Interpolating a blind hole for tapping

Not a biggie, and even I can do something like this, just curious about
opinions on strategies.
For an electrical fixture part.
5/8-27 nps thread -- try finding DAT on a drill chart!
About .5" of thread, will mill/drill hole .650 deep.
Basically the OD of the tap measures .630, and we will start with a .590
hole (.020 thread depth), and finagle from there, mating-wise, with the test
Because of the shitty set up (only 2pcs per cycle), I want to minimize tool
changes and dispense with a pilot drill, and drill (or helix) down with a
5/16 2-flute end mill. About 260 pcs.
I see two ways to do this:
"Drill" straight down in z close to the circumference, and do rough/finish
The Q here is: how many pecks in the rough? (no pecks in the finish, I
Helix down in rough, then a full depth finish pass.
The Q here: what Z per helix revolution?
Which will give the fastest hole? Suggested speeds/feeds?
I've already programmed in the helix method, as I have an idea this is
better for chip clearance (and ergo higher overall feed?), but I'll go with
any consensus here.
Reply to
Proctologically Violated©®
Loading thread data ...
Fastest? Minimize tool changes?
You could always try a "Thriller".
formatting link
Reply to
Plunge cutting (drilling) will give the fastest metal removal; but will probably create long stringy chips. Peck only often enough to break the chips into non-letal springy's. Additional pecks shouldn't be needed for this depth, and they only waste time.
Spiraling into the hole will be slow, and it makes the tool cut with its end and its sides at the same time. Funny results often come from that unless you have a VERY rigid tool and setup.
Why are you using only a 5/16" cutter? Why not 1/2", and then just circ-interp the .045 or so that's left per side after plunging? Much faster, much more rigid, and fewer chips (relative to flute size) in the hole while the tool is milling around. Mebbe plunge, then take one rough mill cut, then back the cutter out to allow coolant to flush most of the chips out of the hole, then back in for a finish pass to size.
Reply to
Kirk Gordon
Oh. Wait. You wanted a consensus. Here's what you'll likely have to choose from:
KG. Plunge it! Blue chips! Turn up the feedrate!!
BB. Use a thriller. If that doesn't work, try an action adventure, or maybe a romatic comedy.
Gunner. .590 caliber, full metal jacket, one shot. Aim carefully.
JB. You can't make a hole like that unless you have a seamless hybrid CAM system with inverted orthopedic surfacing thingies that I only I know how to use, sorta.
Cliff. Typical winger/fundy, looking for the thread specs in an establishment handbook instead of going with the popular consensus about how to end poverty and put holes in Rush Limbaugh.
Vinny. You can't get the metal out of the hole if you don't have a standard to tell you how much metal was in the hole in the first place. Newton was wrong. Einstein said so. And the theory of drilling is only a theory that's never been proven.
Cliff. Have you considered particle vaporization morphology? It's predicted by the latest string theory research.
formatting link
Cliff. Wingers want more holes. You're only helping the military industrial complex.
Cliff. Fundies don't drill holes. They just pray for them and then expect the rest of us to do their drilling for them.
Gunner. George Bush drilled more holes in Iraqi terrorists than you'll ever drill in aluminum.
formatting link
Cliff. Elephants don't have threaded holes.
JB. I think I just drilled a hole in my foot.
Good luck with the consensus.
Reply to
Kirk Gordon
Now THAT was everloving hilarious. This group could use more mood lightening posts, since many take themselves way to seriously.
Reply to
ROFLMAO!!!! Well done! Well done Indeed!!!!!
Reply to
Gunner Asch
Hey, handy shortcut - to find the approximate tap drill, subtract the reciprocal of the TPI (i.e., 1/27 = .037) from the major diameter (.625-.037=.588) This is a very close approximation for a 75% thread.
Reply to
More like jb:
I interpolated 4,000 holes using Siemens MLXIii, in under 1/2 hour, with .00000005 tolerance, at 1,001.457 ipm, at 100,873.2 rpm.
I'd show you how, but I just don't have the time to talk to pedestrian ignerami, because I am consulting with Siemens on their new version MXLXIiii, and they are flying me out tomorrow, on a private jet with a sauna.....
Reply to
Proctologically Violated©®
If this was Craigslist, that would certainly get my Best Of vote!
Reply to
Jon Anderson
Let the Record show that Kirk Gordon on or about Wed, 27 May 2009 00:06:36 -0400 did write/type or cause to appear in alt.machines.cnc the following:
But what about the lasers?
tschus pyotr
No cats were harmed in the making of this post, although several were annoyed. - pyotr filipivich We will drink no whiskey before its nine. It's eight fifty eight. Close enough!
Reply to
pyotr filipivich
Whether you drill, or helix in, you still should put a chamfer on the top of the hole BEFORE you thread it, so you don't fold any chips over into the threaded hole. Another tool change though for the chamfer. At least you'd be eliminating the drill tool change if you helix in.
Personally, I'd helix in with a minimum 3/8" dia. two flute end mill at 7,500 RPM (assuming this is alum.). Then thread mill. Thread mills aren't cheap though.
If you use a tap are you going to use a cut tap or a form tap? Cut taps will push the chips ahead of it and could cram them in the bottom of the blind hole and make picking them out a pita (paper clip with a hook on the end). It could also break the tap if you don't have sufficient clearance. A form tap will require a larger starting hole diameter or you could seize the tap.
Reply to
Didn't see the material, did you specify material?
Not much you can do with a quantity of 260 pcs. Running two parts at a time at best I see you saving maybe 30 seconds per part or nearly 2 hours over the run.
So how much is 2 hours worth to ya?
Option #1 Simi-Standard approach*
Tool #1 Drill Tool #2 Champher (champher hole) Tool #3 Mill (circle interpolate thd minor dia) Tool #4 Tap
You already stated; you didn't have the right sized drill you want to circle interpolate the thread minor You have a tap (assuming cut tap)
Option #2 End mill with tip ground to 90 degree included angle
Tool #1 drill/mill combo tool with 90 degree included angle. Drill to drill point depth. Pull up aprox .050" circle interpolate aprox .588 minor dia. Pull up hole edge circle interpolate thread champher.
Tool #2 Tap
Find a 1/2" carbide end mill, grind 90 degree included angle or buy a tool like this one;
formatting link

