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The " Big" Boheme, Some Comparisons And A Disassembly!


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#1 hari317

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Posted 25 July 2012 - 17:57

I recently acquired a Big Boheme, I wrote about it a few threads down. There were some requests, so this thread has some comparison pictures with a modern 146 and a fairly modern 80's 149. The second part of the thread will deal with instructions for a disassembly that some Bohemes might need, when they go out of alignment.

Flanked by the 146 on the left and the 149 on the right:

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The Boheme's barrel is nearly the same size as a 149:
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Nib sizes, the 146 and the Boheme share the same nib but for the monotone plating scheme on the Boheme.

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The feeders:

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Now we come to the disassembly. The current Bohemes are retractible pens. The procedure to use the pen is as follows:

  • Uncap.
  • Thread the cap to the barrel end.
  • continue to twist, the nib unit will extend out of the barrel.

The barrel end threads are single lead and I am very particular that the clip should should line up with the nib when posted. Now the retractible mechanism in turn is threaded into the barrel. Sometimes the mechanism may go out of alignment with the consequence that the clip will no longer line up with the nib when posted. Also sometimes the clip might become sprung(by clipping into a thick leather case) requiring retightening.

My Boheme suffered from both the issues and I decided to do something about it. Peering into the cap, I observed that a slotted screw held everything together. But the problem was a pin that extended from the centre of the slotted screw. So a special screw driver had to be constructed.

This pin shows MB's attention to details and making their pen as idiot proof as possible. Retractible pens suffer from a typical danger, what if the user tries to inadvertently extend the nib, even when the pen is capped? The nib will be destroyed. but not on the Boheme :). As the nib is extended, a shoulder on the feed buts against the pin in the cap's centre, thus stopping the nib from touching the cap's roof. Very clever!

The Cap:

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The snowcap:
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Cap disassembled:
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Top to bottom: Snowflake holder cum cap nut, cap jewel sleeve, clip, cap, slotted screw with "safety" pin.

The slotted screw with pin:
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The shoulder on the feed which buts with the pin if the nib is extended while the pen is still capped:

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The clip is allowed to be rotated in steps. The top of the cap has teeth which engage with two tabs on the clip ring inner diameter, the clip will lift out straight and can be repositioned. The following photos show the idea:

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Clip removed:
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Just before repositioning:
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The snowcap carrier cum nut also has two vertical slots, this permits only an axial movement for the nut as the slotted screw is tightened:

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These two tabs on the cap ID prevent radial movement:

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The cap jewel sleeve, again not free to rotate, the teeth on the cap top engage with these slots as you can see:
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Once the clip is separated from cap, it can be bent w.r.t to the clip ring to restore the clip tension. Now post the cap sans the clip to the barrel end, extend the nib. Now you can position the clip back in the orientation that pleases you, the following pic shows it positioned:

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Due to the teeth it will not move once positioned, again extremely clever engineering. Now place the jewel cover over the clip as shown below:

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Slide the snow cap carrier cum nut into the cap, hold the assembly pushed with thumb, invert the cap with the cap mouth facing up, drop the slotted screw inside and use the special screwdriver to gently tighten the screw. You are done.

Now we come to the screwdriver, after destroying one stock screwdriver while attempting to saw a slot through the hardened bit, I decided to use this card frame to make the tool. The electronics engineers among us will recognise this frame instantly. Removed from one of the old ISA cards.

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A sketch for the tool drawn with the Boheme, a very juicy writer with some springiness:

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I hope you guys enjoyed this thread and found it of some use.

Cheers!
Hari
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#2 pelman

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Posted 25 July 2012 - 18:09

:notworthy1:

Great stuff Hari. Love the engineering. Always a treat to read your assembly/disassembly posts.

#3 osnofian

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Posted 25 July 2012 - 18:10

Brilliant stuff Hari, you are almost convincing me to go out a buy one of those big bohemes for myself ;)

#4 karmakoda

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Posted 25 July 2012 - 18:30

And Hari knocks another one out of the park!
Educational and entertaining. I hope Montblanc thanks you.
Thank You!

