# Weird Phenomenon.....



## PTownSubbie (Dec 26, 2011)

Alright as some of you know, I have been working on the kitless pens....Tonight, Jason and I did one and the cap doesn't fit on the body. I know it is the cap because if I use a good pen, the bad cap won't thread on the good body.

The cap was drilled at 11.2mm to fit the M12x0.8 triple start tap. The tap was used to create the threads. I used a tap guide to maintain pressure on the threads. The cap was then placed on the mandrel and turned to size. I have been using pressure from the tail stock (wondering if this is causing problems). The threads after turning are now reading 11.7mm in diameter when they should be 11.2mm.

This has happened twice now. Both with the last two pens I have made. The only thing that I changed was the way the tailstock pressure was added. Can you apply too much pressure? And would that possibly cause vibration that would somehow strip the threads out some?

Those that turn your kitless on mandrels, do you use any tailstock pressure? If so, how do you apply it?

I will try some more things tomorrow but I would really like to figure this out so I stop ruining blanks.....

Thanks!


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## PenMan1 (Dec 26, 2011)

Fred, what material are you using? If PR, it could be heat expansion ? Or pressure from the tail.

Look at Texatdurango (George) tutitorials on "another way to make a pen". George shows how to make a "thread jig" in this tut. This little "do dad" has made threading alternative materials much easier for me.

I keep my thread "do dad" in the finished theads and attach the jig via collet chuck, then finish the cap body without issues.

Good luck!


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## PenMan1 (Dec 26, 2011)

I had "similar issues" trying to do custom work on a mandrel. When I threw it away in favor of longer blanks and a collet chuck (George's method) I had much better results.


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## drgoretex (Dec 26, 2011)

Hmmm....perhaps my brain is on hold (entirely likely, to be honest), but I don't quite follow.  Is the 'bad' cap then too tight on the 'good' pen, or too loose?

The measurements - perhaps I am missing something, but from my understanding, assuming 60 degree threads, after tapping with an M12 x 0.8, the inside diameter should be 12 - (0.866 x (2 x 0.8)), or 10.6mm.  So then drilling with an 11.2 bit would probably make far too big a hole.  I believe the drill size I used for this particular die was a 27/64 bit, which is about 10.7mm, and it seemed to work fine.

If I have missed something, I apologize for leading astray 

Cheers,

Ken


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## PenMan1 (Dec 26, 2011)

Oops, missed the 11.2 drill size. My math aligns with Ken's at 10.6. In this case, I would drill at 10.5mm (because that is REAl convenient -jr bottom barrel), but seems that 27/64 would do nicely as well.


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## PTownSubbie (Dec 26, 2011)

The bad cap is too loose..... The material is alumilite.

The way I understand it and it has worked for me is you take the 0.8 and subtract it from the 12 and you get the correct drill to use. 

Which in this case 12-0.8=11.2. That worked fine on other pens....

I read somewhere else that materials like Ebonite may suffer from heat expansion. Is this true from alumilite also?


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## hewunch (Dec 26, 2011)

I think I use a 7/16ths bit as per recommendations on a thread about taps and dies.


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## Dalecamino (Dec 26, 2011)

hewunch said:


> I think I use a 7/16ths bit as per recommendations on a thread about taps and dies.


Yes Hans, that's the one. And, .465 on the tenon works for me. 

Another thought I had was, the adjusting screw on the die could need adjusting. Just a thought.


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## PenMan1 (Dec 26, 2011)

This little calculator may be useful.

how to calculate drill size for tap

Sorry, can't copy over the link. Google the second sentence to get the free calculator.

Fred: 
If 11.2 HAS worked before and now DOESN'T, it seems to me that it would just about have to be expansion of some sort. Did you test fit the threads to body before milling the cap?


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## KBs Pensnmore (Dec 27, 2011)

PTownSubbie said:


> Alright as some of you know, I have been working on the kitless pens....Tonight, Jason and I did one and the cap doesn't fit on the body. I know it is the cap because if I use a good pen, the bad cap won't thread on the good body.
> 
> The cap was drilled at 11.2mm to fit the M12x0.8 triple start tap. The tap was used to create the threads. I used a tap guide to maintain pressure on the threads. The cap was then placed on the mandrel and turned to size. I have been using pressure from the tail stock (wondering if this is causing problems). The threads after turning are now reading 11.7mm in diameter when they should be 11.2mm.
> 
> ...