Option#3 A custom form. would most likely cost too much for a qty of 260 pcs.
Tool #1 Drill & champher (one op form tool, plunge in rapid out) Tool #2 Tap
-- Tom
formatting link
Reply to
Yeah, I scrapped the helixing in, in part because one suggestion here was .05 in Z per rev, which would have been like 13 revs, so a la KG and others, I just went in with a 2 fl 1/2 em.
I have noticed that for good accuracy, I often have to do multiple finish passes at the final finish dimension. Two finish passes, in this case, and even on the last pass I can still hear a bit of a buzz!
Also, I did two G4P500's (one after roughing, one after the last finish pass) to blast the hole clean before tapping.
So, three tools: I chamfered first, w/ .75 drill. Then interp, at the full .64 depth, then tap .5 deep. The finish diam pre-tap is .590. The stuff is coming out good. Will be tumbled.
Note, tho, that when interpolating with an em just slightly smaller than the finish diameter, the programmed speeds have to be fairly modest, mebbe even downright low, because they define the ipm for the tool path centerline, NOT the actual resulting *tangential* feed, which can be *much* greater.
Mebbe cadcam figgers this out in advance.
I actually am not running this job, I just set it up. All my buddy's KMB1 hurcos are on the fritz (those muthafuckas just seem to EAT $1300 circuit boards), his tapping heads gone/bustid, and he found out my fadal has rigid tapping..... :( And he has my truck.....
Thanks all.
Reply to
Proctologically Violated©®
Oh, perhaps an inneresting footnote:
This hole is on one face of an alum cylinder for a lighting fixture. The other face got two 1/8-27 nps holes, which call for an S tap drill.
You can't imagine how long it took to find an effing drill that would give the right effing diameter!! Holy shit... Almost wound up having to interpolate *that* hole! Or having to use a reamer.
Not the best 115 pc drill set, but wow, what variations. Some bits drilled on the money, others .010 over-size. .010!!
And then, when all was said and done, the tap itself seemed to be loose-ish for the sample male thread provided. Man, what an ordeal, that was "solved" by basically saying, Fugit, it's good enough....
Reply to
Proctologically Violated©®
Glad ya got her running!
Reply to
Thanks Kirk, I needed that ;)
Reply to

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.