drill point that grabs the least

[hobgobbln]

I need to drill some roughly 5/32" holes in thin 303/304 stainless and nickel brass. Materials are about 1/16" thick.

What point angle would be the least likely to grab?

Griz

[BadDog]

Brass usually wants a "drubbed" (hand stoned small zero rake land) on the edge/lip. I have drills dedicated to just that purpose. As for angle, I think flatter is better, but haven't done any real experimentation (or been educated) on the matter. For thin stock and sheet metal, brad points work well, as do step drills.

[hobgobbln]

Whoops. Meant naval brass. Not sure if it makes a difference.

These are small round pieces being held in a pot chuck inside a lathe chuck on my drill press table. Basically a cylinder with a bore in each end that leaves a thin cross section. I have to drill an offset hole through that cross section. I did a few while prototyping and the 118 degree drill kept pulling the part up and out of the pot chuck when the tip broke through. Happened with both materials.

Griz

[BadDog]

Generally speaking, less angle breaks through more cleanly, so 135* split point should be better than 118*, but still likely to do the same thing. Probably the best bet is "drubbing", but I'm no authority.

For stainless you DO NOT want to use a drubbed bit. Depending on alloy, it will work harden and you'll be done without carbide or abrasive tooling. Not sure, but I expect the best thing to do there is a shallow (high numeric) angle bit and good control on in-feed (power with little/no back-lash if possible) at the critical moment. But you have to keep cutting (and watch web/chisel or it can work harden there) or it can stop you cold (various alloys more or less sensitive).

[Richard_W]

For sheet metal a pilot point/bullet nose drill works well. I have not tried it in stainless but has worked well in other materials that I have tried. For brass you would want to dub any drill even a bullet nose drill or it will want to suck into the material. I have seen times when it pulled the part right out of the vise.

Example of bullet nose or pilot point drill.

http://www.ebay.com/itm/Dewalt-17-64-Pi ... 19eb522db1

Richard W.

[hobgobbln]

Thanks. I'll give those a shot.

Griz

[BadDog]

That "pilot point" is similar to what I heard called a "brad point". But brad points have little "teeth" at the outer edge of the lip, and are made specifically for thin stock. Google shows good examples. They work great for steel sheet, but not sure exactly how one would work in brass though.

[Bob D.]

I would use a Unibit in thin material. Makes a nice round hole vs the triangular round hole a twist bit gives in thin stock. Won't grab either.
Bob D.

[gwrdriver]

I agree. Definitely a Unibit for even-fraction holes in sheet metal.

[BadDog]

Brad points make clean holes in sheet, and I think they might work for what he's trying to do. Step drills are great, and think they would work great in thin brass, but if I understand correctly, I don't think they will work for his application.

[GlennW]

Double Margin drills would be my choice for this application.

[jpfalt]

Consider putting backing material below the part you are drilling. The bulk of the force of drilling is pushing the point through the workpiece. When you get to the back side of the part, the pressure on the point goes to zero and the drill starts to pull itself through the work. If there is backlash in the spindle feed or if the drill bit compresses due to the pressure applied, the drill bit will either drop into the workpiece or the drill will spring down in length. In either case, the drill grabs.

If you put a backing piece behind the part, the pressure on the drill point is maintained and the compression on the drill is maintained and the drill will not grab as badly.