Bending poplar using Kerf cuts

[Gerry S. Wojtowicz]

Hi all,
I am building q fireplace mantle using poplar. The wall has a slight curve to it. I want to run some kerf cut through the poplar so I can bend it. From what I saw on YouTube, it looked like the cut ended about one quarter inch before going all the way through when people were trying to do this.
I guess my question is, is that a good depth. Will the poplar bend without splitting (most of the videos I saw used plywood). Do I just continue making cuts until I get the bend I want?

Thanks in advance

[Mike Cutler]

Gerry

It seems like it should work, as long as the curve is slight. A 1/4" isn't a lot of material, but it's still got some strength to it.

I don't know if you saw this post, that directs to a calculator for kerf cuts, to bend wood. The website address inside the post is still active.

https://www.sawmillcreek.org/showthr...r-bending-wood

[Derek Cohen]

Why not rather scribe it to the wall, and then cut away the excess on a bandsaw. The mantle will fit perfectly flush against the wall, and the face will remain straight ... unlike if you bend it.

Regards from Perth

Derek

[Lee Schierer]

Why not rather scribe it to the wall, and then cut away the excess on a bandsaw. The mantle will fit perfectly flush against the wall, and the face will remain straight ... unlike if you bend it.

Regards from Perth

Derek

I like this idea as well.

[Al Launier]

Why not rather scribe it to the wall, and then cut away the excess on a bandsaw. The mantle will fit perfectly flush against the wall, and the face will remain straight ... unlike if you bend it.

Regards from Perth

Derek

I also think this is a better idea: retains original strength, will fit & certainly look better & it would be a more professional resolution.

[Bill Carey]

Why not rather scribe it to the wall, and then cut away the excess on a bandsaw. The mantle will fit perfectly flush against the wall, and the face will remain straight ... unlike if you bend it.

Regards from Perth

Derek

#3 on scribing to the wall.

[Jim Becker]

I agree with scribing for a slight bend at the wall and if you still want the front to be curved, cut that after you scribe the straight initial workpiece that's intentionally wider than you need it to be when completed.

[Jim Morgan]

Hold on, guys, it depends on how the piece of wood in question is oriented to the wall. If its wider axis is perpendicular to the wall, then scribing is certainly the way to go. However, if it is parallel to the wall (e.g., a frieze), then kerfing is probably preferable to scribing and attempting to resaw in conformance to the curve. Molding scribed to the wall or to the surface of the frieze then conceals the kerfs.

[Bill Carey]

Hold on, guys, it depends on how the piece of wood in question is oriented to the wall. If its wider axis is perpendicular to the wall, then scribing is certainly the way to go. However, if it is parallel to the wall (e.g., a frieze), then kerfing is probably preferable to scribing and attempting to resaw in conformance to the curve. Molding scribed to the wall or to the surface of the frieze then conceals the kerfs.

I have to defer to anyone who quotes Mr. Natural. Parallel to the wall, kerf it.

[Gerry S. Wojtowicz]

Thanks to all for your input. Mike I will check out your link. To those of you who suggested scribing, the piece in question has the flat side of the wood against the wall (the piece is 1 1/4 thick x 8 wide x 58 long; the 8 inch wide face needs the Kerf cut). I guess I should have led with that information.
Thanks again.

[Jerry Miner]

The wall has a slight curve to it.

It would help to know how much "curve"

Kerf-cutting calculator is here

[Tim Janssen]

Steam bending, maybe?

Tim

[Gerry S. Wojtowicz]

Jerry,
Yes, it would be nice to kow how much curve. Not too sure how to calculate that.
Tim, steambending not really an option.

[Jerry Miner]

Jerry,
Yes, it would be nice to kow how much curve. Not too sure how to calculate that..

Put a straight edge (or a straight board) against the curve and measure the gap at both ends. Given the length of the straight edge and the amount of offset, we can calculate the curvature. Nobody can tell you if a 1/2" deep set of kerfs in a 3/4" piece of wood will make the bend until we know how much bend we are talking about.

[John K Jordan]

Jerry,
Yes, it would be nice to kow how much curve. Not too sure how to calculate that.
Tim, steambending not really an option.

After measuring and calculating I would still do a test piece. The radius of a bend can be calculated from the chord length using the straight edge method Jerry mentioned. You can find arc/chord formulas and calculators with Google.

The last time I did a bend like this I left less than 1/4" beneath the saw cut on a 3/4" board. Based on the radius, the thickness, and the kerf width I calculated the optimum distance between saw kerfs to allow the backs of each standing segment to just touch so I could reinforce with glue. It took a lot of saw cuts with a radial arm saw for my 3/4" thick board. (A thicker board will need less space between each cut (or a wider kerf) than a thinner board without extra work on the back.)

I tested on a piece of scrap to make sure the bend would work correctly and give a smooth surface. It's been over 30 years but I THINK I moistened the face of the board before bending. It probably was not poplar, possibly oak.

JKJ