The quilting bar on my older Janome 4800 also becomes loose. I think the problem is that the screw can only turn one or two threads at most which loosens with the vibration of the machine.
My lightbulb moment was when I used my 1/2" ruler (used for marking 1/4" lines) as a quilting ruler for echoing around a border. I used a normal foot, just being careful not to push the ruler under it. I then echoed that line by putting a the ruler against it, giving a gap of about 3/4".
I have since used my 6 1/4" square ruler for wider gaps. Tape can be put on at different measurements to give various widths between rows of stitching.
Even though I now have quilting rulers, I still grab the ordinary rulers for simple echoing or crosshatching on smaller projects; it saves changing the foot too.