Problem with cutting plywood with a circular saw

[DanEng]

Hello,

I am new to wood work and I have a question regarding the width of cut using a circular saw. I have bought a circular saw taking a 150mm blade. I replaced the blade from the standard 24 teeth to a KWB branded 48 teeth one to get finer work finish. I have a number of shutter plywood (the one used for concrete roof building) which I need to cut in half, keeping both sides of the cut. I am using a guide to get a straight line cut.

The plywood is about 27mm thick, so I am not making a single cut, but a low depth cut to mark the surface and then make another two cuts to cut in two the plywood. My issue is that the blade tends to bend one one side thus going out of my line of cut. Also the width of cut is too large. The blade data states that it produces a 2.8mm wide cut but I am getting a width of about 4mm.

Any help and pointers, please?

Thanks
Dan

Edited the post: The plywood is about 27mm thick and not 40mm. Sorry about this.

 

[ALinCarolina]

My first thought is your saw arbor is wobbly. Do you have a way to measure run-out on the saw? Once you figure that out then look into ways to attach a zero clearance base or insert so you won't have to make two cuts.

 

[Badhabit]

I'm not much of a wood worker either but that is awfully thick plywood to cut with such a fine tooth blade. I am wondering about going back to the 24t blade and trying to cut it in one pass

 

[P0234]

I'm no woodworker but cutting large pieces of wood with a circular saw is miserable work. You need a table saw for this task.

 

[cgrutt]

If blade teeth (kerf) measures 2.8mm but it is cutting 4mm it sounds to me that blade isn't squared up with your fence or isn't running true. Is there any adjustment on saw to square up the fence with motor? Can you check that blade is flat and arbor is true (no wobble, etc). I think you're going to be hard pressed to make an accurate cut from both sides by hand can you clamp or screw a sacrificial board to underside and cut it in one pass? Masking tape along bottom can even sometimes help with tearout.

 

[PCustoms]

I'm no woodworker but cutting large pieces of wood with a circular saw is miserable work. You need a table saw for this task.

Cutting a sheet of plywood on a table saw is miserable, especially a sheet that is 40mm thick

As someone mentioned, a more aggressive tooth count is needed and a single pass in material that thick. The blade is either junk, overheating and wobbling or the arbor is bent.

24tooth and a guide should zip through to break down the sheet.

 

[kaymccampbell]

You might also want to check the blade washers, and the shaft root. A lot of times they're not properly processed after machining, and have burrs and whatnot on them that wobble the blade. Also look for crud in the same areas.

 

[PCustoms]

I'd bet most of the kerf is a result on running 2 cuts. Especially if not held tight to a guide.

 

[Dakotadadv8]

I usually break down or cut 4x8 sheet of plywood with a corded circular saw with no issues, make sure you have a stable base to work on. Good blade and saw helps. Then use a table saw if needed for smaller pieces. I use the circular saw with straight edge as a guide clamped down will help with straight cuts. Practice safety and practice the circular saw is one of the most versatile tool.

 

[jack stand]

If this is something that you'll be need to cut regularly, look I to a track saw.
It seems that most woodworkers have abandoned the table saw and required floorspace for in/outfeed tables for these and a pair of sawhorses.

 

[ALinCarolina]

cgrutt mentioned the most likely scenario if you detect that the blade tends to wander to one side. The edge your baseplate is probably not parallel to the blade thus when the edge runs against the guide it is fighting itself. Making a scoring cut is not that effective with a handheld circular saw because the teeth are exiting the cut at the start of the cut. The scoring blade on my sliding table saw for instance cuts in the same direction as the feed.
Make sure the blade is parallel to the base and then make the cut in one pass.

 

[dogdog]

Hello,

I am new to wood work and I have a question regarding the width of cut using a circular saw. I have bought a circular saw taking a 150mm blade. I replaced the blade from the standard 24 teeth to a KWB branded 48 teeth one to get finer work finish. I have a number of shutter plywood (the one used for concrete roof building) which I need to cut in half, keeping both sides of the cut. I am using a guide to get a straight line cut.

The plywood is about 40mm thick, so I am not making a single cut, but a low depth cut to mark the surface and then make another two cuts to cut in two the plywood. My issue is that the blade tends to bend one one side thus going out of my line of cut. Also the width of cut is too large. The blade data states that it produces a 2.8mm wide cut but I am getting a width of about 4mm.

Any help and pointers, please?

Thanks
Dan

Pointers ?

