Looking to make bowed cawls with Poplar

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I purchased a large chunk of poplar 6/4 12 foot by about 7.5 inches.  I used a small portion of it too make a cheese press for my wife.  I should have some Gouda as repayment next week.  I was trying to make some bowed camping cawls with some pine recently, but the twisted nature of the boards make me rethink dimensional lumber for this, so purchased the Poplar.  I have not used Poplar in years, so don't know it's characteristics other than being fairly soft.  I am looking to start off with some 26 and 38" cawls.

Would 1.5" by 1.75" be sufficient to act as cawls or should i cut them wider to 1.5 x 2.5"?

[GlenS]

Right or wrong mine work & they are only 1 1/2" square. I also made mine from a scrap 2x10 of yellow pine. The outer 2" has vertical or 1/4 sawn grain & remains flat & stable.

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Right or wrong mine work & they are only 1 1/2" square. I also made mine from a scrap 2x10 of yellow pine. The outer 2" has vertical or 1/4 sawn grain & remains flat & stable.

Thanks for your input, the cutting will begin at 1.75 x 1.5.  I meant cauls BTW.