Mounting items to schedule 40 or schedule 80 pipe

[pony]

I am trying to mount things on the some H posts and corner posts I constructed out of schedule 40 and in some cases schedule 80 round pipe.
I have been using self tapping metals screws. I find that about 80% will break off in the hole when they are almost all the way in. I have tried pre-drilling the hole with a regular drill bit, but the hole is either two big to allow the screw to bite, or so small that the screw breaks anyway.
Do I need better quality screws, or is the screw just not up to this. The screws are fairly small, in one case I only want to hang a keypad for an electric gate.
Can one of you fine folks share the secret.
These are the type of screws I have been buying.

[SignTorch Vector Art]

They make some with finer threads that don't bind as bad. I usually pre-drill (and woller the bit around) in thicker metals like that.

[redneckgateart]

If you're having problems with the self-tappers, you could always drill/tap the holes and use regular machine screws...all you need is the right size drill bit and a tap.

[ronsii]

Have you thought about rivets? or do these need to be removable?

Also they do make tougher selftappers, like the ones used to fasten decking to trailers but they cost quite a bit more.

[pony]

All very good ideas.
I don't have a tap, but I do have a rivet gun. Drilling a small hole and using a rivet sounds like a good idea. Hopefully it will not break the plastic backing of the keypad

[ronsii]

Always put as big of a washer as you can find/fit when using rivets with plastic

[redneckgateart]

A tap is only a couple of bucks at the hardware store, so it's not a big deal. Rivets are fine too. The deciding factor would be whether or not you wanted the item to be easily removed....by you or the customer. Screws are easily removed and replaced...all you need is a screwdriver. Rivets would require a drill, bit, rivet gun and new rivets. In the case of a wireless keypad, a client might not want to deal with that everytime he/she needed to change the batteries....so it just depends on your situation.

[pony]

I bought a set of taps and dies. Having watched a few instructional videos on YouTube just now, I think it should be fairly easy to accomplish tapping a hole.

Thanks!

[WSS]

For really fast tapping use two cordless drills. One for the tap drill and the second for the tap. Drill as you normally would maybe use a drop of "cool tool" and then tap on slow speed (two drops of cool tool) and don't wiggle, straight in and straight out. It goes fast. If you have air, blow off the tap each hole or just wipe it with bare hands and then wipe your hands on the front of your shirt (it makes it look like you have been working). A "gun tap" or a "spiral tap" are best if you can go thru. Stay away from "bottom taps". If it is a bottom/blind hole, use the spiral for a few threads then switch to the bottom tap.

Hope it helps!

WSS

[jmsrbrt]

I use these self tappers all the time, and what I do is drive the screw into your metal a little at a time then back it out, then drive it a little deeper, then back it out and so on. I might break one head off every 20-30 or so. Bob.

[ronsii]

X2 on what WSS said, it is the quickest way to go with threading holes but I would add one thing if your cordless drill has a torque setting set it pretty low to start with especially for small taps

[redneckgateart]

And make sure you use the right size tap drill! Tap drill charts are easy enough to find but you can get close with a simple formula (for a 75% , 60 degree thread).... just subtract one pitch length from the major diameter.
For example :
For a M6 x 1 , 6mm -1mm = 5mm tap drill
For a 3/8-16 , 0.375 - 0.0625 = 0.3125 (or 5/16) tap drill