Fred
The .8 on the tap/die refers to the pitch on the thread. To work out the drill size according to my Engineers Black Book is to minus 
0.8P -.6134P =.1866x2 = .3732 of the pitch. which brings it down to 11.6268 = 12mm close enough to your 11.7mm. I think I've worked it out correctly.
Maths was NEVER my favourite subject
Is your die adjustable? Because if it is, that might be where you are having the problem, as what normally happens is that the tap is used first as that is not adjustable.Then the die is loosened right off and then adjusted till the threads match.
Hope this helps.
Regards
Kryn


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## KBs Pensnmore (Dec 27, 2011)

Another way to work it out. 
Drill size= Basic Major Diam. of Thread - %of Full Thread X Pitch (mm)
..................................................................76.98
Example to find Tapping Drill Size for M12X.8 with 70% thread 
Drill Size = 12 - 70X.8 = .7274616 = 11.27
..................... 76.98
This works for any Metric Thread Cutting Taps.

For Imperial Thread Cutting Taps.

..................................................................%of Full Thread 
Drill size = Basic Major Diam. of Thread -.0130 X Threads Per Inch

Example to find Tapping Drill Size for 1/4X20 with 75%

Drill Size = .2500 - .0130X75 = .2010 OR .0021 UNDER 13/64
...................................20
Just realised that this contadicts the other one I put up
Kryn


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## mredburn (Dec 27, 2011)

Some materials will stretch and raise under pressure. I have that problem with silver. As the teeth cut through the material your trying to thread it pushes some of the material up. Some materials will stretch around the teeth as your cutting and drilling. 
I let my tail stock slide when I'm making threads. I put just a little finger pressure on it to keep any chance of the tail stock catching and stripping the material. each material you thread will react a little differently. I use the 7/16 drill for that tap set and I do it in burl woods as well as acrylics and metals. You might try putting it in the fridge for half an hour before you tap it after you drill it. If the heat is softening the material it will deform/stretch the hole as it taps it and then return to round after the tap is removed.

Edit; the rule of thumb for metric is to subtract the pitch from the diameter 12-.8=11.2
the pitch of .8 is the distance between the points and the length of the walls of the thread. The distance from the base of a pyramid to the point is smaller than the length of the sides on an equilateral triangle. That is why your math is off.


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## hewunch (Dec 27, 2011)

mredburn said:


> You might try putting it in the fridge for half an hour before you tap it after you drill it. If the heat is softening the material it will deform/stretch the hole as it taps it and then return to round after the tap is removed.



First my CA now my taps?! My wife is going to think I have lost my ever loving mind. I can just hear it now...."Honey, have you seen my pliers?"

"I think they are next to the butter"


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## mredburn (Dec 27, 2011)

I have had to refridgerate Delrin and uhmw before tapping threads in them for just the exact reasons stated here. Another quick question would be how thick are your pen walls when you drill and tap them. You may be able to leave them much thicker before you tap and then trim then down afterwards. The extra material might be enough to give extra rigidity to your pen material and help keep this from happening.

Im working on one of my wooden rollerball pens that uses ebony for the threaded areas. In order to keep the cap centerband from blowing out as I was threading it I had to leave the piece 3/4 of an inch in diameter to thread the 12mm hole. Even then it was slow going.


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## studioso (Dec 27, 2011)

Math aside, I know I drill my pr 9mm for this tap. 
Sounds small, but it worked (so far) for me.


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## soligen (Dec 27, 2011)

A couple more questions.

Was the cap thread size OK before you mounted the cap to be turned and only bad after?

For tailstock pressure, do you mean while threading or while turning before cutting the closed end off?

Assuming it happened while turning, make sure you have shoulder for the cap to tighten against so that tailstock pressure doesn't affect the threads.

