A couple of comment here...
First what is the issue you are having with ripping the plywood? If it hasn't been covered give us some more details.
If it is support then I think that has been answered...... you need supports, for about $20 each you can get get a couple of the adjustable roller stands. You should think of getting at least 2..... nothing worse then pushing the plywood thru only to find the wood is sagging and will not be going on the roller but rather hitting it. A couple of other bad things come to mind but we will leave them.......
If you don't have the distance for say a 2 foot cut between the blade and the fence you can take a straight 2x4 and clamp it to the plywood such that the edge of the 2x4 aligns with the edge of the table saw table when the blade with the 2 foot cut line...
As was mentioned a plywood blade helps with getting a clean cut.... I have seen people use tape over the cut line or even score the cut line with a utility knife.... Even the amount of blade exposure can change the quality of the cut.
I too own a shopsmith well two of them..... and I have ripped a lot of plywood and never had any problems in fact I can cut an 8 foot sheet at the 4 foot line against my fence (I think the max is like 52" or 54"). It is all a mater of supporting the wood.
Some one else mentioned about the home centers or building places cutting the wood for you...... I have used this service when I had only a small car to haul the sheets with.... a lot easier then trying to tie it to the roof. All of the places I have done this they did not charge me.... some have a sign like up to three cuts free but most often then don't want to do the paper work so they just write down the number of sheets and off you go. BTW the panel saws they use are really the best way to cut plywood but the last time I priced them they were like $1200 US.......
Ed |