Newbie's hole question

[eaglezsoar]

I have an X2 mini-mill and a piece of aluminum 4"L x 4"W x 2" thick.
I need to make a 3/4" hole in the center of the piece with the hole
going completely through the 4" dimension. Question: What is the
best tool to use to make such a hole? A 3/4" drill bit. A boring bar
or something else? I hate to ask such a question but what seems
simple to most of you is not so simple to me.

[juergenwt]

eaglezsoar - I don.t know your mill but depending on the tolerance required I would 1. Center drill. 2 pre- drill 1/4". 3. follow with a 47/64 drill. 4. Ream 3/4.
If you have a wide tol. use a 1/4, 1/2 and a 3/4 drill.

[eaglezsoar]

Originally Posted by juergenwt eaglezsoar - I don.t know your mill but depending on the tolerance required I would 1. Center drill. 2 pre- drill 1/4". 3. follow with a 47/64 drill. 4. Ream 3/4. If you have a wide tol. use a 1/4, 1/2 and a 3/4 drill.

Thanks for your answer. I gather then that the idea is not to drill it in one
step, but use a series of progressive steps.
This leads to a question about reamers, I have seen chucking reamers, hand
reamers, and reamers that have a cutout in the shank that looks like it would
fit into a mill. Are most reaming operations done by hand or with a mill?
I have also found some IMCO Solid Carbide AccuHole Drill router bits on Ebay at
great prices, would these work in a mill? Thanks for taking the time to teach
someone who is just starting out.

[RICHARD ZASTROW]

Chucking reamers are made for just that, holding in a drill chuck or collets etc. A hand reamer is for manually hand finishing a hole to size.

One type of reamer that has a Weldon type flat on the shank is the seldom used anymore Jig Borer Reamer. These are not end mills but are end cutting (plunging) reamers. They are designed to accurately ream a hole in the position the Jig Boring machine places it, rather than follow an existing (pre-drilled) hole. When properly applied, they're as good as boring a hole to size.

Hope that helps.

Dick Z

[ALLtra Mach]

There are some secrets to deep hole drilling, and at over 5 times the diameter deep, that is deep hole drilling.
The biggest problem you face is keeping the hole straight, the deeper you drill the more a hole wants to lead off, or rather the more pronounced lead off becomes.
You need to look at what causes lead off.
#1-the drill starting at an angle, either because the drill was not held parallel to the part or because it "walked" off center when it started. So step 1 is making sure your workpiece is held parallel to the spindle. If you are using a standard drill, you will definitely want to center drill the hole.
#2 - An improperly sharpened drill will cause one side to load heavier than the other, the uneven load causing the drill to pull off center. Solution, make sure your drill is properly sharpened and of high quality, the longer the drill, the more important this becomes!
#3- Chip pack, causes inadequate cooling as well as again a "cutting force" issue. Unload the pack often and use plenty of coolant/oil.
#4 - Improper feed and or speed, get your operating parameters correct!

Assuming a good tight machine and good tools, making a deep hole straight is not a problem. The start is crucial, get started crooked and the deeper you go the worse it gets!

How many holes do you need and how accurate? Just one - fractional tolerance, just drill it, take your time and don't push it! A few holes with high tolerance, now you would want to look at a jig bore or jig reamer, a good solid tool to finish the hole with.
High production on alot of holes - solid body Inserted drill, your choice of quality tooling manufacturer, I'd call Komet!

[eaglezsoar]

Thanks, ALLtra Mach. Your reply took awhile to create and I appreciate the
tips. That's one of the many nice things about this forum, people like you
who take the time to help others. I think I will tram the mill before I attempt
to drill those holes. A lot of good information presented to me just to drill a
hole!

[ALLtra Mach]

One thing I figured out long ago about holemaking.
You mill some parts, you tap some parts, you bore some parts, but almost every part a machinist touches has a hole in it! There are some exceptions to that, but not many!