What kind of bit/tip will do this?

[Lumencraft (Matt)]

Hey cpf,

I have been making an attempt at building some of my own parts, so a bit of new equipment is in order.

What I need to know is what kind of bit will give me the desired effect, and where do I get one. I want to be able to take flat material plastic/wood/or metal sheeting and drill a hole in it that is flat at the bottom rather than rounded at the bottom the way a drill bit makes it( ie so the edges of the hole are as deep as the center). The holes do not need to be deep 1/2 inch at most. I don't have a mill but I do have access to a drill press, so if someone could give me an idea what I am looking for that would be great.

Thanks

 

[LukeA]

A forstner bit will let you drill largely flat-bottomed holes in wood or soft plastic. (flat with a small nub imprinted in the center.) images

 

[Atlascycle]

Start the hole with a standard drill bit and finish it with a flat bottomed bit.

Jason

 

[precisionworks]

Start the hole with a standard drill bit and finish it with a flat bottomed bit.

+1

The flat bottom bit needs to be the same diameter as the starter bit. They are tricky to hand grind, but it can be done. If you don't want to grind one, an end mill can work as long as your set up is rigid - which is often hard on a drill press. At the very least, the part has to be clamped in a vise, and the vise has to be secured to the table. Use the end mill for nothing but flattening the bottom after the starter drill.

 

[KC2IXE]

Flat Bottomed Bit = counterbore - get one with a pilot the same diameter as the through hole, and the diameter you want

 

[Lumencraft (Matt)]

Thanks very much all for the quick reply. I think what I will probably do is either order a set of the forstner bits from harbor freight, or maybe attempt to grind off a bit myself. If I can get a clean result from the homemade one I'll stick with that but I am going to need this to be good quality work so I may spring for the set of bits in a day or two anyway.

 

[gadget_lover]

The choice of end mill VS forstner bit may depend on the diameter of the hole and the material.

Small end mills ( under 1/2 inch diameter) are cheap and plentiful. Large ones are not.

Large forstner bits up to (2 1/2 inch diameter) are fairly cheap. Real small ones (under 1/4 inch) may be harder to find and they DO make a dimple in the middle. As far as I know, Forstner bits are not used for metal. They tend to dig in like a screw.

Daniel

 

[wquiles]

... an end mill can work as long as your set up is rigid - which is often hard on a drill press. At the very least, the part has to be clamped in a vise, and the vise has to be secured to the table. Use the end mill for nothing but flattening the bottom after the starter drill.

+1 that is what I use on my lathe when I need a flat bottom on holes. Like this:

By the way thanks to Brian (Mirage_Man) as he was the one that first suggested to me this simple trick

Will

 

[will]

Forstner bits are intended for wood.

 

[KC2IXE]

Of course, end mills don't give a TRUELY flat bottomed hole - they are slightly deeped on the outside than the middle, due to the mill having a SLIGHT "fishtail" shape -

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