Churchill Fountain Pen tube sizes

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Jans husband

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May 4, 2020
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85
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Doncaster England
I have been working on a Churchill Fountain pen today. The drill sizes are supposed to be 31/64 and 33/64ths

I didn't have those and so I have bought them.
However when I drilled the longer blank with the 31/64th drill bit the tube just rattled around in the hole, suggesting that the hole or the tube were the incorrect size. I glued it anyway to see what would happen, and sure enough there was a gap between tube and blank after the glue had cured.
I turned the blank down to the brass tube and the tube measured just shy of 12mm, quite a bit less than 31/64ths, so I used a 12mm drill and used another piece of the blank (solid green acrylic so no matching problems) and it fitted perfectly-pen completed!!
Has this problem happened to others?
I can't understand why the instructions as to the drill size were so way out.

Mike
 
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magpens

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Feb 2, 2011
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Coquitlam, BC, Canada
Those drill sizes are correct ..... 33/64 for upper (shorter) tube and 31/64 for lower (longer) tube ..... according to the instruction sheet that I have.

I don't have an unused kit/tubes to actually measure the diameters of the tubes.
 

Mullanphy

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Apr 5, 2021
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Florissant, MO
Happens all the time with slimlines. Digital calipers show the tube OD is 6.87-6.89mm, and three of my four 7mm drill bits measure 6.98-7mm - quite a difference. I had a 7mm bit that measured 6.91mm, but I broke it, so I have to get another not-quite-7mm 7mm bit.

Another cause could be excessive runout on the drill press quill. If the drill runout is excessive (not round), the bit will turn in concentric circles providing a slightly wallowed out hole. Add in a vise that isn't secure to the table and the two moving parts will, for sure, give oversized and non-circular holes.
 

Jans husband

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May 4, 2020
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85
Location
Doncaster England
Thanks for your comments.
When drilling I always use the lathe. I thought about the lathe being off-centre but the 2 centres in the headstock and tailstock met perfectly.
I also take the precaution of facing off and using a centre bit, and then creeping up on the final drill size by using 3 or 4 smaller drills and then finally the final size drill. That makes the drilling process easier and in my experience makes it less likely that the drill will wander off centre, or cause a blowout at the end of the hole, particularly since that whole process is completed without the blank moving from its original position in the chuck jaws.
I have never had this problem before, although I have had a very tight fit where I have had to slightly enlarge the hole in the blank so that the tube fits.
The same problem also arose on 2 consecutive Churchill kits.
I suppose the answer is to always check the tube diameter despite what the instructions say before drilling.

Mike
 

walshjp17

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Jul 29, 2012
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Weddington, NC
I have been very successful with the 31/64 and 33/64 drill bits. No issues with "loose holes". See my avatar for some of my results ;)
 
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