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Old 12-06-2018, 07:06 AM   #21 (permalink)
 
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The 10.5mm tube is snug in the prescribed hole size. I've had more than one get bound up about halfway through as well. And I also drill from one end only. I typically sand the hold larger and all is good. The next size up bit would work without all the the fanfare.

Though I can't claim empirically what causes this, perhaps one side of my bit is a little sharper or ground at a different angle than the other (with a Drill Doctor this should not be the case), or there is a small ding in one of the flutes. Or perhaps I have a little runout on my quill that causes the bit to drift. Any way you slice it, there is still little room for glue even in a perfectly drilled hole so opening it up one way or the other isn't a bad idea.
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Old 12-06-2018, 10:18 AM   #22 (permalink)
 
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I hate to belabor this topic and beat to a dead pulp but could it be possible all you people that seem to think the wood shrinks in the middle be seeing some runout in the blank, drill bit or lathe itself. When you start a bit in a blank many times the bit will wander some till it grabs and when it gets about half way into blank it now is drilling straight to the size the bit truely is. That is why you see the hole slightly larger on the ends than the center. The center is drilled to basically what the drill bit measures. I believe the bit is just too tight for the tube to begin with. I still do not believe the wood is shrinking especially that thin. This is one reason it is suggested to use a starter bit all the time. Because if the wood shrinks in the middle than why does it not shrink on the ends too.??? Even if there is a flaw in the bit that flaw passes all parts of the inside the blank as you advance. If there is a problem in one area it would show up throughout the blank. As I said it is a head scratcher for me. Happy turning.
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Old 12-06-2018, 10:39 AM   #23 (permalink)
 
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Quote:
Originally Posted by jttheclockman View Post
I hate to belabor this topic and beat to a dead pulp but could it be possible all you people that seem to think the wood shrinks in the middle be seeing some runout in the blank, drill bit or lathe itself. When you start a bit in a blank many times the bit will wander some till it grabs and when it gets about half way into blank it now is drilling straight to the size the bit truely is. That is why you see the hole slightly larger on the ends than the center. The center is drilled to basically what the drill bit measures. I believe the bit is just too tight for the tube to begin with. I still do not believe the wood is shrinking especially that thin. This is one reason it is suggested to use a starter bit all the time. Because if the wood shrinks in the middle than why does it not shrink on the ends too.??? Even if there is a flaw in the bit that flaw passes all parts of the inside the blank as you advance. If there is a problem in one area it would show up throughout the blank. As I said it is a head scratcher for me. Happy turning.
And now to set the dead pulp on fire...

I don't think there is any "shrinking" in the middle at all. I think it's a combination of imperfect tools, possibly imperfect techniques and the nature of the materials being drilled. Does this occur more often in materials with end grain? How about plastics, both soft and brittle? Tru-Stone?

I would think that if the bit drifts a little in a given direction, then the blank would tend to remain straight (in relationship to the hole) as it is being supported by the bit running through it. The off-center drilling would continue and get worse the deeper the hole is drilled. Once the bit is removed, the blank returns to its natural state, possibly with a non-straight hole. This would be on a small scale, of course, but you get the idea.
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Old 12-06-2018, 10:52 AM   #24 (permalink)
 
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It is not runout, runout causes a larger hole, not a smaller hole. Same with the bent drill bit theory, a bent drill bit will act as a "boring bar" and bore a larger hole than the bit size.

Pool cue makers have a reason for not turning a pool stick in one sitting, they remove a little wood each time over days for a reason. As you remove wood, you remove or change internal stressors inside the wood. The same reason as some of the professional duck callmakers drill their blanks one day with a 5/8" drill bit and then wait a few days and ream them with a 5/8" reamer. The "pressure stressors" at the end of a blank are different than on the center of the blank.
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Old 12-06-2018, 10:56 AM   #25 (permalink)
 
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It is not runout, runout causes a larger hole, not a smaller hole. Same with the bent drill bit theory, a bent drill bit will act as a "boring bar" and bore a larger hole than the bit size.

Pool cue makers have a reason for not turning a pool stick in one sitting, they remove a little wood each time over days for a reason. As you remove wood, you remove or change internal stressors inside the wood. The same reason as some of the professional duck callmakers drill their blanks one day with a 5/8" drill bit and then wait a few days and ream them with a 5/8" reamer. The "pressure stressors" at the end of a blank are different than on the center of the blank.
That makes sense. Now I'm even more curious as to how this applies to different materials. (Wood, acrylic, antler, etc.) Amboyna burls have historically given me grief on a 10.5mm tube. Always had to sand the hole.
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Old 12-06-2018, 11:10 AM   #26 (permalink)
 
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Stuart (the OP) posted an update on his problem earlier today that contains some information that may help clarify what is happening:

"Also I only drilled all the way through it, lol wouldn't trust drill half way and holding my breath hoping the holes meet."

