How do you flatten your boards

[cliffp]

Many thanks for the recent replies.

Jack, I don't expect to get a lot of use out of the machine as I am only a hobbiest and don't make a lot of furniture each year. I take your point about the cost savings over time and realise that if I did keep the machine for a long time it would pay off but at the moment I can't be too sure it would pay off in my case (I realise there are other benefits apart from cost). I will check the cost of the spiral cutter head and give it serious consideration though, following your advice as I know it often pays to take advice from someone with more experience even if your own gut feeling pushes you in a different direction. I remember asking my dad's advice about whether to have a full structural survey on a flat I was buying (the survey was very expensive) - his advice was definitely worth taking as it saved me a lot of money on this purchase and on the other two similar purchases I made where I followed this advice.

Cliff

 

[DanielOB]

You can flatten your board to very perfection. After some time is over check it. No more flat.
It is inherent property of wood to get crooked after changing moisture content.
You have to have a construction under the plate to prevent it. Wood does no crook along longer edge but along shorter edge, so consider this when orienting construction planks.
Another way is join two plates and join them with positive lock like festool tenons so they cannot move relative to each other.