#5 fpupulin

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Posted 25 July 2012 - 19:55

That is a brilliant post and a very useful step-by-step instruction. I also like having the clip lined with the nib when posted (and I always post my big-size Bohéme).

#6 terminal

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Posted 25 July 2012 - 23:58

Hari this is fabulous, thanks for taking the time
"One always looking for flaws leaves too little time for construction" ...

#7 tenney

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Posted 26 July 2012 - 00:32

Might some jaxa style wrench (the kind used to unscrew watch backs) work instead of making one from a card frame? But using that card fame was ingenious.
--
Glenn (love those pen posses)

#8 isaacrn

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Posted 26 July 2012 - 00:41

Great pen. I would really like to pick up a big one myself. I can never really tell the difference when I am looking to purchase one
In order to appreciate the sweet, you must truly taste the bitter....

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#9 hari317

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Posted 26 July 2012 - 03:50

Thank you all. The wrench/screwdriver will need to be long and slim so that it can enter the cap comfortably. A 10mm flatblade screwdriver with a 3mm slot milled in the centre is ideal. I searche the local market for a suitable screw driver, you do get the so called "security" screw drivers, but the slots on those are not deep enough to clear the pin.

An alternative tool can be made out of a hollow metal tube with thick walls. just file the top leaving two pegs which will engage the slots, the pin will pass in the hollow centre of tube.

Best
Hari
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#10 hari317

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Posted 26 July 2012 - 03:51

I can never really tell the difference when I am looking to purchase one


Look for the 18k monotone nib. The smaller one has 14K nib.
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#11 Dr. Eriko

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Posted 26 July 2012 - 07:03

Thank you again Hari. This post it is very interesting and usefull of course. I wish to try the clip alignment on my Midsize Boheme, but there is one small hole inside the clip, and I want to keep that hole covered under the clip. Do You have any ideas?
Regards.
Please excuse my poor english, but it is not my mothern language and maybe it is wrong my grammar. Any Suggestions are welcome.

#12 hari317

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Posted 26 July 2012 - 07:33

Having never seen the small/midsize Boheme, I cannot comment. Surely you cannot reposition the clip as well as keep the hole covered under the clip. Do you see the same pin arrangement inside the cap? is your pen retractible?
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#13 leftyjo

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Posted 26 July 2012 - 12:55

Very interesting post, Hari
I would also disassembly the cap of a Mid-Size Bohème. The cap is like the Bohème Rollerball cap, but with a hole.
It is difficult to photograph.

boheme cap.jpg
I think it is easier to disassembly that the cap from the retractable Bohème.

thanks and sorry for my English
Sorry if my English is bad.

#14 hari317

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Posted 26 July 2012 - 12:59

Hi Josefa,

very interesting. you see those two slots? I think you can use a regular flatblade screwdriver to engage the slots and disassemble the cap.

Your English is good enough.

Best
Hari
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#15 shanbo

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Posted 26 July 2012 - 14:30

Superb post
A pleasure reading

#16 hari317

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Posted 26 July 2012 - 15:03

Thanks Shan.
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#17 Polleke

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Posted 26 July 2012 - 15:30

Great post Hari :notworthy1:
I really enjoyed it
Many Thanks :thumbup:

Polleke

#18 hari317

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Posted 26 July 2012 - 15:32

I am glad you found it useful, Polleke. Thanks!
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#19 Paul Raposo

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Posted 26 July 2012 - 16:56

Excellent work, and photos, Hari. Thank you so much for presenting these postings for us. Not only the work involved, but using your own pens.
There are a thousand thoughts lying within a man that he does not know till he takes up a pen to write.
--William Makepeace Thackeray


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#20 hari317

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Posted 26 July 2012 - 17:03

Thank you Paul. Actually there were a few topics in the past with users complaining about the Boheme clips going out of alignment, so when I got the pen and it also had the same issue, I decided to figure it out and also document it. The pen was disassembled twice, the second time just for the pics.

I sometimes neglect to take disassembled pictures, like the time I had to take apart my Omas Autunno with the cross pin piston securing system. That is an awkward way to put together a piston system but they did it :headsmack:

Best
Hari
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