I take it that you have a QC30 spindle ? If so then yo may need to adjust the QC nut so that it is engaging the lockdown tab more. IF it just barely engages teh vibration will make it slip back and drop out the tool holder. 

IF you are cutting at 50IPM(1272MMPM)  that is way to fast for that rpm and size of tool on a low powered BP.  Lower the feedrate and increase the DOC . For normal cutting you will be MUCH better off if you limit your endmill sizes to .500"(12mm) then plan your feeds/speeds to that size cutter based on available HP. 

The settings and tool Diam/#flutes  you are using now will make the BP chatter badly and damage the Quill/spindle over time.

(;-) TP

Bit more than I would push a BP but everyone to their own

Hood

Thanks for replies
il drop tool diam..to 14mm and run at 3500.....460 feed 0.5 pass

Mike

Why only going 0.5mm DOC?
I would tend to have a lower RPM and lower feed and go deeper.

Hood

at 3000 rpm 1272 feed at 0.5 per pass.....using 20mm 3flt hss long flute

Yikes!
3000 RPM with a 20 mm cutter? Moon, here comes something orbital.
Wrong direction. Much smaller cutter or much lower RPM.
My 2c.

Cheers
Roger

Top spindle bearing goosed........just ordered one (7209)....bottom 2 seem fine.......im using g_wizard for the speed and feeds... i know the mills only 2hp...didnt think 20mm was that bad to be honest....im still learning though.

Thanks
Mike

You have to remember that a Bridgeport is a knee mill and it is not very rigid when comparing to a VMC, add to that the Z axis being a quill and you have even less rigidity. You need to take things much easier on such a machine.
I use HSM Advisor a lot and it usually gives me good feeds and speeds for the type of operations I do, it is also configurable for slotting or high speed machining etc.
For slotting with a 20mm 3 fl HSS in 7075 it is telling me 1553 rpm, 639 feed. On a Bridgeport I would reduce the rpm and  feed a bit due to the lack of rigidity, HSM Advisor allows you to do that and it gives you info on tool life, deflection, HP required etc.

See screenshot for using a generic VMC, you can set the specs of your machine up in a profile so that it is taken into account.

Hood

Thanks Hood i owe you a drink!

replaced the top bearing today and its running noticably quieter.......i wont be taking it past 2500rpm in future, i adjusted the QC nut too, it tightens right up now when before it came to a stop and didnt feel that tight.....i had to make some screws to fit it, and the longer one to stop the nut totally unscrewing, its got 6 screws instead of the 3,
ran it tonight using some 20mm mild steel.......faced it, shaped it, put a couple of 12mm pockets in it then chamfered the whole edge all using the midi function, everything went really well, then i turned the mill off and it tripped the lecky, everything went black and i banged my head trying to get out, then the misses gave me a wollop for bringing chippings in the house,
so im sitting here with 2 lumps on my head...... progress

Mike

HSM advisor looks similar to what i been using, only on g-wizard it only gives 2 options for alu, cast or wrought.

then i turned the mill off and it tripped the lecky,

Yeah, happens. Many CNC controls mix up the neutral and earth, so that the leakage breakers trip.
I had to remove all of them from my CNC circuit to get reliability.

Cheers
Roger