On Mon, 28 Jul 2014 09:14:58 -0500, "Pete C."
wrote:


"Lloyd E. Sponenburgh" wrote:

"Ed Huntress" fired this volley in
:

A 5/16 hole 7-in. long, drilled undersize, isn't going to provide
enough side force to make a reamer run true. The reamer would just
follow the drilled hole.

There is a way to drill a hole like this straight, without a real gun
drill. Start the hole with a regular drill bit, drill it maybe 1"
deep, and follow up with a home-made single-lip drill (a D-bit).
Unlike a real gun drill, you'll have to peck it to get the chips out,
and it's God-awful slow. But it works.


Ed, they make reamers that small with flutes 6" long. That would provide
plently of 'guide' surface. The reamer could bend some, but wouldn't if
you took it slowly.

But anyway... unless you have a coolant-ported drill and a high-pressure
coolant pump, you're going to have to peck anyway, past about six drill
diamters deep.

I didn't even consider a d-bit to be in his options; especially
considering he's talking about just re-chucking to true the piece up.

Pecking IS a pain. Some day, I'm going to make that lever drilling
attachment I've always envied, or put together a right proper carriage
drill holder.

LLoyd

I've thought about improvising a gun drilling setup on the lathe, an
adapter to hold the drill in the boring bar toolpost holder, a cheap HF
electric pressure washer adapted for a coolant pump, and I guess I might
have to make some more gears to get the power feed on the lathe slow
enough. Something to consider if I do more of these.

I did a bunch of OmniTurn CNC lathes with 350lb high pressure coolant
pumps a few years ago at Gertler Industries. We were drilling up to
6" deep with 3/8" and bigger coolant ported drill bits at a dead run
in all manner of alloy steels. .003-..008 per rev feed rates

They liked the first one so well they had me do another 17 machines

Gunner

--
"Living in the United States now is like being a Tampon.
We're in a great place, just at a bad time."