circular saw issue with wider kerf at back of cut than front

[Aaron Connor]

I have an issue with my circular saw, and don't know what to do about it. Hopefully someone here will know.

Been building some stairs and the upper flight required some shimming on treads, as my stringer steps ended up being slightly > 90 degrees. Was a bummer to find, but wanted to avoid the same hassle on the lower flight. The kerf is slightly widening at the back end of the cut. I figured it was the thin kerf blade on the saw, and got the beefiest blade I could find for the Makita LXT 18V saw. That did improve the situation, but onto the second flight stringers, and I seem to have the same issue.

The template I cut out of OSB doesn't have the issue, but when I step up to the cutting the LVL stringers my steps are no longer dead square.

Here's what I've checked:
- blade parallel(ness) to the base, and that is only out about 0.004" between front and back of the blade and base
- ditched the think kerf blade for a Irwin Classic that has steel about 50% thicker, as well as a similar thicker kerf. It was the thickest blade I could find
- every cut has a board as a rip fence clamped into place, aligned with the layout marks, which are marked with an ultra fine tip marker

Anyone have any ideas on this? I'm not sure what to do, other than look for a new saw.

[Richard Coers]

How old is the saw? Bearings okay?

[Aaron Connor]

It's not very old.... maybe 3-4 years - not all that much use. I don't detect any issues with the bearings, but certainly a possibility.

[Lee Schierer]

I think the blade is getting hot from the cut and is warping. Personally I would switch to a full size skill type saw with a thicker plate and larger diameter. Finish the cuts with a sharp hand saw.

[George Yetka]

I vote the thin blade is deflecting as it moves through wood.

[Aaron Connor]

I vote the thin blade is deflecting as it moves through wood.

I think the blade is getting hot from the cut and is warping. Personally I would switch to a full size skill type saw with a thicker plate and larger diameter. Finish the cuts with a sharp hand saw.

The thing is that I went from the ultra thin blade spec'd for the saw at 0.059" Kerf / 0.038" base steel to the thickest one I could find at 0.086" Kerf / 0.056" base steel (Irwin Classic). A larger (7-1/4") blade will stay cooler, but it technically can wobble more since it is further out (unless 7-1/4" blades are thicker than my Irwin, which I doubt) Also, this cut is only about 11-1/2" long... do you think that is long enough for it to heat up and wobble, and if so - would that not lead to the front of the kerf also wider?

Thanks for the additional thoughts.

I'm using a japanese pull saw to finish corners.... have not used one before, and pretty amazing for this.

[Aaron Connor]

If you all do think it is the saw, what is the classic corded 'known-to-be-accurate' saw I should look to?

[George Yetka]

The thing is that I went from the ultra thin blade spec'd for the saw at 0.059" Kerf / 0.038" base steel to the thickest one I could find at 0.086" Kerf / 0.056" base steel (Irwin Classic). A larger (7-1/4") blade will stay cooler, but it technically can wobble more since it is further out (unless 7-1/4" blades are thicker than my Irwin, which I doubt) Also, this cut is only about 11-1/2" long... do you think that is long enough for it to heat up and wobble, and if so - would that not lead to the front of the kerf also wider?

Thanks for the additional thoughts.
I'm using a japanese pull saw to finish corners.... have not used one before, and pretty amazing for this.

Im not sure its the heat. I know the thin kerf I run on my tablesaw has a stabalizer on it to keep it running straight. The harmonics of the blade spinning at high speeds makes it move. That and a very thin blade could be following the grain.

[Mark Wooden]

Sounds like the blade and baseplate are'nt parallel. Ive seen this more than once on newer saws

[Edward Weber]

Sounds like the blade and baseplate are'nt parallel. Ive seen this more than once on newer saws

This is quite common IME as well, I have one

[glenn bradley]

It sounds like he has eliminated the saw's alignment and the thin kerf blade. I would do a test on a piece of scrap. Clamp on your straight edge guide like normal and make a cut about 1/8" deep. Check this cut for square and report back please.

[lou Brava]

Not sure what your problem is but I've cut many many stair stringers, from solid stock & manufactured lumber & have always used a worm drive Skillsaw. The tool with a good blade is amazing (don't drop it or buy a used one) I've never used a guide to make the cuts. I've used one for large crosscuts on dining tables (with a guide) and get amazing accuracy from a hand held tool. There not cheap but IMO it's the best hand held saw you can buy.

https://www.amazon.com/SKILSAW-SPT77...99141192&psc=1

[Aaron Connor]

Im not sure its the heat. I know the thin kerf I run on my tablesaw has a stabalizer on it to keep it running straight. The harmonics of the blade spinning at high speeds makes it move. That and a very thin blade could be following the grain.

Thanks. Would you consider a 0.086" Kerf / 0.056" base steel blade thin?

[Aaron Connor]

Sounds like the blade and baseplate are'nt parallel. Ive seen this more than once on newer saws

It is possible. I've tried to measure between outside of the fence and the blade at front and back, though of course the blade can flex, so it is a bit challenging to measure. Best I could get was around 0.004" difference between front and back. At that, I was afraid any adjustment might come back less accurate.

What's the best way to measure?

[Aaron Connor]

It sounds like he has eliminated the saw's alignment and the thin kerf blade. I would do a test on a piece of scrap. Clamp on your straight edge guide like normal and make a cut about 1/8" deep. Check this cut for square and report back please.

When you say check for square, do you mean the kerf widening?