorators paper tape - I’ll google it.

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  • in reply to 14rhb

    Didn’t think about trying varnish.  I have some spray on clear coat that I could try.  I’ve been been hesitant about using tape because I’m not sure how well it will cut and whether I’ll get residue on the cutter.  Probably just need to find the right tape to use.  Have not heard of decorators paper tape - I’ll google it.

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  • in reply to ralphjy

    aka "Masking Tape", it is normally paper based with an adhesive back - used for masking off window glass or skirting boards/door mouldings when painting. I recall seeing someone use it when engraving metal as, without it, the swarf occasionally caught and scoured the finished surface (not really applies to your case I guess).