In case nobody made this obvious before, machetes aren't designed for heavy wood chopping. They're intended for light vegetation. In places where these tools are used daily, you're more likely to see one being used to cut grass than wood.
I haven't used 3v or s7 for any blades, so I may be wrong, but I can't see any steel being reliable for chopping hardwoods in machete thicknesses. Also, a full tang machete chopping hardwood will put a serious hurt on your hand, and is likely to lodge heavilly in the work.
A khukri with a thicker, 1/4-3/8 spine, as mentioned, would be much more suitable to your task. If you're breaking a machete, even a lower quality one, its because you're using it innappropriately inho.
Sorry if that sounds harsh, but I grew up in Latin America, back when everyone still used a machete every day, so it's a close concern to my heart. Yes, you can *carefully* chop wood with one, as I'm sure you could carefully skin a rabbit with a sharp enough axe, but its not the appropriate tool for the job.
Good luck on the project, and I hope you don't take the criticism personally.

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