The Arrow of Light is the highest rank achieved in the BSA Cub Scout Program. It's usually earned by boys in the 5th grade. Our pack had 9 boys earn the award this year. Most of them went ahead and crossed over to the troop to become Boy Scouts.
It's tradition to award a "career arrow" to signify the accomplishment. Sometimes the arrows are put on a wood plaque or are decorated in another way. I did a lot of hunting but never found a design I really liked so I took a bunch of ideas and merged what I liked from each. The final plaque was cut from 1 inch red oak and finished with a mahogany stain. The arrows were 5/16" pine dowel striped and stained to look primitive and then fletched and pointed. The fletching is a cherokee two feather style. The points are reproductions. I found a great deal on ebay. The overall plaque and arrow design mimics the Arrow of light insignia, shown above. I've been told the design is based on a petroglyph in the painted desert national park. Here's my earlier posts on this project. Click the pictures for a larger version.
I've spent a couple days finishing up the plaques. I'll post again with some final pictures. The finishing touches have all been manual things including:
- I hand routed a corner on the plaques to dress up the edges.
- Sanded and stained
- Rubbed with Tung oil
- The arrows were masked with tape and striped in various colors to signify each boy's achievements
- The arrows were fletched with traditional bar feathers.
- They were pointed with some reproduction points I found on eBay.
- The arrows were epoxied to the posts.
I can't take any credit for the feathers or points. That is a skill I don't possess. Fortunately another parent/leader in our den has mastered those skills and did an outstanding job.
The last CNC operation we need to do is drilling. The arrows will be mounted in the large pocket and will be epoxied to two posts. The posts will be glued into holes drilled into the plaque. I drew two circles in HeeksCNC to represent where I wanted the holes drilled. Then I selected the holes and added a drilling operation. The parameters are all pretty straight forward.
To hang the plaques, I'm going to cut a keyhole on the back. This is done with a keyhole cutter.
The cutting process works like this:
- The cutter does rapid movement to position itself over the hole location
- It plunges into the material to the desired depth.
- It moves forward toward the top of the plaque to create the keyway.
- It stops and moves back to the hole.
- It rapids upward clear of the stock.
HeeksCNC doesn't have an operation like this but it's fairly simple to accomplish anyway.
I started by adding a sketch with a single line segment to represent the key way. I selected the sketch and added a profile operation. I set the parameters so the cutter would cut 'on' the line and at the depth I needed for the bottom of the hole (-9 mm). In the resulting path, steps 1, 2, and 3 are represented, but then the cutter moves up to clear.
All we need to do is hand edit the g-code to add rapid back to the previous location before ascending.
G17(Select XY Plane)
G54(Select Relative Coordinate System)
(tool change to 1/4" carbide 2 flute endmill)
G01Z-9.000F593.970 (descend into the material)
G01X165.048Y304.802F500.000 (forward cut)
G00Z5.000 (retract out)
All we need to do is add this line before the retract:
Now the backplot (shown in emc2) looks like this:
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.
O.K. It's time to get this project rolling. I've already finished the design, now it's time to turn it into some plaques. I'm going to be making nine plaques and each plaque is going to have numerous operations including
- Pocketing the holes
- Profiling the curved edges
- Engraving the names and other information
- Drilling the holes for the arrow holders
- Drilling a keyhole for the wall hanger on the back
The first problem I have to solve is holding and alignment. Since I'd like to do the same operation on all nine before moving to the next operation, I need to find a way to hold the stock material securely and repeatably. Here's the solution I've come up with: I'll attach a piece of MDF to the router table and pocket out a large area to exactly fit the stock. The pocket will only be a 1/4" deep or so to keep the stock from sliding sideways with the force of the cutter. Then I'll attach each piece of stock in the pocket with double-sided tape.
The other advantage of this is that I can cut the stock to the exact dimensions on the table saw and avoid having to profile the entire edge. The only section that will have to be profiled is the two curved corners. This will help speed up the machine time.
In the picture above, you can see the design for the 'jig pocket'. The pocket has round corners to let the cutter move in. Without that, the corners would be cut round at the radius of the cutter and wouldn't accommodate the square corners of the stock.