On 17/10/2019 20:07, firstname.lastname@example.org wrote:
Fair enough and I understand that I was just thinking about things I
production gun drilling just thought it might be an option to try
sometime for some thing I make occasionally the require deep holes.
Well then give it a shot. If you can get a good deal on the drill
itself and don't push the drill it may work. Just be aware that the
drill needs an accurate hole to start the drill, either in the part or
a drill bushing. And you want enough oil flow to push the chips out of
the flute on the drill.
Sterling Gun Drills and Elodorado both supply rules of thumb for oil
pressure and flow.
As a point of reference, the oil pump motor on a deep hole machine is
usually comparable to the spindle HP. I've designed and built oil
systems as large as 30HP; I've seen large machines with 50-100HP
pumps. As Eric says, you need enough flow to keep the chips moving
thru a small passage. I'm sure you can fudge the recommended flow
quite a bit depending on the nature of the chips and how much you're
willing to fuss with clearing chip jams manually.
I bought enough stock so I can experiment a little, but I'm just going
just going to try carbide drills first. I ordered a long reach solid
carbide spotting drill, and a couple jobber length carbide twist drills.
After I ordered the drills it occurred to me I could spiral mill it with
a 1/4" end mill if I had periodic retracts to blast the chips out of the
hole. I've got some long reach 1/4 end mills. If its a little sloppy
the hole might be slightly over sized or if it flexes it might be
slightly undersized, but it will spiral interpolate straight. I could
just adjust for whatever I get after the first one, or chase the hole
with a drill bit afterwards.
Drilling will be faster, so I'll try that first. If I can get "close
enough" with carbide drills I'll keep the long reach end mill in mind
for some future even tougher drilling problem. I actually spiral
interpolate holes all the time on the mini high speed mills for screw
and pin holes. Don't know why I didn't think of it sooner. Its
something I already do.
Not to be insulting or trying to start an argument but you seem to be
going at the problem arse backward. The best method of determining how
to do something is in the pencil and paper stages. As you are
"designing" this "thing" the major thought in your mind should be,
"how am I going to do this".
Granted you have already started on this project and now you have to
solve your problem.... but next time :-)
I'd like to thank you for all the insight and assistance you offered in
your post. Here it comes. The thanks will be proportionate of course.
I'm going to do it in the next sentence. _____ ___ ____ ____. Oh, well
maybe next time.
I already made the part twice. I just was looking for better options.
Several people suggested things. Some I'd already thought of. Sorry
you didn't have anything to add.
One of the problems with setups like your two bosses is that the
flutes of the drill don't provide the best location in the short,
close boss while drilling the farther boss. So a drill with flutes
shorter than the space between the bosses works well in your type of
situation because there will be a solid drill shank locating in the
first drilled boss.
You may be able to use a type of drill called an "aircraft
extension" drill. You could also make up your own short flute length
drill. This can be done by turning down the shank of a 1/4 stub length
split point drill and then soldering it into a piece of straight 1/4
rod. I use drill rod in situations like this becasue it is very
straight. Turning down the shank for about a 1 inch length would be
more than enough for soft solder to have enough grip to prevent the
drill bit from letting go.
Another option, and this may be useful for the long hole, is to
drill with the spot drill deep enough that the whole 1/4 diameter of
the spot drill enters the material for about 3/8 inch. Then drill
undersize all the way through with a .letter B or C drill. Then finish
with a 1/4 diameter "D" bit. With a D bit you may need to peck but
probably not because the hole is a through hole and not much material
is being removed. And D bits can be used to make very straight holes.
Might I suggest trying a split-point drill. Solid carbide if
you can afford it, otherwise at least a cobalt steel one.
Try going a bit undersized, and then following up with a
chucking reamer for your 1/4" size. I think that you can do it from a
If possible, add a bushing to support the drill bit right where
it enters the hinge part. That, plus the lack of a chisel point, will
likely reduce the wandering of the hole.
To keep the other two holes in line, another bushing between the
two ears, hardened steel after drilling to just under 1/4" and reaming
to size. Maybe case-harden the bushing, with the Kasenit packed into
the hole during the heat cycle.
For holding it -- I might consider clamping it to a angle plate
on a faceplate in a lathe, so the hole rotates instead of the bit. (This
tends to minimize the wandering a little, too.)
Normally, I would suggest a screw-machine length bit, instead of
a jobber's length bit, but I think that you may need an over-length bit
to get the full reach.
O.K. Flute length on a 1/4" split point drill that I have in my
index (1/4", 3/8" and 1/2" are split point, along with a few tap drill
sizes -- the rest are the standard chisel point. If you short-chuck it
for the last bit of the hole, and back it out frequently to clear chips,
I think that you could manage it. Keep it fully chucked until just
before the chuck touches, then loosen the chuck, extend the bit enough
and re-tighten the chuck to drill on through. I know that you can get
6" long and 12" long aircraft drills, but wandering would be more of a
problem with them, so if you can keep it to a single jobber's length
split point cobalt steel bit I think that you can do it. (Hmm ...
perhaps an adaptor a bit larger in diameter, and a flat for a setscrew
ground on the side of the shank and you could do it with a single
Oh -- you are talking about the two holes, not the single longer
hole. A jig with a bushing above the first boss, and a 2" long bushing
between them -- all as one piece to keep the bushing holes aligned.
Case harden as above.
Have you ever used a split point drill bit? A lot better at
avoiding wandering when starting, and likely so also down in the hole.
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