As regards square drive bits, if you are going to grind them, do it this way (I leave the actual amount off up to you):

Hey that's a great idea. I hadnt thought about it that way. In fact, the only taper i thought about so far was from the shank out to the tip, but a taper from the tip to the shake is much better i can see right away.
Very good idea i am glad i did not grind one yet because i will do it that way instead. that will also give some wiggle room. Very nice

 

I'll share something about Philips screws. One of the places I worked molded and assembled plastic parts for cars. The parts were held together with small Philips head screws, and used air powered drivers. The driver bits were getting replaced a few times per shift because of problems of them not working good or going bad, so we thought. The engineering department called in somebody from the company selling both the bits and screws.
The tech came and told us to take the bits and grind about 1/64"(0.015") off of the point of the bit. And after doing that the bits would last 3 or 4 days without replacement, running 3 shifts a day.

Seems that while the bits have to be made to a tolerance the screw slots don't. The bits were bottoming out in the internal point of the screw, and not letting the "fins" of the driver bit do the work. After learning this when ever I have to buy a new Philips screw drive that is the first thing I do grind a small amount of the point off. Doing that I end up losing/misplacing a driver before they wear out or start slipping out of the recess..

Wow that's amazing because that was one of my modifications because i realized that the tip, even with healthy ridges, does not contribute much to the torque and yes sometimes bottoms out.
Also, if the bit cams out anyway (which it usually didnt with the mods i did) i think the tip is what rounds out the inner corners of the screw recess which then makes the screw harder to work in *OR* out. I ran into this too and had to use vice grips to get the dang screw out
I also thought about grinding the head to a square so i could use a square socket on it. Was worried about snapping the screw though. The vice grips did not snap the screw though because i think they are made with better metals now.

 

I heard, on WWW, that philips screws/drivers were made that way so they would cam out rather than snapping the screw.

YMMV

Yeah that's true, and that makes regular Phillips a real pain to use sometimes. I am finding that the newer type bits work much better though, the ones with the ribs on all 8 side walls of the Phillips head bit (four main ridges with ribs on both sides). I will try to get a good pic of one of these bits here well worth getting at least one.

 

Here is a little update on the ribbed anti cam out Phillips bits...

The attachment shows pictures of the ACR Phillips bit (red color) and a normal Phillips bit (gray).
The left pic is the original photo, the middle is the photo enhanced just a little to make the inside ribs more apparent, and the bottom is the enhanced pic zoomed in.
The ribs appear as bright white angled lines or 'teeth' and there are 6 of them on each side of every ridge so that is a total of 8 sets of 6. (It may appear that there are 5 ribs in some places because one may have not shown up properly in the photo).
Note the gray regular bit shows some striation marks due to the tooling of the bit but they are on the shaft not on the bit mating surface itself so they dont contribute to the anti cam out mechanism.

 

Also notice that the point of the anti cam out bit isn't as pointy. I like the ones that are grit blasted too.
https://www.sears.com/craftsman-professional-no-3-x-6-in-screwdriver/p-00947187000P

 

Also notice that the point of the anti cam out bit isn't as pointy. I like the ones that are grit blasted too.
https://www.sears.com/craftsman-professional-no-3-x-6-in-screwdriver/p-00947187000P

Yeah that's interesting, i guess sand blasting would make it grab a little better.
All of the #3 bits i have have very blunt tips. The #2 bits are slightly blunt, the #1 bits very pointy.

I also wondered if it would work to grind a slot in the phillips head if it would not come out with a normal phillips bit. I did that with several "security" screws in the past and it worked but they did not require exceptionally high torque to get out. Some of the phillips drywall screws i put in are really really hard to get out, sometimes the head recess just gets too rounded out inside. Grinding with a Dremel thin cutoff disk might work for that problem. Then we can use a slotted screwdriver or bit to get it out. I'll have to try that next. I keep a sample piece of lumber around for these tests

Oh another strange idea hit me while i was looking around for screws and bits and stuff. They are the 'angle' type extensions for 1/4, 3/8, or 1/2 inch drive tools like sockets. They allow an angled drill because they act as a universal joint which allows the motor to be on an angle with the shaft.
I also have an extension that is 'bendable' which is like a long strong spring that has hex on both ends so you can use it with hex bits and power drill. That also allows an angled approach to the screw head. I forgot i had that so i'll have to test that too next.

 

For my part the grit blasted are better than the ribbed ones. To me the ribs lessen the amount of contact unless the screw would be very soft. The contact on the ribs would only be the top of each rib, much less than even a non ribbed driver.

As to the U joints and spring extension they work great with a socket, not so much with a screw driver bit.

Maybe it's time to reveal what your trying to do.

 

Those are only for LSF studs.

Well they work really well in wood too apparently.

 

For my part the grit blasted are better than the ribbed ones. To me the ribs lessen the amount of contact unless the screw would be very soft. The contact on the ribs would only be the top of each rib, much less than even a non ribbed driver.

As to the U joints and spring extension they work great with a socket, not so much with a screw driver bit.

Maybe it's time to reveal what your trying to do.

Oh just general home repairs and mounting shelf brackets.
Well the ribbed bits worked very well for me as i said i put in a 2 inch screw all in one shot with no cam out.
I'll have to look around some more for my "home manufactured" bit also. I hadnt used it in so long i misplaced it.