(This is one of potentially several reposts of questions that never made it to the list due to operator error)
I am unsatisfied with the results of my attempts at gear-milling. I think this stems partly from me not knowing which of the three cutters I have is for what tooth count, or what the addendum and dedendum is meant to be for each cutter. I have decided that as a set of milling cutters comprises about 6 cutters at £10-£20 each, a hobbing cutter which will make any size of gear seems like a good plan. Hobbing, as you almost certainly know, involves rotating a hob and the work on not-quite-right-angles axes in a fixed ratio. Some parts of that are very easy with an EMC-controlled CNC machine (mine is one of these one of these, convertulated) http://www.amadeal.co.uk/acatalog/CX23A-750_Multi-Purpose_Lathe_Milling_Machine.html I have an encoder on the lathe spindle and it is a simple matter of connecting that to the rotary table in HAL to keep them geared together permanently at any arbitrary ratio. (there is even an encoder_ratio module for this sort of thing, but that isn't exactly right for what I want) However, the stepper-driven rotary table tops out at 5rpm. I can swap the motor for a servo, and that gets me 17rpm. The lathe and milling spindles don't really like doing less than 200rpm. I want to cut 12-tooth pinions, and that really isn't enough overhead for the rotary axis to catch up and synch. It is also a major change to the control box wiring and the software setup to swap to servo motor. However here are advantages, and I have all the parts. Holding the rotary axis at the correct angle to a hob held in the milling head is difficult. (though obviously doable) clamping it to the table at an angle to the lathe spindle is easy, but then I can only make gears of one diameter. It would be nice to be able to rotate the milling head. There is presently no facilty to do that, but there is a joint between two castings where the facility could be added. I am thinking of making a faster rotary axis using an ER32 collet holder I have on a 3/4" ground shaft and some taper roller bearings. I would drive that with a spare stepper I have, at about 10:1 ratio. (or one of the little servos) I can't believe that there are very large rotating forces on a gear during hobbing, I think it is probably largely balanced. If I do make this rotary axis, then I can either mount it at an angle to the milling spindle, or at an angle to the lathe spindle. In the latter case I would need a vertical slide, but I do have a spare compound slide that the CNC machine no longer uses. In either case I would need a compound feed on the two translational axes, or the offset angle will mean that the gear moves down the axis of the hob, giving a very slight second-order helix angle (if I am visualising it right) Modifying the milling head to tilt avoids this problem. The lathe spindle already has an encoder, the milling spindle is still waiting. Ideally I would make a hobbing head to clamp to the lathe saddle to cut gears held in the lathe spindle, with a nice powerful servo motor and encoder just like a real gear hobbing machine. But if I had a suitable servo motor like that it would already be my lathe headstock motor. So, rambling over, does anyone have any ideas for ways of arranging the shafts and slides that I have not thought of yet? (one idea has just occurred to me, I could mount a flexible coupling in the milling or lathes spindle. mount a secondary pair of bearings elsewhere, and put the hob on that to get the required angle). I think my favourite so far is a combination of new, faster rotary spindle holding the gear mounted on a vertical slide on the lathe saddle, with the hob in the lathe spindle. -- atp -- 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