You can see picks of Justin's and my version 1 (now retired) in this thread.

http://www.penturners.org/forum/showthread.php?t=80775&highlight=kitless+mandrel


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## soligen (Dec 27, 2011)

mredburn said:


> Another quick question would be how thick are your pen walls when you drill and tap them. You may be able to leave them much thicker before you tap and then trim then down afterwards.


 
Yes, Definitely do this. This was one of my leanings too. Alumilite can stretch.  However, this would make the threads too tight, and as I understand it, the problem is threads being too loose.


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## drgoretex (Dec 27, 2011)

PTownSubbie said:


> The bad cap is too loose..... The material is alumilite.
> 
> The way I understand it and it has worked for me is you take the 0.8 and subtract it from the 12 and you get the correct drill to use.
> 
> ...



I don't think this is correct.

First of all, think of the thread cross section.  The 0.8 refers to the distance between threads, or the width of the base of the thread.  So what you want to know is the _height/depth_ of the thread (you know the major diameter (outside diameter), you want the minor diameter(inside diameter)).  

Assuming the thread is at a 60 degree angle (usually a pretty safe assumption for standard triangular threads), the estimate for the depth of the thread is 0.866 x the distance between threads, which would be 0.69mm.

The minor diameter would then be 12mm minus (2 x the thread depth) (one for each side).  This comes out to about 10.6mm.

You do have some room for error, as the outside threading on the barrel doesn't have to match the inside threading on the cap perfectly.  In fact, if it did, it would be too tight.  That is why sometimes you want to drill out the cap to allow 70% of the thread to contact.  That would mean using a drill bit slightly larger than the calculated 10.6mm.  That is probably why when you used a larger than called for drill bit previously, is still worked out OK.

OK, gotta get back to the salt mines.

Ken


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## Timebandit (Dec 27, 2011)

drgoretex said:


> Hmmm....perhaps my brain is on hold (entirely likely, to be honest), but I don't quite follow.  Is the 'bad' cap then too tight on the 'good' pen, or too loose?
> 
> The measurements - perhaps I am missing something, but from my understanding, assuming 60 degree threads, after tapping with an M12 x 0.8, the inside diameter should be 12 - (0.866 x (2 x 0.8)), or 10.6mm.  So then drilling with an 11.2 bit would probably make far too big a hole.  I believe the drill size I used for this particular die was a 27/64 bit, which is about 10.7mm, and it seemed to work fine.
> 
> ...



Ken, you have me confused.............. How can this possibly work. If  you are drilling a 10.6mm-27/64" and the tenon for your threads has to  be around 12mm(11.8mm for mine) even after you cut the threads, you cant  physically put a 11.8mm tenon into a 10.6mm hole  Freds math is right, the right bit to use is a 11.2mm but that bit is  hard to find and i like a little bit of clearance so i use a 7/16" to  give just a little bit more clearance. Can you explain to me how you  make this work


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## PenMan1 (Dec 27, 2011)

This may also be a difference (although, I think Fred's issue is expansion from cap finishing).

Looking at Fred's first kitless, I notice that his cap overlaps the body of the pen. Naturally, this would require a larger hole.

I butt the cap and the body at the thread joint, with no cap overhang. For my purposes, a 10.5 mm bit works perfectly.

It could be that we are "talking apples and oranges".


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## Timebandit (Dec 27, 2011)

PenMan1 said:


> This may also be a difference (although, I think Fred's issue is expansion from cap finishing).
> 
> Looking at Fred's first kitless, I notice that his cap overlaps the body of the pen. Naturally, this would require a larger hole.
> 
> ...



Again i am confused What size tenon do you make to cut your threads on the barrel. It its around 12mm, which it should be, how can you fit a 11.5-12mm tenon(11.8 for me) into a 10.5mm hole even after you cut your threads. Your tenon must be much smaller.


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## soligen (Dec 27, 2011)

I too use the 7/16" for the M12 x .8 triple start tap.  This size works great.

If you use a 10.5 mm with this tap, then it might work, but your tapping will be more difficult as you will be removing .6 - .7 mm of extra material with the tap.

Want a rough check of your drill diameter?  Use your calipers on the end of the tap.  Measure a little bit in from where the threads actually start - try the second partial thread.  I did this and got 10.27mm.  This method isn't vary accurate, but it can confirm your calculation is it is close.

