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Onoto Seal Screw Information, Anyone?

onoto cork seal screw size ba

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#1 praxim

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Posted 17 March 2018 - 05:20

Some context for the adventure here. The question comes in the last paragraph.

 

I bought a long model Onoto 6234 from Spain recently, expecting it would need some service work. The pen looked to be in very fine shape externally, so that was promising.

 

The plunger was extremely difficult to push down. Before taking it further apart, I removed the section to add some silicone grease to the barrel, as an experiment. Now the plunger moved very easily, but with no suitable 'pop' of vacuum breaking.

 

Removing the rod showed that the "cup washer" was made from two bits of what appears to be bicycle inner tube (it curves floppily on one radius) hand cut with a knife into a random polygon roughly approximating a circle, with no cone washer for support. OK, I can replace that. A lack of ink in the barrel or section suggested the earlier repairer had found their effort was not entirely successful. ;)

I noted also that the plunger cone pin had rust around it! Pushing it out, I found that my predecessor had resorted to a bit of metal for the pin, and not a rust-proof bit, for this pin immersed in dyed water. :rolleyes:

Also, the rod was bent, presumably from trying to force down the ungreased piston. Well, it is ebonite with a wire core. I am trying to ease its bend at the moment. It may need replacement.

Next, I turned to the cork seal at the top of the barrel. Hmm, no seal screw. That does not help. So, to the question:

 

Does anyone know the threading used for the seal screw on top of an Onoto barrel? Given they used 5BA for the rod, I am conjecturing it will be 0BA or 1BA (but normal RH thread). If it is, I may be able to make another.


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#2 Stylomeister

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Posted 26 March 2018 - 16:12

Custom pen parts make all the spares you need for your project including the pins and seals that make it go pop. If you know there is a wire core to the rod its knackered - Roger makes these from peek now which are used in spinal fusion so are quite strong.

Theres a lot of documentation you can find on the web about the threading as well which is in the opposite direction as I remember (I have about 9 of these of various models and ages waiting to be reassembled).

These inners of these pens are super brittle so take care.

Edited by Stylomeister, 26 March 2018 - 16:32.


#3 praxim

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Posted 26 March 2018 - 21:38

Thank you for your reply. I am aware of and have previously purchased some parts from Custom Pen Parts. I am also aware of LH rod threading, having done that myself in the course of servicing or overhauling several plunge fill Onotos. My question did not relate to the rod but to the seal screw, which is RH thread not LH. If I know the threading then I can make it myself, which would entertain me more.


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#4 CS388

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Posted 26 March 2018 - 22:03

...snip...

 

Also, the rod was bent, presumably from trying to force down the ungreased piston. Well, it is ebonite with a wire core. I am trying to ease its bend at the moment. It may need replacement.

 

I hope that works. Heat? Pressure?

Given the constituent parts of the rod, it should be possible.

 

I used to have a few old Onoto's in the parts drawer, once. They often came in with job lots of parts. Some had bent rods - as you point out, probably from people trying to force siezed pistons etc.

 

Sorry I can't help with your question. Only have one Onoto now and it's a different model.

 

Good luck.



#5 praxim

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Posted 26 March 2018 - 22:30

Thank you. I tried warming it over a heat gun as if to open a section then quickly clamping it into a Dremel vice which has soft rubber jaws. After 24 hours there it looked a little straighter. I am going to use it as it now is, see how it goes. Re-using a rod is easier than trying to cut another exactly to length and drill the hole for the shank pin.

 

I have already replaced the cup washer with a CPP part, and the rusting metal plunger pin with a bit of carbon fibre, so the pen is now waiting only on my solution to the seal screw.

 

edit:adding stuff.


Edited by praxim, 26 March 2018 - 22:32.

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#6 CS388

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Posted 26 March 2018 - 23:24

Nice work.

I'd hope that as long as the rod still has sufficient stroke get it past the vacuum, it should work?

 

Thank you. I tried warming it over a heat gun as if to open a section then quickly clamping it into a Dremel vice which has soft rubber jaws. After 24 hours there it looked a little straighter. I am going to use it as it now is, see how it goes. Re-using a rod is easier than trying to cut another exactly to length and drill the hole for the shank pin.

 

I have already replaced the cup washer with a CPP part, and the rusting metal plunger pin with a bit of carbon fibre, so the pen is now waiting only on my solution to the seal screw.

 

edit:adding stuff.

 

I'm afraid that even if I had the part in my hand, I wouldn't be able to tell you the thread!

Do you not have a similar diameter Onoto which you could test for screw thread?

Kudos to you for being able to make the part!

 

Sounds like a geat project.