Use a cutting guide, get to know your circular saw measurements usually one side is 4.5” to blade and the other side is 1.5” to blade so make approximate subtracting or adding dependents how you goes. I cat within 1/16 or 1/32 of my cut measurements. Using this method. The measurement dependents on the brand and saw to saw. So get to know them

Setting your blade depth use a scrap wood that is the same thickness as your cutting material set it just a tiny bit deeper or same depth. Or use that cutting material to set the depth. This prevents the blade wondering give your better control

Use backing material If you have enough money laying around. Buy a piece of foam board for that use. This is to prevent tear outs or splinters on the bottom of the cut

Use of a speed square as a guide if your piece is shorter like 2x4

I used the husky 108” cutting guide for or a full piece with factory edge + clamps or screws and a chalk line to mark the cuts

The hf 48” cutting guide is good for cross cuts

A good large reading measuring tape helps. I got the 25’ dewalt one.. good clear reading lines.

 

[DanEng]

Hi all,

Thanks for the suggestions, I will check the items you suggested.

To be clearer, I am using the circular saw with a straight edge guide with clamp to try to get a straight cut, but not like the Makita which was suggested by Jack Stand. Mine clamps the work and you have to press the circular saw to it while pushing to cut. I bought a simple Parkside cordless circular saw and clamp guide to start with.

 

[dogdog]

If you already have the cutting guide, just try setting your cutting depth. Properly

 

[rdoty]

A cordless circular saw is probably underpowered for cutting 40mm/1.6" thick plywood. This is likely why you need to do three passes to cut all the way through. A thick kerf is likely to result from doing multiple passes with a hand held saw, even if you are using a guide.

I would suggest using a corded circular saw with a good carbide blade and making the cut in a single pass.

 

[DanEng]

I will try a single pass. And I became aware that I have made a mistake in writing the plywood thickness, it is not 40mm but around 27mm, Sorry about this.

This is the plywood I am trying to cut:

https://pmhobby.com.mt/wp-content/uploads/2021/06/F360_P27SH20_21869-scaled-1-1200x847.jpg

 

[PCustoms]

I bought a simple Parkside cordless circular saw and clamp guide to start with.

After looking that up this may be a big part of your problem. 40mm is no light duty cut, using light duty tools you are destined for disappointment.

 

[DanEng]

After looking that up this may be a big part of your problem. 40mm is no light duty cut, using light duty tools you are destined for disappointment.

I have made a mistake in writing down the thickness, it is around 27mm not 40mm, but you are right the tool I bought is not a heavy duty item, it feels.

 

[alfadan]

I have had a saw blade warp when hot from cutting, then straighten out when cool.

 

[Wamsutta]

I suggest you get a Diablo 24T carbide blade and make the cut in one pass. That's what I would do.

 

[danski0224]

I'm no woodworker but cutting large pieces of wood with a circular saw is miserable work. You need a table saw for this task.

Or a track saw.

 

[alfadan]

I hate carpentry.
If I have to break out saw horses and a circular saw, things are not looking up!

 

[whateg01]

I'm no woodworker but cutting large pieces of wood with a circular saw is miserable work. You need a table saw for this task.

Many are abandoning the table saw for sheet goods because it can be cumbersome to control. Track saws are the current trend.

 

[whateg01]

What saw are you using? I have seen cheap saws that had the shoe not square to the arbor.

 

[P0234]

Many are abandoning the table saw for sheet goods because it can be cumbersome to control. Track saws are the current trend.

Interesting. I made more speaker boxes that I could count and always ripped through sheets like butter on a table saw. Set the fence and enjoy repeat cuts of the same width all day long.

 

[whateg01]

I have no idea how many speaker boxes I built when I was younger but probably close to 100. Even back then I didn't cut many full sheets on the table saw. I would but then down to 1/3 sheet of so on saw horses with a circular saw then cut the actual parts on the table saw. I hate dealing with full sheets of mdf or particle board.

 

[RMERR]

I agree with the suggestions regarding the edge of the base plate not being parallel to the blade. Another thought is checking that the blade is 90 degree square to the base with a small machinist square. Maybe check the flatness of the base plate itself, I recently replaced a base plate of a circular saw that had a very slight "bow" in it, letting the saw "rock" ever so slightly. I also think the multi-pass cut strategy is sinking you. If all else fails, a heavier duty saw (corded as someone suggested) might be in order.

 

[Sumboodie]

I'm no woodworker but cutting large pieces of wood with a circular saw is miserable work. You need a table saw for this task.

I've never used a table saw and have built several buildings.

Measure, snap a line or mark it and cut. Or use a saw guide for a really straight cut if it matters.

 

[Sumboodie]

What kind of saw are you using? Form ply is tough stuff, especially if it's been used.

 

[mm08822]

If the saw can only take a blade that is only 150mm (6"), I think you're on the way to burning it out.

I have tried to used "plywood blades" (fine tooth) to cut both plywood and bottoms of doors for a smooth cut w/o tear-out. Anything over 3/8" thick was a problem for the blade. It would warp when heated up. Although it would flatten back out when cooled, it was still slightly warped. It became my new frisbee.

Buy a medium tooth count blade and do one pass with a guide at a slow feed rate.

