There are several Youtube videos showing how to make multi-toned whistles. I liked the one that is square, has 4 tones, and sounds like a real train whistle. Here is a link to that video.
The Youtube guy included 1 sheet with plans on how to make a 3/8" and a 1/2" diameter versions of the whiste. On the video, he made the 3/8" version, but stated the 1/2" hole version sounded more like a real train whistle. He also has a link to a design plan, but it does not show the end cap.
I wanted to make the more realistic 1/2" hole version, so I did.
What did not dawn on me was how fragile the larger hole version was then the smaller 3/8" hole version. For example, there is only an 1/8" of wall thickness on the 1/2" hole version, while the smaller 3/8" hole version has a decent amount of a 1/4".
This thinner section is more prone to breakage while making the larger 1/2" hole version, requires more work to get air passages to each of the 4 reeds, and has less surface area for gluing for strength after it is built.
So if the goal is to be able to use a 1.5 inch thick piece of 2x4 to make the larger hole size whistle, it can be done, but with more difficulty.
I entered the design into Sketchup because it helps me understand the design and I also check for plan errors.
1. Make the square blank from a 2x4
2. Put blank in vise on drill press. Drill all 4 holes to max depth using Forstner bit
3. Move blank to shop workbench vise. Put 1/2" drill bit into hand electric drill. Drill to 4 different depths.
4. Mark notch cuts with pencil. Saw 90 degree notch on band saw by tilting the blank 45 degrees by hand
5. Move blank back to bench vise. Cut angles with hand dovetail saw
6. Clean 4 holes with sandpaper put in notch on 3/8" diameter dowel run by hand drill
7. Make 4 oak reeds about 1.25 inches long so your fingers can move them to tune them. Sand flats onto 4 reeds
8. Find best reed position and glue in. Chop saw off excess length of reeds. Sand bottom on belt sander.
9. Cut end cap about 1 inch long
10. Drill 4 holes 1/2" dia about 1/2" deep
11. Drill 1" hole about 1/2" deep. Drill 1/2" dia blow hole thru cap.
12. Use Dremel with deburr tool to make air passages to each of the 4 reeds. Test
13. Glue on end cap
14. Sand unit
I had to sand down the OD of the 1/2" oak reeds so they would fit the holes. I broke 1 piece off the pine body trying to force it in before I sanded it. Later, I broke another piece off and had to glue it back up.
I had to use the Dremel with a deburr tool to increase the air passages to each of the 4 reeds. There is very little wall thickness left for the glue-up of the end to the body.
The finished whistle was nice and loud and sounds like a real train whistle!
If I am going to make larger batches of these whistles, like 10 at a time, I might want to increase the blank size either using some thicker white oak I have, or glue a 3/4" pine board to a 2x4. This would eliminate the hand Dremel work on the end cap for the air passages and make a stronger glue joint.
I glued up a 9 inch long piece of 2x4 to a piece of 1x4............and then planed down to 1.75 inches, taking most of the stock from the 2x4. I table sawed to get a square 1.75 inch square blank. I cut off a 7 inch piece and a 1 inch piece for the mouthpiece.
I tried using a 1/2" auger bit to drill the holes but that did not work.........so went back to 1/2" standard drill bit.
I used the band saw this time and successfully cut the 4 notches.
On end cap, drill 4 holes at 3/4" diameter, then drill one hole 1-1/4...............no manual cleanout is required to make all the air passages ok.
I was holding the 1-1/4" length dowels with my fingers on the horizontal belt sander.
I decided to try using the Wagner Saf-t-planer on my drill press to put the flat on. I held onto 1 end, kept it from rotating, and slowing fed in the dowel to the cutter.......and it worked great !! Much faster and safer than belt sander, and I can do maybe 12 inches at a time.
I used a dental pick to clean the burrs away, and blowed in each hole to make sure it was clear.