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Modern Montblanc's- Weak Piston Lead Screw?


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52 replies to this topic

#1 fountainbel

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Posted 29 October 2013 - 13:33

Hi all,
Reading again some users are complaining about loose filling knobs and sheared lead screws, I thought I should chime in again...
The injection mould piston lead screws  MB uses for there  actual pens originates from  their 12,14, 72, 22, 32,34 and 24 pens from the 1960's.
On these pens the leads screw needed the 2  flats providing the anti rotation guidance of the lead screw.
On their actual 146/149 range of pens the anti rotation flats are not needed at all, since the piston rod  is splined and provides  the anti rotation guidance with the splines in the brass piston housing. 
Although a plastic lead screw without the flats would be at least 30 % stronger against torsion and shearing , MB continuos using these weak - IMO under dimensioned - lead spindles..
Most probably since they don't want  to invest in making a new mould....
Attached a picture showing the original version (white plastic) and two alternative machined versions: one from black delrin, and the other in brass.
On the two latter versions the flats are eliminated, obtaining a much stiffer and torsion safe lead screw.
I agree that proper and regular maintenance may avoid shearing of the lead screw, but never the less i'm convinced the lead screw design is really "on the edge".
Note the brass version may have the drawback the pen will be more heavy at the rear.
I'll start using these lead screws as from now on on all my repairs, replaced already too many sheared lead screws...
Just my 2 cents..
Francis
 
P1000482.jpg

 



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#2 hari317

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Posted 29 October 2013 - 14:05

wonderful observation and solution. :notworthy1:

 

Is there a possibility that they continue to use a  flat lead screw moving inside the spindle rod means lesser friction and possibility of not needing lubrication ever?


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#3 yus2001fr

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Posted 29 October 2013 - 16:21

Really nice solution, Francis, no more 32 and 34 sacrificed.

 

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#4 Pen Nut

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Posted 29 October 2013 - 19:14

What a great observation and solution Francis !

 

I, as no doubt others, would love to try one of your brass alternatives and wondered if you intend to sell them as a part to those of us who do their own maintenance ?

 

They will no doubt be produced to the same high standard as your tools and I feel there will be a market for them.


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#5 Cepasaccus

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Posted 30 October 2013 - 00:36

The brass might have another drawback, that it can react with the ink.



#6 Dillo

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Posted 30 October 2013 - 00:44

The brass might have another drawback, that it can react with the ink.

 

The screw never touches the ink, so it isn't such a worry. Many piston-fillers have brass parts behind the piston that never touch ink in normal use.

 

In any case, I like the look of those screws. Good work! I'd go for the brass one though because the delrin in sufficiently thin sections can shear and tear. I've seen many pens with thin sections of delrin parts split or tear off. I can't tell how thick the little nub on top of the screw is, but it may be fine if it is thick enough.

 

Dillon


Edited by Dillo, 30 October 2013 - 00:48.

Stolen: Aurora Optima Demonstrator Red ends Medium nib. Serial number 1216 and Aurora 98 Cartridge/Converter Black bark finish (Archivi Storici) with gold cap. Reward if found. Please contact me if you have seen these pens.

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#7 I like mango cheesecake

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Posted 30 October 2013 - 02:45

I've opened up both my 149's and my 146 and they are all black plastic. And yes, the screw does not come in contact with any ink.



#8 fountainbel

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Posted 30 October 2013 - 07:37

I've opened up both my 149's and my 146 and they are all black plastic. And yes, the screw does not come in contact with any ink.

Original MB Lead spindles were alternatively made in white or black, but always featuring the two flats...

Francis



#9 fountainbel

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Posted 31 October 2013 - 15:35

Hi all,

Just installed the brass lead screw in one of my spare modern MB149 pens.
Works perfectly, but the pen becomes effectively a little top heavy, at least compared to the pen equipped with the original plastic lead screw.
The "balance" feeling becomes in fact comparable with the feeling of a vintage 149, equipped with the telescopic filler.
Unfortunately the seat of the C spring - which secures the spindle axially in the filling knob -was worn out, so the C spring did not  hold the spindle well in place on this pen.
Coping with this problem i decided to make/install a hard aluminum enclosure screw in the filling knob.
Using a tap of M6x 0.75 I've tapped the the treads in the rear of the existing knob hole.
The existing bore being 5.3mm, the bore was just perfect for tapping with the M6 x0.75 tap.
Tapping is done so the enclosure screw just bottoms /secures at the end of the threads
Note this is not my standard procedure, only done since the C ring seat was partly stripped.
Although dis assembling the spindle becomes extremely  easy using this approach ! (using the hollow screw driver tool I've made )
Given the pen becomes a little top heavy with the brass lead screw, I will try making a lead screw in Ketron Peek, a very hard, stiff and torsion resistant plastic.
Some of you may think - when installing a stronger lead screw - the piston nut bushing may break at excessive friction triggered by a dirty piston.
I'm nearly convinced this will not be the case, since the piston nut bushing only has 0.1mm sliding backlash in the piston housing so expansion- the first step towards cracking - is nearly impossible.
Francis
 
P1000483.jpg

 



#10 Dillo

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Posted 31 October 2013 - 16:35

Let us know what happens with the Peek. I'm familiar with it, although not in a pen application.

