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-SPT77WML-01-15-Amp-Lightweight-Circular/dp/B00B7EUS46/ref=asc_df_B00B7EUS46/?tag=hyprod-20&linkCode=df0&hvadid=309807921328&hvpos=&hvnetw=g&hvrand=12523469844748694453&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033105&hvtargid=pla-762199141192&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?

[Aaron Connor]

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-SPT77WML-01-15-Amp-Lightweight-Circular/dp/B00B7EUS46/ref=asc_df_B00B7EUS46/?tag=hyprod-20&linkCode=df0&hvadid=309807921328&hvpos=&hvnetw=g&hvrand=12523469844748694453&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033105&hvtargid=pla-762199141192&psc=1

Thanks for weighing in, Lou. I will probably not have anything else in my project that requires this level of accuracy, so it is making the prospective of buying a new saw for one day's work hard, but easily justified by the frustration.

I probably don't have then skill to freehand without a fence. The variance is not great, but part of the challenge is the architect spec'd double LVL's, and getting those aligned when each step is out is more of a challenge... and then the top hangered end and the bottom 'foot' being sloped ever so slightly really throws things out for getting everything installed straight.

In your opinion, over an 11-1/2" step 6-1/2" riser, how accurate should my stringers be from one stringer to the next? I might need some context here to make sure the solution isn't just adhesive.

[Aaron Connor]

All, just to make sure I'm being realistic about the expected results... how much wider should I expect the kerf to be at the back of a cut than the front of a cut with a good circular saw with a good blade?

[lou Brava]

Thanks for weighing in, Lou. I will probably not have anything else in my project that requires this level of accuracy, so it is making the prospective of buying a new saw for one day's work hard, but easily justified by the frustration.

I probably don't have then skill to freehand without a fence. The variance is not great, but part of the challenge is the architect spec'd double LVL's, and getting those aligned when each step is out is more of a challenge... and then the top hangered end and the bottom 'foot' being sloped ever so slightly really throws things out for getting everything installed straight.

In your opinion, over an 11-1/2" step 6-1/2" riser, how accurate should my stringers be from one stringer to the next? I might need some context here to make sure the solution isn't just adhesive.


Double LVL's must be a fairly long run, are you gluing and screwing those LVL's together ? I would to avoid any squeaking down the road. As far as accurate for me it would depend on the tread materiel and stair construction & width & number of stringers. Also using very straight riser materiel can help. If you have more than 2 stringers install the the outside ones than install the inboard ones checking every tread/riser with a straight edge so it's not higher than the outside stringers if it's a bit low no problem it's ok to shim if needed. The LVL's I'm guessing will be completely covered up, since it's "rough framing" don't worry too much about if they "look" perfect just as long as they don't create problems with your finished treads & riser's just make em work. Remember using a pattern, transferring pencil marks, installing a guide and cutting all done freehand is that your going to get differences in your cuts. Plus it's highly unlikely what your attaching the stringers to & the floor or landing there sitting on is perfect all these variables can add up to a WTF situation that is easily fixed weather it's shimming or reworking a stringer.
Have fun & good luck !

[glenn bradley]

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

Yes, sorry. I am trying to figure out if it is the saw, the blade, or a method issue. With a shallow cut and all else being done the same we remove a lot of the stress put on the blade itself.

[glenn bradley]

All, just to make sure I'm being realistic about the expected results... how much wider should I expect the kerf to be at the back of a cut than the front of a cut with a good circular saw with a good blade?

Let me be clear about how you are measuring. You cut part way through a board using a guide and then measure the kerf at the entrance versus the stopping point, yes?

[John Pendery]

Sounds like tension release in the lvl as it’s cut for a stringer. LVL’s were designed primarily to act as beams/headers and can move when notched out. They aren’t as stable as cross laminated plywood. I’m guessing your saw is fine. Troubleshooting to the thousandth of an inch in regards to framing a house might be all that needs reevaluation here. Best of luck

[Cameron Wood]

Sounds like tension release in the lvl as it’s cut for a stringer. LVL’s were designed primarily to act as beams/headers and can move when notched out. They aren’t as stable as cross laminated plywood. I’m guessing your saw is fine. Troubleshooting to the thousandth of an inch in regards to framing a house might be all that needs reevaluation here. Best of luck

+1.

I've had good results making stair stringers from 3/4" plywood- 12" rips, stagger end joints, glue and clamp with sheetrock screws, which are removed after. Two layers is usually enough, since most stairs are fastened to walls or supported. With plywood sub treads and risers glued, you end up with a very stiff, stable and squeak-free structure.