Tapped screw holes?

[lowell]

My amp has a cage and I've been attaching the cage w/ machine screws and lock nuts. This is annoying because I have to take the bottom plate off the amp to access the lock nuts. I'm curious if anyone has a good cure for this. I've thought about tapping the chassis holes but wanna pick everyone's brain on this.

[Jazz P Bass]

Tapped holes

Tapping the holes will give a very secure mount.
The good thing about tapped holes, if they are not overtorqued, is that they are reusable. With the proper screw size & pitch they are a very durable attachment method.
Please keep in mind that you must use an engineering approach when deciding on a screw diameter & thread pitch (threads per inch).
Analyze the requirements.
Hold back force
The thickness of the material to be tapped.
The type of material.
It all comes into play.
Engineers don't wear those little blue/striped hats for nothing.
Also, a self tapping screw is good if there is no real force on the attachment point. They are not very reuseable.
Happy train driving!

[Enzo]

I swear to God this is my all time best shop tip that I drill into my trainees.

When you have sheet metal screws or wood screws to re-install, turn them backwards at first until the screw drops into the old threads in the hole. Then tighten the screw. That way you don;t cut new threads in the hole each time. Doesn;t take many times cutting new threads that you have no threads left at all.

Nothing wrong with sheet metal screws to hold your cover in place. A bazillion Fender capacitor vault covers can;t be wrong. They don;t require nuts.

Tapped holes and machine screws works fine and is reusable, but so do sheet metal screws if you follow my tip.

[lowell]

ok good tip enzo. these screws, if they fail, will allow the entire chassis to fall on the ground. i'm thinking they need to be more fail-safe than sheet metal screws. i just tapped it at 8-32 and seems pretty tight.

[defaced]

PEM nuts (provided you can press them and have clearance to do so):
PennEngineering - home of PEM, SI, Atlas & PEMSERTER brands.
http://www.pemnet.com/fastening_products/pdf/cldata.pdf

[tubeswell]

Either before or after the self tapped hole wears out, you can use blind nuts/fasteners - the type made of spring sheet metal that slip/clip over the edge of the sheet metal you want to fasten the screws to. (They have a tapped hole through them that the screw bites into)

[loudthud]

Two threads is considered full strength for a machine screw. This means that if you are using an X-32 screw, the sheet metal you tap into should be 1/16th inch thick. A 4-40 is good on .050 sheet metal.

[lowell]

good to know, my chassis is 3/32 aluminum!