Odd problem ripping ply with a circular saw

[Bill Turnquest]

I was attempting to cut a 4'x8' sheet of 3/4" plywood in half using my Ryobi ZRCSB133L circular saw along a clamped straight edge and when I would get about 1/3-1/2 way through the cut the saw would start bogging down and would appear the cut starts turning into the straight edge. My initial thought was a blade issue but a new blade did not resolve the issue. I can make smaller cuts off the edge of the board just fine but when cutting anything towards the middle (same issue with a 30" cut) I run into this.

Now the work tables i had the full sheet resting on had about 1/2-3/4" height difference so maybe that caused the blade to bind up? My other thought was to adjust the cut depth on the saw to the proper cut depth as opposed to me running it as far down as it goes (nasty habit of not adjusting that). I could see that helping but before I ruin another sheet I figured I'd see if anyone knows why it could be doing this.

Thanks in advance!

[Prashun Patel]

First, yes, adjust the blade so the bottom is cutting into free air - not the substrate. This could be making the saw work too hard, causing it to bind.

Next, is your plywood properly supported throughout? After getting into the cut, the weight of the cut side could be causing the wood to sag, which can also cause the blade to bind.

Is your straight edge defect free?

Last, are you pushing straight ahead or pulling the saw across your body? A bind free cut is easier straight on.

I'm grasping here; 3/4" plywood should be a cinch to cut. normally.

[Bill Turnquest]

I would say the wood is not properly supported more adequately supported. I use two 2'x3' tables spaced to support both sides. The wood may sag a bit in the middle which could be the issue. My thought process was if it sags it will just be separating a bit on the bottom causing the cut to slightly separate and not cause the blade to bind up, but maybe I'm wrong on that. Most of the cut is done with me pushing the saw in front of me and the straight edge is fine.

[Ted Reischl]

It does not have to separate a bit on the bottom as you posted, it can also squeeze in a bit at the top.

When ripping plywood I toss some junk 2 X 4's on the bench so the piece is supported PERPENDICULAR to the direction I am cutting. The blade is set so that about a tooth protrudes. Doing it this way gaurantees no sagging, pinching, etc.

In other words if I am ripping along the 8 foot length, I have the scrap pieces running in the 4 foot direction.

[Alan Schwabacher]

Are you sure the guided edge of the saw base is perfectly parallel to the blade? If not, that could be the problem. When you cut only a little from the plywood edge the waste can deflect away from the blade, allowing a straight cut that is not perfectly aligned with the blade direction. But when you cut toward the middle of the sheet, the waste can not deflect, and forces the saw toward the straightedge. If this is correct, cutting with the straightedge on the other side of the saw would cause deflection away from the straightedge.

[Bill Turnquest]

I will see if I have any means to try to support the ply across the cut, that seems like a good start. And as best I could verify the blade is parallel with the guide edge. I would think if it wasn't it would be really poor design. The turning in only seems to happen when the blade starts to bind up.

[Prashun Patel]

You're thinking like a chainsawyer; in that case, the sag sometimes works to your advantage. But with a circular saw, you're cutting the full thickness at once. So sagging and opening on the bottom means pinching at the top of the cut.

[Art Mann]

Are you sure the guided edge of the saw base is perfectly parallel to the blade? If not, that could be the problem. When you cut only a little from the plywood edge the waste can deflect away from the blade, allowing a straight cut that is not perfectly aligned with the blade direction. But when you cut toward the middle of the sheet, the waste can not deflect, and forces the saw toward the straightedge. If this is correct, cutting with the straightedge on the other side of the saw would cause deflection away from the straightedge.

That is exactly what I thought. If the soul plate of the circular saw is being used with a straight edge as a guide, then the saw blade and the reference edge on the saw must be parallel. If that isn't true then the angled saw kerf will bind more and more as the saw moves across the wood until it may actually stall the motor. I found this out the hard way.

[Lee Schierer]

This might be a dumb question, but is your straight edge really straight. If you are using a bowed board as a straight edge it would gradually make the blade start to bind.

