I’m trying to rotary a car model again using poplar and being mindful of the pass depth recommendations of my bit. However, my robust hogging 1/4" bit keeps breaking during the first roughing pass! Do I need bigger bits like 1/2" for roughing? I’m reluctant to reduce the pass depth as it’s already 5…

I would run .250 DOC, .063 WOC and a chip load of .006. At your 22k rpm that will put your feed rate at 396 ipm, but lighter cut, thicker chip so no rubbing and the heat from the cut will go with the chip so cutter will stay cooler. It also will increase your MMR to 6.24 in^3/min. vs 5 in^3/min wi…

Hey Eric - My bit is sitting at zero and in the center of the rotary: [IMG_4017] [IMG_4016] However, with my project diameter of 7.99, my bit touches the top of the piece around 3.4 (probably more like 3.5 since i’ve already cut some stock off in the first pass). My machine won’t even go up to…

I’ve never really messed with chip loads before…usually I got with the stock settings when I import the tool database. Correct me if I’m wrong but essentially what you are saying is by decreasing the steopover to .063 (or roughtly 25% vs 80% before) and a faster IPM at a chip load of .006, the bit i…

[image] graysenKobi: Trying to get more clarity from @djdelorie regarding speeds/feeds comment… If you’re talking about my “dig” comment, consider… if you’re milling on the “side” of your stock (i.e. way off center but close to Z=0, mostly using the bit’s edge) and your recipe is for 50% dept…

Chip load is simply how big a bite each cutting edge (tooth/flute) takes every time it passes through the material or for each rpm of that cutting edge (for an end mill). With a .0015" chip load the cutting edge is taking a very thin cutting, and because of that it could very well just rub and not …

I will add that chip load is only half of the problem - you need to get those chips out of the flutes and out of the way, too. Make sure there’s an ejection path and/or air jets or good dust collection to make sure those chips don’t stay in the cut and get jammed into the bit. That would be instan…

I do have dust collection, but not for the rotary. I’m reluctant to run dust collection for several hours on end. What kind of air jets would you suggest?

I bolted one of these onto my carriage: https://www.amazon.com/dp/B07JVKBS4V but I had an air manifold there already and still needed to 3D print a custom bracket for it. Then I took it off because I’m designing something different… (I didn’t use the coolant part, just the loc-line and air input…

Also, the rotary-spiral pattern always seems to have good chip ejection. So much so I ended up putting a board there to keep them in one place.

You have your pass depth at .25" From the looks of your pictures your first pass it’s way deeper than .25" which is likely what snapped that bit. If that’s true you need to figure out why that happened

Bits keep breaking

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djdelorie April 23, 2026, 11:37pm 19

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Bits keep breaking

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