It inspires me to fix my old Onoto up - currently used eye-dropper/guerilla style. (Some where in that box with all those other pens that I was going to fix up, one day)

 

Good luck



#7 ralfstc

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Posted 27 March 2018 - 02:51

Hi Praxim,

 

Good for you for giving it a go! I don't have a plunger in parts at the moment or I could check the thread (plus I'm away from home). Might be worth a cheeky email to Eric Wilson or Laurence Oldfield?

 

Good luck!

 

Ralf



#8 praxim

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Posted 27 March 2018 - 03:54

I have another seal screw out of its pen, so I have diameters for top and bottom of thread but the screw itself is so short that I can not measure the pitch reliably enough to distinguish clearly between different possible standards, consisten with the measurements. The 0.7 mm mentioned on CPP does not work with the other dimensions either, so I am taking it that some errors or rounding here and there are throwing me off. I am about to thread a bit of acetal with 1ba to see how it goes. That appears to fit the thread diameters. edit: in theory :)

Edited by praxim, 27 March 2018 - 03:55.

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#9 praxim

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Posted 27 March 2018 - 08:01

Experiments and further measurement completed.

 

1BA is too narrow a screw, hardly touches the sides.

 

0BA is a good size but far too coarse.

 

Measuring again in fiddly fashion under a loupe, the answer on a Whitworth thread gauge is 0.7, which I find to be Fine (BSF). I supported this by measuring the 2-3 available threads against a fine millimetric ruler. The answer from that approximated 30 tpi which is consistent with BSF, 28 tpi, 5.56 mm outer diameter, but not with BSW which would be 20 tpi and probably 6.3 mm rather than 5.6 mm OD.

 

Umm, I need another die....

 

 

eta: by the way, gentlemen and ladies, this is a family-friendly forum. :)


Edited by praxim, 27 March 2018 - 08:03.

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#10 fountainbel

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Posted 27 March 2018 - 11:54

Experiments and further measurement completed.

 

1BA is too narrow a screw, hardly touches the sides.

 

0BA is a good size but far too coarse.

 

Measuring again in fiddly fashion under a loupe, the answer on a Whitworth thread gauge is 0.7, which I find to be Fine (BSF). I supported this by measuring the 2-3 available threads against a fine millimetric ruler. The answer from that approximated 30 tpi which is consistent with BSF, 28 tpi, 5.56 mm outer diameter, but not with BSW which would be 20 tpi and probably 6.3 mm rather than 5.6 mm OD.

 

Umm, I need another die....

 

 

eta: by the way, gentlemen and ladies, this is a family-friendly forum. :)

 

It would not suprise me if the threads were "non standardized" 36TPI threads…

Pitch of 36TPI being 0.7056 mm

Threading on the lathe will be the only possibility then.

Francis



#11 praxim

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Posted 27 March 2018 - 22:06

I should be able to check that this morning. If so, perhaps I could approximate it with a metric 0.7 on the lathe given it is only a couple of threads to bind. I will see what emerges from some further checks.

 

As an aside, I see that BA was developed in the early 1880s and made an official standard in 1903, a couple of years before the first plunge-fill Onoto appeared. BSF was made a standard in 1908, although of course it existed already. Source:Wikipedia


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#12 praxim

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Posted 27 March 2018 - 23:05

Yes, it is non-standard with 36 TPI. The nearest "standard" I can find to it is something called a Holtz N or M which are 5.1 and 6.1 mm diameters respectively, 36.1 TPI. Mr Holtzapfel wrote about screw threads back in the mid-19th Century. I will try for a 0.7 on my lathe or else ask my son to have a go on his bigger brighter better one which does TPI directly rather than being metric only for threads.

 

That, of course, means I must first finish the new lathe bushing to reduce slop in the threading gears.

 

Oh, the ever-increasing layers of indirection. :rolleyes:

 

 


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#13 eckiethump

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Posted 30 March 2018 - 19:51

Hi Praxim,
 
Good for you for giving it a go! I don't have a plunger in parts at the moment or I could check the thread (plus I'm away from home). Might be worth a cheeky email to Eric Wilson or Laurence Oldfield?
 
Good luck!
 
Ralf

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#14 Cjayant

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Posted 13 July 2018 - 13:34

I found three pens Onoto " The pen"  recently and bought them thinking I am able to refurbish  them myself. They are old and yellowish  with deoxidising by the time . All there pens need rubber cup washers and cork sealing replacement before they get to work. I believe we can buy all the parts for replacements. I am planing a project to work on these pens and see what I can do.

 

One of a plunger on a pen is stuck and it opens from <<ink opening >> thread. but hard to move up-down movement.  Dose anyone knows what to do to get the piston  losen ?  



#15 lcoldfield

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Posted 17 July 2018 - 18:32

It is 36tpi right hand, but as the threading is so short anything between 28tpi and 40tpi would probably be OK.

Laurence







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