I’ve always known that materials expand with heat, but recently while machining 2.5”+ OD 6061 aluminum involving deep large diameter drilling followed by boring and turning to diameter. I was making internal bearing pockets in parts that needed the OD press-fit in a cylinder so the dimensions were fairly critical. I rarely aim for .0005” accuracy but this project needed it to hold bearings in pockets and an OD to fit snugly in a cylinder. Some parts became hot enough that I couldn’t comfortably handle them during the process (lots of heavy turning cuts). I was happy with my results, until the next day, NOTHING fit perfectly as they had while in the lathe.! WOW! I found some OD’s changed by as much as .005”, and my internal slip-fits were now tight press-fits. That blew my hopes for .0005 accuracy out the window. On the remaining parts, I tried removed them periodically and cooled them in water before final cuts and got much better results. The moral is, keep your material near room temperature during machining if you really need accuracy.... This is probably old news to most here, but it may be of help to some, like myself, than never really saw the actual effects of heat buildup... Keep it cool!