Hi - It is not possible to quote specifics as the grip and upward pull of the
3/4" R8 collet if affected by many variables. I do heavy machining in tough steels at times and have found:
Check you have a suitable thrust face for the draw bar on the top of the spindle (I use a nitrided thick machined washer with moly grease)
Check the draw bar thread is clean, as smooth as possible and lub it with moly grease.
Check the R8 bore and 3/4" TTS Collet is clean and lub it with a not oily moly coating - you dont want this to migrate to the 3/4" shank surface
Which should be clean and dry.
A lot of grip and upward force can then be applied. This will withstand fairly heavy cuts on medium size cutters.
You should aim to never enter the zone where the TTS is levered down by the cutting force. - You can quickly have a nasty meltdown.
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