Drawing up plans for your project seems to be a good idea whether or not you’re going to reproduce the item being made but it isn’t the holy grail of woodworking and the measurements should be taken as a grain of salt.
In the world of hand tool woodworking you will never thickness a piece of material spot on to the exact thickness your plans state, even using the “Paul Sellers thicknesser” which I find invaluable when I need it but it will never be exactly to that decimal inch or mm which leads to many frustrations down the road if you head down that path.
I’m going to keep this as short as possible because I’ve had a long day and I still haven’t had a single bite to eat yet I still need to work late into the night because I am so far behind, these are the joys of self-employment which I wouldn’t wish on my worst enemy.
Take my current project it is a simple box comprising of splines, grooves and rabbets which hopefully in the future will become a video but for now it’s in the mock up stage. I drew up the plans in AutoCAD and they are mathematically correct yet nothing fits. Nothing fits because I followed the measurements to the letter and somewhere down the line I am off I did something wrong. Computers are accurate and in a perfect world the timber planed would be evenly thicknessed, perfectly flat and crosscut dead on to the accurate mark but that’s all fantasy hog wash the reality is your planning is never dead on accurate.
Working with hand tools is not like working with machinery, you’re going to be off somewhere which means that you take those measurements and throw them out the window but you measure off the piece itself and everything should work out hunky dory.
In my case I didn’t do that because I firmly believed I could do it but hey this lesson cost me dearly and it was worth it just to get it out of my head that I can be as accurate as a computerised machine. I can’t and no one can no matter how long you’ve woodworked for but still I aim for that insane level of accuracy and I sincerely hope that one day even though it is completely unnecessary I achieve that.
All in all, the moral of this story is use measurements as a guide, oversize everything and cut or shave it to fit. You will breeze through your work effortlessly and you’ll have more hair left on your head than I do.