And - - -

"However, over here in Australia it states to use a 10.5mm bit for Sierra pens and this is where the problem is... I think. Reading instructions from the States, it states to us a 24/64 drill bit, which in mm's is slightly larger then 10.5mm. "

Obviously, there is no 24/64" bit; 24/64 is actually 3/8", and that is far too small. That may just be a typo.

The actual recommendation for the US version of a Sierra is 27/64 which is just a hair larger than a 10.5mm bit. And there is an assumption here that the pen kit he purchased in Australia labeled 'Sierra' is the same as the kit by the same name in the US.

He doesn't actually state which bit he is using, but I would assume that since he is in metric-land, its 10.5 mm. In that case, the hole he is drilling is slightly undersized. My suggestion would be to try the next larger standard metric size - 10.8mm.
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Old 12-06-2018, 02:35 PM   #27 (permalink)
 
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John (and others),

Don't let it be a head scratcher or a head shrinker.
Wood has elasticity just like every other material.
When you force a bit through it, it expands.
When you back out the bit, the wood contracts ... it is not shrinking, per se.
At the ends you don't experience the same expansion and contraction because the bulk is not there ... also, the elasticity is not isotropic but has different effects in different directions (across the grain, parallel to the grain) partly because wood is not a homogeous material. . On top of that, the elasticity is temperature dependent and the there is more frictional heating as the drill approaches the longitudinal center of the blank, partly because there is more wood surrounding the bit and partly because there is less cooling for the business end of the drill.

Therefore you expect different behaviour near the center as opposed to the ends. . Perfectly normal when you consider the physical properties of the materials involved.

This will happen even with a "perfect" drill bit, with perfectly centered drilling which is aligned perfectly with the axis of rotation.

Of course, it would be extremely complicated for even a person with a PhD in materials science to write down an exact equation for the process and solve it mathematically, or even numerically. . There are just too many factors to consider and too many unknowns for any material (eg. wood). . But in spite of the fact that we can't do a complete quantitative explanation we can understand the principles involved. . Ask any qualified mechanical engineer and I have no doubt he would agree.
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Old 12-06-2018, 02:44 PM   #28 (permalink)
 
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Quote:
Originally Posted by magpens View Post
Wood has elasticity just like every other material.
When you force a bit through it, it expands.
When you back out the bit, the wood contracts ... it is not shrinking, per se.
At the ends you don't experience so much expansion and contraction because the bulk is not there ... also, the elasticity is not isotropic but has different effects in different directions (across the grain, parallel to the grain) partly because wood is not a homogeous material. . On top of that, the elasticity is temperature dependent and the there is more frictional heating as the drill approaches the longitudinal center of the blank, partly because there is more wood surrounding the bit and partly because there is less cooling for the business end of the drill.
And I would expect this problem to be aggravated if the hole is snug to begin with, as OP has suggested.

So Mal is correct - it may not be rocket science after all.

However that does suggest another question - how long is OP waiting between drilling the hole and attempting to insert the tube. I would expect that dimensional changes associated with heating would change over time after the hole has been drilled.

So is it better to insert the tube quickly, while the wood is still warm, or wait until it has cooled down?
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Old 12-06-2018, 04:14 PM   #29 (permalink)
 
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Hi Stuart,

That happened to me just last week on two pens ! The problem is the wood itself, cherry burl, very hard. I drilled straight thru taking my time, no heat, the wood still moves after drilling. Tube seemed to fit right after drilling, but come glue in time not even close ! I let it sit and drilled again with a tiny bit larger bit. donīt give up

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Old 12-06-2018, 04:25 PM   #30 (permalink)
 
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Mal I have been wood working for over 40 years. I know how wood moves. I know how heat creates problems. I know how temp from the outside can affect wood and also finishes. I know how water within has a great effect on wood. I know all that but again you are talking 1/4" at best all around the internal stress is so minimal the pool cue thing was brought up again the diameter is 3 times that of a pen blank. They work with balance to their end product. We do not. Why is it I never encountered this problem?? That is why it is head scratching. I have done exotics that are known to be prone to movement such as pink ivory, holly, ebony, burls of all kinds, and such and not once has a tube gotten stuck in the middle of a 3 inch long piece of wood. Heck i have used pens with blanks longer than that. I do drill and also glue the same day so maybe there is something to that . When I drill I usually start with recommended bit size. If I need to step up the tube does not go in right from the end and I make note in instructions to step up the bit for next time. I think theories are being thrown around here an there is something more to the operation of the OP then wood shrinking.

Love for someone to give me an example of a wood that they found prone for this to happen. I may have some and will give it a try. Also explain your operation of drilling the blank and when you notice the tube does not go all the way in. Hope that is enough smileys.
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