 

[bb29510]

i remember 25 year ago, watchiing a carpenter cut through 4 sheet of 3/4 at one time with a regular Milwaukee circular. I bought a milwaukee on the way home, still got it. maybe its the saw

 

[bwringer]

I suggest you get a Diablo 24T carbide blade and make the cut in one pass. That's what I would do.

What kind of saw are you using? Form ply is tough stuff, especially if it's been used.

Agreed, get a more aggressive blade and do it in one pass. And make sure the blade isn't wobbling or warped, and that the base of the saw is square. Many saws are not right out of the box.

If you're building concrete forms, then it's hard to see how surface finish would make any difference; accuracy is more important, and you'll never be accurate making multiple cuts. If the plywood has been used before, the bigger carbide teeth in a 24 tooth blade are more likely to survive.

 

[P0234]

I've never used a table saw and have built several buildings.

Measure, snap a line or mark it and cut. Or use a saw guide for a really straight cut if it matters.

So are you saying a circular saw is easier to make repeatable straight cuts with less effort than a table saw? Doesn't sound like it to me. You literally set it and forget it. All you do is feed the saw wood. And it sounds like that's what OP wants, same cut over and over.

I know of a guy that walked across the country, doesn't mean that's the route I'd take.

 

[Sumboodie]

So are you saying a circular saw is easier to make repeatable straight cuts with less effort than a table saw? Doesn't sound like it to me. You literally set it and forget it. All you do is feed the saw wood. And it sounds like that's what OP wants, same cut over and over.

I know of a guy that walked across the country, doesn't mean that's the route I'd take.

Stack the sheets.

 

[tarbellb]

Make sure your saw has zero movement while IN the track.

On my Makita there is a cam adjustment to tighten the track guide. Without this your blade could be non parallel, creating a wider kerf and stressed cut.

 

[Walkers]

Use the coarser blade, mark the kerf on both sides, then score with a razor knife. you generally only need to do this on the saw side to keep splintering down, then cut the full depth in one cut.

 

[acer66]

Make sure your saw has zero movement while IN the track.

On my Makita there is a cam adjustment to tighten the track guide. Without this your blade could be non parallel, creating a wider kerf and stressed cut.

He does not have a track but a guide.

 

[gahrajmahal]

Hello GJ’ers attempting to help DanEng with his circular saw issues. First, all good suggestions, but may I offer a few suggestions. I notice that DanEng lists his location as Malta. If I understand correctly this is a small island in the Mediterranean which I have visited. A beautiful place, but not a bastion of sources for wood working equipment.

My suggestions come from four years of teaching Adult Education Carpentry classes, where I focused heavily on using a circular saw. I quit teaching this class for many factors, but a big one was the very poor condition of the saws the class had to use, and the large class sizes. Frankly, I was afraid someone was going to slice themselves with a saw!

Using DanEng’s metric measurements of 150mm, his circular saw is just under 6” diameter and he did not say it was carbide tipped so I am going to assume it is (for Americans) an old style carbon steel blade. If you haven’t used one of these in a long while you will remember they wear out very quickly and have a high ratio of surface area since most do not have a set to the teeth to make the cut wider than the blade. This makes the blade drag in the cut especially in a small, underpowered battery saw. So, Dan, I’m going to add some images and links to better explain the great suggestions the GJ members have been giving you.

How to check for blade runout

Woodpeckers Saw Gauge

Woodworkers spend hundreds or even thousands of dollars on a table saw then spend hundreds more on high quality saw blades and still get burn marks when doing rip cuts. Even getting accurate results with a miter gauge can be difficult when the blade alignment is off. In most cases this is the...

www.woodpeck.com

Setting the blade depth correctly




A carbide tipped blade will turn faster and cut easier because the individual teeth are wider than the round blade thickness


Using a sheet of styrofoam to support your cut. I use a straight board clamped to each end to get straight cuts on plywood and I use a sacrificial sheet to support it.

Tip for Cutting Plywood Safely and Accurately - Woodworking | Blog | Videos | Plans | How To

Our tip for cutting plywood safely, accurately, and cleanly: instead of trying to balance the sheet across a table saw try a foam backer board.

www.woodworkersjournal.com

Good luck, and be safe!

 

[Hohn]

I'm no woodworker but cutting large pieces of wood with a circular saw is miserable work. You need a table saw for this task.

Track saw works much better in my experience. Wrestling a big sheet on a table saw is all but impossible to do with precision if you're working alone.

 

[cgrutt]

I don't think this is problem with OP but I don't think it's been mentioned the importance to install the blade correctly (in the right direction) as it's easy to put it on backwards with a circular saw. I probably cut more sheet goods than the average person and would love to get a track saw as has been recommended above, but I've been avoiding buying one mostly due to cost. My preference would be Festool but would probably buy Makita when I finally breakdown and get one. Even with a corded Makita you're looking at $500 or more purchase with tracks and I've read about alot of issues with Makita track. Not sure this is a practical recommendation for OP's project. Mafell is probably among the best if money were no object.