Glen, I see where you just joined the forum yesterday, so welcome. I don't want to presume anything because I don't know how much experience you have. This might sound like overly basic advice, but are you applying the spindle lock when you're trying to loosen the chuck? If you can lock the spindle, you could try a strap-type wrench like plumbers use occassionally on pipe fittings. Most big box stores have them. Get one with a long handle, if possible, to get a little extra leverage. As Brian mentioned some turners use a plastic washer where the chuck seats. I haven't personally needed them. I'm sure you've already applied some PB Blaster or other shot of penetrating oil?