Deep hole "D" bit advice needed.

I have a job that comes up every year or two for a Customer. He needs a 1/2" hole 10"-12" deep in Aluminum. He wants no mismatch in the middle. I get a thousand or two when drilling from both ends. He notices it and does not like it, even for His application it does not hurt anything.

Would a "D" bit stay straight over that length?

Withdrawing very frequently would slow things down a lot.

Could I drill a 1/32nd or 1/64 of an inch smaller from both ends and expect the "D" bit to straighten out the hole?

What's the longest 1/2" reamer available. Meaning to drill undersize & ream to 1/2".

Steve.

I've just bought a long series 1/2" reamer for a part that is about 7" long. Longer than that and I suspect you're into specialised (equals expensive) tooling. Best bet would be a gun drill, but ideally they need thru drill coolant at considerable pressure and are not simple to set up. A D-bit will probably sort of stay straight, but there's going to be a very long length of D-bit that is a close fit in the final hole. That's a recipe for something seizing.

Personally I'd explain to the client that it's going to cost him x pounds more per part and does he really want to cough up the extra readies?

Andrew

These might just do the job from one end. Not expensive.

**LINK**

Long series drills will certainly give you a long hole, but it wont be straight. As Andrew Johnson has already said, gun drills are the only real way to produce long, straight, round holes and that set up is NOT cheap.

Andrew.

Try drilling 12mm from both ends and then a d bit. See if it works.

Martin C

I had to ream out a deep hole and only had a standard hand reamer in the correct size. I turned down the end and bored a slightly smaller rod and silver soldered them together. I held the reamer in aluminium soft jaws in a vise to make sure the cutting edges did not overheat and it worked. Starting with a drill 31/64" would probably work fine.

Drill undersize from both ends as before. Make a D bit with a pilot section up front that is the width of the initial hole and of course a lead in taper. After a bit for alignment behind the cutting point relieve the diameter to reduce chance of seizure.
You mentioned not wanting to withdraw the tool for chip clearance. No need as you have a hole already put a pipe down from the back end with a flow of coolant, lube etc.
The tricky point is the meeting place of the two holes. You know exactly where it is so you might want to make a drill for just this bit with a modified pilot that copes with the transition.

As you are a professional you might want to try asking on the PM forum. Just don't mention you are using an Atlas lathe for the job.

Edited By Bazyle on 24/02/2020 20:02:10

In toolmaking when a mould tool is heated you have to fit heaters and they were 1/2 inch diameter and they could be up to 3 feet long. We just reamed them with a 1/2 inch ream welded on to a 12mm diamiter extension bar.

David

When I worked in the mould making industry we had our own gun drill set up. Prior to getting this I sub contracted to a company in Coventry who where reasonable cost.

Shaped charge explosive?

Can you use a chucking reamer where shank is smaller diameter thsn the cutting flutes. Slver solder an extension on the shank. Drill from both ends and ream from one.

Or cheat and do it the way you have been then get rid of the small ridge in the middle by using a length of wooden dowel with a hacksaw cut in the end to hold a strip of emery cloth etc as a flapper. Spin with electric drill and viola! ridge gone.

Would a core drill do the trick?

It takes around an hour of buffing to get the ridge out. Will try a D bit next time He orders.

Hi Guys,

A "D" bit, like a drill, will try to follow an existing hole, so wont straighten a curved one. A properly made "D" bit will create a straight hole that is accurately sized. But it takes a lot of pecking even with a reduced shank.

I think that Hoppers idea of extending a reamer might be the way to go !

The hole would be bell mouthed.

Mark, Plus another 1 for extending a reamer, however it does depend on how accurate you need the hole with regard to straightness and location at either end. If you go this route I would use tin solder to join the reamer to the extension thus less chance of affecting the reamer hardness.

For a D bit of that length, although I have never used one that long I would consider either make a flat on the top of the bit or maybe better a V groove along the full working length of the D bit to facilitate lubrication.

Another method that you could use is spill boring - used in the past to bore gun barrels, shotgun in particular. It achieves an very straight hole but its an old fashioned method and very slow really superseded by modern tooling but its cheap to produce and does work.

Lastly you could make a draw reamer from silver steel [drill rod] as the name implies you pull this through the hole rather than push it through the pull rod being smaller than the hole.

John

Might try a draw reamer the next time, or doing it in the lathe which has the needed length. Don't know how accurate it would end up.

I was going to suggest line boring on the lathe, if the part will fit.

If he's that pedantic; & you don't need the job, which clearly gives you some stress, politely tell him where to go ..

George.