Tube fitment

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sorcerertd

sorcerertd

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I am finding with capped pens, such as PSI classic rollerball and Jr. series pens, that my tubes seem to easily slide in either end of the blank after drilling, but get stuck part way through. Its as if there is a slight bend to the drilled hole. This is even with the shorter cap blank. It's hard to imagine a 12.5 mm bit bending going through a short blank for a pen cap. I see it now and then with other pen types, but not as often. I think it has to do with there being less clearance between the drilled hole size and the tube in some pens. It's been working out in the end product, but l have been wanting to do more with synthetic blanks that will require me to paint the tube. I have no doubt whatsoever that any paint will scrape off when I try to insert the tube.

Admittedly, I do have problems getting a hole straight through a blank. I'm drilling on the lathe with a Nova G3 chuck and dedicated pen jaws. Also, as I learned here, I am using a drill centering bit like these to start the hole. I'm kind of at a loss here. Is this common? Should I try a slightly larger bit? Maybe my lathe is just not running true? Any other suggestions?
 
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sorcerertd said:
I am finding with capped pens, such as PSI classic rollerball and Jr. series pens, that my tubes seem to easily slide in either end of the blank after drilling, but get stuck part way through. Its as if there is a slight bend to the drilled hole. This is even with the shorter cap blank. It's hard to imagine a 12.5 mm bit bending going through a short blank for a pen cap. I see it now and then with other pen types, but not as often. I think it has to do with there being less clearance between the drilled hole size and the tube in some pens. It's been working out in the end product, but l have been wanting to do more with synthetic blanks that will require me to paint the tube. I have no doubt whatsoever that any paint will scrape off when I try to insert the tube.

Admittedly, I do have problems getting a hole straight through a blank. I'm drilling on the lathe with a Nova G3 chuck and dedicated pen jaws. Also, as I learned here, I am using a drill centering bit like these to start the hole. I'm kind of at a loss here. Is this common? Should I try a slightly larger bit? Maybe my lathe is just not running true? Any other suggestions?
Click to expand...
When you're drilling is the bit wobbling? What type of bits?
 
With some woods the act of drilling creates enough heat to swell the wood. Redrill slowly after the bit cools and the tube will go through smoothly. It's the wood not you. Highly figured wood does this more for me. I drill on the lathe so chucking it up again rarely is an issue. Good luck
 
sorcerertd said:
It does wobble some. They are standard jobber bits. Really haven't seen much use yet, maybe 5 sets of blanks.
Click to expand...
It has happened to me a couple of times and every time it has been when the bit wobbled a bit. How that makes a tight hole, I haven't a clue.
 
The bit is wandering on entry and by the time it gets to the center it straightens out. As for cause it could be the chuck not running true. The head and tailstock lined up properly. The jaws not gripping the blank square. You will need to test for these things. No one answer so unless it is something you can not deal with then you need to investigate. No, do not go to larger bit unless the hole is too tight and being you want to paint you may need to step up a size.
 
You are drilling on the lathe ... that is a good practice in order to get a hole which is accurately aligned to the blank axis.

However .... the accuracy of the resulting hole can depend on the nature of your lathe chuck, as well as the starting shape of your pen blank + material.
For best results, the pen blank should be turned round before drilling on the lathe.
The pen jaws you can buy to fit onto a lathe headstock are not particularly accurate ... after all, we are talking about an error of only a few thou.

I think one should not expect too much from those jaws.

In your case, I would recommend touching up the tight part of the hole with a round file ( rat-tail file ).

Another help would be a variable-diameter, adjustable reamer such as these which I buy from Busy Bee Tools in Canada.
Surely Grizzly or HF has them in the US.
I use these reamers a lot for adjusting the drilled hole for tight-fitting tubes. . But take care with these not to enlarge too much.

www.busybeetools.com

Buy Adjustable Blade Reamer Set Of 7pcs at Busy Bee Tools

B3125 7pc Adjustable Blade Reamer Set The blades have hollow ground cutting edges for minimal friction and the ends are center drilled. Size: 1/4" - 9/32" to 7/16" - 15/32"
www.busybeetools.com www.busybeetools.com

Bear in mind another couple of facts. . First, the actual size of a drill bit ( jobber size drills ) is usually just a shade ( 0.002" or so ) under specified size.
Why that is so, I do not know, but I have measured many brand new drill bits and found that to be the case.
Second, after you remove the drill bit from the drilled hole the hole collapses in size by a few thou due to the elastic properties of all materials.
This "elastic collapse" is in addition to any "thermal collapse" due to the heating of the material from the friction of drilling.

So, the bottom line is that drilling is inherently an inaccurate process and the inaccuracies can vary with the choice of materials and the details of your drilling process. . The inaccuracies are not very much, but they are enough to affect the fit of the brass tube .

As an example, consider making a Sierra pen kit. .
The recommended drill size is 27/64" diameter = 0.422" ( not counting the undersizing of the drill bit ). . Your brass tube measures at 0.408".
So already, the difference in those two numbers is only 0.014" .... at the most. . That would be your MAXIMUM clearance between tube and hole.
If an elastic shrinkage of the hole by only 1/2 % occurs, that can reduce your hole by another 0.002".
Allow the thermal shrinkage of about the same amount.

So due to those 3 effects, the hole is down from the MAX clearance of 0.014" by about 0.006" to about 0.008" not considering anything else.

I am just trying to give you a rough idea of SOME of the reasons for an undersize hole.

Another thing you mention is a slight tapering of the hole .... tighter towards the center of the blank, looser towards the drill starting point.
At the drill starting point, the accumulated time that the drill has been in contact with the blank is longer than near the blank's mid point.
So you see that the "drilling action" has been going on longer near the blank end ... hence removing a little more material.

Add to all this, the slight wandering of the drill bit as it enters the material at the end of the blank, just as John T. has said above.
This slight wandering will be worse if the end of the blank is not exactly square with the blank axis.

I realize that none of this is 100% quantitative, but I have confidence in the general ideas.
And what you have described is totally consistent with my own experiences.

I hope this helps a little in the understanding. . Of course, I stand to be corrected if I am in error on anything.
 
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It's funny how that works. A little here, a little there...
I've even run the bit through a few times with a hand drill after the fact and it still doesn't fix it. Maybe I'll try a file inside the hole. Should be easy enough to tell where it's rubbing with a little paint in there anyway. I might have better luck with a brad point, but then expect problems at the exit (unless I cut the blank long and don't go all the way through).
 
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