BTW the very tip of my tap (the part that has no threads) is 11mm, so it will have trouble fitting in a 10.5 mm hole.  It could maybe be forced in, but not ideal.

I think we may well be talking about different things on the whole 10.5 mm thing.


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## Texatdurango (Dec 27, 2011)

PTownSubbie said:


> Alright as some of you know, I have been working on the kitless pens....Tonight, Jason and I did one and the cap doesn't fit on the body. I know it is the cap because if I use a good pen, the bad cap won't thread on the good body.
> 
> The cap was drilled at 11.2mm to fit the M12x0.8 triple start tap. The tap was used to create the threads. I used a tap guide to maintain pressure on the threads. The cap was then placed on the mandrel and turned to size. I have been using pressure from the tail stock (wondering if this is causing problems). The threads after turning are now reading 11.7mm in diameter when they should be 11.2mm.
> 
> ...


 After reading your post three times to make sure I am understanding the problem correctly I think I might have something you need to look at.

First, you're drilling with the right size drill bit, I like to use the very simple formula for metric sizes of subtracting the pitch from the diameter and in my case I use the 7/16" bit since I don't have metric drills.

Second, I don't see any reason to be applying ANY pressure whatsoever to the tailstock when tapping.  This is Alumilite not aluminum!   When I tap alumilite (or acrylic and ebonite) I chuck the tap in the tailstock Jacobs chuck and *HAND FEED* the tap with the tailstock loose on the lathe.

I've tapped well over 100 pens using this particular tap and dies set and have NEVER run into a situation where the alumilite stretches while tapping and I just grabbed a handful of pens I made, some new, some older, and checked the finished inside diameters of the threaded cap and none exceeded .440".

Now to what I think MIGHT be your problem and I think it might be a simple fix. * I think you could be drilling your holes a little crooked!*

I do most of my pens on my Jet mini lathe and the tailstock is loose as a goose and can be tightened either dead on with the headstock or several thousandths in either direction so I have to be careful when I clamp it down for use.

Just for grins I chucked a practice piece in my collet chuck then deliberately tightened the tailstock ever so slightly off center then drilled a hole.  Sure enough my 7'16" drill bit drilled a pretty hole that measured .455" when it should have drilled a hole closer to .438".

So, what I might recommend are two things; First, always start with a center drill.  This will make sure you are as close to dead center as you can be when drilling.

Second, make sure your tailstock is aligned with your headstock and make sure your quill tightening lever is snug to keep your Jacob chuck from wobbling left and right when drilling.

I think a LOT of our problems are caused by our equipment and some can be so minor that we never think of them, instead we start looking into all sorts of scenarios, some of which get pretty convoluted!:biggrin:

I certainly hope you find a fix to your problem.


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## PenMan1 (Dec 27, 2011)

soligen said:


> I too use the 7/16" for the M12 x .8 triple start tap. This size works great.
> 
> If you use a 10.5 mm with this tap, then it might work, but your tapping will be more difficult as you will be removing .6 - .7 mm of extra material with the tap.
> 
> ...


 

Dennis:
You have described my method exactly. I did forget to mention that I do chamfer the hole to start the tap!!!! Handy information, that I forgot to include. Sorry!


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## PTownSubbie (Dec 27, 2011)

WOW! Lots of good things to check! I appreciate everyone's input. I should have done a few more and checked each of these things you guys asked about. I am going to give these a shot today...I will update if I find what the problem turns out to be.....



mredburn said:


> Some materials will stretch and raise under pressure. I have that problem with silver. As the teeth cut through the material your trying to thread it pushes some of the material up. Some materials will stretch around the teeth as your cutting and drilling.
> If the heat is softening the material it will deform/stretch the hole as it taps it and then return to round after the tap is removed.
> 
> Edit; the rule of thumb for metric is to subtract the pitch from the diameter 12-.8=11.2
> the pitch of .8 is the distance between the points and the length of the walls of the thread. The distance from the base of a pyramid to the point is smaller than the length of the sides on an equilateral triangle. That is why your math is off.


