Brake bore diameter

[CJ6]

I have a radial style brake that needs to be bored for use in 30 cal.. what is the proper bore diameter to use for this.
TIA Roger.

 

[Sniperhandle]

I have a radial style brake that needs to be bored for use in 30 cal.. what is the proper bore diameter to use for this.
TIA Roger.

0.020 over bullet diameter.

 

[ChristianSilver]

.020 over as stated above, needs to have true concentric alignment…

 

[CJ6]

Thanks guys.

 

[Old Navy]

0.020 over bullet diameter.

And you can do it on a drill press in your garage.

 

[ridgeway]

And you can do it on a drill press in your garage.

Garage is acceptable, but gonna nay the drill press. Get the bore running true then bore(boring bar in lathe) the brake ID will be the fool proof way. A drill will just follow the existing hole.

 

[jackieschmidt]

Garage is acceptable, but gonna nay the drill press. Get the bore running true then bore(boring bar in lathe) the brake ID will be the fool proof way. A drill will just follow the existing hole.

And since you are drilling/reaming through interrupted cuts, that is not something I would want to attempt in a drill press.

Perhaps in a Mill if you secured the brake in the vertical and indicated the brake straight and truly square with the Milling Machine’s Quill.

Drills and reamers do tend to follow a hole. When you add the interruptions of the slots or holes in the brake, you would want the most fool proof method available.

 

[Old Navy]

And since you are drilling/reaming through interrupted cuts, that is not something I would want to attempt in a drill press.

Perhaps in a Mill if you secured the brake in the vertical and indicated the brake straight and truly square with the Milling Machine’s Quill.

Drills and reamers do tend to follow a hole. When you add the interruptions of the slots or holes in the brake, you would want the most fool proof method available.

I knew the gunsmiths/machinists would take exception to that.

 

[ISS]

Why would a drill press not work, if the original hole is straight? Asking because I do not know any better!

ISS

 

[Preacher]

Why would a drill press not work, if the original hole is straight? Asking because I do not know any better!

ISS

Of course a drill press would do that, but depending on the particular drill press, it's not near as ridgid and will cause a bit of chatter. I final ream with a chucking reamer .020 over bore diameter in a lathe...

 

[linebaugh]

The biggest reason a drill press is a bad idea is because .010 clearance is a tight tolerance especially on longer brakes. If it is not done with a boring bar wirh the bore indexed correctly its possible to have a bullet touch the brake and it will give uneven pressure dispursion causing accuracy problems.
You can go bigger on the clearance and probably not affect the efficency much... that solves some of the problems.
As per usual there are probably gobs of guns out there with brakes that were drilled and either no issues or not considered issues. Just because it works does not necessarily mean it is right or could not be done better. Just stacking tolerences.

 

[tobnpr]

If it is not done with a boring bar wirh the bore indexed correctly its possible to have a bullet touch the brake and it will give uneven pressure dispursion causing accuracy problems.

Bah humbug.
Minutiae.
Done hundreds of them running a chucking reamer of correct size into them after clocking the brake onto the muzzle tenon. If anyone is buying brakes where the bore hole isn't concentric to the threads, suggest you buy your brakes elsewhere.

Dealing with deflection of a skinny boring bar a couple of inches long isn't worth the time and number of passes needed for a consistent hole diameter that's guaranteed with a reamer.

 

[Alex Wheeler]

And since you are drilling/reaming through interrupted cuts, that is not something I would want to attempt in a drill press.

Perhaps in a Mill if you secured the brake in the vertical and indicated the brake straight and truly square with the Milling Machine’s Quill.

Drills and reamers do tend to follow a hole. When you add the interruptions of the slots or holes in the brake, you would want the most fool proof method available.

Exactly. I wouldnt even do it in the lathe. Drills dont drill straight. Angled ports make them drill realy bad. Boring bar is the only way to do it right. Had many brakes sent that have been drilled by the manufacturer. Terrible.

 

[Randfal]

All wives-tales and smoke and mirrors aside….Letter Q , R, or S. And 21/64” and even 11/32” will all work fine. I would not use a hand drill. If your drill press is decently rigid and has a vise that can secure the brake perpendicular/square to the drill bit, it will work just fine. I do mine in the lathe when I make them and drill the bores(I also like boring them from time to time if a specific size is wanted). But it really is a waste of time. Your drill bit is going to follow the previously drilled hole regardless of how you “drill” it. After all, you are drilling over-caliber size to allow clearance for the bullet. Plus or minus a couple thousandths will make no difference. I’ve been machining brakes for years and have cobbled together a bunch on different junk for myself just for testing and giggles. .015-.035” over bullet diameter is fine; you will feel no difference. If you feel you can’t maintain concentricity with your press, drill it on the bigger side. You’ll really have to screw it up for you to get a bullet strike on a normal length brake if you drill it over those amounts. I believe much bigger and you start losing some efficiency in your brake.
-pictures are for reference; speaking from experience-