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Fountain Pen RepairFaye has a nice Shaeffer White Dot fountain pen, and brought it to me with a problem. The gold nib is screwed onto the plastic section assembly ("section" is the name for the part of a fountain pen between the nib and the barrel; the bit one holds when writing) with a few fine threads which had stripped. I had initially planned to bodge the nib back on with glue, or some such, but in dismantling the pen, I created some more problems. The lower part of the section screws into the upper part with one thread, and the nib screws onto it by another. The latter was already stripped, and I stripped the former as I unscrewed it from the rest of the section! The lower part also contains a thin-walled tube section which is a push fit onto the feed. I managed to destroy this as I removed it from the feed. The part is made from some kind of flexible plastic sometimes referred to as "hard rubber'". In my defense, it doesn't seem to be very chemically stable - the ink had eaten away at it from the inside. In dismantling the pen, the lower section part had progressed from damaged to completely destroyed. Both threads were stripped, and the tube section had broken in two. There was no alternative but to turn a complete replacement part. I chose aluminium as it's nice to machine, and I could anodise it black to blend in with the rest of the pen. I could see no reason to use plastic as Sheaffer had done - the nib is only retained by ~3 very fine threads, which seems pretty dodgy even for the strongest engineering plastics. Before I could machine a new part, I had to know its precise dimensions. Relying solely on measurements of the mangled threads would be a bit of a gamble, so I first tried googling around for thread data on Sheaffer pens. No luck. I was somewhat hindered by not knowing the model number/name of the pen. The only markings on the pen, other than the signature white dot on the clip, are engraved on the nib. "Sheaffer. Made in USA". Not much help, but at least I knew to expect crazy imperial dimensions and thread standards. Measuring the section thread pitch was easy enough with a thread gauge, as there were around 6 threads and they were not too horribly mangled. The section thread is 40TPI. The nib thread was much harder to measure, as the plastic was totally munged and there were only three threads to begin with. Instead, I took an impression from the inside of the nib with a bit of blutack on a cocktail stick `and held it against the thread gauge under the microscope. 54TPI for the nib thread. I was expecting the thread major diameters to be preferred imperial sizes, eg. 1/4", but this did not seem to be the case. Nor did they look like integer or half millimetre sizes. I had to resort to measuring their intact female counterparts with a vernier caliper, and adding on a probable thread depth. This seemed a bit error-prone, but with a bit of trial and error during cutting it worked out ok. I needed to know the thread profile to calculate the thread depth, and to make an appropriate cutting tool. Looking at the blutack impressions of the female threads in the nib and upper section under the microscope it was clear that they were trapezoidal. The American manufacture prompted me to guess at the ACME form. It's a pretty simple standard - 29 degrees between the thread faces, and the depth is simply equal to half of the pitch. Since the two threads had quite different depths, I needed a custom cutting tool for each one. For each I started with a piece of tool steel, ground it to a 29 degree point, then carefully filed a flat on the tip with a diamond file, repeatedly eyeing it up against the blutack impression under the microscope.This was pretty fiddly - the 54TPI tool was only around 200µm across at the point, and the finished thread was cut only 240µm deep! Unfortunately I neglected to photograph the microscopy, the blutack, the cutting tools or any of the turning process! Sorry about that.
Here is the finished part next to the mangled corpse it replaces. From left to right: barrel, upper section, decorative ring, feed, lower section, nib, lid.
Nib screwed on and feed pushed in This was a really interesting repair job. A fountain pen is on my list of up-coming projects, so it was great to strip one down and see how they are designed. Nothing magic in there; pretty sure I can make one. We decided not to anodize the part, as it is a nice complement to the brushed stainless components.
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Cool
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Faye's Pen
Absolutely fantastic this would look good on a CV as it demonstrates innovation, patience and practical ability - well done you!!
Thanks!
Cheers, most kind.
I was not looking forward to
I was not looking forward to telling her it was broken!!)
Lots of Love xxx
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I had initially planned to
I had initially planned to bodge the nib back on with glue, or some such, but in dismantling the pen, I created some more problems.
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Thank you
The pen is in splendid working order, and I can now use it all the time without having to carefully balance the main body of the pen on the nib!! I can't believe you did this in such a short amount of time, and managed to make it look like an original part of the pen...
Thank you so much... and also for getting me out of a tight spot (the pen originally belonged to my Mum and I have to admit that I was not looking forward to telling her it was broken!!)
Lots of Love xxx
The particulars and exact
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If you can choose just two
If you can choose just two words to write to check a pen is working and your name is Jeff what do you choose? 'Lathes!' and 'Bees', obviously
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Thread standards
Cool project, but I feel bound to mention, somewhat pedanticly, that most American screws don't have an oddball thread standard -- they use the Unified Thread Standard, which is the same as the ISO metric screw thread, just with different preferred values. Sadly, it's unlikely that *your* screws are Unified, since there is no 54TPI. There is a 56, which might be within your margin of error (though it sounds like you were quite exacting, so probably not), which would be a #2 = 0.0860 in maj dia UNC (unified coarse). There are several 40TPI -- #4 = 0.1120 in and #5 = 0.1250 (hey, not an evil number!) UNC, #6 = 0.1380 UNF.
Unfortunately, you don't give a major dia on either of those, so I can't give any better guesses. Also, it looks to me like your threads are fairly flat at the top (outside), so trapazodial is a good bet, and there are only two trapazodial thread standards, and they are quite close -- ACME at 29 deg, and metric at 30deg, but otherwise identical. However, there are no standard sizes below 1/4inch, and that seems like it'd be too large.
I'm afraid, though, that I don't have much pratical experince, just too much reading of wikipedia.
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Informative
well, this is really a nice post.. the way you presented this blog is very impressive.. Thank you so much for this information. keep blogging.. Technical Support
As for me it's so annoying
As for me it's so annoying when something is going wrong with your technique!
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also for getting me out of a tight spot (the pen originally belonged to my Mum and I have to admit that I was not looking forward to telling her it was broken!!)
impression
it up against the blutack impression under the microscope.This was pretty fiddly - the 54TPI tool was only around 200µm across at the point, and the finished thread was cut only 240µm deep!
Nothing magic in there;