On Sunday 24 January 2016 04:18:27 Erik Christiansen wrote: > On 23.01.16 12:27, Gene Heskett wrote: > > Now we are getting more precise than we can drill with the typical > > drill bit, which usually drills oversize because the tip flats are > > un-avoidably off center. Even to a small extent for pricy carbide > > bits in the smaller sizes. Yesterdays finished tapping looked > > great, but I think I could have used the next larger #drill. Yeah, > > my back of a napkin said a .089 drill, kcalc says > > 0.0984251968503937008 for a 3mm.5 screw. > > > > No wonder I felt like I should peck it, the hole WAS too small. > > Ahem, it was WAAAY too small. ;-) > > Just a glance at the table upthread shows that 2.6mm (0.102") gives > 65% engagement, which is as much as I ever want on M3, to avoid > busting the tap. Even kcalc's 2.5mm (0.098") drill is too small, > giving a dangerous (to small taps) 82% engagement. > > And that .089 (2.26mm) gives an engagement of: > > E = (OD - Drill_Size)/2kp > = (3 - 2.26)/(2*0.613*.5) > = 120% > > That has the tap drilling as well as tapping! > You did superbly to not break the tap, Gene. > Considering it was an Irwin/Hansen tap, downright, I was holding my mouth dead right, miraculous.
But I had a hunch, and since I was doing it from the mdi command line, as I only had 2 hole to tap an inch apart, I started at 1mm increments, and was amazed once it actually started cutting, at how much debris there was on the tap when it withdrew. Since I was driving it all the way thru a 1/2" piece of what I think is 7076-T6, I only drove it an additional 3mm per plunge until the 12mm mark, then 1mm at a hit till I could see it coming out of the bottom, which, since the screw was going to enter from that side, meant I had to take it out of the vise and finish the bottom to full depth threads by hand using the drill chuck and its R8 rear end for grip. That was because the tip if I went any deeper would have been hitting the vise and that would have broken it sure as taxes. Sure was beautiful threads though. :) Dumbass here should have shimmed it up a 1/4" when I tightened the vise. More of that famous 20-05 hindsight many of us are so familiar with. :( > I tried a 2.5mm (0.098") drill for M3. Once. > Although the tap didn't break, I went straight out and bought a couple > of 2.6mm drills. Now I can tap M3 without my hair standing on end. I bought that Drill Hog set I posted a link to. Now all I have to do is train this old fart to put the bit back in the drill index when I'm done with it. But from the pix, those look well enough finished that they will be very easily identified should I forget. What I have surviving from a rot-gut whiskey chinese yard sale special bit set, which is about half of the numbered drills it had, might get stuff below 3/16 or so thrown in the rubbermaid bag holder in the corner. None of it was the size stated when mic'd across the flutes. I will not cry when they go out in the bottom of a contractors cleanup bag. I have several things on trucks, but I don't expect to see any of them tll the middle of the week. As for making circuit boards, I think this mill can do it IF we can get camview-emc and friends running on wheezy. Otherwise the cutest thing thats exactly what I'd need is the Taiwanese Sable 2015 for 700 some USD & shipping. All in needs is a computer and I have, stashed away in the basement, just waiting for such an occasion, 3 switch boxes that can switch a whole db25 parport. So I'd flip the two switches since I have some stuff on my 5i25's P2, and load the config to drive it. Stated accuracy with its antibacklash nuts on conventional screws is .02mm, and that will carve decent pcb's. Rinky-dink belt driven 10k rpm spindle, but that motor could be replaced eventually. The only thing that bothers me about the demo video on their site, is that it wasn't touched off right, so the tool was digging a good 10 thou into the glass. Thats pure hell on tools. Its a moving table design for X, and any Y tilt errors can probably be shimmed out. Good design for a small pcb router IMNSHO. Now if I could be assured of making enough PCB's to warrant buying it, but I cannot see enough sales to justify it. There was no response to the offer of pcb's for that charge pump board. And if I revert my registration to the precision pallet per each new board I make method, this one will do a better job than the little mill I made the first few boards on, such as the lathes encoder carrier. But with the little mill's 10 tpi acme drive Z screw anchored a foot plus above the head, Z drift with temperature is a major problem, cold morning to warm afternoon is about .009" downward, all I think from radiated heat from its spindle motor warming up the nearby screw as there has never been a spindle bearing heating problem. A small fan on the machine to help equalize the temps helps quite a bit. This G0704 OTOH, seems to drift upwards about .002" for a 40F rise in bearing temps. Which it will do at 2500 revs in 30 minutes. Thats opposite the little HF mill but not near as large a shift. I have some snow to move come daylight, so I'd better go hybernate the rest of the night. Thanks Erik > > ---------------------------------------------------------------------- >-------- Site24x7 APM Insight: Get Deep Visibility into Application > Performance APM + Mobile APM + RUM: Monitor 3 App instances at just > $35/Month Monitor end-to-end web transactions and take corrective > actions now Troubleshoot faster and improve end-user experience. > Signup Now! > http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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> ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
