On 7 March 2010 09:29, Erik Christiansen <[email protected]> wrote:
> The hob must always cut at the gear helix angle, so that alone > determines the hob helix positioning. The hob axis then ends up where > the hob helix puts it. There does not appear to be any options there. > (According to the grindings of my mental gears, anyway.) Indeed not, I checked this with my dad. The textbook explanation of a helical gear is that it is a stack of conventional gears side by side with a phase difference, to that the tooth meshing and un-meshing is evened out. However if you try to cut it like that then the hob will cut excess material from the adjacent "conceptual gears" and you end up with very thin teeth. For this reason the hob always runs at right angles to the tooth flanks. > They insist on feeding "parallel to the blank's axis of rotation", and > cite a supporting reference. I can't see that working, though, except > for free-wheel hobbing. If you look at that picture again: http://school.mech.uwa.edu.au/~dwright/DANotes/gears/photos/BrownHobbing.jpeg You can see that the direction of travel of the cutter is parallel to the blank axis. (it is the slide covered by the bellows). In a conventional hobbing machine there is a differential gear arrangement such that the gear rotational position is a ratio of the hob rotational position, plus a proportion of the cutter axial position. (This would be very easy to do in EMC, as I think you have already mentioned). I have seen a pretty good diagram of the gear train that does this, but I can't find it now. Anyway, I have concluded that I don't have the axis separation I need to make the gears I want to make using the lathe spindle as the cutter axis, and I could not see an easy, rigid, way to adjust the blank-to-hob distance, so I am now back to Plan A, which involves making my milling head tilt-able (which will also mean that I need to add an encoder on the milling head, which was always the long-term plan anyway) -- atp ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
