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Trying to tap for a Bock 250 nib assembly...



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chugbug

Hello All,

 

I'm embarrassed to ask this, but I haven't been able to find information elsewhere so I thought I'd ask here.  First time for using a Bock nib, so I'm trying to tap threads for the 250 (#6) housing threads.  But I can't seem to get the threads to engage properly.  I'm using the M7.9 x 0.6 Tapco tap for a standard 250 housing, and started out with the recommended 7.3mm bit.  But  with that hole diameter, the threads won't engage at all--like the hole is much too small.  I had to go up to 7.7mm bit before I could finally get them to engage at all.  My bits run a little small, so I assumed I'd have to use something a little bigger, but with the 7.7mm hole the threads are very tight.  And the (major) diameter of the housing threads are 7.8mm, so with a 7.7mm hole, there isn't much thread height there to engage with.  So I don't think the hole diameter is my problem.  When looking closely at the housing threads, they appear to be much FATTER (wider across) than the tap threads.

 

I'm using the Tapco tap that everyone is selling for the Bock nibs (from Beaufortink).  Attached is a photo showing both tap and nib assembly so you know what I'm working with.  I checked both with a thread gauge, and the pitch matches.   So I don't get what I'm missing.

 

Can anyone offer a suggestion? 

 

Thanks...JEB

_jeb_bock-250_nib-and-tap.jpg

JEB's PENs

www.jebspens.com

Hand-made Pens / Pencils

& Custom Fountain Pens.

http://www.jebspens.com/fpn_sig_pic.jpg

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hari317

You first drill 7.3mm. Then you drill/machine the contour right above the threads going upto the base of the exposed feeder. This enlarges the bore progressively along the axis. The last step is to tap the lowest diameter portion (7.3mm) with the tap. 
 

now your nib unit can enter the section and engage the threads. 
 

good luck. 
 

eta: to check just the threads simply drill a 7.3mm hole and ream it out with 7.3mm reamer. Then tap it. Then test by engaging only the lowest part of the nib unit. 

In case you wish to write to me, pls use ONLY email by clicking here. I do not check PMs. Thank you.

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chugbug

Yes, thanks for the suggestion.  I know about drilling the larger hole for the larger diameter at the front of the housing.  Nothing else is binding or interfering--it's just the threads that won't engage as they should. When I couldn't screw the housing in the section I drilled out (with both hole sizes), I drilled and tapped a single test hole in another piece of material just for the threads.  So with that piece, I eliminated anything else interfering.  

 

JEB

JEB's PENs

www.jebspens.com

Hand-made Pens / Pencils

& Custom Fountain Pens.

http://www.jebspens.com/fpn_sig_pic.jpg

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chugbug

I should have stated, that I basically did what you were suggesting.  I drilled just a single 7.3mm hole in a short piece of material, tapped it, then drilled (reamed) it again.  I also added a taper at the front to help guide it in.  But I couldn't get it to screw in with the 7.3mm hole.  Nor 7.4, 7.5, or 7.6.  Not until I drilled one with a 7.7mm (and I wanted clean hole, so I drilled each size in a separate piece of material).  It screws in the 7.7mm hole ok once I apply a little silicone to the threads, and  they seem secure--they don't slip, nor can I pull it out.

So it may be OK.  But since the 7.7mm was much larger than what was recommended, I wanted to try and find out if this was normal (others had to do the same), or whether I was missing something.  I even purchased nibs for two different  sources to make sure the housings were the same.
 

_jeb_bock-250_thread-test.jpg

JEB's PENs

www.jebspens.com

Hand-made Pens / Pencils

& Custom Fountain Pens.

http://www.jebspens.com/fpn_sig_pic.jpg

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hari317

Thanks for the details. 
 

Is there per chance some mold flash in the threads area of the nib unit affecting the minor diameter ? Maybe chasing the threads on the nib unit to remove flash might help?  Or possibly the nib unit is slightly oval due to moulding errors? 
7.7 mm leaves just 0.1mm each side. The nib unit might just push out if someone tightly inserts the converter or pierces a cartridge. 
 

 

In case you wish to write to me, pls use ONLY email by clicking here. I do not check PMs. Thank you.

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fountainbel

Bock 250 housing screw-in threads are effectively 7.9x0.6mm, so pre-drilling  should be done with 7.4 mm

Note your tap features a long conical entry, so I would suggest to ground the top of your tap off till you just have a small conical entry.

Doing so you will be able to tap deeper...

Francis

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  • 4 months later...
GeoffMartin

I'm having EXACTLY the same problem... tried with a 7.3 mm hole in a section made from ebonite, tapped with the 7.9x0.6 tap (made by dabex, purchased from fpnibs.com - not beaufort) and the threads just won't grab at all.

 

So, I tried just drilling a 7.3 mm hole in a small piece of ebonite (just like the one you show in your photo), tapped it all the way through - and nothing... The Bock 250 insert won't grab the threads at all. Tried again with a 7.4 mm hole - same effect.

 

I'll try the 7.7 mm, but my suspicion is that this is just getting some kind of mild friction effect - not actually screwing in.

 

The weird thing is that I had an older nib insert (I think that it's from a Conklin Omniflex - which would make it a Jowo #6 - but I'm not really sure - the nib has been in another pen for a long time, and I just had the threaded insert lying around) and that one grabs the threads nicely. Can't go all the way in - so the pitch isn't quite right... The threads on the insert that words are much coarser than the ones on my Bock 250 inserts - but I have no real way of measuring them accurately or precisely.

 

I fear that something weird is going on here.

 

Cheers

-geoff 

 

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GeoffMartin

Following your footsteps, I reamed the threaded hole to 7.5, 7.6, then 7.7 mm, trying to screw in the Bock insert each time.

 

It finally grabs at 7.7 mm - but, looking at the walls of the hole, I think that there's not enough left in there to be worth talking about (in theory, only 0.1 mm-deep threads remain). Now I'm more certain that the threads in the insert aren't really mating with the 7.9x0.6 mm threads in the ebonite - there's just enough groove in there to grab something....

 

I was assuming that the tap I purchased was mis-labelled, but now I think that there's a problem with the Bock inserts.

 

Cheers

-geoff 

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  • 2 weeks later...
Addertooth

Perhaps it is time to make friends with someone with a engine lathe.   You will have to provide them your screw-in nib.

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