I just finished a job where I drilled 700 holes .468 diameter 1.600 long in 4340. I used one drill that had already been used at least a little. The drill was a .468 split point stub length cobalt HSS drill. So this tool drilled through 93 feet of material removing 61 cubic inches of 4340 in the process. I'm pretty impressed. I ran the drill at 650 RPM at .006 IPR feed. Actually the drill fed while the part spun. The drill is still in good enough shape to run at least another
And the drill was made by ...........................? And bought from......................?
I recently bought an annular cutter off ebay. Due to circumstances beyond my control, I have not used it for real work. But I think it will be the bees knees for drilling largish holes.
Dan
Whoops! Precision Twist Drill. Available from all the usual suspects.
" snipped-for-privacy@krl.org" fired this volley in news: snipped-for-privacy@googlegroups.com:
When did 0.468" become a "largish" hole? What we want to know is the make and model of the drill bit. That's an extraordinarily good life for a 'common' twist drill... split point or not.
Lloyd
snipped-for-privacy@whidbey.com fired this volley in news: snipped-for-privacy@4ax.com:
Thanks. Will investigate (meaning will buy some, and see what works!)
Lloyd
.458 is not a largish hole. But the annular cutter I bought is a 20 mm drill. Not all that large, but big enough that I would drill a pilot hole if using a regular drill.
Dan
Dry? coolant? cutting oil?
" snipped-for-privacy@krl.org" fired this volley in news: snipped-for-privacy@googlegroups.com:
I might 'pip' the hole to make sure it started without any vibrations, but pilot? (I assume you mean full-depth) With THAT small of a bit?
If my machines can't hold center better than that, I'd better quit or rebuild their spindles!
Lloyd
My son was working at a boat builder and they were having a terrible time drilling a 1 inch hole through a 3/4 inch thick 304SS plate. He suggested that they let me try. So I got out a small drill, 5/16 I think, and drilled through pretty fast. Then I put the 1 inch drill in the machine and slowed it way down. My son was surprised about the low RPM of the drill. I told him it was the correct RPM. I then proceeded to drill through the plate with a heavy feed. So the whole thing took about 5 minutes. Drilling a hole to provide clearance for the web of a larger drill can really speed things up. On the other hand it is not always necessary. I have a repeat job where I drill a 7/8 hole 2 inches deep in 6061 aluminum in 1.6 seconds. The part is spinning 3000 RPM and the drill is fed at .016 IPR. Well, really, the CNC lathe is doing the drilling. The spade drill I use has high pressure coolant through. If someone turns off the coolant for some reason and presses the start button the spade drill and part are destroyed. I know this because an employee twice forgot to turn the coolant back on after turning it off for some reason. GRRR. Eric
snipped-for-privacy@whidbey.com fired this volley in news: snipped-for-privacy@4ax.com:
Ayup, and yes.
And a twist drill can do that all day long, too, so long as the spindle is rigid and the coolant is keep on.
Lloyd
The pilot hole is not to make sure that the machines hold the center . It is to eliminate the pressure needed to have a decent feed rate. On staines s as Eric describes it in his message, it makes a huge difference with norm al hobby grade drill presses. If you do not do that , you end up work hard ening the stainless and or stalling the drill press.
Sure if I buy an industrial grade drill press, it is not necessary. But th is lets me use a cheap ( less than $600 ) drill press. I just can not just ify spending more for a drill press since I do not do production work.
Dan
Dan
" snipped-for-privacy@krl.org" fired this volley in news: snipped-for-privacy@googlegroups.com:
Yeah... I guess my Solberga (with power down-feed) would be overkill for that, huh?
Lloyd
I wish you lived close enough that I could visit when I want to drill big holes.
Dan
Greetings Dan, If I was drilling the same hole in one of the CNC machines with a twist drill I would still drill a pilot hole just because it would put the hole in faster. With a coolant through spade drill and the 15 HP CNC lathe I would probably drill a 1 inch hole in one shot. But I did a job where I had to put a large hole in several 17-4 PH SS parts and even though I used a coolant through spade drill the hole was so large that I drilled a pilot hole. I was able to then nearly triple the spade drill feed compared to using the spade drill to remove all the material. Eric
If we look at the surface being drilled - the center of the drill the cross point helps on the drill or spade - the surface speed is all but zero and the drill is pushing itself through. Further out there is cutting because surface speed is reasonable.
Mart> >
It is to eliminate the pressure needed to have a decent feed rate.
On stainess as Eric describes it in his message, it makes a huge
difference with normal hobby grade drill presses. If you do not do that ,
you end up work hardening the stainless and or stalling the drill press.
ut this lets me use a cheap ( less than $600 ) drill press.
I just can not justify spending more for a drill press since I do not do production work.
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