I need to tap some aluminum stock. So I went out and purchased one of these cheap tap and die sets.

http://www.harborfreight.com/21-pc-carbon-steel-sae-tap-and-die-set-61398.html

Never used a tap and die in my life. I would think that it would list some whre the drill size for the bit but it does not. The bit I want to use is simply marked 5/16"-18. What drill size would I use? 5/16"?

 

This chart might help:

 

This chart might help:

Thanks

So I need a 5/64" bit?

 

Thanks

So I need a 5/64" bit?

I don't get it? what it looks like is 5/16 - 18 is F? I'll go out to my tap set to see the chart.

kv

 

Interesting. My research says to use a 17/64" drill bit if you can't find an F sized bit. Quite a difference from 5/64"

 

My book is gone, thanks to my kid.

kv

 

Looking at the "Tap Drill Chart" section at the bottom, they recommend an "F" drill for a 5/16"-18 fastener. Then, looking up above at the "Decimal Equivalent Chart" section, an "F" drill measures 0.257", about halfway between 1/4" and 17/64".

I'd try the 17/64" bit first on a piece of scrap stock and make sure it's not too loose. If it is, try the 1/4" bit and make sure it's not too tight. If it is, I'd guess you'll just have to find an "F" bit.

 

This might be a better chart, I'll print this and put it in the case.

http://www.lincolnmachine.com/tap_drill_chart.html

kv

 

Unfortunately they do not include a tap set for each size, when tapping you need to use a taper tap first followed by a second and plug or bottoming tap, the latter is needed if the hole is blind and not a through hole.
If just thin material, a taper alone will work.
Don't expect too much for $10.00
BTW, for aluminum, use kerosene or WD-40 for a tapping lubricant.
Max.

 

Unfortunately they do not include a tap set for each size, when tapping you need to use a taper tap first followed by a second and plug or bottoming tap, the latter is needed if the hole is blind and not a through hole.
If just thin material, a taper alone will work.
Don't expect too much for $10.00
BTW, for aluminum, use kerosene or WD-40 for a tapping lubricant.
Max.

So I can't do it with what I have?

 

Yes, but with those taps it is a little harder to start the thread, sometimes a slightly larger hole will be a work-around.
If thin sheet, you may be OK, although with sheet you need a fine thread tap.
The one shown appear coarse thread.
Max.

 

I am trying to tap 3/4" aluminum btw.

 

Maybe I should explain what I am trying to do and I might get better ways to do it. I am trying to create a clamp jig for my cheap CNC machine.

I plan to have 2 rails that run the length of the X-axis.

I will make 2 clamps that will ride on the x-axis rails. I will likely also place a plate on this clamps that will hold down the PCB. I need to have a way to secure the clamps to the X-Axis rails but make the clamps adjustable along the rails. My plan was to drill holes all along the rails and move the clamps as needed. If there is a better way to hold down the clamps, I am open to suggestions.

 

3/4?
If it was 0.090, I would just wallow the hole with a 1/4 bit. What's the problem with 0.007 inches in aluminum?
At 3/4 inches deep, you might find a 1/4" hole fights you all the way down, and I just hate snapping off a tap in a hole.
You might get away with it if you clear the chips every three turns...and you might need the right drill bit.

 

One place that has some nice work holding devices and general hardware for CNC etc, it Misumi USA, the free Cat. is worth it just a s a reference and to get idea's from.
They have Toggle clamps that may work.
Max.

 

BTW aluminum is not really a good medium to continually use a threaded clamp in, the threads get stressed over time and start binding etc.
Max.

 

3/4?
If it was 0.090, I would just wallow the hole with a 1/4 bit. What's the problem with 0.007 inches in aluminum?
At 3/4 inches deep, you might find a 1/4" hole fights you all the way down, and I just hate snapping off a tap in a hole.
You might get away with it if you clear the chips every three turns...and you might need the right drill bit.

Won't go all the way. 1/2" at the most. They will be blind holes.

 

Here's a couple of worksheets that I put together a long time ago to help me with the tapping issues. Enjoy!

 

Won't go all the way. 1/2" at the most. They will be blind holes.

It can be a little more stressful on a shallow hole due to thread distortion over time, if tapping a blind hole you really need the set of three.
Max.

 

. If there is a better way to hold down the clamps, I am open to suggestions.

My siggestion is that you use additional rails, instead of tapped holes, to slide the clamps along the axis.