Hofmann Dividing head - lubrication?

[bambuko]

What is the size of the thread that screws it into spindle housing?
The reason I ask, is that like @Iwik I am thinking about converting mine to this design.

 

[bambuko]

Thanks @bR39Da
My plunger housing is 16mm dia (of course no outside thread), so it is possible that they just used existing thread in spindle housing to secure modified locking plunger housing.
I just need confirmation from @Iwik what is the thread (he has removed his and his is identical to mine) before I start butchering mine...
Thanks for the offer of modelling, should manage without it

 

[bambuko]

BTW - I have to admit to failure...
My plunger which worked well for few days is now failing miserably

I suspected copper washer, sealing bleed hole - there were signs of seepage and I have tightened it quite few times, so I was guessing that it has work hardened...

OK, fitted new o-rings, annealed copper washer and everything works perfectly again
I shall monitor it and report here how it performs.

If it goes soft on me again... I will have to consider modifying the plunger and it's housing

 

[citizen kane]

Hi @citizen kane

Could you get some more pictures/measurements of you plunger? I believe my unit is identical to yours.

Just spotted this, probably too late now but let me know if you still need pictures and measurements.

 

[citizen kane]

From memory I have sealant rather than a seal, looking at it its probably some RTV silicone gasket but its been a long time since I was in there . For reference the top of the flange of the plunger body sits about 0.5mm proud of the spindle body.

I use ISO32 in both, mainly because its what I had lying around.

 

[bambuko]

There are two different oils:
- one is in the main body (and is visible through sight glass) no one really got confirmation from Hofmann as to what should it be...
- other is in the spindle locking mechanism (for that Hofmann specifies ISO 22, but 32 shouldn't make any difference)

The two are not mixing and are not connected.

 

[bambuko]

...
Good news, the spindle lock works. I realised I've got a rubber seal between the plunger body and the spindle.
...

Very happy for you
I am looking at all your photos in detail (with a view to copy this design for my diving head) and there is one picture that puzzles me?
What is the thing that black arrow points to (black thing next to the plunger?) :

The second question is about the picture below. Is the finger pointing to what I think is some kind of a seal between plunger housing and spindle housing?
and if yes - what is it made off?

 

[bambuko]

Got fed up and given up on trying to make "locking thingy" work
Unscrewed locking plunger housing (without doing any damage )
The thread is M12x1.0 (so not your regular coarse M12), but it is much smaller than the one @bR39Da took out of his dividing head,
(reported to be M16x1.5).
That of course limits my ability to copy exactly, but does not prevent me doing something similar...
I still need to understand, please @bR39Da (or anybody else who took similar contraption one apart) - what is the black thing in front of locking plunger, as per my previous post....

 

[Mark Davison]

That looks the same as mine. The one on the red background.

 

[citizen kane]

Its a rubber seal, similar to what you see in a slave cylinder on a car drum brake.

 

[bambuko]

Yes and thank you for replying @Mark Davison
Just looked through your posts and yours is indeed the better/later version (which everybody here seems to have apart from me )
Can you help please with the questions I have asked?
- what is the black thing in front of the metal plunger?