How Do I Tell When ....

Thumbnails for fish hooks rule was set the hook point down on your thumb nail and if it would glide off easily it was dull, if it grabbed and left a scratch mark it was sharp.

Jim
 
Great question and great answers. Having been a woodworker for too many years I can tell instantly when a tool is dull just by how it is interacting with the material, what the machine is doing, and what the cut looks like. I usually notice the first two and then confirm with an inspection of the cut. I think that all of us rookies need to put some chips under our belt and experience will be our teacher. A retired machinist gave me a bunch of used tooling some of it actually no good and told me to try them all out on scrap to see what the results were. It has been a great learning experience for me. I can see what a chipped mill does vs. a dull mill vs. a bent mill... I spent most of one day trying them out at different speeds and feeds and materials. When I took out a new high dollar 1/2" 4 flute to try on some steel is was amazing to feel the difference. Looking at your cuts under magnification is also a good experience.

I spend a great deal of time at least skimming posts here as you never know what little tip one of the experienced guys will mention, or a short story. This is an awesome group that has thought me so much as I dive into the world of metal.
 
I seldom use HSS. Good to start with. Yesterday I was using a 3/8" endmill that looked new but I knew it was going dull on me .Finally it starting pulling out of the collet and cutting deeper than desired...That could be disastrous on some projects...Another thing to watch for- milling slots will want to cut to the side opposite endmill rotation...A really dull endmill will mill a slot well over to the side as the endmill flexs away from the cut.
 
+1 on this fantastic forum where I learn from threads I was just perusing for the heck of it! Ha hah
 
brav65 said:
Great question and great answers. Having been a woodworker for too many years I can tell instantly when a tool is dull just by how it is interacting with the material, what the machine is doing, and what the cut looks like. I usually notice the first two and then confirm with an inspection of the cut. I think that all of us rookies need to put some chips under our belt and experience will be our teacher. A retired machinist gave me a bunch of used tooling some of it actually no good and told me to try them all out on scrap to see what the results were. It has been a great learning experience for me. I can see what a chipped mill does vs. a dull mill vs. a bent mill... I spent most of one day trying them out at different speeds and feeds and materials. When I took out a new high dollar 1/2" 4 flute to try on some steel is was amazing to feel the difference. Looking at your cuts under magnification is also a good experience.

I spend a great deal of time at least skimming posts here as you never know what little tip one of the experienced guys will mention, or a short story. This is an awesome group that has thought me so much as I dive into the world of metal.
Click to expand...
I agree with the magnification tip. Myself, I am very new in this game but decided up-front to get myself a good magnifying glass. After every cut I inspect the tool to see how it is doing, and either change my process or my tools to suite the next time I have to do a similar cut. I quickly learned from these observations that its sometimes much beter to increase the feed rate than to stay on the safe side and dull the tool through rubbing.
During my very first cut on the lathe I chipped the first carbide insert while trying to cut the thread off a high tensile bolt. After the break the cut went much smoother and I could not understand why. Under the magnifying glass, the reason became evident. The break resulted in a large negative angle, which was much better for the interrupting cutting required to remove the thread!
 
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