Securing Aluminum to Aluminum

[webgeek]

This might sound like a really silly question but I've been wracking my brain for days to find the "perfect" answer. I'm using my CNC mill to make parts for a robot that I'll be using to compete at the robogames next year. The robot has been designed with many small parts in mind so it is highly modular and I can re-work the areas of the design that don't cut the mustard, so to speak.

To that end, I need to secure a lot of different pieces of aluminum together. Keep in mind the robot is quite small overall - or at least many of the parts are quite small. So, to my questions...

1) Are 2-56 cap head screws a good way to secure 1/8" aluminum plate to 1/4" plate edge on? IE: the face of the 1/8" attaches to the edge of the 1/4".
2) Is there a better way to do this but still keep it removable and machinable as many parts?
3) Will 2-56 effectively secure something to keep it sturdy? I've attached some CAD drawings I'm kicking around. All of those holes are generally assuming 2-56 screws. 4-40's seem too big to screw into 1/4" wide pieces.

Any advice from people who've done this would be greatly appreciated. I know it seems simple but I've never really tried to make a many part assembly and I don't want to cut a ton to find out I've got the wrong screws for the job and waste all that effort. Thanks!

Mike

[Geof]

Use 4-40, 1/4" wide is plenty wide enough to tap 4-40 on the centerline; get a 4-40 nut and compare it with the 1/4" aluminum.

Actually you could even use 6-32 for better strength, there will still be plenty of material between the thread and the sides of the 1/4" material.

[webgeek]

Good to know; 4-40 is a far more common size and I'd rather work with it. Just to confirm, I show the hole size to go with pre-tap 3/32" and the clearance hole is 1/8". That correct? And thanks much for the input - without having either 4-40 or 2-56 available it's a bit hard to know what I'm really working with. This really helps!

Mike

[aucran]

I agree with the other posters, 1/4" is plenty of room to get a 4-40 or M3 screw in.
Also, to keep it secure, consider a flat and lock washer or Locktite.

Tap Drill for a 4-40 is #43, or 0.089"
Clearance hole should be about 0.125"