Breaking Down Plywood

[jackellis]

I think I've figured out the answer but I'll ask anyway.

I have to put up garage shelves in the new house. Found my favorite 3/4" Arauco plywood at HD for $25/sheet, which is a good price, and bought 3 sheets (I needed 5 but had a brain freeze while calculating).

Today I started ripping 15 3/4" wide pieces the long way using a factory edge as a fence and a plywood blade in a Craftsman circular saw. First cut was perfect. On the second cut, the blade stopped cutting about 2/3rds of the way through. I reversed direction but was unable to keep the saw close to the fence. Finally got a badly mangled piece. Then went to trim off piece number 3, which ended up about 1" too wide. The saw wandered...into the fence. Not quite sure how I pulled that off.

I think my problem is using a plywood blade on 3/4 inch plywood. Instead I should be using a regular rip blade and cleaning up tearout on the edges, which I'd planned to do anyway using a 1/4" roundover bit.

If anyone has any other ideas, I'm all ears.

[dbhost]

Not sure why using a plywood blade on plywood is a bad thing. BUT...

For plywood / circ saw I use a Freud Diablo DO740R (anyone notice a trend here?). A 40T plywood / finish blade, and I go slow and easy, let the blade do the work. I have only once had a wander problem and it was due to the least reliable component in the system. The operator...

Just FWIW, my entire arrangement is...

Skil 13 amp circ saw, circa 1994, bought in 1997 (old stock from a hardware store I worked at, got it at wholesale which was CHEAP, even for the lousy money I made then).
Freud Diablo DO740R for plywood and crosscutting.
Freud Diablo DO724R for ripping.
Freud Diablo DO706CH for Cement Fiberboard.
DeWalt (I forget the model #s) abrasive blade for metals.

My edge guide is a factory edge ripped ply that I have to keep remaking as I keep using up the edge guide thinking it is scrap... Dummy...

I almost wonder if your blade is square to the shoe on the saw. (Or vise versa...) You really shouldn't get any wander at all unless you are somehow directing the saw away from the fence...

[gary]

Sounds like your ply flexed and your straight edge didn't which allowed the saw to sneak under it. Happens to me if I don't watch it. I resolved almost all my ply cutting by using a sawboard. see here http://www.rochesterwoodworkers.org/...r/Sawboard.pdf

I do use a ply blade as the tearout is less and cut 1/2 to 1" oversize with the circular saw and them clean it up on the tablesaw.

[master53yoda]

I use a 60 tooth blade on the skill saw that iI use for my panel cutting area. Here are some pictures of the area and the way it is used I can do dead accurate cuts that i don't need to resaw on the table saw

[dbhost]

Hadn't thought of the ply flexing. I cut mine on the ground, with 1" foam board under the ply, and the blade depth set so as to just get a tooth past the ply, not past the foam. No flex. No wood walking away from the fence...

[LinuxRandal]

Let me ask a stupid question. When you say a plywood blade, is this one of the old metal only, plywood blades, or is this a current style blade with carbide teeth?

[Lonnie in Orlando]

Are you sure that the edge of the base of your saw is parallel with the blade? The base of my DeWalt CC is adjustable. It wandered away from a straight-edge fence until I adjusted the base.

The thicker kerf on your standard blade may hog out the error. But the smaller kerf of the plywood blade did not.

- Lonnie

[Pappy]

I use a Freud TK303 blade in my PC saw with a saw board. If I need a Super clean edge I over cut by ~1/8" and finish with a spiral up cut bit in my router.

[jackellis]

Let me ask a stupid question. When you say a plywood blade, is this one of the old metal only, plywood blades, or is this a current style blade with carbide teeth?

Metal.

I'm going to switch back to a rip blade since I have to round over the edges anyway. I'll also check to see whether the blade is parallel.

Funny thing is, the first cut was perfect. Then the saw bogged down. Might have been due to overheating the metal blade.

[cabinetman]

Metal.

I'm going to switch back to a rip blade since I have to round over the edges anyway. I'll also check to see whether the blade is parallel.

Funny thing is, the first cut was perfect. Then the saw bogged down. Might have been due to overheating the metal blade.

