This is not so much a tutorial as much as a guide, since every table is different. But my hubby started with a fairly cheap, rickety, cast-off dining table.
First, the legs needed to be braced so the table was good and sturdy. There's no point going further if the table isn't going to support the machine well and take all the vibration of stitching. This table already had some leg damage, so these 1x6 boards were bolted around three sides. The bolts may have been overkill, but I'll take sturdy over pretty. Plus hubby is not a finish carpenter kind of fella, more of a "git-er-done" type. He says that some tables might need a 2x4 or bigger wood as the boards he used were a special hardwood known as Ipe or Ironwood, leftover from a dock he built as part of his job as project manager of a marine construction business.
I placed my machine on freezer paper and carefully traced around it, making allowances for any areas above the bottom that might need a larger opening. (Picture above taken further along in the process)
Edited 2/9/2015 for important update: This post was written about the table made for a Janome 6600, a flat bed machine with no free arm. This makes it very easy to cut a hole to fit the machine. I have since gotten a larger machine with a free arm and we adapted this table to fit it. We used a method that simplifies the hole that is needed to fit the machine and still results in a great fit! Read here: DIY Sewing Table: Updated and Improved. You still need to provide your machine with adequate support as outlined in the rest of this post. There are also a fabulous bunch of tips and variations given by readers in the comments here.
Then a 2x4 support was added underneath the table top alongside the hole. This placement will vary for each table and quilter. It is important to figure out how much of the table is real wood or 'wood product' (press board, chipboard, etc.)
Ideally, he would have ran two boards along two sides of the hole to support the machine, but this table had multiple braces in the way for the cheap press board top. So the bulk of the support comes off that newly installed 2x4.
He just used some scrap wood for this. But a lot of drywall screws! And the machine rests on the piece he cut out from the top of the table.
It's tricky to get it all level and perfectly at the right height for the top of the machine to set level. See the the little wood shim/wedge on the left?
Don't forget a hole for the power and pedal cords! And access to the lever or what-have-you to lower the feed dogs for free motion quilting fun!
Hubby says the hardest part was marking where to drill the hole for the knee lift! After the hubby finished the structure, I began sanding. I should have sanded more than I did, we had some residual varnish crinkle under the first coat of paint. But since the table was mostly press board, we were afraid to remove too much.
Then I applied 3 coats of Davis brand, heavy duty enamel, fortified with urethane. I lightly sanded after each coat wherever it was rough and where we had that varnish issue. The finish isn't completely perfect, but it is surprisingly smooth.
I had thought to cover the ugliness of the legs with a skirt, but I am not sure I will do that. I like the hardwood floors showing more than I want to hide the bolts and such. Makes this room look bigger.
Love this table! It is solid and sturdy. Doesn't shake at any speed of my machine. And so totally affordable. Take a look for a table at Goodwill or thrift stores. My previous work surface was done in a similar manner but was a laminate countertop installed in a closet type nook.