Carpentry and Woodworking - Cutting a straight edge with a circular saw?

What’s the best way to get a straight edge when cutting plywood with a circular saw?

I normally clamp a board to the plywood and use it as a guide, but I think there must be a better and more efficient way.

When you find it, let me know. I see they have a saw and track now. The track CLAMPS down to the wood you are cutting and the saw has a runner that the saw travels on. Same theory, more money.

I just saw this today. Looks interesting...

Tru-Grip™ Clamp 'N Tool Guide™
http://www.grizzly.com/products/G3578

I have something similar to that, but about half the cost. It clamps down with a couple of small C-clamps.

We just clamp a 4-ft level to the ply. If you don't have a quick-release hand clamp like the Irwin Quick-Grips or Jorgensen (the best!), get a pair of them, very much worth the cost when doing clamping of this type a lot.

http://www.eurekazone.com/
http://www.festoolusa.com/ProductDetails.aspx?id=3&prodid=561174

You can do a lot of different things. Clamp a 4' straight edge, a piece of strut, a level, another piece of plywood, aluminum or steel flatstock or buy one of those clamping straight edges. I think i've used every method I mentioned already.

Thanks for the advice!!!

I have 2 gadgets for this, one works well, the other not so.

The one that doesn't work well is a pair of 4' long aluminum beams that attach together then the whole thing attaches to your wood with 2 baby c-clamps. The reason it doesn't work well is that it flexes in the middle on a long cut and you can end up with a bow. Perhaps if one were real careful it would be ok, or if not using the whole 8'. I ruined a wooden screen door with mine by pushing the saw against the edge too hard. It bowed, I didn't realize it until the cut was done.

The one that does work well is called "Rip Master". I got mine at Lowes for about $30. It attaches to your saw's baseplate and an arm goes out to the side with a little foot thing that runs down the edge of the work. The only downside of it is that the widest rip you can do is 24". For anything up to 24" where you have a straight edge on the board its excellent.

For me the bottom line is that I'm buying a table saw. It seems I'm constantly needing to make these long cuts so I need the proper tool.

http://www.eurekazone.com/
http://www.festoolusa.com/ProductDetails.aspx?id=3&prodid=561174

They look great but for the price of either of those you can have a decent table saw....

I'll concede that point on the Festool, but I don't know where you can get a decent table saw for under $200. And, while you can have my Powermatic 64 when you pry it from my cold dead fingers, there are things that a guide and circular saw can do that a table saw can't. Like break down a 4x8 sheet so I can get it to my table saw. Now while it's true that I could just do a couple of quick cuts to get a piece I can manage in my shop, with the EZ guide (no Festool in my budget, although it's one of those tools that makes you go "wow!" when you use it) I can make my cuts without having to take a second pass on the table saw. And it fits in my Rav4, which the tablesaw won't do.

What’s the best way to get a straight edge when cutting plywood with a circular saw?

I normally clamp a board to the plywood and use it as a guide, but I think there must be a better and more efficient way.

Yea, that's the normal way, a 1/2" thick 8' or 4' length of plywood about 4" wide and some spring clamps is the way I used to do it. Now I have 4 foot and 8 foot aluminum clamp/guides that do the same job for about $125 dollars. I never use them. It turns out when making cabinets or furniture it is very rare when you actually need 4 or 8 foot pieces, so I rough it out using a circular saw with no guide at all and then size it exactly on the table saw with a factory edge on the fence. Straight cuts, clean edges.
These clamping guides work poorly where you really need them anyway like when you are cutting 1/4" thick plywood backing for a 6 foot high cabinet. Since the clamps squeeze from the edges, they bow the thin plywood and lose their grip. In these cases, I draw or snap a chalk line and I leave an extra 1/16", and again skip the guide. Then I clean up the edge on the jointer.

Most of the time that you need to cut an 8 foot piece of plywood along its entire length it's for construction work like sheathing or flooring. Then you rarely care about being *exact*.

My friends always say you use 1/4" tolerances in construction work and 1/16" in furniture making. Though I strive for 1/64" in most of my work :-)

To snarksdad. You are still not as bad as an engineer friend of mine. We share cad drawings for ideas. The only thing is he sends them to me in 10/1000ths of an inch increments. I have to convert them to more realistic wood butcher sizes. Drives me crazy.

I'll concede that point on the Festool, but I don't know where you can get a decent table saw for under $200. And, while you can have my Powermatic 64 when you pry it from my cold dead fingers, there are things that a guide and circular saw can do that a table saw can't. Like break down a 4x8 sheet so I can get it to my table saw. Now while it's true that I could just do a couple of quick cuts to get a piece I can manage in my shop, with the EZ guide (no Festool in my budget, although it's one of those tools that makes you go "wow!" when you use it) I can make my cuts without having to take a second pass on the table saw. And it fits in my Rav4, which the tablesaw won't do.

How does the EZ Guide rail attach to the wood? For example, if you were ripping an 8 x 4 sheet up the middle would it just clamp at the 2 ends, 8' apart? If so I would think it could bow if you pushed at all sideways on the saw (which might be easy to do with your arm extended way out over the work)? Maybe I'm missing something on how the thing works.

The track does clamp to each end of an 8' sheet. It's a 7 or 8 inch wide extruded track that the plate for the saw rides on. It is incredibly rigid and there is no lateral play at all. I've used all manner of shop made and commercial guides. There is nothing that compares to this (except the Festool system). It's not worth the money for occasional use. But if you regularly have to break down sheet goods then one of these systems, with a dedicated saw, is worth every penny.