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Old December 1st 19, 12:30 AM posted to rec.crafts.metalworking
Bob La Londe[_7_] Bob La Londe[_7_] is offline
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Default 3 Flute Split Point - More Deep Drilling

On 11/28/2019 10:31 AM, Bob La Londe wrote:
On 10/22/2019 2:25 PM, Bob La Londe wrote:
More on long reach deep(ish) drilling.

My stock for the 50 link pieces arrives today, so I figured I better
review what I have on hand.* As I was reviewing the various tools I
have on hand or have picked up for this I noted that the gun drill is
indeed the type intended to be used with high pressure through oil.
It will go in one of the specialty tools drawers, but will probably
not be used for this project.* I don't have the time to setup a high
pressure system for it right now.

The carbide drills I picked up surprised me though.* They were not
expensive.* No more than any other similar size carbide drill.* They
are three flute split point.* I don't remember that when I ordered
them, but I'll certainly give them a try.* If there is a web its so
small I can't see it with just my glasses on.* I may look at them
under the magnifier later.* I am certainly looking forward to seeing
how they perform in the test cuts.* Probably try just spot drilling
and drilling first to see how it comes out.* I'll be making a holding
fixture so I can position them consistently.


For the linked hinge ear parts I used the three flute carbide drill to
start the holes, and a hand ground hand split point drill to finish with
the part clamped to a right angle plate.* I've finished about half of
the parts and I could not see a line or ledge in any of them so far.


As a side note: I have another deep drilling job for a different
application.* 1/16 all the way through a piece 1.8125 inches thick.
These do not have to be particularly straight, but they are relatively
close together and they can't collide with each other.* Most 1/16
drills are to short to do the job, but I figured I'ld find some long
enough if I looked.* My plan is to drill a starter hole with a .0625
carbide stub drill.* I have them on hand. As mentioned before I buy
them from Precise Bits.* Usually 4-10 at a time.* Then drill with a
longer jobber drill. The problem was I wasn't finding any long enough
to do the job.* When I searched for long 1/16 bits I came up with 6"
aircraft bits.* Found MSC stocked Hertel aircraft bits.* I have one
Hertel drill index and have found them to be decent, but there was no
way I wanted to have to push 6 inches of a 1/16 bit though the air.* I
started looking closer, and its Cobalt, only has a 7/8 flute, and its
split point for under $5.* I bought a couple of them.* I can just cut
it off to the length necessary to do the job.* The part is literally a
piece of aluminum flat bar with a bunch of holes drilled through it
edge wise.* If it doesn't work or I break bits the cost won't be very
high to try again.* This is a one off part and if it takes me a couple
tries I'll still make a dollar.* Maybe two.



Well, when I got down to it the deep drilling 1/16 holes was only 1.29
inches.* I drilled to 1.4 with a sacrificial backer.* Starting the hole
with a carbide stub drill worked well.* I drilled to .375 inches with
that.* I hope the carbide drill was good enough to drill pretty straight
being so short.* The I checked up one of those 6 inch long split point
aircraft extension drills.* I could easily see 1/2 diameter runout at
the tip in a collet.* That was pretty scary.* I unmounted it, and the
back of the drill seemed to be able to sing like a tuning fork.* I cut
it off just long enough to fully engage in the collet and leave 1.5
inches of stick out.* Then I spun it up to 5120 RPM and it still seemed
to be pretty bad.* Maybe not as bad as before, but atleast 1/3 diameter
wobbling around.* At 5120 RPM with that much stick out my FS software
told me I could plunge at 10 IPM and peck half a diameter for deep
drilling.* I was skeptical but as soon as it entered the hole made by
the carbide drill it settled in and did its job.* In fact a visual
inspection shows it drilled much straighter than I expected from such a
flimsy drill bit.* I guess it really does have a split point.* After
drill 80 holes I flipped the part over and compared the top and bottom.
It might not be perfect, but its good eno




The second part didn't look as good as the first. The holes had started
to drift a little. For the application it was ok as long as one didn't
break through into another. By the third part there were more than a
couple that broke through from one hole into another. I was pretty bummed.

I figured the runout I was seeing was just because of the length of the
drill stickout, but just for the heck of it I cut a fresh drill to the
right length for a small drill chuck I have with the same tool holder
base for the machine. I chucked up the tool holder, and spun the
machine up to full speed. Hardly any visible runout or blurring of the
tool tip at 5120 RPM. The reason I considered this is the 1/16 ER
collet was not tight on the drill when I slid it in. I measured a
couple of the drills and the shanks all measured 0.62(+). About what I
should expect. A properly sized collet should have held the drill, but
allowed it to move when pushed or puled before tightening down the
closer. It was loose in the collet even though the coollet was clearly
marked 1/16. I had to tighten the closer down almost a full turn from
first contact to get it to grip the drill.

The drill chuck is being used right now to drill the next 80 holes. I
guess I'll see how it comes out soon enough.

I also looked at the used drill under magnification. It looked like one
flute corner was very slightly rounded or chipped. Maybe the runout
caused it to wear unevenly, and maybe a couple hundred deep holes is
just to much for cobalt drill bit that size.

I threw the old drill and the collet in the trash.

I hope I can get this done, but in case I can't I did find some solid
carbide drills just long enough to do the job. I'll order them on
Monday if this job doesn't finish ok today.