dethatcher tine fabrication

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I have this nifty strimmer/brush cutter attachment that's a tiller. I noticed that there are other brands in the UK and US that offer dethatcher attachments. I want to fabricate dethatcher tines for my tiller attachment. do you know what kind of shaft this is? the cylindrical kind with a flat grind to retain the tine that fits over it. when i google I get woodruff keys.

I was thinking I could either get some... I dont know what they're called. the part that slots onto this kind of shaft and weld some cut carbon steel plates onto it or weld some aerator coring tubes into it or both.

thing is that dethatchers and aerators are pretty rare in australia and cost about $100 to rent for a day. since i'd be using it maybe twice a year it doesnt make sense to spend the money on renting one or buying a dedicated unit.