On Wednesday 21 May 2014 01:59:34 Kirk Wallace did opine And Gene did reply: > On 05/20/2014 08:39 PM, Gene Heskett wrote: > > Greetings docs maintainers; > > > > I found this after noon that there is a large interaction between the > > driveline value, and the J and K values. > > My understanding from studying the G76 source is that the J value is > intended to be depth of cut for the first pass. But the first pass is > based on I, and I is based on the drive line location, which is based > on the initial tool location just before G76 is invoked. I is intended > to be the tool clearance, or space between the initial tool position > and the surface of the workpiece. This assumes that the workpiece has > already been turned down to the thread's major diameter in the case of > an external thread. The position the tool is in is sort of a data > input defining one end of the drive line and therefore the thread > diameters and thread length. So if you find the major diameter of the > thread in question and add I, that will be the X value the tool needs > to be in before starting G76. Also note that I, J and K follow the > setting of the G7 diameter or G8 radius mode. Figure out the distance > you want for the tool clearance, for G7 enter it for I, for G8 double > it and enter for I. The same goes for J and K, even though none of > theses values correspond to any real diameters. If you happen to set J > equal to K, G76 should take one cut with a depth of cut equal to J, > except I believe setting J equal to K will throw an error so make K > just a tiny bit bigger. > > After G76 cuts J, the next depth of cut is J multiplied with a > digression factor which makes the depth of cut smaller for each pass. > Passes are run until just before reaching K. At this point K is used > for the final pass and any spring passes. So the last pass ends up at > the initial tool position, plus I and K. R sets the behavior of the > digression factor, with 2 giving the chip produced on each pass the > same cross sectional area, or close to the same chip load. Which is > not the same as equal depth of cut in this case. > > The number of passes needed will depend on J, and the rate of > digression (R) on J. The source code looks like this: > > depth = full_dia_depth + cut_increment * pow(++pass, 1.0/digression); > > Making J as large as you can really reduces the number of passes. > Changing the value of I should not have any affect on the number of > passes.
I think that is all assuming a stiff tool and a stiff machine. In this case I am boring threads about 19.5mm in diameter, using a rubber machine and a rubber boring bar, so its almost a necessity that I am working with cutting forces that aren't much more than scraping, with a thread shaped tool. And using an advance angle of 30.1 degrees. 30 and under chatters to beat hell, and even this needs a pair of vice grips on the tool shank, raising the squeak to several kilohertz. So most of my threads are 40 to 50 pass, 5 to 10 minutes runtime affairs, to get a decent looking thread. My mill is laid up, the table is out at a local machine shop, getting about 90 thou deeper a screw clearance groove in the bottom, making room for a nut holder that might be 21.5mm tall when I am finished with it. Present clearance for the factory nut is around 19.15mm, these ball nuts are 19.07mm, and it needs enough steel wrapped around it to maintain the integrity. I will have to put the mill back together long enough to carve a small pocket on one side for the ball return tube. That will destroy about 9mm of the threads I just cut yesterday, and will require that once the ball nut retainer disk has been screwed in and torqued up against the felt, a dollop of loctite's Goop to seal out the dirt where the threads are missing. There is room in the depth of this pocket of this nut holder for a disk cut from one of my old Woolrich western hats, with a 1/4" center hole, forced over the screw on each side of the nut, that will serve as a swarf cleaner and lubricating wiper, with the lube being fed in by some weed eater fuel line hooked to a small manifold with a flip top oil cover, with an elevation above the nuts of perhaps 4". Same felt wiper idea is already done for the Y screw but it hasn't been cut to length yet. As there are no home/limit switches on the mill, I need to survey its .hal file and see if I left a pin for shared limits, because I need to figure out a means of absolute shutdown in order to stop it from unscrewing itself from the nut, treating them as a limit switch I can move away from if its tripped. As its setup 4 axis plus probe, + pwm & reverse for the spindle, (thats 10 outputs) I'm not entirely sure I have any port pins left. Seems like I ought to be able to lay the flat spring lever of a microswitch alongside the screw and detect when the end of it is within about 3mm of the nut holder. Anybody have a better idea for limit switch location? Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> US V Castleman, SCOTUS, Mar 2014 is grounds for Impeaching SCOTUS ------------------------------------------------------------------------------ "Accelerate Dev Cycles with Automated Cross-Browser Testing - For FREE Instantly run your Selenium tests across 300+ browser/OS combos. Get unparalleled scalability from the best Selenium testing platform available Simple to use. Nothing to install. Get started now for free." http://p.sf.net/sfu/SauceLabs _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
