Sheaffer Vac-Fil Blind Cap Unscrewing

[Prolix]

Hi! Perhaps a noob question, but I couldn't find anything in the forums that addresses this particular issue.

 

I have a circa 1940 Sheaffer Balance Vacuum-Fil that works great, with one exception. Every time I unscrew the blind cap to pull out the plunger rod, the cap unscrews not just from the body of the pen, but also from the end of the rod. I'm afraid that if this happen repeatedly, the screw will be stripped. What is the best way to safely secure the cap without causing damage or doing something irreversible? I could just super-glue the thing, but that seems like a terrible idea. What is the best practices for this situation?

[adyf]

Don't use super glue or it will be extremely difficult/impossible to disassemble the pen in future. Apply a little shellac to the threads at the end of the plunger rod and then screw the blind cap on. Heat will soften the shellac should the blind cap require removal in the future.

[fountainbel]

I honestly don't expect applying shellack will hold the filling knob on the (partly) stripped threads.

In my opinion the only efficient repair approach is to drill the threads out - diameter

3.5mm, 4mm deep - and make/install a Ketron Peek plug - diameter 3.55 , 4 mm long - having the original inner threads.

I've done so several times with excellent results.

Alternatively you could surely look out for a replacement filling knob.

Francis

[The Pensmith]

I have a love/hate relationship with Vac Fills. On good days, they slide together after restoration (and always with the replacement of the seal in the barrel capsule), and work brilliantly. On other days, always a problem including finding stripped threads in the blind cap. That problem is more prevalent on the "wobbly knob" variety possibly due to ill-informed owners (and prior owners), not accepting the "wobbly knob" concept and trying to over-tighten the aluminium threaded insert in the blind cap.

 

The advice of Fountainbel is entirely correct. Super Glue (not so "super") and shellac are not the answer. There is too much force placed on the blind cap for either method to work, disregarding the destructive aspect of applying Super Glue.

 

Hard work with kedron or as I often prefer to use, Delrin provided one understands it gluing limitations.

[adyf]

I missed the part of the OP that said the threads were stripped, I thought it was just a simple case of securing the blind cap on the plunger rod with all threads in tact.

[3rdlakerobert]

I have a love/hate relationship with Vac Fills. On good days, they slide together after restoration (and always with the replacement of the seal in the barrel capsule), and work brilliantly. On other days, always a problem including finding stripped threads in the blind cap. That problem is more prevalent on the "wobbly knob" variety possibly due to ill-informed owners (and prior owners), not accepting the "wobbly knob" concept and trying to over-tighten the aluminium threaded insert in the blind cap.

 

The advice of Fountainbel is entirely correct. Super Glue (not so "super") and shellac are not the answer. There is too much force placed on the blind cap for either method to work, disregarding the destructive aspect of applying Super Glue.

 

Hard work with kedron or as I often prefer to use, Delrin provided one understands it gluing limitations.

 

And provided one has a tap to create the original threads in the repair plug for the rod.

[Prolix]

Thanks for all the responses!

 

To clarify: the threads are not stripped. The blind cap seats firmly on the end of the rod and doesn't wobble at all when it is screwed down. It just unscrews from the end of the rod every time I unscrew the blind cap from the body of the pen.

[fountainbel]

Thanks for all the responses!

 

To clarify: the threads are not stripped. The blind cap seats firmly on the end of the rod and doesn't wobble at all when it is screwed down. It just unscrews from the end of the rod every time I unscrew the blind cap from the body of the pen.

In this case the thread fit was not "blocked"

You should screw the filling knob FIRMLY- till blockage- on the rod , so the shoulder of the rod - behind

the threads- axially contacts the filling knob.

As adyf rightfully suggested,applying a small amount of shellack on the threads could help to increase the loosening torque.

Francis