On Saturday 09 September 2017 20:21:02 andy pugh wrote: > On 9 September 2017 at 08:50, Gene Heskett <ghesk...@shentel.net> wrote: > > So I am still puzzled by dialing in a -0.0500" cut, and only getting > > a .0324" radius change. > > My experience is that lathes are just like that. Some tools cut the > same at any chip load, some cut extra with a bigger cut, some cut less > with a bigger cut. > > In production you just dial in the last cut, with an one off, when you > really care, you have to creep up on it. (This is exactly the same > with a manual lathe, but you don't notice because manual lathes are > always used in incremental mode[1] > > [1] Which makes the dials on on Holbrook lovely, but pointless. They > have internal gearing so the the metric and imperial scales are both > always correct. If you turn the knob one turn then the carriage moves > 0.1", The imperial scale moves one turn, but the metric dial graduated > in 2.5mm per turn actually rotates 2.5 / 2.54 of turn.
I am a bunch closer tonight. I tightened up a 3/4" boring bar in a QC holder and locked it up tight this afternoon, and ran it up to the outside of the chuck. Then I put the 1" dial mag mounted to the back of the bed, stinger riding the rear of the chuck close to the centerline vertically. Then I parked my .0001" dial first on the right side of the saddle with its tip riding the top of the saddle above the v-way. So I could measure the crossfeed, referenced against the saddle with a linear scale still superglued to the crossfeed and the saddle. The absolute spindle deflection against the rear of the bed. And how far it lifted off the v-way when the push was greater than the saddle weight. Then I ran it in .0100" on the lcnc dro. Depending on the phase of the moon, the linear scale said between .0060 and .0075. The chuck had deflected to the rear from .0009 to .0013" And the saddle had climbed the v-way about .0040"! Now you'll recall the OEM apron, QCGB, and OEM screw are hanging on the front of a set of storage shelves, no longer weighing down the front of the saddle with that 100+ lbs of iron, and that my new apron plate is 1/2" solid ALU plate minus the machining I did to make room for a 4 lb nema 24 motor, switches and dials. It might, if the bolts are all pulled, weigh 10 or 12 lbs. The rear had a factory gib plate, steel, with intentional clearance, and apparently some accumulated error from the torque of the tapering kit it came with, and a heavy prybar can lift the saddle until it hits that gib plate, probably 15 to 20 thou. When I had the saddle off it had a steel tab under the left end, worn by at least 3/32", and again with 45 to 50 thou of clearance with that bolt tightened enough to stretch it some, and another tab on the right front intended to serve as a saddle lock. It had been tightened far enough to bend that bolt, rendering that much less useful. So I turned the saddle over and drilled and tapped it thru a 3/16" thick by 1" brass bar about an inch shorter than the saddle's front leg, putting about 9 or 10, 4mm cap screws in it. So that what it has for a front gib, with a slightly shorter piece of the same brass for a rear gib. But neither comes in contact with the bed to restrict its movement until the saddle has climbed the v-way quite a ways. That 90% reduction in apron weight now lets it climb much much easier when cutting forces vector toward my belly button. And thats 95% of the error right there. Sooooo, it looks like I'll have to make another set of tapered gibs. As soon as I can figure out how much room I actually have. That also means I'll have to get rid of the rest of the paint on the bottoms of the beds lips. I tried to clean it up some when I had it apart but Acetone seemed to not be the proper solvent. Nominally 3 gallons of that and 2 boxes of Scotts towels did not get rid of all of it. I have 2 ea 1/2"x1" x 12" brass bars I bought to make brass sliders for the steady, but the whatever is in it now worked well a month ago while working on the 6.5 barrel for AT&T, so I can make gibs out of that and some cold roll strap. Because its so long, I am tempted to design it in a saw tooth pattern with a steeper slope. After all, I do have an almost milling machine too. That will keep me out of the bars for this winter. But I'll likely have to make an annealing furnace, that toaster oven with its 450 degree limit takes days to take the work hardening out of this stuff, needs around 950F to do it right in a reasonable time frame from what I've read. If I can find an ir thermostat, I'd just short circuit the builtins & control it thru the pyrex door glass. But I can't find anything that goes to over 110C. An ntc would work but its own packaging would fall apart. A Weller WTCP used to have tips as high as 800F, but that tech is 60 years old now. One could stick the hand assembly thru a hole, leaveing the heater unpowered but use that curie temp setup to trigger some real heater power. But the problem is, I may have the last working model of that on the planet. OTOH I have a junk box with at least 2 of the platinum thermisters in it. I think one of those might be the ticket for the controller sensor. I'll have to look tomorrow once I get the honeydoo's caught up. Thats getting harder to do though. What do you guys think about the sawtooth pattern as a way to conserve vertical space of a really long taper. I sort of like it. Oh, and we should thank Don Williams, the "gentle giant" for all his beautiful music. He passed at 78 yo today. It will be a while before another voice like that is heard in our land. 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
