Debate: Should you dial in feeds and speeds on the machine or on paper first?

Overheard two old timers arguing yesterday at a shop in Detroit, one swears by doing all the math on paper before touching the control while the other just tweaks everything on the fly at the machine. The paper guy said it saves him from scrapping parts and the on-the-fly guy said he gets done faster without overthinking it. Which side do you lean toward and has one way ever burned you?

4 comments

4 Comments

evanpalmer1mo agoTop Commenter

Ngl I dialed in a part once without checking feeds first and blew a $400 endmill in under 10 seconds.

graytorres6d ago

Man oh man, that story about the $400 endmill gave me flashbacks... I once spent a whole afternoon setting up this big aluminum plate job, figured I'd just eyeball the speeds and tweak it on the fly. First pass sounded fine, second pass... BANG. The whole part shifted in the vice and gouged out a chunk the size of my thumb. Had to start over from scratch with a fresh block, wasted half the day and the material cost. Paper all the way after that for me. I don't trust my gut on anything over a few bucks of material anymore.

barnes.morgan6d ago

Man, I gotta side with the paper guy on this one! My buddy runs a small shop near me and he's a super talented machinist but he's always been an on-the-fly type. Last year he was rushing on a rush job for a local auto parts place, a batch of custom brackets out of 4140 steel. He figured he'd just bump up the feed rate a little to shave off some time, didn't write anything down. Halfway through the first part the tool started chattering like crazy and before he could hit the stop button it snapped off the endmill and gouged a nice spiral into the part. The whole batch was toast because the runout ruined the rest of the blanks in the setup and he had to reorder material and retram the vise. He said the math would have told him his speeds were way too high for that depth of cut. He's a paper guy now for anything thicker than sheet metal.

mason2091mo ago

That bit about blowing a $400 endmill in under 10 seconds is exactly why I side with the paper guy. I've been machining since the late 80s and I can't count how many times I saved a job by sitting down first with a calculator and a feeds and speeds chart. The on-the-fly method works great until it doesn't and then you're out real money and possibly a whole work shift. What a lot of younger guys don't get is that the math gives you a safety margin so you can sneak up on the cut without wrecking things. I've seen guys skip the paper work and end up with a chatter mark that ruined a part worth more than the tool did. It takes five minutes but it buys you peace of mind and keeps the scrap bin from filling up.