3 Flute Split Point - More Deep Drilling

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.
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
Reply to
Bob La Londe
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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.
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
Reply to
Bob La Londe
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.
Reply to
Bob La Londe
The second piece with drill chuck looks worse than the third piece using the collet chuck. I think this may just be the limit of life for the tip on this drill in this application.
Reply to
Bob La Londe

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