You said "metal". How many teeth does it have? Do the teeth now look like they are coated with a resinous material?
.

[Bill in Buena Park]

Jack,
Not sure what kind of shelves you are constructing or length - but have you considered enclosing ~48in shelves in carcases and hanging using a cleat system?

If you can use such, you might be able to cut the ply in half, and rip 15-3/4 shelves from the 48x48 pieces on your table saw; I'd use a carbide ripping blade with a ZCTP.

In fact, I'd use a ZC bottom plate on my circular saw if I needed to use that. Don't forget that painter's tape also helps prevent tearout.

[conwaygolfer]

I have had the same problem with the blade walking. It only happens with 5/8 and 3/4 in ply. I use the same cheap plywood blade. Apparently they are made for thinner material. So now I have a friend help me cut it on the table saw. Perhaps a different blade is the answer?

Conwaygolfer

[jking]

I think I've figured out the answer but I'll ask anyway.

I have to put up garage shelves in the new house. Found my favorite 3/4" Arauco plywood at HD for $25/sheet, which is a good price, and bought 3 sheets (I needed 5 but had a brain freeze while calculating).

Today I started ripping 15 3/4" wide pieces the long way using a factory edge as a fence and a plywood blade in a Craftsman circular saw. First cut was perfect. On the second cut, the blade stopped cutting about 2/3rds of the way through. I reversed direction but was unable to keep the saw close to the fence. Finally got a badly mangled piece. Then went to trim off piece number 3, which ended up about 1" too wide. The saw wandered...into the fence. Not quite sure how I pulled that off.

I think my problem is using a plywood blade on 3/4 inch plywood. Instead I should be using a regular rip blade and cleaning up tearout on the edges, which I'd planned to do anyway using a 1/4" roundover bit.

If anyone has any other ideas, I'm all ears.

Unless there is something wrong with your plywood blade, I can't think of why using it on plywood would be a problem. I've always used the cheapest plywood blade I can buy & have never had problems with it cutting plywood.

When you say the blade stopped cutting on the second cut, what did the blade do? Did the saw bog down? Was the blade still running at normal rpms & you physically couldn't push the saw forward? When you came in from the other direction & couldn't keep the saw against the fence did the saw feel like it was pushing against you?

Unless the plywood you were cutting seriously gummed up the blade, I don't see the blade being the problem. At least, not on its own. Check that the blade is square to the base. Check that your fence didn't flex & allow the base to get stuck in between. Also check whether the blade height adjustment was secured tightly. If the blade started pulling up out of the plywood & you were just barely breaking through the underside, that could cause problems, too.

[jackellis]

Bill,

These are going to run the length of the garage (20+') using K&V heavy duty wall brackets and standards.

On the second cut, the blade did bog down and became quite difficult to push. This is softwood plywood so it is possible that the blade gummed up. It's a Sears plywood blade with metal (not carbide) teeth. I used the first 15 3/4" wide shelf as my fence for the second cut so it's hard to see how the fence could flex but then again... The fence was clamped plenty tightly - I verified that the fence did not slip.

Although the second board looks pretty awful, I'll need some 4' sections and 4' of the 8' cut is fine.

A TS is not perfect for this, but I'm thinking it may be better than what I'm doing now. I also have some leeway to make the shelves narrower (to hide the mistake).

[jabe]

The saw board guide has been around forever, only thing I did different was to place the fence board (used a 1X2) centered on a 8" wide 1/4" plywd. two reasons for this is whenever the cut edge gets damaged, you could move the fence and recut it or you could use the other edge as a router guide to make DADOs. I would make several different lengths like a 30", 50" and a 8 footer, drill a hole on one end so you can hang it when not using. I've used those cheap plywd blades b4 with no problems on cabinet grade plywds, for cheaper grades of plywd, it would be better with a 24T to 60T carbide blade depending on your application. So your wandering problem could be your saw base not square to the blade, plywd not supported properly while cutting and your fence not clamped properly. On a 8' cut, I would center a 1x2 butt to & perpendicular to my fence and clamp it to the opposite edge of the plywd. It will keep the fence from flexing in the center. Hope this helps.