so i need to mill a slot through a block of mild steel 4.5" x 1.5" x 1.25", the slot runs the length of the bar and is 1.125" deep and 0.875" wide.
Into the vice it goes, clamped to half-depth and I throw in a 3/4" two-flute slot-drill with an R8 collet so its right up in the quill (Bridgeport). Speed was 375rpm.
Anyways, first cut i take it lightly, say 1/3rd of a turn on the knee lift and things look good so i thinks to myself, slot-drills can go to half-width in depth (so my chart says) and i crank it a fat half-turn on the knee and throw in the power feed (about 3.5"/min). It appears i have some bad slack in my bed that i hadnt noticed before!! The whole table was moving side to side as it went along, the head was bucking a bit and it looked like the whole machine had turned to jelly!
I clenched them up :-) and crossed my fingers and nothing serious happened, the cut finished, no tools broke, the work was not torn from the vice and so on. The swarf was coming off in nice thick curls.
Now, what i want to know is, what happened?
1 - Was it just too much of a cut for an ageing BP?
2 - Too big a cutter?
3 - Knackered leadscrew (wouldnt stop the head bucking though)?
4 - Wrong tool, should i have used a three flute cutter or other?
5 - Am i an idiot :-) ?
6 - Something else?
Anyway, the next cut was back to 1/3rd of a turn lift for DOC and the job progressed at a steady pace with no more excitement. I know i will be tramming in again soon!
BTW this was a low accuracy job so i thought to open the slot with the 3/4" then go in with a smaller 4-flute to each side.
Thanks in advance for any tips.