[Jim Dwight]

When I used a circular saw to break down plywood, I used a saw board. A piece of 1/4 luan with a separate piece of luan glued to it to guide the saw. The single thickness part was a little wider than the distance from the edge of the saw to the blade. Then when you use the added piece to guide the cut the first time it shows you where the saw will cut on future uses. An advantage of this kind of guide is there is no way for the saw to go under the guide. I wonder if you saw might be going under your guide due to sag in the sheet goods.

I use a 1x4 lattice work support for sheet goods placed on saw horses. It makes the plywood flat.

[Rich Engelhardt]

I have the same saw, I had the same problem.

Hey, it's about a $40.00 saw you can't expect precision at that price point - - there's like two chances the blade and the base are in any type of alignment - Slim and None & Slim just left town.

It all came to a head one hot August day.

It was above 90 degrees and the humidity was close to being a liquid atmosphere.
The saw binding in the plywood was the final straw. I told my wife I'd had it with the frustration of trying to do such a simple task & was going to go spend $1000.00.
I promptly drove to Hartville Hardware and bought a Festool TS55EQ.
Expensive - but - worth every penny since it eliminated so many odd ball problems.

Cutting sheet goods is still an unglamorous thing to do, but, it's no longer a dreaded ordeal.

In all honesty too, the price isn't al that bad - - all things considered.
A good new circular saw (the Ryobi is a good "rough in" type saw, but it's not even close to being a decent "finish" saw) runs between $150 and $200.
Hardwood plywood runs between $50 and $150 a sheet - so - you only have to risk screwing up a couple sheets to be at the point of putting a real dent in the price of a track saw (along with an upgraded circular saw).

[David Spurr]

No support under the cut causes the plywood to pinch the blade. 2X4's under neath provide adequate support preventing binding, kickback and injury.

[john bateman]

I have had on occasion something similar.
In my case, the ply was sagging as I pushed the saw along, and the saws base plate would begin to slide under the straightedge.
And since my arm was trying to push the saw against the straightedge, it just continued getting worse as the cut progressed.

[Phil Barrett]

+6 or 7 on saw base and blade misalignment. I had a circular saw like that and, there was no possible adjustment - it was riveted in place. Fortunately, I got it free. Unfortunately, I discovered this problem in mid cut... Now I know why it was free.

Life is too short for bad tools.

[Tony Zona]

I'm pondering whether the saw cord is catching on something. Just a thought.

[Jim Dwight]

I wanted to bring up track saws and now that subject has been opened so I will add my thoughts. I have a DeWalt tracksaw with a 59 and 106 inch track for about $600. That was a lot for me to spend on a tool but roughly half what a Festool would cost. It is good for a lot more than breaking down sheet goods. I built parallel guides to increase it's usefulness and will soon build a MFT/Paulk style workbench to make it even more functional. Now you don't even have to spend as much as I did. There is a Makita at about the same price as the DeWalt but there is also a Grizzly for less than $300 with one 59 inch track and about $300 with two. The reviews would indicate the Grizzly is not quite as nice as the others but is still pretty good with roughly table saw quality cuts - probably after you put on a better blade.

A track saw is also an ideal tool to cut down doors and to put a straight edge on a saw before ripping it on a table saw. It is safer than a table saw and has, if anything, better dust collection. It saves having to handle full sheets of plywood through the table saw and, for me at least, eliminates the need for extension rails. It also is great for small shops because you do not need the space for a sheet of plywood on both sides of the table saw. I sometimes just cut up the plywood on the trailer I use to bring it home not bringing it into the shop until largely cut to finished size.

[Bill Turnquest]

So I wanted to follow up on this to answer a few possible solutions here.

For starters my straight edge is http://www.amazon.com/E-Emerson-Tool-C50-Contractor/dp/B003TXSAHU/ref=sr_1_1?ie=UTF8&qid=1427673540&sr=8-1&keywords=clamping+straight+edge one of these and it's pretty much dead nuts as I've used it for dados before.

As far as I can tell my circular saw guide edge is parallel with the blade. Using a small combi square it seems to be square from back to front of the blade (post adjustment).

I think my problem was I was running the blade "all out" and hadn't adjusted it to cut size. After doing this I made my cuts without issue. In all fairness I was only taking 24" off the board instead of 48" but it seemed to run decent. I also was sure to have adequate support on all ends.

Thanks for all the advice from everyone!