small hole drilling & tapping

[dneisler]

I have been working hard on a peice made from 1/8" alum and I need to drill and tap 4 holes. The thread being 3mm.

What process to use, mill, or drill?
What size bit?
2 or 4 flute? Does it really matter?

I have never done this before so....

[mxtras]

No biggie.

The tap drill for an M-3 X.5 (standard thread) is a 2.5mm drill. I would just use a sharp, standard 2.5mm drill (which will likely drill a hole that's about 2.65 or so) and I would use a three flute, spiral flute tap. The point angle for aluminum is 100 degrees but a standard drill will work beautifully. Start the tap square, use tapping fluid and smooth motion all the way through. If you are really concerned with perfection, drill a little undersize then ream the hole but that's a bit over the top and is not usually necessary below maybe 18mm or 20mm threads.

Everything mentioned can be purchased just about anywhere - MSC is the place I usually get this kind of stuff from. Plus they sell Titex taps which I have used for many years. They also sell Balax which I think is pretty good stuff, too.

Scott

[One of Many]

A couple of other issues you could be concerned with.

Do the holes need located to match another part?

Can you transfer punch them? Scribe lines and lay them out for center punching?

If not, you might do them on the mill if you can measure close enough, then setup the mill to locate them properly in relation to the part and each other. Drill and tap each hole on location and square to the surface. Spot/center drilling for a start would be a good idea too. Small drills love to wander off center.

With small taps like this, it is advisable to use a chuck center(spring loaded or solid) in the back side of the tap handle to help support the tapping operation. Side loads will snap them taps like a toothpick.

You should cut the threads in 1/4-1/2 turns and back off to break that chip, then continue cutting the next 1/4-1/2 turn etc. You can grip the tap in the chuck also, and turn it by hand with the same sequence. It is harder to feel the tap torque limit this way, but with experience it can be done. With thin materials it may not be essential to back off, but it is a good habit to get in to. It adds to the feedback feel of the cutting progress before it locks up and cannot be backed out or just snaps off just for trying your patience. Power tapping is a lot more risky.

DC

[dneisler]

Thanks everyone, a little guidence goes a long way. Guess I need to by a 2.5mm drill and a 3.. tap. Any suggestions or part #'s? If this works, I will need to use it alot, as 3mm is a common size I will use.

[One of Many]

Most HSS cutting tools are decent quality. I'd avoid the carbon steel taps and drills if at all possible. There should be a local supplier in your area. Big box hardware stores sometimes carry both. Don't let the cheaper price of carbon junk get the best of you in the long run.

DC

[NC Cams]

Sears sells decent taps and are easy to get. Never broke one and asked them to replace it under their tool warranty but the worst they could say is "no".

HSS is plenty adequate for aluminum and light duty ferrous work. YOu would want better material for more serious steel or iron.

The imported stuff may be adequate but it won't be the quality of a premium non-imported item.

MSC sells mail order as does Grizzly, Emco and many others. I'd consider the imported stuff as "use and toss" quality as opposed to something you'd had down to your kids...

We use it (import or "world quality")for odd ball jobs that you HAVE to get done and don't expect to do again any time soon and don't have a fortune in the tooling budget.

Invest in a drill/tap chart. In hard to tap materials, if you go 0.002 to 0.005 oversize of recommended hole, it is much easier to tap (threads are still quite adeqate) and less chance of tap breakage (a nightmare regardles of the tap source).

[DareBee]

In thin material you really should be using roll form taps to get maximum strength out of your thread.
Remember rule of thumb, thread depth should be minimum 1.5X diameter.
In Aluminum this will be a weak thread, I do not know your application but just thought to let you know.
I good design for strength would be to use NutSerts for your thread.