Yesterday I did a bit of what I have to consider as "SCARY" milling.
Using a HSS 3/32" end mill on a case-hardened, angled surface, for a two diameter long "notch" that ended up at the deep end as being about equal to diameter of the cutter. I had four such notches to make in a single piece of metal, and by the fourth cut I was getting definite evidence of grab and chatter that could well have broken that weak little bit. Clearly, that bit became progressively duller during its torturous ordeal. I was expecting for it to snap at any moment, leaving me with this critical task uncompleted.
I initially tried a plunge cut, but saw that poor little bit deflect down-slope on the angle, so knew that wasn't going to work. Coming in slowly and laterally at a fixed depth from open air allowed me to initiate the movement of metal, but the feed had to be so slow as to almost qualify as an abrasive rather than a cutter.
However, by nursing that poor brutalized little mill bit along at about 1400 rpm and feeding it at less than .010" depth per cut, I managed to complete all four notches without incident, though it seemingly took me forever to accomplish each of the four cuts. I doubt if I was feeding more than a very few thousandths a second, and still would feel the bit grab and catch in what must have been almost certain near breakage.
In reality I should have been using a 5/64" end mill but I didn't have one, and of course I also should have been using carbide, but didn't have that either, and as actual size of these notches was not super critical, going a little bit oversized was an acceptable option in this instance!
Think I was holding my breath the entire time, as this was the only end mill anywhere near that small that I had, so breakage would have left me short of completion, and would have meant needing to buy another end mill and wait for its arrival.
Whew!
I have more expertise in breaking bits than milling. I find the small bits thrilling also. Nice you had the patience to persevere. I try to have two on hand of some of the smaller sizes I find myself using most.
Len.
Good thing it let you nurse it through. If it would have snapped, would you raise the chuck
and leave everything as is until a new bit arrived. Seams like that would leave everything
lined up but it would also tie up the mill. Just wondering.
Yes, I would have left the set-up intact until I could source another end mill. While I almost always have many tasks that I am behind on, none of them is so critical or pressing as to have broken down that set-up. However, the actual issue that is faced every time I wish to use the mill, is moving everything out of the way so I can get to the mill to make any use of it! ;c)
Weather actually also enters into the "equation" of mill usage, as the garage (to be read as: Shop) door must be open to make any use of my mill.
I have more expertise in breaking bits than milling. I find the small bits thrilling also. Nice you had the patience to persevere. I try to have two on hand of some of the smaller sizes I find myself using most.
Len.
I'm sure there was a time when I did have two 3/32" end mills, but just as a guess ... I broke the other one sometime in the past and failed to replace it!?!?
Next time I'm feeling my wallet bulging (may not ever happen) I'll have to get a mill bit order going .... or should I just buy another engine instead?!?!
;c)
I feel your anxiety, many is the time I have pushed my little micro mill waaaay past its stated limits, hence my wanting I mill on par with your excellent machine. 😀
I have more expertise in breaking bits than milling. I find the small bits thrilling also. Nice you had the patience to persevere. I try to have two on hand of some of the smaller sizes I find myself using most.
Len.
That is my expertise as well, I have learned the hard way to alway buy more than one of the small sizes.
While it is generally true that mill bits get progressively more expensive as they get larger, it is also true that their price tends to skyrocket as they get small, going under about 1/8th inch.