Yarn: Paton's SWS in Natural Geranium (70% wool 30% soy); 4-5 skeins, 109 yards each
Needle: Size 11
Gauge: 3 sts/inch

Measurements of my sewing machine: 14" wide, 11" tall, 6" deep
Finished measurements of cover: 14" wide, 10" tall, 6" deep

CO 52 sts
Work in st-st for 30 rows
(top of cover will be purl side of st-st)
Pick up 30 sts on the short side
Pick up 52 sts on the long side
Pick up another 30 sts on the other short side.
Place marker and join
Knit round and round and round for 78 rows. I was running very low on skein #4 and stopped at row 65. If you want your cover taller than 10", use 5 skeins of yarn and complete all 78 rows.
BO, weave in ends

** Paton's SWS felts extremely fast. ** Do not leave unattended when felting. Pull the cover out and measure it so you don't felt it too much. Roll it up in a towel and squeeze out excess water gently. Block the cover on your machine or similar sized box. I still had my plastic cover and kept this on my sewing machine while it blocked. If you don't have a plastic cover for your machine...try a large plastic bag. Don't put the wet wool directly on your machine! 
 
Another wool yarn such as Cascade 220 or Galway should work just fine. It will, however, take longer to felt to these measurements. I will test this soon with one of these yarns.

Embellish to your heart's content. I used some scrapbooking brads and buttons to decorate mine. Have fun.
If your machine is a different size and you need help figuring out how many sts and rows you need, just e-mail me.