Airway off center left to right

[Walldepartment]

This has been driving me nuts lately. When I drill an airway in a bent pipe on the lathe, the airway is often off center on the left–right axis. It’s a pretty small amount, usually like 1/100th of an inch or so. This is most noticeable in the keyhole. It seems to me like the airway moves towards the center as it goes toward the bowl. I have tried two different lathes with two different chuck jaws, so I’m thinking I’m doing something wrong.

So, I have a few ideas, but I really want to know the cause of this. Firstly, when turning and drilling the shank, the chuck jaws usually grip a lot less wood than when it’s gripping the airway or bowl. I have been drawing the pipes somewhat close to the edge of the block, so there is not as much wood to grip onto for the shank.

Another idea I have is that the unevenness of the block might be causing the jaws to grip the wood out of alignment. By unevenness, I mean like how parts of wood are missing on one side of the block or the other, either from being sawed off or just naturally there.

Or maybe the way I chuck the block has something to do with it. When the airway is off like this, it’s usually to the right of the mortise.

[JMG]

Squaring the block may a huge difference in securing the block in the jaws. Definitely do that before chucking it in the lathe. Also, make sure you are going slow and not applying too much pressure when drilling, and clear the chips as you go.

[LatakiaLover]

Another variable is drill bit rigidity. Ideally, use the shortest bit possible. They are much whippier than most people would guess, and easily deflected. Varying wood hardness within the same block can play hell with hole straightness.

Finally, an old machinist's trick to minimize wander (that also works with wood) is to BARELY dull the outside corners of the bit with a touch of fine sandpaper. Too much will inhibit cutting, but dulling a smidge will keep the bit from "taking off" sideways---trying to "start" a new hole---every time something deflects it.

[Walldepartment]

Yeah, so I square every block on the bandsaw. I also drill very slow. I really don’t think that’s it. I even cut the keyhole with an endmill, which is very rigid, and it’s a tad bigger than the drill bit.

[JMG]

Yeah, so I square every block on the bandsaw. I also drill very slow. I really don’t think that’s it. I even cut the keyhole with an endmill, which is very rigid, and it’s a tad bigger than the drill bit.

Well then...you're not holding your mouth right.

[LatakiaLover]

Now that's funny rat thar, don't care who y'ar

[caskwith]

Airway drill bits wander given the slightest chance. Luckily there are 4 directions they can move and only 2 of them matter. Get a centre drill and a machine length drill (a stubby one), that should help, as will squaring the block well.

If the deviation doesn't cause a problem though and is aesthetic in a usually hidden part of the part, just ignore it.

[Walldepartment]

Ok, to be more accurate, I‘m specifically talking about the keyhole, the notch at the bottom of the mortise on bent pipes. If I cut this with a rigid endmill, it can’t be drill bit wander. Something is out of alignment. I’m thinking it might be from not having enough wood gripped by the chuck.

[DocAitch]

I am trying to visualize a 1/100” deviation and why you are distressed about it.
I am pleased not to leave a significant dead space (1/2-1mm-0.02-0.04”) under the draft and to be within 1 mm (0.04”) of dead center laterally.
I don’t think that you need better accuracy for smoking purposes.
As I am wont to say “we ain’t making Swiss watches here.”
If I am within those parameters, I concentrate on other stuff.
DocAitch

[seamonster]

So, thinking about it this way:
You drill the draft hole, and then reposition the block to drill the mortise (or vice versa, depending on your level of crazy)
and now you are not on the same axis. Either your headstock and tailstock are misaligned, or your block is not square enough and you are shifting alignment when you re-chuck.

[linearone]

What seamonster said. When it happens to me it's only ever on pipes that I reposition the block in the jaws and only ever on blocks I didn't make perfectly square. I also drill my airways in three steps, I use a center drill to start, then a short drill to drill it as far as I can, perhaps1/3 or half of the way, this drill being short is more rigid than the last drill which is 5+" long, perhaps it's 6"..

My idea has been to start the hole with the stoutest drill (center drill) I can to it has a nice short little bore to get started with. Then progress from shortest to longest. I almost never have an issue any more unless it's a block that requires repositioning.

[Walldepartment]

I am trying to visualize a 1/100” deviation and why you are distressed about it.
I am pleased not to leave a significant dead space (1/2-1mm-0.02-0.04”) under the draft and to be within 1 mm (0.04”) of dead center laterally.
I don’t think that you need better accuracy for smoking purposes.
As I am wont to say “we ain’t making Swiss watches here.”
If I am within those parameters, I concentrate on other stuff.
DocAitch

Because I want to sell. And I imagine people won’t be pleased paying several hundred dollars for a pipe with an off center keyhole.

[DocAitch]

OK
I sell a few. They all smoke to the bottom of the chamber.
I also don’t drill on a lathe.
To be clear, yes - perfect drilling is wonderful and desirable, and I probably hit 80-90% of mine on first try, and I can adjust most of those that I don’t hit perfectly. The rest, I smoke or give away. I just don’t sweat it.
Just sayin’ that fixation on 1/100th of an inch is going to take away from your enjoyment in the process.
DocAitch

[caskwith]

I am trying to visualize a 1/100” deviation and why you are distressed about it.
I am pleased not to leave a significant dead space (1/2-1mm-0.02-0.04”) under the draft and to be within 1 mm (0.04”) of dead center laterally.
I don’t think that you need better accuracy for smoking purposes.
As I am wont to say “we ain’t making Swiss watches here.”
If I am within those parameters, I concentrate on other stuff.
DocAitch

Because I want to sell. And I imagine people won’t be pleased paying several hundred dollars for a pipe with an off center keyhole.

Never had a complaint yet.

[JMG]

I am trying to visualize a 1/100” deviation and why you are distressed about it.
I am pleased not to leave a significant dead space (1/2-1mm-0.02-0.04”) under the draft and to be within 1 mm (0.04”) of dead center laterally.
I don’t think that you need better accuracy for smoking purposes.
As I am wont to say “we ain’t making Swiss watches here.”
If I am within those parameters, I concentrate on other stuff.
DocAitch

Because I want to sell. And I imagine people won’t be pleased paying several hundred dollars for a pipe with an off center keyhole.

I'm with Walt on this one. I can't even really envision 1/100th of an inch off being perceptible. I once sold a pipe pretty much at cost that was maybe 1/16th off. A couple years later the customer told me I was stupid because he couldn't even tell it even though I told him about it and said it smoked wonderfully. If 1/100th is bothering you, I'd say take an extra anxiety med (or maybe just a long walk in the woods) and shake that mess off.

[LatakiaLover]

IAWJMG

[Walldepartment]

Thanks guys. I get the point.