To personalize each plaque, I'm going to engrave the Pack information, the year, and the boy's name. In HeeksCNC, engraving is just a profile operation with the 'tool on side' parameter set for 'on'.
That isn't to say that engraving is easy. It's not. At least it's not easy to get decent results. The complexity comes from primarily two issues. First, with engraving we're not usually cutting very deep. In fact, if we were engraving in metal, the depth of cut would be only a fraction of a mm. So if the top of the material isn't perfectly flat or if the CNC machine isn't perfectly aligned, a V cutter will make a deeper/wider cut in one place and shallower/narrower in another. The red oak stock I'm using has quite a bit of variability in thickness and I couldn't get results I liked. I chose to use a 1/16" two flute router bit and cut deeper - a full millimeter. Since it's a straight sided cutter, the width is consistent even if the depth varies. The final results were acceptable.
The more challenging problem with engraving is fonts. Truetype fonts are vector based so they scale well and you would think they would lend themselves naturally to CNC. However, the geometry of the font defines curves that enclose the entire letter. So a capital 'L' will have two parrallel lines defining the vertical part of the letter. A profile operation will outline the letter and leave an island in the center. For engraving, what's needed is a 'stick font' or a centerline font that has only a single line down the middle of each letter. There aren't many fonts available like this. The only ones I know about are the Hershey fonts. Fortunately they are bundled with Qcad and work with HeeksCAD. Not much choice, but it's something.
The corners are just a simple curve and the profile operation is similarly simple. Since I don't want the cutter to travel all the way around the plaque but rather just cut the corners, I have to move those arcs and line segments into a new sketch. Then I select the sketch and add a profile operations. I'm cutting in red oak which is quite hard so I want the cutter to step down just a little bit at a time and make many passes.
With profiling operations, one thing to consider, is what will happen at the end of the cut when the stock and the part are no longer connected. The profile operation has a feature for 'tags' which are just material left uncut that can be removed by hand. Without them, the part might move into or away from the cutter and be damaged. In this case, the stock is well secured and the pieces cut off shouldn't cause a problem.
This is the most time consuming operation in the project. Each of the pockets must be cleared to a depth of 3mm. The geometry defining the pockets is all in a single sketch and a single pocket operation has been added.
Ideally, the cutter would move forward as it descends into the material, either in a ramp or a helical motion. Unfortunately, HeeksCNC doesn't have the ability to calculate those entry moves so I have to use a cutter that can 'plunge'. In this case I'm using a fairly small (1/4") router bit. That means the paths have to be close together and the overall cutting time is going to be large. If I was going to do this commercially, I'd have to find a way to use a larger cutter.
Dan Heeks has recently rewritten the zigzag operation of HeeksCNC to use the opencamlib library instead of pycam. This is a huge improvement in speed. Just messing around, I designed this spider in blender and exported the .STL file. I went ahead and cut it on the router in blue styrofoam.
Here's the stl file if you're interested.
A user on the #cam IRC channel had a problem pocketing a shape in HeeksCNC. I've been stung by this myself. In the first picture below you can see the six identical pockets have not pocketed the same. The user had designed the oblong shape and copied and was confused why all the copies didn't pocket the same way.
If we pan the view we see additional geometry below.
The user had designed this part in another package and imported the file to HeeksCNC. The user is designing and building a 3d part in the sense that it has real depth to it, but for all practical purposes, this pocket operation is really a 2d (actually 2.5d) operation. Since both the top edge and bottom edge of the oblong shape are included in the sketch along with the vertical lines connecting them, HeeksCNC was getting confused trying to order the segments to create a closed sketch. After we realized this, the user deleted the lower level of the geometry and reordered the sketch. Everything worked perfectly after that.
The thing to remember is that in pocket operations, the depth of the pocket is controlled by a parameter of the operation and not by the geometry of the drawing.
I've launched The Magic Clock (http://www.themagicclock.com) to show the build log for my Harry Potter clock. I built the site in Google Sites because it could be one of those sites that gets a lot of clicks for a short time and I'd rather not hammer my own server.
I've been making some sample files for the basic operations in HeeksCNC. I'll have one for profiling, pocketing, etc and I'll upload the .heeks files to the wiki. Here's a link. Maybe this will help newbies learn HeeksCNC a bit easier or maybe they'll be useful for testing new features.
This is a custom design I did as a gift. The "cap" of the "bottle" is a removable plug that conceals the pegs. I did the layout in qcad and sequenced all the drilling, engraving, and profiling operations in HeeksCAD.