On Monday 29 January 2018 09:19:01 John Kasunich wrote: > On Sat, Jan 27, 2018, at 12:43 AM, Gene Heskett wrote: > > As for the live centers, I guess I'll have to throw both what > > I have and bigger money out for a good one. These 2 $22 ones are > > sure junk. I wouldn't use them within 18" of the chuck, I've already > > had them make a well tightened workpiece walk in the chuck. At about > > 10" away. > > If your tailstock barrel is not aligned with the spindle, any center > (including a perfectly good one) is going to make work want to walk > out of the chuck. It will force the end of the part to rotate around > a point that is not on the spindle axis, and that means the part is > being rocked back and forth in the chuck once per revolution.
John, my quick, and likely dirty measurement method consists of chucking up something round, putting a suitable center drill into the 3/4" chuck, letting it walk to center and make a place to put the center into, backing away and swapping the chuck out for a center. Bring it back and see how close it is the the dimple. Rotate the center a 1/4 turn, wash rinse and repeat, each time seeing the offset has moved with the rotation of the center. Offsets with these 2 new centers, sourced from different vendors on fleabay, average around 30 thou. When I was working on the new barrel for old AT&T, I had to use a gentle touch, and because the cat head was made from std steel pipe, pulled seriously out of round by the tension of the brass bolts I used to grip the barrel, getting it round enough to run in the steadies was a chore. But I did get it good enough to cut the threads and do the chambering, most of the time with the tailstock out of the way because it was relatively easy to bring the steadies tips to the point it was not forcing a walk of the cat head. I get the impression the tailstock is going to need more shimming at the rear as I see the average offset with a worn dead in it, is above the spindle center of rotation by about 20 thou. And its worse with the live centers. Bed wear s/b in the other direction according to my thinking because the bed wear is worse a few inches from the chuck. There is also a just detectable rotation of the saddle, looking down from the top, amounting to about a half thou difference in the cut, depending of which direction the saddle is being pushed, at the tool tip. My impression of this lathe it that while the admittedly recent paint job is decent, its been thru a lathes version of hell in the past, perhaps a long time in the past. So I am working on the fixes as the itches occur. The current itch was the 3 jaw, visibly wobbling even after a 35 thou cleanup cut to get a clean face, done about 3 thou at a time. Finding the spindle was bent I'll have to admit, was discouraging. But about a 6 or 7 thou bore of the short MT5 brought that back to usable. Now I'm trying to make the chucks run true. The new 8" 4 jaw is doing well, but this 6.25" elderly Bison 3 jaw is being a problem, its nowhere near round, by several thou. And with a freshly cut faceplate, its face was running out several thou, so laying it on the mills table and turning it by hand to take some of the 4 thou diff in front to rear depth back out of it, should help, but I need to source at least 3 more mounting bolts and drill the backing plate for them, drilling the holes 15 to 20 thou bigger. I've already trimmed the register, but the bolts are such a close fit I still cannot center it. With the Missus fadeing, I have maybe 3 or 4 hours a day to play. Not complaining mind you, as its part of life when you've outlived all your enemies. ;-) A secondary problem is uneven wear in the spindle thrust bearing in front of the rear bearing cap, its causing a very slight, a thou, of end travel, that is not synchronous with the spindles rotation, more related to the rotation of the ball cage from what I can see. So after the chucks are running acceptably true, I'll consult the bearing sites and see if I can find a replacement, and while its out, put some powerflex belts in it as these are about shot. I understand that needs a helper to do. :( Thanks John. -- 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
