Modding cutting screw holes for 120mm fan

ok so i've cut the main hole into the case to let air in, but how do i go about cutting the screw holes? i have tried many a time previous and 1 or 2 are always out therefore no screws can go in them unless i can squash/warp the fan
this time i want them to be purrrrfect

what's the best way? i don't have a 120mm fan grill to use so must be another way eh ?

thanks for any help

 

use your 120mm fan?..., just position and then w/ a sharp point mark a spot or use a really small pen, or its ink cart

 

yea i could use that but i have problems seeing that its lined up properly lol!

 

i do it this way:

mark and drill one hole, put the fan on that hole and line it up with a screw.

mark a second hole, remove the fan, drill the hole replace the fan and line it up with 2 screws.

mark the last 2 holes, remove the fan and drill the holes, hopefully the fan fits now.

It's much easier to do than it is to describe.

 

good idea man! i'll use that method cheers

 

Either that or make a jig. That is what i do. I just use a fan to draw everything on like a peice of cardboard. Then drill and cut it out.

 

The tool you need is a "transfer punch", just a steel pin with a sharp tip in the center of one end. They come in sets that look like http://www.precisionmeasure.com/tool10.htm. If you only need that one size you can try to make one yourself.

Get a drillbit, preferably one that is broken off. It should fit tightly into the hole on the fan. Put the bit into the drill so the dull end sticks out. Turn on drill and grind a tip onto the bit with sandpaper or a file. It's not as easy as it sounds to get the tip centered check the result carefully before you use the modded bit as transfer punch.

 

I have perfected that method for when i made some carbide tipped drawing pins for hard metals.

I put a diamond coated cutting disc in the flex-arm of my dremel copy and secured the flex-arm pointing straight up in the vice-clamp or whatever you call one of these.
Then i put a worn out carbide endmill in a battery drill and held it at a fixed angle to the flat diamond covered side of one of the diamond coated cutting disc until it had a nice sharp tip.

this should work just as fine with a worn out drill, just don't push too hard or you will get the HSS-steel drill too hot and take the hardening out, making it as soft as regular iron.