On 9/4/2014 8:04 PM, Len Shelton wrote: > We have a customer who is wanting to make a motor controlled rifling > machine. I spent a good bit of time researching it for him today and I > was surprised that it seems that no one is doing it with motors (or at > least I couldn't find anyone). I understand the need for the linear > relationship of the cutter to the position of the indexer in such a > machine. But I wanted to hear your guys thoughts on doing this with > motors, which will inherently have some degree of granular positioning. > > Here is the best machine design I could find that really demonstrates > the issue: > https://www.youtube.com/watch?v=L_yemjfgkE0
Amazing what was done with purely mechanical methods before being replaced with CNC. Neat to see how rifling cutting a grove at a time was automated before single pass 'button' cutting was invented. I'd have the cutting slide just run straight and put the barrel in a computer controlled rotator to both index and control the twist of the rifling. That would make it a fairly simple task to cut any twist including gain twist which always has to be cut, can't be hammer forged on a mandrel. The cutting bit advance control could also be operated by a stepper. Those two changes, put under computer control, would drastically simplify the construction of the rest of the machine. Instead of the crank to run the cutter back and forth you could use a motor driving a ballscrew. With a rotary encoder on that and the barrel indexer/rotator you'd have complete CNC rifling with infinitely adjustable twist and length of stroke. Something else I'd try is backing the bottom of the cutter bar with a half round of UHMW. That would make it slide easy in the barrel and wouldn't make any lengthwise scratches. As for the motor turning the barrel, to get fine, step-free positioning there are a few ways to do it. Got $ to spend? Try a direct drive with a hollow shaft servo motor. Not so much $? A double-enveloping, high ratio worm gear set driven by a fast motor, with the encoder mounted to directly read the barrel position. Well, that might not be so "inexpensive" but compared to a hollow shaft servo with a hole large enough to pass a rifle barrel... Then there's ye olde cogged pulleys and toothed belts. Use two belts off both ends of a double shaft stepper just for added strength of doubling up on belts and balancing pressure on the motor bearings. Whatever is used to rotate the barrel it must have enough torque at very slow speeds to keep the cutting pressure from moving it from the movement the control commands. No problem with the worm drive since those can't be back-driven unless specially designed for it. Like so many things, how precise do you want it? How much money do you have or how good are you at scrounging for bargains on precision equipment? Is this for competition grade tack driving guns or for mass produced everyday shooters? --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com ------------------------------------------------------------------------------ Slashdot TV. Video for Nerds. Stuff that matters. http://tv.slashdot.org/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
