We have a very large dining room table that seats 10. The chairs are solid wood, very heavy, and in great condition, but the juke webbing under each seat cushion has stretched. When someone sits in one of the chairs, it sinks a little. After going to the YouTube University, I found a couple videos that use various techniques to repair this issue.
This is the type of table we have, but there are 10 chairs and a sheet of glass over the table top.
This is the underside of one of the chairs and you can see that the juke webbing has stretched. I don't have the upholstery skills to take the chair apart and reattach the material because material wraps around the seat base and onto the sides of the frames. I would tear the cushion material.
I used dense 1" foam wrapped in Dacron, sprayed with adhesive to fill the juke cavity of each seat base.
I stuffed the cushion into the cavity and used the adhesive spray to hold the new cushion in place.
I made a template of the space I wanted to fill and cut 1/2" plywood to cover it. I installed 4 metal "L brackets" to hold the wood in place and applied pressure toward the seat cushion to ensure that each had a little more solid cushion in place. I used 2"x2" wood to frame around the edges and across from front to back and against the grain to provide support.
The last part is cutting and stapling a material dust cover for the bottom of each chair. Total cost was about $200 and 3 days of my retirement!
Rock on, David