View Full Version : Flat Bottom Hole

07-30-2003, 08:42 PM
Can anyone offer suggestions as to how to make a flat bottom hole.
The project calls for a .281 reamed hole through 3 inches of 360 brass. This .281 hole needs to bored to .420 dia. for a depth of 1.500 inch. The .420 dia has to have a flat bottom. I've heard that you can make a "D" reamer but I don't have any idea as how to proceed

07-30-2003, 10:10 PM
I don't know how precise or flat your hole needs to be. I've made flat bottom holes by grinding drill bits flat on the end and carefully grinding relief and splitting the points.

These would be used only to follow a regular drill to remove the cone left by the ordinary drill point.

I've also made ball pointed drills. Much more difficult to sharpen though.

Pretty much any profile can be made.

As for D bits. A D bit is just a round piece of tool steel with about half of the diameter milled or ground off at the business end, leaving one cutting edge, then hardened. The profile looks like a "D". They can be made tapered straight or profiled. They can also cut on the end although you will probably have to make an allowance for a little nib left at the center.

They are run at low speed with lube or coolant and should only remove a small amount of material (finishing pass).

07-30-2003, 10:22 PM
If you grind your boring tool with no end relief and run slow it should work as you only have a land .0695 wide. Just a skim at the end i.e 1.499 deep clean the last .001.
Thats one way I have done it.

07-30-2003, 11:46 PM
frbush -- sounds like you're making a 'carrier block' for some unmentioned item. I went the 'D' bit route it took a bit to get it the way I wanted but did a great job. Just be sure to lube the crap out of it or it will start to chatter.

07-31-2003, 01:38 AM
When using the d-bit, run it in a short way, then withdraw it and check the build-up of chips. Get an idea of how far you should push it before withdrawing it, to avoid 1, jamming the bit from too much build-up, and 2, removing and cleaning too many times. The fewer times you need to remove, clean, and recut with it, the better, but you also don't want to bugger up the bit or the hole with trapped debris.

Paul Alciatore
07-31-2003, 03:19 AM
I think I would rough drill the .420 diameter with a standard milling cutter (3/8") or drill (13/32". Stop a bit from the finished depth. Then use a reamer to finish it off. You'll have to resharpen the end of the reamer to produce the flat bottom.

Another approach would be to bore it with a small boring bar. Again, I would use a drill or milling cutter to remove as much metal as possible first.

07-31-2003, 04:40 AM
omefford is correct in his guess. Thanks guys for the valuable info. Off to give it a try.

Peter S
07-31-2003, 05:57 AM
I started looking for stuff that I've got on D-bits, then realised you are looking for a reamer rather than a cutter?? Anyway, here is some good info, taken from the manual for a Deckel SO cutter grinder, and some other articles too. (yeah, yeah, its mostly Yahoo Groups, I can't do much about that!)


and this, look for pdf file 'd-bits 1'


look for pdf file '2850-D-bits' here,


also, look for '3387-Dbit' here,


And here is another one (I collect this sort of info, don't know how good it is, tho')


08-01-2003, 11:42 PM
what I would do is put an endmill in a spin index and then grind it down to .420 on a surface grinder.

steve schaeffer
08-02-2003, 08:26 AM
you can email me at kungfuonu@msn.com and i will reply with a pdf file with illustrations on making these bits and others out of steel, h.ss, or other material that is on hand., it is from the ml projects mailer, and the author is Geometer. nice ol' english lad
best regards,

08-02-2003, 10:51 AM
Being a sucker for interesting tools, I ordered a copy of the Deckel SO from Horrible Freight. From the photos I've seen it looks identical to the SO. I'm sure the quality will not match up to Deckel but maybe it will serve my needs. Hope it doesn't turn out to be a $600 piece of garbage.