On Thu, 10 Nov 2022 at 01:03, John Dammeyer <jo...@autoartisans.com> wrote:
I think it was on this forum that the discussion came up on the holding > power of R8 collets and how they were essentially only useful for light > machining. Bridgeport machines were (are?) all R8 for decades and I don't think that anyone considers them toys, It's often said that the key (peg, in some cases) is the issue, but in the case of a collet the friction grip on the outside should equal that on the inside, but at a larger radius so higher torque. The key should not even be in play. For solid-mounted R8 (I have an R8 flycutter with integral shank) this analysis is irrelevant, but does suggest that you should tighten them at least as hard if not harder, to keep the key out of the load path, This is not in any way an answer to your question, though. To calculate the drawbar tension you need to know the thread coefficient of friction (unknown) and then there is a standard calculation involving torque (known) and thread diameter (known). Though you also should really also allow for the torque lost in drawbar to spindle friction (unknown) Then the clamping force depends on the cone angle (known) and the collet to spindle friction (unknown) Then the gripping torque depends on the tool radius (known) and the friction (unknown) At this point we are deep into unknown friction ^ 3. (or maybe not, cone to spindle probably cancels rather than multiplies) Why not experiement? Put a bolt (ideally of the same material and surface finish as your fly cutter) in the collet. Torque the drawbar to a low value. (with a torque wrench) Measure the torque to spin the bolt in the spindle with the same wrench. Increase the drawbar torque Repeat. Several times. Now plot the graph of drawbar torque to tool torque. Now you know, Then you need to compare the to the torque the flycutter needs to operate at various depths of cut (unknown :-) -- atp "A motorcycle is a bicycle with a pandemonium attachment and is designed for the especial use of mechanical geniuses, daredevils and lunatics." — George Fitch, Atlanta Constitution Newspaper, 1912 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