 
Thanks for the confirmation on the math for the bit. I used a new bit and didn't clean it when I drilled my hole and remember seeing some smoke and the bit being very hot. I think I got some heat deformation and when I tapped, it didn't do something correctly....



soligen said:


> A couple more questions.
> Was the cap thread size OK before you mounted the cap to be turned and only bad after?
> 
> For tailstock pressure, do you mean while threading or while turning before cutting the closed end off?
> ...


 
Unfortunately, I didn't check the size before tapping. I only checked the size when I tried to fit it to the body.....I will do this from now on though.

The pressure I was talking about was during the turning process. When the material is on your mandrel, do you use the tailstock to stabilize the end of the blank? Kind of like a closed end pen....I use pressure on the blank end to stabilize it while turning. Despite how tightly you make your mandrel, you will get some vibration on the end of the blank while turning....

My mandrels have shoulders to tighten against. Mine are not very different than what others have shown here.



Texatdurango said:


> After reading your post three times to make sure I am understanding the problem correctly I think I might have something you need to look at.
> 
> First, you're drilling with the right size drill bit, I like to use the very simple formula for metric sizes of subtracting the pitch from the diameter and in my case I use the 7/16" bit since I don't have metric drills.
> 
> ...


 
I use a Tap Guide. It installs in my Jacobs chuck and is nothing more than a spring that applies a little pressure to the tap and keeps it straight while starting the threads. The pressure with this is not too extreme so I don't really think this is causing the problem.....

Yep, I always start the holes with a center drill. I have various sizes and try to get as close to the final diameter as possible when I choose which one to use. I also step up in drill bit sizes so as to not try to hog out too much material in a single pass. I don't try to drill too fast and clean the flutes often while drilling. I just realigned my lathe a week or two ago. It was of a little but is dead on now so I do't think it is an alignment thing.


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## soligen (Dec 27, 2011)

PTownSubbie said:


> When the material is on your mandrel, do you use the tailstock to stabilize the end of the blank? Kind of like a closed end pen....


 
Yes, I always use the tailstock as much as possible. Vibration = bad. I only remove the tailstock after I part off for the closed end, which I do last.


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## drgoretex (Dec 27, 2011)

Timebandit said:


> drgoretex said:
> 
> 
> > Hmmm....perhaps my brain is on hold (entirely likely, to be honest), but I don't quite follow.  Is the 'bad' cap then too tight on the 'good' pen, or too loose?
> ...



Sure.  Quite correct, the tenon is 12mm.  So once I use the die on it, the MAJOR diameter of the tenon threading is 12mm (thread peak to thread peak), while the MINOR diameter is 10.6mm (thread valley to thread valley).   The cap is drilled to 17/64", or about 10.7mm.  So once I use the tap, the MINOR diameter (smallest diameter of the threading) will be the drill size, 10.7mm, and the MAJOR diameter (largest diameter of the threading) will be 12mm.  Thus the barrel tenon will not SLIDE into the cap, but will thread into it.

Lots of fun this math.  Though I was done in high school...

Cheers,

Ken


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## PTownSubbie (Dec 27, 2011)

Alright, I just went out and did a few more tests. Despite my lathe headstock and tailstock being perfectly aligned (I just rechecked it) my 11.2mm bit creates a 11.45mm hole. This is obviously too large and is likely the cause of my problem. Despite this I tapped the hole and whala...the hole doesn't thread to the body or threads but only very slightly and is not tight at all.

So, I drilled the other end with a 7/16" bit as others have suggested. This gave me a 11.2mm initial hole and when tapped, threads onto the pen just fine.....

Like I said, I rechecked alignment and it is good so there must be a slight bend in the drill bit. However, I placed the drill bit on my tablesaw top and rolled it. It rolled fine and there doesn't seem to be any bend. At least not noticable to the human eye.....So much for spending money on an 11.2mm drill bit! 

Atleast I have an idea where the problem is now. Thanks for all the suggestions!



drgoretex said:


> Sure. Quite correct, the tenon is 12mm. So once I use the die on it, the MAJOR diameter of the tenon threading is 12mm (thread peak to thread peak), while the MINOR diameter is 10.6mm (thread valley to thread valley). The cap is drilled to 17/64", or about 10.7mm. So once I use the tap, the MINOR diameter (smallest diameter of the threading) will be the drill size, 10.7mm, and the MAJOR diameter (largest diameter of the threading) will be 12mm. Thus the barrel tenon will not SLIDE into the cap, but will thread into it.
> 
> Lots of fun this math. Though I was done in high school...
> 
> ...


