Thread: D section drills, who wants to make me a couple?

I thought flute bores were ever so slightly tapered...

So the 0.05mm accuracy that you are speaking of - is that bore diameter, straightness, concentricity?
How thick is the wall section after boring and finish turning?
What is the hardwood?
Why a D bit? Do you drill a pilot hole first? Do you have a finish reamer or similar to size the bore afterwards?
Is 11 or 17mm important or is it more important to be around that but have a constant bore? (For example, if the hole was a constant 11.2mm would that matter?)

Michael

Hi Sebastian,

I made some of these for a friend a few years back, he was having trouble drilling long 6mm holes through end grain walnut, the problem ( as you are probably well aware ) is that pointed twist drills tend to follow the grain, so making long straight holes in end grain almost impossible.

You need a pilot hole to start. How are you drilling, is it in a lathe, or a drill press, that is, is the work turning or is the drill turning?

I could make them, provide you aren't in too much of a hurry I'd need to check, but I think I have some O1 drill stock..

I also have some gun drills that would be long enough ( but wrong diameter ) could be handy to drill a pilot hole however..

Ray

0.05 accuracy Wow!! What have you got in mind Sebastiaan?

0.05mm tolerance in WOOD?

One would think that needs to be kept in a constant temperature/humidity room. That is 2 thou.

Originally Posted by burraboy

0.05 accuracy Wow!! What have you got in mind Sebastiaan?

Maybe he has plans of being the next Pied Piper. I'm sure a flute like that would have to be made to super fine tolerances, .1mm too big and you might attract possums instead of rats.....

FWIW silver steel/drill rod is accurately ground to size as it is, so all you need to do is machine the d on the end and harden it.

Ew

I suspect the 0.05mm accuracy required refers to the grind on the drill not the finished wooden product. This is the accuracy required for each cutting edge on a standard 2-flute drill to get drilling accuracy of 0.1mm. Rather difficult to achieve without precision grinding tooling; or a red rubber nose, oversized pants on elastic suspenders and really big shoes . In this case it's "merely" the need to put a flat on round bar; not beyond the abilities of a steady hand and a file but a surface grinder is easier and quicker!

I wouldn't have thought though that this would have been any good for drilling/reaming on end grain; wouldn't the wood fibres end up being torn?

Probably a silly question, but what about making the body in two halves, grooving down the middle of each with a core box bit and then tightly gluing them together around a mandrel? Which you can then use as a mount in a lathe chuck for turning the outside?

I found this article in the Practical Machinist forum which goes some way to explain what I believe Sebastian is trying to have made.

All very well to get a drill that is accurate to 0.05mm but that doesn't mean the drilled hole will be that accurate, particularly over the length involved.

Being wood we are dealing with grain, in this case end grain, and the influence of temperature and humidity.

Originally Posted by Chief Tiff

I wouldn't have thought though that this would have been any good for drilling/reaming on end grain; wouldn't the wood fibres end up being torn?
.

I guess you've never used them? They cut nicely, but slow.

You aren't related to another Tiffie by any chance?

Ray

Originally Posted by Ueee

FWIW silver steel/drill rod is accurately ground to size as it is, so all you need to do is machine the d on the end and harden it.

How does it clear the sawdust, especially @ 350 mm long?
It would need to be turned down or a side piece brazed onto a narrower shaft.

Originally Posted by BobL

How does it clear the sawdust, especially @ 350 mm long?

It doesn't, you have to keep pulling it out to clear the chips, mind you if the D section is fairly long you can drill a fair way before it gets packed too tightly with chips.

Gun drills have a flute along one side, and a hole through the bit for coolant. (for metal obviously) You can hook up compressed air and blow the chips backwards as you go, I tried it once... makes a mess.

Ray

Originally Posted by RayG

Gun drills have a flute along one side, and a hole through the bit for coolant. (for metal obviously) You can hook up compressed air and blow the chips backwards as you go, I tried it once... makes a mess.

Ray

From memory compressed air into the lube hole on gun drills worked really well on acetal - blew long streamers of swarf out the back...

Originally Posted by RayG

I guess you've never used them? They cut nicely, but slow.

You aren't related to another Tiffie by any chance?

Ray

Not on timber, no. I've only ever made simple ones for drilling into ally and brass for one-off applications where proper tooling wasn't available. My thoughts were along the lines of the edges trying to plane or scrape against the wood grain; in my mind it would dig in and rip. So you've used them in timber? Is there any difference in surface finish between hard and softwoods?

Hmmm... take a "proper" wood screw, solder it onto a bit of bar, file off the threads then grind it in half; finally replacements for my old Stanley screw-mates!

Oh, the "Tiff" is short for "Artificer". I used to be a Chief Petty Officer Marine Engineer Artificer in the Royal Navy; colloquially known as a "Chief Tiff".

Originally Posted by RayG

It doesn't, you have to keep pulling it out to clear the chips, mind you if the D section is fairly long you can drill a fair way before it gets packed too tightly with chips.

What about milling up the head and then turning a couple of mm off the rest of the outside of the shaft front about 20 mm back from the head? It's all end grain cutting so the chips are going to be fairly fine.

It appears that the D drill bit may be used as a reamer after the main bore is drilled with a gun drill

http://www.mcgee-flutes.com/making.html

Interesting read.