My friend/carpenter is building a custom cabinet with the machine (and extension) dropped into the table. Do I make it regular table height ... or the height I'm now using (with the machine 3 1/2" above the table)? It will not be "pretty" but mostly for utility. Any suggestions would be helpful. I know one side will be an open bookcase and the other side is just square legs. The size that will fit my space is 28x54.

I recommend finding the chair your comfortable with then build to that height. MY DH made mine and it's wonderful, but finding the chair to fit the height was the issue.

I have the Roberts Quilting setup and the actual height of my table is 30" and then has an insert (depth) area for my machine that adjusts to the height of the table with another insert (piece that was made specifically for the machine) that fits around the machine so my machine sewing area is level with the table. Geeze, hope I'm explaining this correctly.

I went to the Roberts Quilting Cabinets website and they don't offer the setup I have anymore. I will try and check further for you to help in understanding what my words lack.

Okay, this is what I have but have added additional pieces. It is the first picture shown:

http://sewingsupplywarehouse.com/mo898ulquta.html

My ideal sewing cabinet would be about 3-4 inches lower than table height. How tall or more precisely, how long torso you are will determine your ideal height. Adjust your sewing chair so that when sitting, your knees are at a 90 degree angle. Sit up straight and put your elbows at a 90 degree angle to your forearms. How far your elbows are from the floor should give you the correct height. Most people lean forward a bit while sewing so the comfortable height may be a couple inches lower. Other people put rubber door stoppers under their machine to tilt it towards them slightly to correct that posture. Whatever is most comfortable for you would be the correct answer. I don't like the rubber door stopper trick because then I bend my wrists.

How wonderful that you can have the height custom made for you :D:D:D