Thanks Guys, we are off making swarf again
The rear cover has been mounted in my collet and faced.
I am guessing that the cover should be 2 1/4" diameter what actually is going to be depends on what can come out of the casting, without leaving any marks. What I got was 57mm.
So now we need to cut the boss that will go into the cylinder. I have chosen to use a flange thickness of 4mm and this edge is 5.6mm thick so that will mean the cover will stick into the cylinder by 1.6mm. First mark the depth of the boss by taking a cut 1.6mm from the front surface and if you have it set your stop.
Now we turn the material away by turning in to just over the required diameter, so 32mm. I am taking 0.4mm cuts as the cover is only held by that small depth in the collet.
We now turn the centre so that it fits the cylinder. This is too tight as the fit holds the cylinder in place:
So another gnats whisker
1 is turned off and it slides on nicely and has to be held to check the fit:
The front cover starts the same and 57mm diameter was achieved on the second cover. Once faced the piece is 8.4mm thick. The boss needs to stick out 1.6mm to go into the cylinder so it seems that we have lots spare. What we are going to do with this is keep this spare and add it to the boss on the other side.
So inner faces and edge turned but
before we take it down we drill and ream for the piston rod. This guarantees that the piston rod hole is right in the middle of the cover. The hole is first drilled using a centre drill which, unlike a longer standard drill, will while cutting pull itself into the centre:
Now a drill will go in true but that is no guarantee it will continue through the piece true (drills get bored and go for a wander if the work is too deep
). For this I started with a 4mm drill, then stepped up to a 6mm diameter before finally reaming 6.35mm (1/4"):
And now we can remount the cover the other way round and increase the length of the boss and counter drill and tap for the gland. As this now has a hole in the centre I can support the cover using a rotating centre while I take the cuts:
Not forgetting to rub a file over any sharp corners:
We now need to drill and tap for the gland. Yes it is a horrible threaded gland. I do not like them but we are going for authentication rather than prettiness. I have chosen a 1/2" 32 tpi thread for the gland: This is a special model engineering thread you can use anything you fancy but they look better (if that is possible) with finer threads. To tap the thread the hole must be taken out to the correct tapping diameter for the thread, the great thing about the 1/2 3s thread is it has a nice 12mm tapping size which is a common size.
So how can we do the hole? You could bore this or drill it: I am drilling it so its worth using a centre again on this side to make sure the drill goes where I want it:
The cover is 13mm thick so I made the counterbore 9mm deep. Remember if you use a drill the point of the drill will go in further than the full diameter of the drill and the bit of the cover doing the guiding will be thinner. To avoid this I have used an end mill to cut the bottom of the hole:
We are going to use a tap to cut the thread and the thread must go in true to the bore. I do this by holding the tap in a tap wrench that is supported by a spring loaded point in the tailstock:
I am not going to drill the holes in the covers just yet - that will wait until I am set up on the mill. So a quick pic of the two covers and the cylinder (and yes I also made one of the glands I will cover those in another post)
I wonder if its Ice Cream time
Jo
1. Technical engineering term for a very small amount