 
Doesn't that leave the threads ultra tight? Almost to the point of not being able to open and close the pen?


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## soligen (Dec 27, 2011)

drgoretex said:


> So once I use the die on it, the MAJOR diameter of the tenon threading is 12mm (thread peak to thread peak), while the MINOR diameter is 10.6mm (thread valley to thread valley).


 

You must have a different tap/die than me, Justin & Fred. My minor diameter is about 11.2mm If I turn the threads off of something I used the die on, I am usually left at about 11.1mm, which means the minor diamerter must be greater than 11.1mm.

What you are describing sounds more like a M12 x 1.25, which is likely a single start size found in tap & die sets.  We are discussing M12 x .8


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## drgoretex (Dec 27, 2011)

PTownSubbie said:


> Alright, I just went out and did a few more tests. Despite my lathe headstock and tailstock being perfectly aligned (I just rechecked it) my 11.2mm bit creates a 11.45mm hole. This is obviously too large and is likely the cause of my problem. Despite this I tapped the hole and whala...the hole doesn't thread to the body or threads but only very slightly and is not tight at all.
> 
> So, I drilled the other end with a 7/16" bit as others have suggested. This gave me a 11.2mm initial hole and when tapped, threads onto the pen just fine.....
> 
> ...


 
Good question.  I had mentioned earlier that if the thread matches too closely, it would indeed be too tight (I have done this by using a drill bit smaller than the minor diameter on the cap, so the threading was matched...and very tight).  However, with the 27/64 bit, which is 10.7mm, it calculates out to about 90% contact.  With the expected 'slop' in the drilling, I would expect it is closer to 80%.  With a 7/16 bit, only 1/64 bigger, you get an 11.1mm hole, or likely even a bit bigger than that with a bit of drilling slop.  This would give you 64% contact, which is awesome _if_ the drilling is very accurate, and the barrel tenon threading accurate.  With a bit of drilling slop, it's going to drop the contact, or thread overlap too low, and to my mind, this may account for threads not engaging.   

One other thing to consider is that the group purchase triple start was an open die (ie adjustable).  May be worth checking it to ensure it is accurate, and not 'too tight', as that would make the barrel tenon threading to too small a diameter, further reducing the thread contact.  I mention this because the little screw in the die stuck out a bit on mine, and resulted in a very tight fit in the die-holder.  This could well reduce the inside diamteter of the die.

With all that said, whatever works :tongue:  I just figured I'd share my own way of working through this in case it was of help.  Great thread!

Cheers,

Ken


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## Texatdurango (Dec 27, 2011)

drgoretex said:


> I had mentioned earlier that if the thread matches too closely, it would indeed be too tight (I have done this by using a drill bit smaller than the minor diameter on the cap, so the threading was matched...and very tight). However, with the *27/64 bit*, which is 10.7mm, it calculates out to about 90% contact. With the expected 'slop' in the drilling, I would expect it is closer to 80%. With a 7/16 bit, only 1/64 bigger, you get an 11.1mm hole, or likely even a bit bigger than that with a bit of drilling slop. This would give you 64% contact, which is awesome _if_ the drilling is very accurate, and the barrel tenon threading accurate. With a bit of drilling slop, it's going to drop the contact, or thread overlap too low, and to my mind, this may account for threads not engaging.
> 
> One other thing to consider is that the group purchase triple start was an open die (ie adjustable). May be worth checking it to ensure it is accurate, and not 'too tight', as that would make the barrel tenon threading to too small a diameter, further reducing the thread contact. I mention this because the little screw in the die stuck out a bit on mine, and resulted in a very tight fit in the die-holder. This could well reduce the inside diamteter of the die.
> 
> ...


