Are there any DIY's or MIY's (Make It Yourself) turners that create their own center bands for slimline pens? Do you use metal, acrylic, plastic or a contrasting wood? I noticed that the center bands from Woodcraft have concave faces that seems to help in mating the upper and lower body. Kits from Rockler have concave faces also but not as deep. Do you create a slight concave face on the bands and if so how do you do it? I know that I could buy larger center bands but I thought, why not try to make some.