On Saturday 13 January 2018 13:17:19 [email protected] wrote: > Gene, > > > On Jan 13, 2018, at 8:18 AM, Gene Heskett <[email protected]> > > wrote: > > > > This is confusing Tom. From the video I'd assume the enco is a slant > > bed machine. So this s/b equ to a regular lathe, with the z axis > > rotated some arbitrary, might not be 90 degrees CCW as viewed from > > the tailstock end. All G76 values are positive except for I, which > > determines the internal/external toolpath. I s/b positive for an > > internal thread. From the video, the g76 toolpath looks correct IF > > the spindle is turning toward you, or CCW viewed from the tailstock. > > I cannot, from the video, determine which way the spindle is > > turning, but it looks like the tool tooth "top" is faceing us, which > > implies the spindle s/b turning CCW, normal IOW. This would cut the > > thread in the lower wall of the hole, and which looks correct to me, > > Your observations are correct. This is a slant bed lathe. Z is > negative to the left (toward spindle from tailstock). X is positive > up. In the video the spindle is turning CCW as viewed from the > tailstock. The (cutting) face of the tool is toward the camera. > > Yes, as you say, it would cut the thread in the lower wall of the > hole. BUT this is because my G76 is set to external thread (that is, > I had a -I value), it “thinks” it is cutting an external thread on the > outer edge of a diameter… > > > Thats not an external path to me, its proper motions for an internal > > thread. A positive I IOW. > > Except that it wasn’t! I am not near the machine or I would show you > a proper G76 with “I” being positive. It moves deeper into the thread > by moving up (positive X direction as it should) and if I turn my tool > around (pointing up) that would work. Also, when I run with positive > “I” it comes out of the work at the end of the cycle - unlike what you > see here where it moves up rather than out. > > > Still confused. If the top of the tool is faceing the camera, the > > path looks correct, but check your tools clearance when at the drive > > line, and fully into the hole. I broke a chip just this week because > > I used too much I. The back of the tool shank hit the back of the > > hole, flexing it so the chip dug in and snapped. Tool had a tapered > > shank, and I wound up turning the toolpost about 3 degrees CW to > > gain clearance. Thread worked fine. > > Yes, I will keep that in mind as well. When/if we do this we will > have very little clearance. Tool is .490 diameter and the Max Minor > Diameter is specified as 0.5062. So we need to drill/bore it to > 0.5062 dia and then will have only 0.016 of clearance, yikes!
Thats not a yikes! Thats a broken tool, if I is more than a couple thou. I've been known to grind some off the back of the tool just to get adequate clearance. A lot easier to do with brazed boreing bars resharpened to the correct profile. With the flat top of the acme thread, you may need an H to make it use several spring passes. > By the way, we don’t have much travel in the negative X direction on > this lathe (below spindle center). With the tool geometry I think it > it enough to get the thread depth we need using the external G76 we > are talking about, but I haven’t verified that yet. If it isn’t this > discussion is moot and probably the right thing to do would be to > grind a flat on the other side and turn the tool upside down, But > again. I am wondering if there is a way I am not seeing to do it. > > -Tom I think I see, in which case if you don't have the working room below center, you must turn the tool point up, change the sign of the I, which will then cut the correct internal thread in the upper internal surface of the hole. I have to assume the carriage can absorb the lifting that implies. As in adjustable tapered gibs. Probably on both front and rear edges. I don't have that luxury on my Sheldon, when I did the cnc, the gibs were designed only as catchers, so both front and rear of the carriage can actually be lifted off the bed by 10 to 20 thou. And its much easier to do on the front v-way w/o that 50 lbs of gears and clutches that was the apron I removed. So a hard push against a dull tool can actually make it climb the front v-way, and of course cuts smaller when it does. ======== I did get the mt5-5c adapter running pretty true, about half a thou of runout in the bore of an ER-40 adapter plugged into it, but the nut on the ER-40 is absolute trash. You can see it wobbling, and it pulls the nose of a collet sideways so bad the runout is .0045" at the front of a collet. And I haven't a clue how to polish that back out of its off-centered cone in the nut. Chinese crap. But I've so much (>$200) in the whole kit, I've got to throw even more money at another nut. 50mm x1.5 threads. Even the half spanner that came with it is way small. But that isn't your problem of course, I'm just crying in my nightly bottle of Miller64. ;-) Sigh, and good luck if that hole is that tight on wiggle room. There is litterally no room for mistakes. I also have zero experience with cutting acme's. Std 60 degree, and square are all I can claim on my resume. 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> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
