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.Â* 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.Â* It will go
in one of the specialty tools drawers, but will probably not be used for
this project.Â* 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.Â* They were not
expensive.Â* No more than any other similar size carbide drill.Â* They are
three flute split point.Â* I don't remember that when I ordered them, but
I'll certainly give them a try.Â* If there is a web its so small I can't
see it with just my glasses on.Â* I may look at them under the magnifier
later.Â* I am certainly looking forward to seeing how they perform in the
test cuts.Â* Probably try just spot drilling and drilling first to see
how it comes out.Â* 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.Â* 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.Â* Most 1/16 drills
are to short to do the job, but I figured I'ld find some long enough if
I looked.Â* My plan is to drill a starter hole with a .0625 carbide stub
drill.Â* I have them on hand. As mentioned before I buy them from Precise
Bits.Â* Usually 4-10 at a time.Â* Then drill with a longer jobber drill.
The problem was I wasn't finding any long enough to do the job.Â* When I
searched for long 1/16 bits I came up with 6" aircraft bits.Â* Found MSC
stocked Hertel aircraft bits.Â* 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.Â* I started looking closer, and its
Cobalt, only has a 7/8 flute, and its split point for under $5.Â* I
bought a couple of them.Â* I can just cut it off to the length necessary
to do the job.Â* The part is literally a piece of aluminum flat bar with
a bunch of holes drilled through it edge wise.Â* If it doesn't work or I
break bits the cost won't be very high to try again.Â* This is a one off
part and if it takes me a couple tries I'll still make a dollar.Â* 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