There are many 'solutions' to what you are trying to do. I'll share mine.
FWIW I have a Festool TS75 (their big track saw) and she's a great tool. Lots of adjustability and features that set it apart from the average/everyday circular saw for panel work.
Their guide rails are insanely expensive for what they are. Honestly, I'd consider them in the "fair" category if they were half their going rate (new). The mid sized ones (~48" & under) are what I end up using most often, but the need to rip an 8' panel does come along from time to time. That span calls for their
FS 3000 (118") guide rail, which they think is worth $385. Not at this time for me... thank you.
I did a combination what others have suggested:
*** Ideally this is done on a flat and stable surface, not just some supports like 2 sawhorses, but do what you have to do. ***
- Get a sheet of 1/2" MDF (you could use melamine, formica, baltic, whatever isn't too coarse and rough), and identify the cleanest 8' edge on the panel.
- Rip a strip ~8~10 inches measured from the edge identified above using any saw you like (straightness doesn't matter in this step)
- Place that strip on the remaining panel it was ripped from with the mill-cut (straight) edge facing the rough edge you just cut
- On whatever circular saw you will be using with this straight edge, measure the offset from the blade to the farthest edge of the saw's foot and add 1~2"
- Position the mill-cut edge of the strip (from step 2) the distance (from step 4) from the rough cut of the panel you made in step 2
- With the ~8~10" strip laying on the panel, make sure it's straight and flat, then clamp the two together tightly without bending or twisting
- Tack it in place every ~6" with a finish nailer so it won't shift
- Screw together to your liking and un-clamp
- Once the two are joined, use the straight edge of the top strip as a fence for your saw to ride along to trim the lower panel parallel
- Now you have a track saw - just be mindful to clamp the track you just made to the panel you're cutting whenever using it, as you'll be pushing your circular saw against it to maintain a straight cut. Don't rely on friction or "nonslip" liners, as they lose all credibility when loads of dry sawdust become involved. The clamps you end up using might have to be as low profile as possible in order for your saw not to interfere with them.
The two layer portion of the guide rail can be whatever size you want.
Narrower -> lighter, easier to maneuver, less area to clamp to away from your saw & cut, not as rigid and resistant to bending and twisting
Wider -> heavier, more difficult to maneuver, more area to clamp to away from your saw & cut, more rigid and resistant to bending and twisting
some projects maybe more advanced then a shop table