 

Dillon


Stolen: Aurora Optima Demonstrator Red ends Medium nib. Serial number 1216 and Aurora 98 Cartridge/Converter Black bark finish (Archivi Storici) with gold cap. Reward if found. Please contact me if you have seen these pens.

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#11 fountainbel

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Posted 01 November 2013 - 22:57

wonderful observation and solution. :notworthy1:

 

Is there a possibility that they continue to use a  flat lead screw moving inside the spindle rod means lesser friction and possibility of not needing lubrication ever?

 

Hi Hari,
Thanks for your comment !
The original flattened spindle does not have any advantage in the perspective of friction, even to the contrary.
Friction is triggered by, and proportional to resistance.
A higher moving resistance of a "dirty" piston will lead to a higher contact friction between the lead spindle and the piston nut threads.
The screw-thread contact surface of the new - non flattened- spindle is at least 100% higher as on the original spindle.
Consequently the screw thread contact surface pressure between screw and nut will be only half the value of the original spindle.
Note also that the thread fit of a solid-non flattened thread spindle engages over its full circumference.
This makes the thread spindle/nut fit much stiffer and more resistant to bending at increased axial loads.
The spindle will  be greased initially but will not require regular lubrication.
Francis


#12 Rowbo

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Posted 02 November 2013 - 13:03

I'm thinking twice about posting this ...

 

171162889992

 

No affiliation etc.

 

For interest and to stimulate conversation only.

 

Acrylic!


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#13 hari317

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Posted 02 November 2013 - 13:07

I'm thinking twice about posting this ...

 

171162889992

 

No affiliation etc.

 

For interest and to stimulate conversation only.

 

Acrylic!

interesting stuff.

 

http://www.ebay.com/...=1&_ipg=&_from=


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#14 hari317

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Posted 02 November 2013 - 13:08

Francis, have you developed the tools to remove and reinstall the c ring for people who want to retrofit? 


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#15 fountainbel

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Posted 02 November 2013 - 14:49

Thanks for the link !

Very interesting seeing I'm not the only one who's convinced there is effectively a problem !

Francis



#16 fountainbel

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Posted 02 November 2013 - 14:57

Francis, have you developed the tools to remove and reinstall the c ring for people who want to retrofit? 

No Hari,I've tried several approches to get the (dammed ) C ring out... with little success 

In the end I've decided drilling a 1mm bore through the top of the filling knob.

This allows to knock the spindle through, together with the C ring.

This always works. The 1mm bore is plugged with a HR pen afterwards.

Reinstalling the C ring is rather straight forward using a bushing which just goes over the spindle and having an outside diameter of 5 mm.

I expect MB always installs a new filling knob/ spindle/ C ring assembly, and does not remove the C ring at all.

Francis



#17 Rowbo

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Posted 02 November 2013 - 14:59

Research reveals fpn member "Custom Pen Parts". I've pm'd him - to draw his attention to this thread.

 

Francis, I do hope I'm not 'stealing your thunder', as we might say here, but let's face it you have enough for a strength 5 supercell anyway :-)


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#18 fountainbel

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Posted 02 November 2013 - 15:43

Research reveals fpn member "Custom Pen Parts". I've pm'd him - to draw his attention to this thread.

 

Francis, I do hope I'm not 'stealing your thunder', as we might say here, but let's face it you have enough for a strength 5 supercell anyway :-)

No problem Rowbow, in fact - since my lathe does not allow cutting these large pitch screws - I wanted to point out in a later stage that I work together with "Custom Pen Parts"  for making these lead screws !

Francis



#19 hari317

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Posted 02 November 2013 - 16:39

Thanks Francis for the insight into the reassembly of the aftermarket spindle.

Research reveals fpn member "Custom Pen Parts". I've pm'd him - to draw his attention to this thread.

 

Francis, I do hope I'm not 'stealing your thunder', as we might say here, but let's face it you have enough for a strength 5 supercell anyway :-)

I think he specialises in ONoto parts, onoto website also mentions him as a legit source of parts.


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#20 fountainbel

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Posted 04 November 2013 - 15:38

Thanks Francis for the insight into the reassembly of the aftermarket spindle.

I think he specialises in ONoto parts, onoto website also mentions him as a legit source of parts.

Yes, "Custom pen parts" made the moulds for making all vintage Onoto plunger seals.

Further on he also made a mould for making the PFM snorkel tube lip seal, completely identical to the original one.

Same for the vintage Pelikan 100N and 400 piston seals he has available.

I use his Onoto seals, PFM seal and Pelikan seals for my repairs and I'm very happy with all of them!

Francis








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