Coventry Diehead CH Reassembly

[Tony RayParticipant @tonyray65007]

Hi, this is for the benefit of anyone struggling to reassemble a CH style head but may be of use for other variants and to avoid the 3 hrs I spent figuring it out in a 30C workshop!

The Book of The Coventry Die Head ( The Book) is available as a free download and should be referred to alongside these notes. First a few notes on refurbishment.

My 1/2 head was missing the Front Plate. I made one from a tough steel but did not harden it, is approx 50mm dia. so I turned it from bar stock and coordinate drilled the mounting holes on the mill. NB the csk angle for the front plate mounting screws is NOT 90 degrees! Ask me how I know… I made it 5mm thick but I think it would benefit from being thinner as it obstructs the view of the chasers in use.

Screws – as noted in other posts the CH head uses non standard threads like BA but  under nominal dia. so eg standard 3BA will not fit the front plate. After several attempts at making them I gave up and bought them and the closing springs from Wiseman who were very helpful, but be warned there is a minimum order value and commercial carriage – ouch! It may be worth exploring Turbine John as an alternative. I think the csk angle is 60 degrees but please check for yourself.

During disassembly I removed what I think is called the Adjusting Spring Peg from the back of the head, it constrains the Adjusting Spring and is a pin with a thread and screw slot. As it achieved nothing I replace it and wound it into the free spring damaging it irreparably.  DO NOT remove it until the head is apart if you need to at all.

Having already bought parts from Wiseman I did not wish to go through the whole expense for one spring. Tip: if you need to do an order make it up with common parts you can probably sell them on to recover some of your outlay.  At the suggestion of friends I wound a new one from Piano wire using Clicksping, This Old Tony and Blondihacks using the best bits from each and Marv Klotz spring winding calculator called Mandrel. Please with my success I made a new Detent Spring as the old one was ropey.

Assembly to follow

 

 

 

 

 

 

 

 

[bernard towersParticipant @bernardtowers37738]

Good job you didn’t send it to wiseman for refurb have you seen their prices!

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