Flutes are cool little grooves that run parallel to a turned object's long axis. Lots of people do em by hand, or have specialized machines/jigs to help them do them.
I made a quick jig to run flutes along some cool little muddlers I had turned.
Step 1: Build the Sliding Base
The lathe at techshop has a handy gap that runs along its bed for the tool rest to slide along. I used this gap to put a guide on and keep my jig from tipping over.
One piece of wood, cut exactly the width of the gap (2.5") and 6 inches wide forms the guide. Another piece, slightly larger (3"), goes underneath the bed and keeps the jig from tipping over or sliding out.
The gap was 1.5" deep, so I made another piece 2.5" wide, and slid it in between the two. However, it needed some sanding down to keep the slide flush with the top of the lathe bed.
Two pieces of threaded rod slid through all three pieces are for tightening your jig down. (with a nut on the backside or glued to the 3 pieces)
This whole slab slides up underneath the lathe bed and fastens to your jig
Step 2: Adjustable Base
The dimensions for your base are up to you, just figure how much adjustment you want for your jig.
If all your pieces are a similar size, you wont need nearly this much adjustment, or this large of a base. The rotating section is completely unnecessary, but it does add a little more flexibility for doing interesting pieces.
Mine is 6" wide, and 12" long. I cut it out with the CNC Shopbot at TechShop to make sure the grooves and the arc for rotating were cut perfect. You can probably do it fairly easily with a router though.
Bolt it all together with some wingnuts, and you can fasten the whole piece to your slide.
Step 3: Build the Support for the Router
Now, I built walls off of my rotating base. They are supported by little pieces at the bottom, to keep em nice and firm.
I also used the shopbot to cut curved pieces that would clamp the router down perfectly. The inside diameter of these match the diameter of the router I am using, and have threaded rod going through them to clamp them down with a wingnut.
Lastly, clamp your router down securely, and adjust the height.
The tip of the router bit should line up EXACTLY with the axis of the piece being turned. its easiest to do this while there is no piece on the lathe, and line up the bit with the tip of the tailstock on the lathe.
Screw in the router base to fix it securely at that height! I made the height adjustable on mine, but in retrospect, realized I don't have any need to adjust the height.
Once everything is secured, you can set the router at a depth where it will pass through part of the material you are working with, and clamp the base down tight.
Make sure your piece is securely attached to the lathe, and the lathe is NOT spinning (if it has a locking index, this is helpful).
After that, turn on your router and do a few passes! Rotate the piece each time, slightly, taking advantage of the index to lock it into a new position each time.
I made it at TechShop!