Preparing the latch for reassembly

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Here we have the lock body as we left it after dismantling. First we need to deepen the two drillingswhere the steel plate was removed. The drillings should be no more than 5mm deep or you are likely to drill right through the casting.

Now we come to the tricky bit. We need to drill two more holes in the casting adjacent to the recess where the steel lock retaining plate will fit. The holes should be dead centre in the metal to avoid breaking out at the side and close enough that a 3mm countersunk screwhead will overlap the plate to retain it in place. The depth here should not be deeper than 7mm to avoid drilling right through the casting. Once again I would suggest starting with a 1.5 mm drill then drill out to 2.5mm.

All four holes should now be tapped to 3mm using a blind tap.

The holes in the retaining plate should be countersunk to take the heads of 3mm countersunk screws.

The lock retaining plate can now be (temporarily) fitted using two M3 x 6 countersunk screws. Both the plate and the casting should be countersunk to take the heads of the screws. 

Here we have the latch fully reassembled (temporarily) to ensure that it fits together. It is possible, if one of the lock retaining screws is not exactly central in the casring, that it will will impede the closing of the latch. If this happens, merely grind away the side of the screw until the lock closes completely. You will also notice that there are two curved recesses filed in the backplate near the retaining screws ro allow the screws to enter there threads cleanly.