I bought a piece of 120 TPI (teeth per inch) 8" x 8" carding cloth from a vendor on etsy.com for about $30. I often spin angora and alpaca, but for recommendations on TPI for other types of fibers, see the comments below.
These supplies cost about $20 from a home improvement store:
(1) 2" PVC pipe (2ft)
(2) 2" PVC end caps
(1) 1/2" threaded rod (3 foot)
(1) 1/4" threaded rod (1 foot)
(9) 1/2" nuts
(6) 1/2" lock washers
(2) 1/4" nuts
(2) 1/4" lock washers
(1) small paint roller
(1) tube silicone adhesive
The "licker in" brush is a "regular" hand carder with maybe 72 TPI that I had on hand.
Step 1: Prepare the Drum
Lay the 8" x 8" carding cloth next to that line (making sure that the margins devoid of teeth are on the outsides and not where they would overlap). Mark the length of the other end cap and cut. Drill holes about 1/2" in from the line to aid in sewing the carding cloth to the pipe.
Trim the carding cloth if it overlaps more than 1", but know that a layer of the silicone adhesive will add 1/16" or so in diameter to the pipe. Don't panic if the ends don't meet completely; you can fill in the seam with more silicone later.
Step 2: Secure the Carding Cloth
Ask a friend to help you close the seam while you duct tape the cloth on as tightly as possible. The duct tape will not stick to the teeth, so you have to pull it tight just as you stick one side to the other.
If some silicone squeezes through the crack, that's okay; it can be trimmed down later. If you spread it on too thick, however, and a very large glob arises through the crack, take off the carding cloth and wipe the excess off.
Set the drum aside for a day and a half to cure. Poke it gently with a knitting needle at the seam to see if it has cured. If the seam needs additional adhesive, run a small bead of silicone and leave for a while longer to dry.
Step 3: Drill Holes in the End Caps
Step 4: Make the Wood Ends
The height from the bottom of the wood to the holes should be at least 3" or so.
Cut a 2 1/4" wide strip to serve as the handle connector; I used the same piece of wood. The length of the handle should be at least 3" (any longer and your hand might hit the board you clamp the drum to).
Step 5: Fashion a Handle
Step 6: Assemble the "Butt" End
Thread a 1/2" nut and lock washer on the threaded rod. Add your end cap and thread another lock washer and nut on top of that. Leave enough room to add the piece of wood and two nuts on the end. Tighten the nut near the end cap until it doesn't turn any more.
Step 7: Assemble the Handle End
Bear in mind that once the end cap is pushed onto the pipe, it will not be removed easily. It would be best to over-estimate where the lock washer will fall (and leave a small gap between the carding cloth and the end cap) than to underestimate.
The drum should not twist on the threaded rod; if it does, you may have to tighten the nuts more. If you tighten the nut too much, the PVC pipe might flex a little and your drum will be closer on one side than the other due to the distortion.
Step 8: Attach the Handle
Do the same with the 1/4" nut, a lock washer, the handle holder, a lock washer and another nut (for the handle). Tighten.
Step 9: Mount the Drum and Licker
When you fill your drum, use another slicker brush to "burnish" the wool and brush it a little more on the outside.
When you're ready to pull off your bat, slide a knitting needle under the wool at the silicone seam.