Not saying anyone is right and anyone is wrong but let us know how well you like using the 27/64" bit after a few dozen pens!  I started out using one and quickly got tired of fooling around with VERY TIGHT fitting pen caps.  I found that customers don't want to wrestle with a pen just to open it so I opted for the 7/16" bit which still allows for plenty of thread engagement but opens and closes very easy!


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## Texatdurango (Dec 27, 2011)

PTownSubbie said:


> Alright, I just went out and did a few more tests. *Despite my lathe headstock and tailstock being perfectly aligned* (I just rechecked it) my 11.2mm bit creates a 11.45mm hole. This is obviously too large and is likely the cause of my problem. Despite this I tapped the hole and whala...the hole doesn't thread to the body or threads but only very slightly and is not tight at all.
> 
> So, I drilled the other end with a 7/16" bit as others have suggested. This gave me a 11.2mm initial hole and when tapped, threads onto the pen just fine.....
> 
> ...


Not disputing your findings whatsoever but consider this as a possibility especially since you think your drill bit is pretty true......  I think most of us check the tailstock alingment by sticking a 60 degree live center in the tailstock, a 60 degree dead center in the headstock spindle then bringing them up to meet.  That's a great way to check BUT..... now remove the centers, add a chuck of sorts to the headstock to hold the blank which is probably sticking out a few inches then probably a Jacobs drill chuck in the tailstock, slip in a drill bit that's close to 5" or 6" long and all of a sudden you have all sorts of oppornuties for a hair off here and a hair off there over the total distance involved and it's very possible for a perfectly round bit to cause an oversize hole.  Don't take this as me knocking your ability to check your lathe out, like the others, I'm just trying to help.  Just chuck everything up and look at all the ways tolerances can build up to cause the problem.

There's also the possibility that while the tailstock and headstock meet perfectly 1" away from the headstock that the spindle could be slightly out of alignment with the bed itself and the further away from the headstock the tailstock gets, the worse it gets.  Keep in mind that when drilling the tailstock is what... 8" or more from the headstock now!


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## drgoretex (Dec 27, 2011)

Texatdurango said:


> drgoretex said:
> 
> 
> > I had mentioned earlier that if the thread matches too closely, it would indeed be too tight (I have done this by using a drill bit smaller than the minor diameter on the cap, so the threading was matched...and very tight). However, with the *27/64 bit*, which is 10.7mm, it calculates out to about 90% contact. With the expected 'slop' in the drilling, I would expect it is closer to 80%. With a 7/16 bit, only 1/64 bigger, you get an 11.1mm hole, or likely even a bit bigger than that with a bit of drilling slop. This would give you 64% contact, which is awesome _if_ the drilling is very accurate, and the barrel tenon threading accurate. With a bit of drilling slop, it's going to drop the contact, or thread overlap too low, and to my mind, this may account for threads not engaging.
> ...



Admittedly I have only done a few with this particular tap and die, so appreciate the heads up.  Might have to try the 7/16 with the next one and see how it goes.

Ken


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## PTownSubbie (Dec 27, 2011)

Texatdurango said:


> Not disputing your findings whatsoever but consider this as a possibility especially since you think your drill bit is pretty true...... I think most of us check the tailstock alingment by sticking a 60 degree live center in the tailstock, a 60 degree dead center in the headstock spindle then bringing them up to meet. That's a great way to check BUT..... now remove the centers, add a chuck of sorts to the headstock to hold the blank which is probably sticking out a few inches then probably a Jacobs drill chuck in the tailstock, slip in a drill bit that's close to 5" or 6" long and all of a sudden you have all sorts of oppornuties for a hair off here and a hair off there over the total distance involved and it's very possible for a perfectly round bit to cause an oversize hole. Don't take this as me knocking your ability to check your lathe out, like the others, I'm just trying to help. Just chuck everything up and look at all the ways tolerances can build up to cause the problem.


 
Busted again....LOL!! Now, I thought about this some when I checked it again. Maybe the word perfect is not the right word. Nothing is perfect afterall.....

I did use a dead center in the headstock but in the tailstock I put in my jacobs chuck and tap guide. These aligned as close as anyone would desire.

I am not certain I have anything other than a dead center to use in the headstock.

I will admit, the thought of amplification crossed my mind when I couldn't find a problem with the bit.....


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