A better quill lock

Pending any unexpected events I plan to have my (hobby) EZ-Trak running in the next week and am looking for a couple quick projects to make some chips. I'm also teaching a couple of the lab techs at work basic machining on an old Series 1 so I'm looking for a couple not too hard projects that use a variety of tools.

A split cotter quill lock seems like a good one, but I have a couple questions:

1) Do you need to index the threads or just trim down the brass piece in the front so the lock lever comes out at the right angle? I've seen lots of stock machines with washers in there and one of the online solutions uses a hex so they can get it oriented right. I'm not seeing any other obvious adjustment. How did they do this from the factory?
2) Is it better to slightly overshoot or slightly undershoot on diameter? I'd guess slightly under, but will a couple thou even matter? My only other experience is in clamps for round objects (bicycle stems and such) where slightly under was preferred and the mating part would deflect a bit.
3) Several people mention putting it in the back so that gravity opens it. I like the concept of gravity opening it, but not having it on the back. Other than the cost of a tap and die (or lathe work) is there a reason not to just use a left hand thread?
4) I'll be making these for two or three mills (all Series 1 heads). The gap for the bolt on mine is somewhere around 0.42" so I won't be able to get really close with a drill bit. There is a set of plug gages near only one of the mills. Is this dimension likely to be tightly held on all Bridgeports, or is it likely where ever it happened to end up?
5) Other than maybe sliding a cutter up into a collet is there anything that locking the quill more securely is likely to let a new person mess up?

One example:
Bridgeport Split Cotter Quill Lock | Dezign Shack Blog

I'm getting ready to order the taps and material for this. Any thoughts suggestions or warnings from anyone?

Why don't you like the standard BP style lock? The way I improve the standard parts is to put a good stiff compression spring between the 2 lock blocks with the locking screw going through the center of the spring. Now when you release the lock lever it stays where you put it and the lock blocks do not drag on the quill

I missed this thread earlier, on account of the holiday...

The quill lock, as I understand, functions somewhat like a brake. As the mating surfaces wear, the angle of the lever will have to be increased in order to give enough pressure to the lock. The threads might be the most susceptible, perhaps. I added a shim washer to my quill to adjust the angle.

I was not able to open the link, so I'm in the dark on your proposed improvement(s).

moonlight machine said:

Why don't you like the standard BP style lock? The way I improve the standard parts is to put a good stiff compression spring between the 2 lock blocks with the locking screw going through the center of the spring. Now when you release the lock lever it stays where you put it and the lock blocks do not drag on the quill

Click to expand...

The issues I've had over the years with the standard BP quill lock are:
1) The quill lock lever needing adjustment (washer behind it) due to wear, and not being able to fully lock. These were machines I had access to (college shop, prototype lab where I work, etc), but where the owner was unwilling to have me "tinkering" with the machine. I suspect a washer behind the lock would have fixed it, but couldn't test.

2) On about half of them the weight of the tiny little lever seems to be enough to make the quill stick. I'm not sure why, but it does.

3) Somehow these same machines require a solid tap on the lever to keep the quill from moving up or down during some cuts. I'd put a longer lever on it, but issue 2 would get worse.

Your suggestion of a spring and a longer lever might get me where I want to be, I didn't realize there was enough space in there for a spring, but I haven't exactly measured either.

Mark W. Ingalls said:

I missed this thread earlier, on account of the holiday...

The quill lock, as I understand, functions somewhat like a brake. As the mating surfaces wear, the angle of the lever will have to be increased in order to give enough pressure to the lock. The threads might be the most susceptible, perhaps. I added a shim washer to my quill to adjust the angle.

I was not able to open the link, so I'm in the dark on your proposed improvement(s).

Click to expand...

It looks like the other page is at least temporarily down. Here's another guy who did the same thing:

HomeShopTech

OK, so bigger brakes then, number one... And you can rotate the clamping threads, number two. Seems like a good idea.

(My old BP has a 2MT quill, and the endmill moves in the collet before the quill itself if I try to go too heavy. So, I wasn't aware of the problem.)

I just reverse the pieces as shown in this youtube video and it works a treat, just need some spacers/washers to get the lever where you want it but took all of 10 minutes to do

The Bridgeport Quill Lock Hack - YouTube

Thanks
Marc