Drilling/tapping threads: advice requested

[keevon]

I'm interested in drilling and tapping a hole in a solid 8mm diameter aluminum rod for a 4mm bolt. Since I've never done this before, I have a few questions:

1) What size pilot hole should I drill?
2) What type of tap should I use?
3) How do I determine thread pitch?
4) Can this be accomplished with a hand drill, or do I need a drill press?

Thanks in advance, and pardon my ignorance!

[Mikej]

I'm interested in drilling and tapping a hole in a solid 8mm diameter aluminum rod for a 4mm bolt. Since I've never done this before, I have a few questions:

1) What size pilot hole should I drill?
2) What type of tap should I use?
3) How do I determine thread pitch?
4) Can this be accomplished with a hand drill, or do I need a drill press?

Thanks in advance, and pardon my ignorance!

By 4mm bolt do you mean the actual outside diameter (o.d.) or is that the size of the allen head tool? Drill press, for sure, especially of it is under force or on a critical component. Offsetting could compromise the integrity. Thread pitch is best matched by bringing bolt to place where you buy the tap. Metric may be a bit more difficult to find in the Big Box stores, so consider an auto parts store if HD doesn't have it.

[Jaq]

I'm interested in drilling and tapping a hole in a solid 8mm diameter aluminum rod for a 4mm bolt.

1) What size pilot hole should I drill?
2) What type of tap should I use?
3) How do I determine thread pitch?
4) Can this be accomplished with a hand drill, or do I need a drill press?

Thanks in advance, and pardon my ignorance!

http://www.wikihow.com/Use-a-Tap

http://www.efunda.com/designstandards/screws/screwm_coarse.cfm

4 mm machine screws are pretty much only coarse (.7 pitch) thread, so pitch selection shouldn't be an issue.

You could do it with a hand-drill, but a drill press is better & more precise. If you use a hand-drill, make sure you use a punch to start a tiny pilot hole so that the drill-bit doesn't skip across the surface. Drilling into the side of a round rod is especially difficult.

[keevon]

The bolt uses a 4mm allen wrench. I'll have to verify the thread diameter... oops!

It's for an adjustable-height rear rack: Axiom Journey adjustable (http://www.axiomgear.com/img/prod/journey-adjustable-2429-2.jpg)

[JLP]

never mind...

[Dave]

The thread should be a 5mm x .8mm, if the bolt takes a 4mm hex wrench.

Here's info on the tap drill sizes.

http://www.engineersedge.com/manufacturing/metric-iso-tap-drill-chart.htm

You should be able to buy a kit with both the tap and the required drill bit.

[Peter P.]

1. 1/8" pilot hole.

2. The type of tap depends on the type of hole. If the hole goes completely through the 8mm rod, use a PLUG tap. If the hole has a blind bottom, you will also need a BOTTOMING tap. For the blind hole, you will first cut the threads with the plug tap, then repeat with the bottoming tap. The difference is the plug tap makes it easier to start cutting threads and ensures the threads with start in straight. The bottoming tap ensures there will be threads right to the bottom of the hole, but they're more fussy when starting to tap the threads.

3. You will need a thread pitch gauge to determine thread pitch. Alternatively, take the bolt you're going to use to the store you'll buy the taps from and ask them to match the taps to the threads. Or just take your bolt to a good hardware store such as True Value and lay the threads of your bolt against the bolts they have in stock. If they mesh completely along their length, the read the thread pitch from the store's packaging. I show 2 thread pitches for 4mm bolts; 0.70 and 0.75mm.

4. Some large hardware stores sell gadgets/drill guides the permit a hand drill to function as a drill press. Depending on how straight you need the hole to be, you can get away with a hand drill. Practice first on some scrap pieces to get an idea how things go.

[cachagua]

*Especially* that last. Make a few mistakes first on scrap pieces that don't matter. Always a good tactic...